WO2024042675A1 - Signal processing device and signal processing method - Google Patents

Signal processing device and signal processing method Download PDF

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Publication number
WO2024042675A1
WO2024042675A1 PCT/JP2022/032041 JP2022032041W WO2024042675A1 WO 2024042675 A1 WO2024042675 A1 WO 2024042675A1 JP 2022032041 W JP2022032041 W JP 2022032041W WO 2024042675 A1 WO2024042675 A1 WO 2024042675A1
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signal
satellite
orthogonal
signal processing
processing device
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PCT/JP2022/032041
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French (fr)
Japanese (ja)
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大地 田中
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日本電気株式会社
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Priority to PCT/JP2022/032041 priority Critical patent/WO2024042675A1/en
Publication of WO2024042675A1 publication Critical patent/WO2024042675A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques

Definitions

  • the present invention relates to a signal processing device and a signal processing method.
  • Synthetic Aperture Radar (SAR) technology is a radar antenna mounted on a flying object (such as an artificial satellite or airplane) that transmits and receives electromagnetic waves while the flying object (satellite, airplane, etc.) is moving.
  • This is a technology that artificially synthesizes apertures to obtain an image (SAR image) equivalent to
  • an artificial satellite will be used as an example of a flying object.
  • Artificial satellites are sometimes called SAR satellites.
  • Patent Document 2 describes an example of a terrestrial projection method (terrestrial projection conversion).
  • FIG. 17 is an explanatory diagram schematically representing the spectrum A after imaging based on the observed signal. Specifically, FIG. 17 shows a spectrum A after Fourier transform of the observed signal. Spectrum A can also be said to be a region where a signal exists. In FIG. 17, a rectangular region B consisting of sides parallel to the azimuth frequency axis and sides horizontal to the range frequency axis shows a spectrum when there is no inclination.
  • the spectrum A has a wide bandwidth in both the azimuth frequency direction and the range frequency direction.
  • region C that includes spectrum A.
  • sampling is performed along each of two axes: the azimuth frequency axis and the range frequency axis. For example, if a region B spectrum A of the same size as spectrum A is sampled, aliasing may occur. Therefore, sampling covering a wider area C than the spectrum A is required. If sampling is performed on area C, the amount of data will increase. That is, when squint photography is performed, there is a problem that the amount of data of the radar image increases.
  • One of the objects of the present invention is to suppress the increase in the amount of data of radar images.
  • a signal processing device is provided in a plane formed by a first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction perpendicular to the traveling direction of the satellite, the traveling direction and the orthogonal direction.
  • Information representing a reflected signal with respect to the signal is created in a data format representing the second direction orthogonal to the first direction.
  • the signal processing method according to the present invention is performed in a plane formed by a first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction perpendicular to the traveling direction of the satellite, the traveling direction and the orthogonal direction.
  • a computer creates information representing a reflected signal with respect to the signal in a data format representing a second direction orthogonal to the first direction.
  • the signal processing program provides a computer with a first direction representing a direction in which a satellite irradiates a signal in a direction different from the orthogonal direction perpendicular to the direction of travel of the satellite, and a first direction in which the direction of travel and the orthogonal direction are different.
  • a process for creating information representing a reflected signal with respect to a signal is executed in a data format expressed along a second direction perpendicular to the first direction in a plane formed by the signal.
  • FIG. 2 is an explanatory diagram for explaining a projection plane of a radar image, a flying object such as an artificial satellite, the ground surface, and various directions.
  • FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image.
  • FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image.
  • FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image.
  • FIG. 1 is a block diagram illustrating a configuration example of a signal processing device according to a first embodiment.
  • FIG. 2 is a block diagram showing a configuration example of a signal processing device according to a second embodiment.
  • 7 is a flowchart showing the operation of the signal processing device according to the second embodiment.
  • FIG. 1 is a block diagram illustrating a configuration example of a signal processing device according to a first embodiment.
  • FIG. 2 is a block diagram showing a configuration example of a signal processing device according to a second embodiment.
  • FIG. 3 is a block diagram showing a configuration example of a signal processing device according to a third embodiment.
  • 7 is a flowchart showing the operation of the signal processing device according to the third embodiment.
  • FIG. 7 is an explanatory diagram for explaining shift processing in a third embodiment.
  • FIG. 7 is a block diagram showing an example of the configuration of a signal processing device according to a fourth embodiment.
  • FIG. 2 is an explanatory diagram for explaining zero Doppler. It is an explanatory view for explaining zero Doppler processing in a 4th embodiment.
  • FIG. 7 is a block diagram showing an example of the configuration of a signal processing device according to a fifth embodiment.
  • FIG. 7 is a block diagram showing a configuration example of a signal processing device according to a sixth embodiment.
  • FIG. 12 is a block diagram showing a configuration example of a signal processing device according to a seventh embodiment.
  • 1 is a block diagram showing an example of a computer having a CPU.
  • FIG. 2 is an explanatory diagram schematically representing a spectrum A after Fourier transform of an observed signal.
  • FIG. 1 is an explanatory diagram for explaining the projection plane of a radar image, a flying object such as an artificial satellite, the ground surface, and various directions.
  • FIG. 1 shows the traveling direction of the artificial satellite and the antenna direction, which is the direction in which the antenna of the artificial satellite faces. A plane formed by these two directions is shown as a projection plane. Further, a direction that is perpendicular to the traveling direction and included in the projection plane is shown as a direction perpendicular to the traveling direction.
  • the antenna direction will be referred to as the range direction. Further, the direction perpendicular to the satellite traveling direction is the direction in which Doppler becomes 0, as will be described later. Therefore, this direction is also called the zero Doppler direction.
  • the angle formed by the zero Doppler direction and the antenna direction is defined as the Squint angle, and the case where this angle exceeds approximately 5 degrees is defined as the High Squint angle.
  • Satellites are equipped with antennas.
  • the electromagnetic waves emitted by the antenna in the direction of the range hit the area shown by the ellipse, and the phase delay and strength of reflection are recorded for those that bounce back.
  • projection in radar images for a certain position on the satellite orbit, reflections from all positions that are the same distance from that position in a plane perpendicular to the direction of travel of the satellite are added, and all of the reflections are added. It is recorded at a position that intersects with the radar image projection plane. Furthermore, as the satellite advances, the irradiation position of the electromagnetic waves shifts, and the reflection of electromagnetic waves from different positions on the ground is recorded for different satellite positions.
  • the reflection of electromagnetic waves emitted from a certain satellite position in a small spread is calculated by combining the reflections of electromagnetic waves emitted in a small spread from multiple satellite positions.
  • the satellite position after the synthesis is called azimuth etc.
  • the azimuth direction is the direction in which the satellite is traveling.
  • the coordinate axis developed in that direction is called the azimuth axis.
  • FIGS. 2A to 2C are explanatory diagrams for explaining examples of coordinate systems of radar images. That is, FIGS. 2A to 2C show coordinate systems within the projection plane shown in FIG. 1.
  • FIG. 2A shows a coordinate system whose two axes are the traveling direction of the artificial satellite 1 and a direction perpendicular thereto. The axial direction of the coordinate system corresponds to the direction of sampling.
  • FIG. 2B shows a coordinate system whose two axes are the traveling direction of the artificial satellite 1 and the range direction of the artificial satellite.
  • FIG. 2C shows a coordinate system whose two axes are the range direction of the artificial satellite 1 and the direction perpendicular thereto.
  • the lattice refers to each of a plurality of vertical lines and horizontal lines that divide a space.
  • a rectangular mesh surrounded by a grid corresponds to a pixel. That is, a radar image is composed of many meshes.
  • one mesh, ie, one pixel, is clearly marked.
  • the range direction will be referred to as the antenna direction.
  • the spectrum is tilted as illustrated in FIG. 17.
  • the amount of data increases to avoid aliasing.
  • the observation signal is stored in a storage device, for example.
  • the time in the zero Doppler direction corresponding to the observation signal is stored in the storage device.
  • Zero Doppler is the direction in which the Doppler produced by the movement of the satellite becomes zero.
  • the direction in which Doppler becomes 0 is the direction perpendicular to the moving velocity vector of the satellite.
  • zero Doppler is the direction perpendicular to the orbit or the direction plus the speed of movement of the observed object depending on the Earth's point in time.
  • the time in the zero Doppler direction is the time when the observation target passes directly in front of the zero Doppler direction (direction perpendicular to the orbit) as seen from the satellite. That is, the satellite image processing system is generally capable of calculating the position of the satellite at each pixel by linking the orbit of the satellite with the zero Doppler time of each pixel.
  • the spectrum will be parallelogram-shaped. As a result, less data is required to avoid aliasing than if the coordinate system shown in FIG. 2A were used.
  • the processing load increases.
  • the delay time relative to the antenna direction and the time when the scatterer comes in front of the antenna assuming that the antenna continues to face the range direction during the imaging time. are stored in the storage device in association with the observed signals. Note that the delay time is the time from when the electromagnetic wave is emitted until the reflected wave is received.
  • the coordinate system shown in FIG. 2C is a coordinate system used in the embodiments described below.
  • unnecessary signals do not need to be sampled. Therefore, an increase in the amount of radar image data is suppressed.
  • the coordinate system shown in FIG. 2C is a coordinate system that can be used, for example, when a satellite irradiates a signal in a direction different from the direction perpendicular to the direction of travel of the satellite.
  • the signal is emitted from a radar mounted on a satellite toward an observation target such as the ground surface. Then, the presence or absence of the observation target and the shape of the observation target are observed depending on the strength of the signal in the reflected signal representing the reflection of the signal.
  • the strength of the observed signal is expressed, for example, in a data format measured in the coordinate system shown in FIG. 2C.
  • One axis in the coordinate system is an axis along the direction in which the satellite irradiates a signal (for convenience, this may be referred to as a "first direction").
  • first direction is a direction different from the orthogonal direction perpendicular to the direction of travel of the satellite.
  • second direction is an axis along a direction perpendicular to the first direction (for convenience, it may be referred to as a "second direction") in a plane formed by the traveling direction and the orthogonal direction. Therefore, information regarding the reflected signal is created in a data format representing along the first direction and the second direction.
  • FIG. 3 is a block diagram showing a configuration example of the signal processing device according to the first embodiment.
  • the signal processing device shown in FIG. 3 includes an inclined image generation section 100 and a satellite observation data storage section 130.
  • the satellite observation data storage unit 130 stores observation signals 131 and satellite information 132.
  • the observation signal is a received signal received by a radar of an artificial satellite. Satellite information includes satellite position, antenna direction, bandwidth, etc.
  • the tilt image generation unit 100 generates, for example, two axes illustrated in FIG. 2C based on the satellite information. Then, the tilted image generation unit 100 calculates the scattering intensity of each pixel using a predetermined method.
  • the tilted image generation unit (or information generation unit) 100 generates information regarding the scattering intensity in a data format expressed along the first direction and the second direction, as described above with reference to FIG. 2C. create.
  • the first direction is a direction in which a satellite emits a signal in a direction different from the orthogonal direction that is perpendicular to the traveling direction of the satellite.
  • the second direction is a direction orthogonal to the first direction in a plane formed by the traveling direction and the orthogonal direction.
  • FIG. 4 is a block diagram showing a configuration example of a signal processing device according to the second embodiment.
  • the signal processing device shown in FIG. 4 includes an inclined image generation section 100 and a satellite observation data storage section 130.
  • the tilted image generation section 100 includes a grid generation section 111 and a back projection section 112.
  • the signal processing device of the second embodiment corresponds to a specific example of the signal processing device of the first embodiment shown in FIG.
  • the grid generation unit 111 generates the grid illustrated in FIG. 2C in advance based on the satellite information.
  • the back projection unit 112 uses a back projection method to find the scattering intensity of each pixel.
  • the grid generation unit 111 generates a grid based on the satellite information (step S101).
  • the grid generation unit 111 generates a grid based on parameters that can be used for resolution calculation, such as bandwidth, and the antenna direction.
  • the lattice generation unit 111 generates the lattice along two axes: the antenna direction, and a direction that exists on a plane defined by the vector of the antenna direction and the satellite movement direction and is orthogonal to the antenna direction.
  • the two axes do not have to be strictly orthogonal. Furthermore, the two axes do not need to be strictly on a plane defined by vectors in the antenna direction and the satellite movement direction.
  • the antenna direction may be a representative direction among a plurality of directions. That is, the antenna direction may be part of a plurality of directions.
  • the moving direction of the satellite may be a representative direction among a plurality of directions. That is, the direction of movement of the satellite may be part of a plurality of directions.
  • the back projection unit 112 performs Back Projection on each mesh formed by the grid (step S102).
  • Back Projection is a method of generating each pixel by calculating a correlation integral value for each pixel to be generated. That is, the back projection unit 112 can generate a radar image in a region including a plurality of meshes formed by a plurality of lattices parallel to the two axes, the antenna direction and a direction perpendicular thereto.
  • FIG. 6 is a block diagram showing a configuration example of a signal processing device according to the third embodiment.
  • the signal processing device shown in FIG. 6 includes an inclined image generation section 100 and a satellite observation data storage section 130.
  • the tilted image generator 100 uses the Omega K algorithm.
  • the tilted image generation section 100 includes a two-dimensional (2D) Fourier transform section 113, a range spectrum shift section 114, an azimuth spectrum shift section 115, and a 2D inverse Fourier transform section 116.
  • the signal processing device of the third embodiment corresponds to another specific example of the signal processing device of the first embodiment shown in FIG.
  • the general Omega K algorithm includes range spectrum shift processing and azimuth spectrum shift processing that are executed after two-dimensional Fourier transform.
  • the delay time with respect to the antenna direction and the time when the scatterer comes in front of the antenna, assuming that the antenna continues to face the range direction during the imaging time, are associated with the observation signal.
  • the information is stored in the satellite observation data storage unit 130 as satellite information 132.
  • the 2D Fourier transform unit 113 performs two-dimensional Fourier transform on the observed signal.
  • the range spectrum shift unit 114 performs spectrum shift processing in the range direction.
  • the azimuth spectrum shift unit 115 performs spectrum shift processing in the azimuth direction.
  • the 2D inverse Fourier transform unit 116 performs two-dimensional inverse Fourier transform.
  • FIG. 8 is an explanatory diagram for explaining shift processing.
  • the 2D Fourier transform unit 113 performs two-dimensional Fourier transform on the observed signal (step S103).
  • the range spectrum shift unit 114 shifts the spectrum in the range direction (step S104).
  • the range spectrum shift unit 114 shifts the spectrum by a shift amount corresponding to the azimuth frequency.
  • the azimuth spectrum shift unit 115 shifts the spectrum in the azimuth direction (step S105).
  • the spectrum illustrated on the left side of the upper row in FIG. 8 is obtained. Note that such a spectrum corresponds to the spectrum in the coordinate system illustrated in FIG. 2B.
  • a spectrum curved in the azimuth direction as illustrated on the right side of the upper row in FIG. 8 is obtained.
  • range time be ⁇ and azimuth time be ⁇ .
  • the observed signal be s( ⁇ , ⁇ ).
  • the antenna direction be ⁇ sq .
  • k carrier be the range wave number corresponding to the wave number of the electromagnetic wave frequency.
  • k rg be the spatial frequency in the range direction.
  • k az be the spatial frequency in the azimuth direction.
  • a two-dimensional spectrum S(k rg , k az ) is obtained by two-dimensional Fourier transformation of the observed signal. Note that the 2D Fourier transform unit 113 also executes scaling processing by (velocity of light/2) in the range direction and scaling processing by satellite velocity in the azimuth direction.
  • the azimuth spectrum shift unit 115 corrects the inclination of the spectrum in the azimuth direction (see the right side of the upper row in FIG. 8). Specifically, the azimuth spectrum shift unit 115 moves (k' rg , k az ) to (k' rg , k' az ). However, k' az is expressed by equation (4). In formula (4), C 2 is an arbitrary constant. Note that sin ⁇ sq corresponds to the slope in the spectrum illustrated on the right side of the upper row in FIG.
  • tan ⁇ sq in equation (1) and sin ⁇ sq in equation (4) may be values close to tan ⁇ sq and values close to sin ⁇ sq . That is, ideally, a precise squint angle is used based on the control information of the positioning system and antenna on board the satellite, but for example, when accurate positioning system information is not available, the Doppler shift of electromagnetic waves reflected from the ground is used.
  • the trajectory of a curved line may be approximated as a straight line, or the ground of a curved surface may be approximated as a plane, but the equivalent of the squint angle in the approximated geometry is, for example, ⁇ sq , which is the effective The Squint angle may also be used. Furthermore, the angle of incidence of the reflected wave as seen from the ground may be used as ⁇ sq .
  • the 2D inverse Fourier transform unit 116 performs two-dimensional inverse Fourier transform (step S106).
  • a radar image is substantially generated in a region including a plurality of meshes formed by a lattice parallel to either of the two axes, the antenna direction and the direction perpendicular thereto.
  • FIG. 9 is a block diagram showing a configuration example of a signal processing device according to the fourth embodiment.
  • the signal processing device shown in FIG. 9 includes an inclined image generation section 100 and a satellite observation data storage section 130.
  • the tilted image generation section 100 includes an up-sampling section 117, a zero-Doppler imaging processing section 118, a rotation processing section 119, and a down-sampling section 120.
  • the tilt image generation unit 100 uses a general zero Doppler algorithm as an imaging algorithm.
  • the zero Doppler algorithm refers to a general imaging method that images in two axes: the zero Doppler direction and the satellite orbit direction.
  • the up-sampling unit 117 performs processing to increase the number of pixels.
  • the zero Doppler imaging processing unit 118 performs imaging processing based on a zero Doppler algorithm, that is, zero Doppler processing as imaging processing.
  • the rotation processing unit 119 performs processing to rotate the spectrum of the imaging processing result.
  • the down-sampling unit 120 performs processing to reduce the number of pixels around the spectrum.
  • FIG. 10 is an explanatory diagram for explaining imaging processing using zero Doppler.
  • time information called zero Doppler time is saved.
  • the zero Doppler time is different from the time when the radar actually receives the signal.
  • the squint angle ⁇ sq is small, the deviation between the reception time and the zero Doppler time is small. Therefore, even if the radar image is projected onto the ground using a satellite position interpolated at zero Doppler time, no deviation will occur in the radar image.
  • the reception time and the zero Doppler time are significantly different, so a shift occurs.
  • the occurrence of aliasing is avoided even when zero Doppler processing is used.
  • FIG. 11 is an explanatory diagram for explaining zero Doppler processing. As illustrated on the left side of the upper row in FIG. 11, the spectrum is tilted when an image is generated based on the observation signal. Therefore, the up-sampling unit 117 adds pixels with a pixel value of 0 around the actual spectrum so that the entire spectrum can be sampled (see the upper right side of FIG. 11).
  • the zero Doppler imaging processing unit 118 executes zero Doppler processing. Radar images are obtained by zero Doppler processing. However, as illustrated on the left side of the lower row in FIG. 11, the spectrum is tilted.
  • the rotation processing unit 119 performs rotation processing on the image so that the tilt of the spectrum is eliminated. Correct the spectral tilt.
  • the rotation processing by the rotation processing unit 119 is executed, the slope of the spectrum disappears, as illustrated in the center of the lower row in FIG. 11 .
  • the down-sampling unit 120 deletes pixels in a portion where no spectrum exists (see the lower right side in FIG. 11).
  • the signal processing device of the fourth embodiment can avoid aliasing by upsampling. Further, the signal processing device can suppress an increase in the amount of data of the radar image by down-sampling performed after rotation processing.
  • each of the above embodiments is also applicable to a bistatic configuration in which the transmitting antenna and the receiving antenna are located at different positions.
  • one axis is the direction of the bisector of the angle formed by the direction of the transmitting antenna with respect to the target object and the direction of the receiving antenna with respect to the target object, and the other axis is the direction perpendicular thereto.
  • each of the above embodiments can be applied to tomography that performs three-dimensional synthetic aperture processing by performing imaging in multiple trajectories.
  • tomography for example, as with two-dimensional squint images, one axis is the antenna direction, and the other axis is a direction perpendicular to the antenna direction and within the plane formed by the satellite orbit and the antenna direction. shall be. If a three-dimensional lattice is created with the normal direction to the plane constituted by such two axes as the elevation direction, aliasing can be effectively prevented from occurring.
  • a radar image is substantially generated in a region including a plurality of meshes formed by a lattice parallel to either of the two axes, the antenna direction and the direction perpendicular thereto.
  • Embodiment 5 The signal processing device of the fifth embodiment is effectively applied to high resolution mode or wide area mode.
  • high resolution mode in order to increase the resolution of SAR images, it is conceivable to increase the synthetic aperture length by directing a radar antenna mounted on an artificial satellite toward the imaging area for a long period of time.
  • a mode in which processing for increasing the resolution of a SAR image is executed is referred to as a high resolution mode.
  • the photographing area can be expanded.
  • a mode in which a wide range is photographed is called a wide-area mode.
  • changing the squint angle of the antenna may be expressed as shaking the antenna.
  • the signal processing device shown in FIG. 12 includes a tilt image generation section 101, a satellite observation data storage section 130, and a phase modulation estimation section 200.
  • the tilted image generation unit 101 has the same function as the tilted image generation unit 100 in the first embodiment.
  • the tilted image generation unit 101 performs the imaging process in consideration of the influence of swinging the antenna.
  • the imaging results include phase modulation information representing the phase modulation dependent on the direction of the antenna at each time. Therefore, it is possible to calculate a change in the band depending on the position of the image from the phase modulation information, and to remove the influence thereof.
  • the tilt image generation unit 101 outputs a radar image
  • the phase modulation estimation unit 200 outputs phase modulation information.
  • the phase modulation estimation unit 200 calculates the amount of phase modulation at each coordinate in a direction orthogonal to the antenna direction. Note that in the antenna direction, the amount of phase modulation is approximately constant.
  • the Doppler frequency is high.
  • photography is performed with the distance between the satellite and the scatterer being almost constant, the satellite neither approaches nor moves away from the scatterer, so the Doppler frequency is 0.
  • the antenna is swung, a state in which the satellite approaches the scatterer and a state in which the distance between the satellite and the scatterer remains almost constant appear repeatedly.
  • the signal processing device provides phase modulation information to a device such as an image processing device that uses the output of the signal processing device.
  • a device such as an image processing device will be referred to as another device.
  • the phase modulation is removed from the radar image by interference processing, etc., and then the images are aligned with each other by movement, and then the phase modulation is re-added. After that, interference processing can be performed.
  • other devices perform interference processing between aligned images and interference processing between phase modulations added to each image, and add the interference processing results between phase modulations to the interference processing results between images. By adding this, it is possible to perform interference processing that accurately maintains the phase while preventing the occurrence of aliasing.
  • phase modulation information for the imaging result in an oblique coordinate system
  • the phase modulation information is calculated by a quadratic function in the direction perpendicular to the antenna direction.
  • processing such as expansion/contraction by deformation can be easily performed as polynomial deformation processing.
  • the signal processing device of the fifth embodiment when using the signal processing device of the fifth embodiment, such as when another device generates an image by interference SAR (Synthetic Aperture Radar Interferometry), it is possible to align them with each other with phase modulation removed. Two radar images can be made to interfere. Other devices re-add the interference results between phase modulations to the interference. By performing such processing, other devices can perform interference processing while avoiding aliasing and the like during processing.
  • SAR Synthetic Aperture Radar Interferometry
  • phase modulation estimation unit 200 can calculate the phase modulation using a combination of coefficients used in the imaging algorithm. Further, the phase modulation estimating unit 200 can also calculate the phase modulation only from the satellite orbit, the squint angle, and the position of the gaze point. The phase modulation estimating unit 200 can also calculate the phase modulation only from the satellite orbit, the position of the object to be photographed, and the position of the gaze point.
  • FIG. 13 is a block diagram showing a configuration example of a signal processing device according to the sixth embodiment.
  • the signal processing device shown in FIG. 13 includes an inclined image generation section 100, a satellite observation data storage section 130, an image processing section 300, and a ground projection section 301.
  • the tilted image generation section 102 has the same function as the tilted image generation section 100 in the first embodiment.
  • the configuration of the signal processing device of the sixth embodiment is such that an image processing unit 300 and a ground projection unit 301 are added to the signal processing device of the first embodiment.
  • the image processing section 300 and the ground projection section 301 may be added to the signal processing apparatus of embodiments other than the first embodiment.
  • the tilted image generation unit 102 also has a function of creating oblique coordinate information.
  • the image processing unit 300 performs image processing on the data generated by the tilted image generation unit 102, that is, the radar image.
  • the ground projection unit 301 performs ground projection processing to project the image processing result onto the ground.
  • Image processing that narrows the spatial frequency may be performed, such as conversion to an absolute value image or change detection results.
  • the image processing unit 300 performs image processing using the data generated by the tilted image generation unit 102 as is, and then the ground projection unit 301 performs ground projection processing. The amount of calculation required for processing can be reduced.
  • the oblique coordinate information includes the amount of shift from the satellite orbit, the coordinate axis direction, etc. However, if the oblique coordinate information includes information as shown in FIG. 14, for example, the range direction, the direction perpendicular to the range direction, and the image center distance, the ground projection unit 301 Can perform projection processing. Note that the range direction and the direction perpendicular to the range direction are configured to be output from the tilted image generation unit 102 because these do not necessarily have to be exact information.
  • the terrestrial projection unit 301 executes terrestrial projection processing, for example, as follows.
  • the ground projection unit 301 calculates at what satellite time each pixel in the radar image is received and at what distance from the satellite orbit, based on the pixel number and oblique coordinate information. Then, the terrestrial projection unit 301 performs terrestrial projection. For example, the ground projection unit 301 calculates the intersection of a circle equidistant from the satellite orbit and a solid object on the ground based on the three-dimensional shape on the ground. The ground projection unit 301 may more simply calculate the intersection of the center of the imaging target point with the tangent surface of the earth ellipsoid.
  • the ground projection unit 301 uses the Ground Control Point, that is, the ground position and the SAR pixel, by slightly modifying the method described in Patent Document 2.
  • Projection processing and alignment correction processing can be realized by alignment of points that can reliably align the positions and simple deformation. Note that while the method described in Patent Document 2 uses a coordinate system with two axes: the antenna direction and the satellite traveling direction, in the sixth embodiment, a coordinate system with two axes: the antenna direction and the direction perpendicular to the antenna is used. be modified so that it is used.
  • FIG. 15 is a block diagram showing a configuration example of a signal processing device according to the seventh embodiment.
  • the signal processing device shown in FIG. 15 includes an inclined image generation section 100, a satellite observation data storage section 130, a vector data extraction section 302, and a ground projection section 301.
  • the tilted image generation section 102 has the same function as the tilted image generation section 100 in the first embodiment.
  • the configuration of the signal processing device of the seventh embodiment is such that a vector data extraction section 302 and a ground projection section 303 are added to the signal processing device of the first embodiment.
  • the vector data extraction section 302 and the ground projection section 303 may be added to the signal processing apparatus of embodiments other than the first embodiment.
  • the configuration of the signal processing apparatus according to the seventh embodiment is such that a vector data extraction section 302 is provided in place of the image processing section 300 in the signal processing apparatus according to the sixth embodiment.
  • the terrestrial projection unit 303 performs terrestrial photographing processing similarly to the terrestrial projection unit 301, but the input to the terrestrial projection unit 303 is vector data.
  • the tilted image generation unit 102 has the function of creating oblique coordinate information in addition to the function of the tilted image generation unit 100.
  • the vector data extraction unit 302 obtains vector data from, for example, an image obtained by performing image processing on a radar image. As an example, when semantic segmentation is performed as image processing, polygons connecting pixels or pixel groups can be obtained.
  • the terrestrial projection unit 301 performs terrestrial projection processing based on vector data.
  • the processing load of terrestrial projection processing based on vector data is relatively small. That is, the signal processing device of the seventh embodiment can perform terrestrial projection processing in a short period of time while preventing aliasing.
  • vector data extraction unit 302 may include an interference data analysis function.
  • Each component in the above embodiment can be configured with one piece of hardware, but can also be configured with one piece of software. Further, each component can be configured with a plurality of pieces of hardware, and can also be configured with a plurality of pieces of software. Further, some of the components can be configured with hardware, and the other parts can be configured with software.
  • Each function in the above embodiment can be realized by a computer having a processor such as a CPU (Central Processing Unit), memory, and the like.
  • a program for implementing the method in the above embodiment may be stored in a storage device, and each function may be realized by executing the program stored in the storage device with a CPU.
  • FIG. 16 is a block diagram showing an example of a computer having a CPU.
  • the computer is implemented in a signal processing device.
  • the CPU 1000 implements the functions of the signal processing device in the above embodiment by executing processing according to the signal processing program stored in the storage device 1001.
  • the computer realizes the function of the tilted image generation section 100.
  • the computer implements the functions of the grid generation section 111 and the back projection section 112.
  • the computer realizes the functions of a 2D Fourier transform section 113, a range spectrum shift section 114, an azimuth spectrum shift section 115, and a 2D inverse Fourier transform section 116.
  • the computer implements the functions of an up-sampling section 117, a zero-Doppler imaging processing section 118, a rotation processing section 119, and a down-sampling section 120.
  • the computer realizes the functions of the tilt image generation section 100 and the phase modulation estimation section 200.
  • the computer realizes the functions of the tilted image generation section 102, the image processing section 300, and the ground projection section 301.
  • the computer realizes the functions of the tilted image generation section 102, the vector data extraction section 302, and the ground projection section 303.
  • the storage device 1001 is, for example, a non-transitory computer readable medium.
  • Non-transitory computer-readable media include various types of tangible storage media. Specific examples of non-transitory computer-readable media include magnetic recording media (e.g., hard disks), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Compact Disc-Read Only Memory), and CD-Rs (Compact Disc-Recordable), CD-R/W (Compact Disc-ReWritable), and semiconductor memories (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), and flash ROM).
  • magnetic recording media e.g., hard disks
  • magneto-optical recording media e.g., magneto-optical disks
  • CD-ROMs Compact Disc-Read Only Memory
  • CD-Rs Compact Disc-Recordable
  • CD-R/W Compact Disc-ReWritable
  • semiconductor memories for example, mask
  • the satellite observation data storage unit 130 can be realized by the storage device 1001.
  • the program may also be stored on various types of transitory computer readable medium.
  • the program is supplied to the temporary computer-readable medium, for example, via a wired or wireless communication channel, ie, via an electrical signal, an optical signal, or an electromagnetic wave.
  • the memory 1002 is realized by, for example, RAM (Random Access Memory), and is a storage means that temporarily stores data when the CPU 1000 executes processing. It is also conceivable that a program held in the storage device 1001 or a temporary computer-readable medium is transferred to the memory 1002, and the CPU 1000 executes processing based on the program in the memory 1002.
  • RAM Random Access Memory
  • the signal processing device may include a phase modulation estimating means (in the embodiment, realized by the phase modulation estimating section 200) that calculates the amount of phase modulation at each coordinate in a direction orthogonal to the antenna direction.
  • a phase modulation estimating means in the embodiment, realized by the phase modulation estimating section 200 that calculates the amount of phase modulation at each coordinate in a direction orthogonal to the antenna direction.
  • the signal processing device includes an image processing unit (implemented by the image processing unit 300 in the embodiment) that performs image processing on a radar image, and a ground projection unit (implemented) that performs processing to project the result of the image processing on the ground. In some embodiments, it may be realized by the ground projection unit 301.)
  • the signal processing device includes a vector data extraction unit (in the embodiment, realized by a vector data extraction unit 302) that acquires vector data from an image obtained by performing image processing on a radar image, and a ground projection unit based on the vector data. It may also include a terrestrial projection means (in the embodiment, realized by the terrestrial projection unit 303) that performs processing.

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Abstract

One purpose of the present invention is to control an increase in the size of the data of a radar image.　This signal processing device creates information indicating a reflected signal of a signal, in a data format indicating using a first direction and a second direction. The first direction indicates the direction in which a satellite (1), which emits a signal in a direction different from a perpendicular direction which is perpendicular to the advancing direction of the satellite (1), emits the signal. The second direction is perpendicular to the first direction in a plane formed by the advancing direction and the perpendicular direction.

Description

信号処理装置および信号処理方法Signal processing device and signal processing method
　本発明は、信号処理装置および信号処理方法に関する。 The present invention relates to a signal processing device and a signal processing method.
　合成開口レーダ（ＳＡＲ：synthetic Aperture Radar）技術は、飛翔体（人工衛星や飛行機等）が移動しながら、飛翔体に搭載されたレーダにおけるアンテナが電磁波を送受信し、大きな開口を持ったアンテナの場合と等価な画像（ＳＡＲ画像）が得られるように人工的に開口を合成する技術である。以下、飛翔体として、人工衛星を例にする。人工衛星をＳＡＲ衛星ということがある。 Synthetic Aperture Radar (SAR) technology is a radar antenna mounted on a flying object (such as an artificial satellite or airplane) that transmits and receives electromagnetic waves while the flying object (satellite, airplane, etc.) is moving. This is a technology that artificially synthesizes apertures to obtain an image (SAR image) equivalent to In the following, an artificial satellite will be used as an example of a flying object. Artificial satellites are sometimes called SAR satellites.
　広い領域が撮影されたＳＡＲ画像に対する需要が高まっている。また、高解像度のＳＡＲ画像対する需要が高まっている。また、ビデオＳＡＲに関する研究が進められている。ＳＡＲ画像を高解像度化するために、長期間に亘って撮影領域にアンテナを向けることによって合成開口長を長くすることが考えられる。また、スクイント撮影（スクイント観測）を行うときに、アンテナのスクイント角を大きくすることによって、撮影領域を広げることが考えられる（例えば、特許文献１参照）。スクイント撮影では、アジマス方向またはその逆方向にアンテナを傾けて撮影領域が撮影される。また、スクイント撮影では、アンテナの傾きが変動することもある。 There is a growing demand for SAR images that capture a wide area. Additionally, demand for high-resolution SAR images is increasing. Research on video SAR is also underway. In order to increase the resolution of SAR images, it is conceivable to increase the synthetic aperture length by directing the antenna toward the imaging area over a long period of time. Furthermore, when performing squint photography (squint observation), it is possible to widen the shooting area by increasing the squint angle of the antenna (for example, see Patent Document 1). In squint imaging, the imaging area is photographed by tilting the antenna in the azimuth direction or the opposite direction. Furthermore, in squint photography, the tilt of the antenna may change.
　なお、特許文献２には、地上投影方法（地上投影変換）の一例が記載されている。 Note that Patent Document 2 describes an example of a terrestrial projection method (terrestrial projection conversion).
特開２０１２－０９３２５７号公報JP2012-093257A 国際公開第２０１０／１４９１３２号International Publication No. 2010/149132
　スクイント撮影が実行される場合、人工衛星に搭載されたレーダが受信した受信信号（観測信号）に基づいて画像が生成されるときに、図１７に例示するように、スペクトル（強度分布）Ａが傾く。傾きの程度は、スクイント角に依存する。図１７は、観測信号に基づく画像化後のスペクトルＡを模式的に表す説明図である。具体的には、図１７には、観測信号をフーリエ変換した後のスペクトルＡが示されている。スペクトルＡは、信号が存在する領域であるともいえる。図１７において、アジマス周波数軸に平行な辺とレンジ周波数軸に水平な辺からなる矩形の領域Ｂは、傾きがない場合のスペクトルを示す。 When squint imaging is performed, when an image is generated based on the received signal (observation signal) received by the radar onboard the satellite, the spectrum (intensity distribution) A is Lean. The degree of tilt depends on the squint angle. FIG. 17 is an explanatory diagram schematically representing the spectrum A after imaging based on the observed signal. Specifically, FIG. 17 shows a spectrum A after Fourier transform of the observed signal. Spectrum A can also be said to be a region where a signal exists. In FIG. 17, a rectangular region B consisting of sides parallel to the azimuth frequency axis and sides horizontal to the range frequency axis shows a spectrum when there is no inclination.
　スペクトルＡは、アジマス周波数方向とレンジ周波数方向のそれぞれに、帯域幅が広がっている。スペクトルＡ内の全ての信号を対象としてサンプリングしようとすると、スペクトルＡを包含する領域Ｃを対象とする必要がある。なお、サンプリングは、アジマス周波数軸とレンジ周波数軸と２軸のそれぞれに沿って実行されるとする。例えば、スペクトルＡと同サイズの領域ＢスペクトルＡをサンプリングすると、エイリアシングが生じる可能性がある。したがって、スペクトルＡよりも広い領域Ｃを対象とするサンプリングが求められる。領域Ｃを対象とするサンプリングを行うと、データ量が増大する。すなわち、スクイント撮影が実行される場合などには、レーダ画像のデータ量が増大してしまうという課題がある。 The spectrum A has a wide bandwidth in both the azimuth frequency direction and the range frequency direction. When trying to sample all the signals within spectrum A, it is necessary to target region C that includes spectrum A. Note that sampling is performed along each of two axes: the azimuth frequency axis and the range frequency axis. For example, if a region B spectrum A of the same size as spectrum A is sampled, aliasing may occur. Therefore, sampling covering a wider area C than the spectrum A is required. If sampling is performed on area C, the amount of data will increase. That is, when squint photography is performed, there is a problem that the amount of data of the radar image increases.
　本発明は、レーダ画像のデータ量の増大を抑制することを目的の一つとする。 One of the objects of the present invention is to suppress the increase in the amount of data of radar images.
　本発明による信号処理装置は、衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、進行方向および直交方向がなす平面において第１方向に直交する第２方向とに沿って表すデータ形式にて、信号に対する反射信号を表す情報を作成する。 A signal processing device according to the present invention is provided in a plane formed by a first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction perpendicular to the traveling direction of the satellite, the traveling direction and the orthogonal direction. Information representing a reflected signal with respect to the signal is created in a data format representing the second direction orthogonal to the first direction.
　本発明による信号処理方法は、衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、進行方向および直交方向がなす平面において第１方向に直交する第２方向とに沿って表すデータ形式にて、信号に対する反射信号を表す情報を、コンピュータが作成する。 The signal processing method according to the present invention is performed in a plane formed by a first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction perpendicular to the traveling direction of the satellite, the traveling direction and the orthogonal direction. A computer creates information representing a reflected signal with respect to the signal in a data format representing a second direction orthogonal to the first direction.
　本発明による信号処理プログラムは、コンピュータに、衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、進行方向および直交方向がなす平面において第１方向に直交する第２方向とに沿って表すデータ形式にて、信号に対する反射信号を表す情報を作成する処理を実行させる。 The signal processing program according to the present invention provides a computer with a first direction representing a direction in which a satellite irradiates a signal in a direction different from the orthogonal direction perpendicular to the direction of travel of the satellite, and a first direction in which the direction of travel and the orthogonal direction are different. A process for creating information representing a reflected signal with respect to a signal is executed in a data format expressed along a second direction perpendicular to the first direction in a plane formed by the signal.
　本発明によれば、画像を生成するためのデータ量の増大を抑制できる。 According to the present invention, it is possible to suppress an increase in the amount of data for generating an image.
レーダ画像の投影面、飛翔体例えば人工衛星、地表面、各種方向を説明するための説明図である。FIG. 2 is an explanatory diagram for explaining a projection plane of a radar image, a flying object such as an artificial satellite, the ground surface, and various directions. レーダ画像の座標系の例を説明するための説明図である。FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image. レーダ画像の座標系の例を説明するための説明図である。FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image. レーダ画像の座標系の例を説明するための説明図である。FIG. 2 is an explanatory diagram for explaining an example of a coordinate system of a radar image. 第１の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 1 is a block diagram illustrating a configuration example of a signal processing device according to a first embodiment. 第２の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 2 is a block diagram showing a configuration example of a signal processing device according to a second embodiment. 第２の実施形態の信号処理装置の動作を示すフローチャートである。7 is a flowchart showing the operation of the signal processing device according to the second embodiment. 第３の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 3 is a block diagram showing a configuration example of a signal processing device according to a third embodiment. 第３の実施形態の信号処理装置の動作を示すフローチャートである。7 is a flowchart showing the operation of the signal processing device according to the third embodiment. 第３の実施形態におけるシフト処理を説明するための説明図である。FIG. 7 is an explanatory diagram for explaining shift processing in a third embodiment. 第４の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 7 is a block diagram showing an example of the configuration of a signal processing device according to a fourth embodiment. ゼロドップラーを説明するための説明図である。FIG. 2 is an explanatory diagram for explaining zero Doppler. 第４の実施形態におけるゼロドップラー処理を説明するための説明図である。It is an explanatory view for explaining zero Doppler processing in a 4th embodiment. 第５の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 7 is a block diagram showing an example of the configuration of a signal processing device according to a fifth embodiment. 第６の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 7 is a block diagram showing a configuration example of a signal processing device according to a sixth embodiment. 斜交座標情報を説明するための説明図である。FIG. 3 is an explanatory diagram for explaining oblique coordinate information. 第７の実施形態の信号処理装置の構成例を示すブロック図である。FIG. 12 is a block diagram showing a configuration example of a signal processing device according to a seventh embodiment. ＣＰＵを有するコンピュータの一例を示すブロック図である。1 is a block diagram showing an example of a computer having a CPU. 観測信号をフーリエ変換した後のスペクトルＡを模式的に表す説明図である。FIG. 2 is an explanatory diagram schematically representing a spectrum A after Fourier transform of an observed signal.
　図１は、レーダ画像の投影面、飛翔体例えば人工衛星、地表面、各種方向を説明するための説明図である。図１には、人工衛星の進行方向と、人工衛星のアンテナの向く方向であるアンテナ方向とが示されている。その２つの方向がなす平面が投影面として示されている。また、進行方向に対して直交し、投影面に含まれる方向を進行方向直交方向として示している。以下、アンテナ方向をレンジ方向と呼ぶ。また、衛星進行方向直交方向は、後述するようにドップラーが０になる方向である。よって、その方向を、ゼロドップラー（Zero Doppler）方向とも呼ぶ。ゼロドップラー方向とアンテナ方向とがなす角をスクイント角とし、この角度がおおよそ５度を超える場合をハイスクイントとする。 FIG. 1 is an explanatory diagram for explaining the projection plane of a radar image, a flying object such as an artificial satellite, the ground surface, and various directions. FIG. 1 shows the traveling direction of the artificial satellite and the antenna direction, which is the direction in which the antenna of the artificial satellite faces. A plane formed by these two directions is shown as a projection plane. Further, a direction that is perpendicular to the traveling direction and included in the projection plane is shown as a direction perpendicular to the traveling direction. Hereinafter, the antenna direction will be referred to as the range direction. Further, the direction perpendicular to the satellite traveling direction is the direction in which Doppler becomes 0, as will be described later. Therefore, this direction is also called the zero Doppler direction. The angle formed by the zero Doppler direction and the antenna direction is defined as the Squint angle, and the case where this angle exceeds approximately 5 degrees is defined as the High Squint angle.
　一般に、レーダ画像においては、ゼロドップラー方向とレンジ方向とを同一として扱うことが多い。しかし、ハイスクイントの場合にはその違いを無視することができないため、明確に区別して扱うことにする。衛星は、アンテナを備えている。アンテナがレンジ方向に照射した電磁波が楕円で示されている部分に当たり、跳ね返ってきたものについて、その位相の遅れや反射の強さ等が記録される。なお、レーダ画像における投影については、衛星軌道上のある位置に対して、その衛星進行方向と垂直に交わる平面内でその位置からの距離が等しい全ての位置からの反射が加算され、その全ての位置の中でレーダ画像投影面と交差する位置に記録される。また、衛星が進行するごとに電磁波の照射位置がずれていき、異なる衛星位置に対して異なる地上の位置の電磁波の反射が記録される。 Generally, in radar images, the zero Doppler direction and the range direction are often treated as the same. However, in the case of Heisquint, the differences cannot be ignored, so we will treat them clearly. Satellites are equipped with antennas. The electromagnetic waves emitted by the antenna in the direction of the range hit the area shown by the ellipse, and the phase delay and strength of reflection are recorded for those that bounce back. Regarding projection in radar images, for a certain position on the satellite orbit, reflections from all positions that are the same distance from that position in a plane perpendicular to the direction of travel of the satellite are added, and all of the reflections are added. It is recorded at a position that intersects with the radar image projection plane. Furthermore, as the satellite advances, the irradiation position of the electromagnetic waves shifts, and the reflection of electromagnetic waves from different positions on the ground is recorded for different satellite positions.
　合成開口レーダにおいては、複数の衛星位置から広がりをもって照射された電磁波の反射を合成することにより、ある衛星位置から仮に小さな広がりで照射された電磁波の反射が算出される。その際の合成後の衛星位置のことをアジマス等と呼称する。実態として衛星位置との違いはないため、ここではアジマスと衛星位置とを区別しないことにする。すなわち、アジマス方向とは衛星進行方向のことである。その方向に展開される座標軸をアジマス軸と呼称する。なお、図１に示すように平らな地表面とそれに平行となる直線である軌道に基づいて説明したが、現実の衛星における球面である、地表面と曲線である衛星軌道に対しても同様である。また、曲面と曲線である地表面と衛星軌道によって取得されたレーダ画像に対して、それに近いレーダ画像を取得できる平面と直線である地表面と衛星軌道を近似的に導出できることは公知である。この近似幾何上でのスクイント角を実効スクイント角等と呼称するが、以下の説明では特にそれらを区別しない。 In synthetic aperture radar, the reflection of electromagnetic waves emitted from a certain satellite position in a small spread is calculated by combining the reflections of electromagnetic waves emitted in a small spread from multiple satellite positions. The satellite position after the synthesis is called azimuth etc. In reality, there is no difference between the azimuth and the satellite position, so we will not distinguish between the azimuth and the satellite position here. That is, the azimuth direction is the direction in which the satellite is traveling. The coordinate axis developed in that direction is called the azimuth axis. Although the explanation is based on a flat earth surface and a straight line orbit parallel to it as shown in Figure 1, the same applies to an actual satellite's spherical earth surface and curved satellite orbit. be. Furthermore, it is known that for a radar image obtained using a curved surface and a curved surface of the earth and a satellite orbit, it is possible to approximately derive a surface of the earth and a satellite orbit that are a plane and a straight line from which a radar image close to the surface can be obtained. The squint angle on this approximate geometry is referred to as an effective squint angle, but these will not be particularly distinguished in the following explanation.
　図２Ａ～図２Ｃは、レーダ画像の座標系の例を説明するための説明図である。すなわち、図２Ａ～図２Ｃは、図１に示す投影面内における座標系を示している。図２Ａには、人工衛星１の進行方向とそれに直交する方向とを２軸とする座標系が示されている。座標系の軸方向は、サンプリングの方向に対応する。図２Ｂには、人工衛星１の進行方向と人工衛星のレンジ方向とを２軸とする座標系が示されている。図２Ｃには、人工衛星１のレンジ方向とそれに直交する方向とを２軸とする座標系が示されている。なお、格子は、空間を分割する複数の縦の線と横の線との各々を意味する。格子で囲まれた四角形のメッシュは画素に相当する。すなわち、レーダ画像は、多数のメッシュで構成される。図２Ａおよび図２Ｃには、一つのメッシュすなわち一つの画素がマーキングで明示されている。以下、レンジ方向をアンテナ方向という。 FIGS. 2A to 2C are explanatory diagrams for explaining examples of coordinate systems of radar images. That is, FIGS. 2A to 2C show coordinate systems within the projection plane shown in FIG. 1. FIG. 2A shows a coordinate system whose two axes are the traveling direction of the artificial satellite 1 and a direction perpendicular thereto. The axial direction of the coordinate system corresponds to the direction of sampling. FIG. 2B shows a coordinate system whose two axes are the traveling direction of the artificial satellite 1 and the range direction of the artificial satellite. FIG. 2C shows a coordinate system whose two axes are the range direction of the artificial satellite 1 and the direction perpendicular thereto. Note that the lattice refers to each of a plurality of vertical lines and horizontal lines that divide a space. A rectangular mesh surrounded by a grid corresponds to a pixel. That is, a radar image is composed of many meshes. In FIGS. 2A and 2C, one mesh, ie, one pixel, is clearly marked. Hereinafter, the range direction will be referred to as the antenna direction.
　図２Ａに示された座標系が用いられる場合には、図１７に例示されたようにスペクトラムが傾く。その結果、エイリアシングを回避するためにデータ量が多くなる。なお、観測信号は例えば記憶装置に格納されている。図２Ａに示された座標系が用いられる場合には、一例として、観測信号に対応する、ゼロドップラー方向での時刻が、記憶装置に保存されている。ゼロドップラーは、衛星の移動で生じるドップラーが０になる方向のことである。一般に、ドップラーが０になる方向は、衛星の移動速度ベクトルと直交する方向である。多くの場合に、ゼロドップラーは、軌道直交方向またはそれに地球の時点に依存した観測対象の移動速度を加味した方向ことである。また、ゼロドップラー方向での時刻は、観測対象が衛星から見てゼロドップラーの方向（軌道直交方向）の真正面位置を通過した時刻である。すなわち、衛星画像処理システムは、一般に、その衛星の軌道と各画素のゼロドップラーの時刻とを結びつけることによって、各画素における衛星の位置を算出することができるようになっている。 When the coordinate system shown in FIG. 2A is used, the spectrum is tilted as illustrated in FIG. 17. As a result, the amount of data increases to avoid aliasing. Note that the observation signal is stored in a storage device, for example. When the coordinate system shown in FIG. 2A is used, as an example, the time in the zero Doppler direction corresponding to the observation signal is stored in the storage device. Zero Doppler is the direction in which the Doppler produced by the movement of the satellite becomes zero. Generally, the direction in which Doppler becomes 0 is the direction perpendicular to the moving velocity vector of the satellite. In most cases, zero Doppler is the direction perpendicular to the orbit or the direction plus the speed of movement of the observed object depending on the Earth's point in time. Further, the time in the zero Doppler direction is the time when the observation target passes directly in front of the zero Doppler direction (direction perpendicular to the orbit) as seen from the satellite. That is, the satellite image processing system is generally capable of calculating the position of the satellite at each pixel by linking the orbit of the satellite with the zero Doppler time of each pixel.
　図２Ｂに示された座標系が用いられる場合には、スペクトラムは、平行四辺形状になる。その結果、図２Ａに示された座標系が用いられる場合に比べて、エイリアシングを回避するために要するデータの量は減る。しかし、レーダ画像を加工する場合、例えば移動させるような場合に、処理の負担が大きくなる。図２Ｂに示された座標系が用いられる場合には、一例として、アンテナ方向に対する遅延時間と、撮影時間中にアンテナがレンジ方向を向き続けていたと仮定した場合に散乱体がアンテナ正面に来る時刻とが、観測信号に対応付けた形で記憶装置に保存されている。なお、遅延時間は、電磁波が発射されてから反射波が受信されるまでの時間である。 If the coordinate system shown in FIG. 2B is used, the spectrum will be parallelogram-shaped. As a result, less data is required to avoid aliasing than if the coordinate system shown in FIG. 2A were used. However, when processing a radar image, for example when moving it, the processing load increases. When the coordinate system shown in FIG. 2B is used, as an example, the delay time relative to the antenna direction and the time when the scatterer comes in front of the antenna, assuming that the antenna continues to face the range direction during the imaging time. are stored in the storage device in association with the observed signals. Note that the delay time is the time from when the electromagnetic wave is emitted until the reflected wave is received.
　図２Ｃに示す座標系は、下記の実施形態において用いられる座標系である。図２Ｃに示す座標系を用いて、２軸のそれぞれに沿ってサンプリングが実行される場合、不要な信号をサンプリングの対象にしなくてよい。したがって、レーダ画像のデータ量の増大が抑制される。 The coordinate system shown in FIG. 2C is a coordinate system used in the embodiments described below. When sampling is performed along each of the two axes using the coordinate system shown in FIG. 2C, unnecessary signals do not need to be sampled. Therefore, an increase in the amount of radar image data is suppressed.
　図２Ｃに示された座標系は、例えば、衛星が、該衛星の進行方向に直交する方向とは異なる方向に信号を照射する場合に用いることができる座標系である。該信号は、衛星に搭載されたレーダから地表等の観測対象に向けて照射される。そして、該信号に対する反射を表す反射信号における信号強度の強弱に応じて、観測対象の有無や、該観測対象の形状が観測される。 The coordinate system shown in FIG. 2C is a coordinate system that can be used, for example, when a satellite irradiates a signal in a direction different from the direction perpendicular to the direction of travel of the satellite. The signal is emitted from a radar mounted on a satellite toward an observation target such as the ground surface. Then, the presence or absence of the observation target and the shape of the observation target are observed depending on the strength of the signal in the reflected signal representing the reflection of the signal.
　そして、観測された信号の強度は、たとえば、図２Ｃに示された座標系で計測されたデータ形式で表される。座標系における１つの軸は、衛星が信号を照射する方向（便宜上、「第１方向」と表すことがある。）に沿った軸である。スクイント角が０よりも大きな値の場合に、第１方向は、衛星の進行方向に直交する直交方向とは異なる方向である。他方の軸は、該進行方向および該直交方向がなす平面において、第１方向に直交する方向（便宜上、「第２方向」と表すことがある。）に沿った軸である。よって、反射信号に関する情報は、第１方向と第２方向とに沿って表すデータ形式で作成される。 Then, the strength of the observed signal is expressed, for example, in a data format measured in the coordinate system shown in FIG. 2C. One axis in the coordinate system is an axis along the direction in which the satellite irradiates a signal (for convenience, this may be referred to as a "first direction"). When the squint angle is greater than 0, the first direction is a direction different from the orthogonal direction perpendicular to the direction of travel of the satellite. The other axis is an axis along a direction perpendicular to the first direction (for convenience, it may be referred to as a "second direction") in a plane formed by the traveling direction and the orthogonal direction. Therefore, information regarding the reflected signal is created in a data format representing along the first direction and the second direction.
　以下、本発明の実施形態を図面を参照して説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
実施形態１．
　図３は、第１の実施形態の信号処理装置の構成例を示すブロック図である。図３に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０とを備えている。 Embodiment 1.
FIG. 3 is a block diagram showing a configuration example of the signal processing device according to the first embodiment. The signal processing device shown in FIG. 3 includes an inclined image generation section 100 and a satellite observation data storage section 130.
　衛星観測データ記憶部１３０には、観測信号１３１と衛星情報１３２とが格納されている。観測信号は、人工衛星のレーダで受信された受信信号である。衛星情報は、衛星位置、アンテナ方向、帯域幅などを含む。 The satellite observation data storage unit 130 stores observation signals 131 and satellite information 132. The observation signal is a received signal received by a radar of an artificial satellite. Satellite information includes satellite position, antenna direction, bandwidth, etc.
　傾斜画像生成部１００は、衛星情報に基づいて、例えば、図２Ｃに例示された２軸を生成する。そして、傾斜画像生成部１００は、所定の方法を用いて、各画素の散乱強度を求める。 The tilt image generation unit 100 generates, for example, two axes illustrated in FIG. 2C based on the satellite information. Then, the tilted image generation unit 100 calculates the scattering intensity of each pixel using a predetermined method.
　言い換えると、傾斜画像生成部（または、情報作成部）１００は、図２Ｃを参照しながら上述したような、第１方向と第２方向とに沿って表すデータ形式にて、散乱強度に関する情報を作成する。第１方向は、衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が、該信号を照射する方向を表す方向である。第２方向は、該進行方向および該直交方向とがなす平面において、該第１方向とに直交する方向である。 In other words, the tilted image generation unit (or information generation unit) 100 generates information regarding the scattering intensity in a data format expressed along the first direction and the second direction, as described above with reference to FIG. 2C. create. The first direction is a direction in which a satellite emits a signal in a direction different from the orthogonal direction that is perpendicular to the traveling direction of the satellite. The second direction is a direction orthogonal to the first direction in a plane formed by the traveling direction and the orthogonal direction.
実施形態２．
　図４は、第２の実施形態の信号処理装置の構成例を示すブロック図である。図４に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０とを備えている。第２の実施形態では、傾斜画像生成部１００は、格子生成部１１１と逆投影部１１２とを含む。第２の実施形態の信号処理装置は、図３に示された第１の実施形態の信号処理装置の一具体例に相当する。 Embodiment 2.
FIG. 4 is a block diagram showing a configuration example of a signal processing device according to the second embodiment. The signal processing device shown in FIG. 4 includes an inclined image generation section 100 and a satellite observation data storage section 130. In the second embodiment, the tilted image generation section 100 includes a grid generation section 111 and a back projection section 112. The signal processing device of the second embodiment corresponds to a specific example of the signal processing device of the first embodiment shown in FIG.
　格子生成部１１１は、衛星情報に基づいて、あらかじめ、図２Ｃに例示された格子を生成する。逆投影部１１２は、逆投影法（Back Projection）を用いて、各画素の散乱強度を求める。 The grid generation unit 111 generates the grid illustrated in FIG. 2C in advance based on the satellite information. The back projection unit 112 uses a back projection method to find the scattering intensity of each pixel.
　次に、図５のフローチャートを参照して、第１の実施形態の信号処理装置の動作を説明する。 Next, the operation of the signal processing device of the first embodiment will be described with reference to the flowchart in FIG.
　格子生成部１１１は、衛星情報に基づいて格子を生成する（ステップＳ１０１）。ステップＳ１０１で、格子生成部１１１は、帯域幅等の解像度算出に利用しうるパラメータと、アンテナ方向とを基に格子を生成する。なお、格子生成部１１１は、格子を、アンテナ方向と、アンテナ方向と衛星移動方向のベクトルが張る平面に存在しアンテナ方向と直交する方向との２軸で生成する。 The grid generation unit 111 generates a grid based on the satellite information (step S101). In step S101, the grid generation unit 111 generates a grid based on parameters that can be used for resolution calculation, such as bandwidth, and the antenna direction. Note that the lattice generation unit 111 generates the lattice along two axes: the antenna direction, and a direction that exists on a plane defined by the vector of the antenna direction and the satellite movement direction and is orthogonal to the antenna direction.
　なお、２軸は厳密に直交していなくてもよい。また、２軸は、厳密にアンテナ方向と衛星移動方向のベクトルが張る平面に存在していなくてもよい。現実の人工衛星は、地球表面の曲がり具合等に応じて宇宙空間上の曲線を飛行するので、アンテナ方向や衛星の移動方向が１つに定まらない。よって、アンテナ方向は、複数の方向のうちの代表的な方向であってもよい。すなわち、アンテナ方向は、複数の方向のうちの一部であってもよい。また、衛星の移動方向は、複数の方向のうちの代表的な方向であってもよい。すなわち、衛星の移動方向は、複数の方向のうちの一部であってもよい。 Note that the two axes do not have to be strictly orthogonal. Furthermore, the two axes do not need to be strictly on a plane defined by vectors in the antenna direction and the satellite movement direction. In reality, artificial satellites fly along curves in space depending on the degree of curvature of the earth's surface, so the direction of the antenna and the direction of movement of the satellite cannot be determined in one direction. Therefore, the antenna direction may be a representative direction among a plurality of directions. That is, the antenna direction may be part of a plurality of directions. Further, the moving direction of the satellite may be a representative direction among a plurality of directions. That is, the direction of movement of the satellite may be part of a plurality of directions.
　逆投影部１１２は、格子によって形成される各メッシュに対して、Back Projectionを実行する（ステップＳ１０２）。Back Projectionは、生成されるべき画素毎に相関積分値を計算することによって各画素を生成する方法である。すなわち、逆投影部１１２は、アンテナ方向とそれに直交する方向とを２軸とし、軸に平行な複数の格子によって形成される複数のメッシュを含む領域に、レーダ画像を生成することができる。 The back projection unit 112 performs Back Projection on each mesh formed by the grid (step S102). Back Projection is a method of generating each pixel by calculating a correlation integral value for each pixel to be generated. That is, the back projection unit 112 can generate a radar image in a region including a plurality of meshes formed by a plurality of lattices parallel to the two axes, the antenna direction and a direction perpendicular thereto.
実施形態３．
　図６は、第３の実施形態の信号処理装置の構成例を示すブロック図である。図６に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０とを備えている。第３の実施形態では、傾斜画像生成部１００は、オメガＫアルゴリズムを使用する。第３の実施形態では、傾斜画像生成部１００は、２次元（２Ｄ）フーリエ変換部１１３、レンジスペクトルシフト部１１４、アジマススペクトルシフト部１１５、および２Ｄ逆フーリエ変換部１１６を含む。第３の実施形態の信号処理装置は、図３に示された第１の実施形態の信号処理装置の他の具体例に相当する。なお、一般的なオメガＫアルゴリズムは、２次元フーリエ変換後に実行されるレンジスペクトルシフト処理およびアジマススペクトルシフト処理を含む。 Embodiment 3.
FIG. 6 is a block diagram showing a configuration example of a signal processing device according to the third embodiment. The signal processing device shown in FIG. 6 includes an inclined image generation section 100 and a satellite observation data storage section 130. In the third embodiment, the tilted image generator 100 uses the Omega K algorithm. In the third embodiment, the tilted image generation section 100 includes a two-dimensional (2D) Fourier transform section 113, a range spectrum shift section 114, an azimuth spectrum shift section 115, and a 2D inverse Fourier transform section 116. The signal processing device of the third embodiment corresponds to another specific example of the signal processing device of the first embodiment shown in FIG. Note that the general Omega K algorithm includes range spectrum shift processing and azimuth spectrum shift processing that are executed after two-dimensional Fourier transform.
　第３の実施形態では、例えば、アンテナ方向に対する遅延時間と、撮影時間中にアンテナがレンジ方向を向き続けていたと仮定した場合に散乱体がアンテナ正面に来る時刻とが、観測信号に対応付けた形で衛星観測データ記憶部１３０に、衛星情報１３２として保存されている。 In the third embodiment, for example, the delay time with respect to the antenna direction and the time when the scatterer comes in front of the antenna, assuming that the antenna continues to face the range direction during the imaging time, are associated with the observation signal. The information is stored in the satellite observation data storage unit 130 as satellite information 132.
　２Ｄフーリエ変換部１１３は、観測信号を２次元フーリエ変換する。レンジスペクトルシフト部１１４は、レンジ方向のスペクトルシフト処理を行う。アジマススペクトルシフト部１１５は、アジマス方向のスペクトルシフト処理を行う。２Ｄ逆フーリエ変換部１１６は、２次元逆フーリエ変換を行う。 The 2D Fourier transform unit 113 performs two-dimensional Fourier transform on the observed signal. The range spectrum shift unit 114 performs spectrum shift processing in the range direction. The azimuth spectrum shift unit 115 performs spectrum shift processing in the azimuth direction. The 2D inverse Fourier transform unit 116 performs two-dimensional inverse Fourier transform.
　次に、図７のフローチャートおよび図８の説明図を参照して、第３の実施形態の信号処理装置の動作を説明する。図８は、シフト処理を説明するための説明図である。 Next, the operation of the signal processing device of the third embodiment will be described with reference to the flowchart in FIG. 7 and the explanatory diagram in FIG. 8. FIG. 8 is an explanatory diagram for explaining shift processing.
　２Ｄフーリエ変換部１１３は、観測信号を２次元フーリエ変換する（ステップＳ１０３）。レンジスペクトルシフト部１１４は、スペクトルをレンジ方向でシフトする（ステップＳ１０４）。ステップＳ１０４において、レンジスペクトルシフト部１１４は、アジマス周波数に対応するシフト量だけスペクトルをシフトする。次いで、アジマススペクトルシフト部１１５は、スペクトルをアジマス方向でシフトする（ステップＳ１０５）。 The 2D Fourier transform unit 113 performs two-dimensional Fourier transform on the observed signal (step S103). The range spectrum shift unit 114 shifts the spectrum in the range direction (step S104). In step S104, the range spectrum shift unit 114 shifts the spectrum by a shift amount corresponding to the azimuth frequency. Next, the azimuth spectrum shift unit 115 shifts the spectrum in the azimuth direction (step S105).
　第３の実施形態では、衛星観測データ記憶部１３０における衛星情報１３２が用いられる場合、図８における上段の左側に例示されたスペクトルが得られる。なお、そのようなスペクトルは、図２Ｂに例示された座標系でのスペクトルに相当する。ステップＳ１０４の処理が実行されると、図８における上段の右側に例示されているような、アジマス方向において湾曲するスペクトルが得られる。 In the third embodiment, when the satellite information 132 in the satellite observation data storage unit 130 is used, the spectrum illustrated on the left side of the upper row in FIG. 8 is obtained. Note that such a spectrum corresponds to the spectrum in the coordinate system illustrated in FIG. 2B. When the process of step S104 is executed, a spectrum curved in the azimuth direction as illustrated on the right side of the upper row in FIG. 8 is obtained.
　以下、シフト処理の具体的な処理の一例を説明する。 Hereinafter, a specific example of shift processing will be described.
　レンジ時間をτとし、アジマス時間をηとする。観測信号をｓ（τ，η）とする。アンテナ方向をθsqとする。電磁波の周波数の波数に対応するレンジ波数をｋcarrierとする。 Let range time be τ and azimuth time be η. Let the observed signal be s(τ, η). Let the antenna direction be θ sq . Let k carrier be the range wave number corresponding to the wave number of the electromagnetic wave frequency.
　また、レンジ方向の空間周波数をｋrgとする。アジマス方向の空間周波数をｋazとする。観測信号の２次元フーリエ変換によって、２次元スペクトルＳ（ｋrg, ｋaz）が得られる。なお、２Ｄフーリエ変換部１１３は、レンジ方向に対する（光速／２）のスケーリング処理、および、アジマス方向に対する衛星速度によるスケーリング処理も実行する。 Also, let k rg be the spatial frequency in the range direction. Let k az be the spatial frequency in the azimuth direction. A two-dimensional spectrum S(k rg , k az ) is obtained by two-dimensional Fourier transformation of the observed signal. Note that the 2D Fourier transform unit 113 also executes scaling processing by (velocity of light/2) in the range direction and scaling processing by satellite velocity in the azimuth direction.
　レンジスペクトルシフト部１１４が、（ｋrg, ｋaz）で示される位置の値を（ｋ’rg, ｋaz）に移動されると、すなわちシフトさせると、図８における上段の右側に例示されたスペクトルが得られる。ｋ’rgは、（１）式で表される。（１）式において、Ｃ1は、任意の定数である。 When the range spectrum shift unit 114 moves the value at the position indicated by (k rg , k az ) to (k' rg , k az ), that is, shifts it, the value illustrated on the right side of the upper row in FIG. A spectrum is obtained. k' rg is expressed by equation (1). In formula (1), C 1 is an arbitrary constant.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　なお、Ｃ1を（２）式で表されるようにした場合には、ｋ’rgの周波数特性は、元の観測信号の周波数特性に最も近くなる。また、Ｃ1を（３）式で表されるようにした場合には、レンジ帯域の中心が０になり、画像の移動処理などにおいて必要になる補間処理が最もやりやすくなる。また、レンジ方向でエイリアシングを回避しやすくなる。 Note that when C 1 is expressed by equation (2), the frequency characteristic of k' rg becomes closest to the frequency characteristic of the original observation signal. Furthermore, when C 1 is expressed by equation (3), the center of the range band becomes 0, making it easier to perform interpolation processing required in image movement processing and the like. Also, it becomes easier to avoid aliasing in the range direction.
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　第３の実施形態では、アジマススペクトルシフト部１１５が、スペクトルのアジマス方向の傾き（図８における上段の右側参照）を是正する。具体的には、アジマススペクトルシフト部１１５は、（ｋ’rg, ｋaz）を（ｋ’rg, ｋ’az）に移動させる。ただし、ｋ’azは、（４）式で表される。（４）式において、Ｃ2は、任意の定数である。なお、sinθsqは、図８における上段の右側に例示されているスペクトルにおける傾きに対応する。 In the third embodiment, the azimuth spectrum shift unit 115 corrects the inclination of the spectrum in the azimuth direction (see the right side of the upper row in FIG. 8). Specifically, the azimuth spectrum shift unit 115 moves (k' rg , k az ) to (k' rg , k' az ). However, k' az is expressed by equation (4). In formula (4), C 2 is an arbitrary constant. Note that sin θ sq corresponds to the slope in the spectrum illustrated on the right side of the upper row in FIG.
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　アジマススペクトルシフト部１１５が、（ｋ’rg, ｋaz）を（ｋ’rg, ｋ’az）に移動させることによって、図８における下段に例示されるようなスペクトルが得られる。なお、Ｃ2＝０の場合には、アジマス帯域の中心が０になり、アジマス方向でエイリアシングを回避しやすくなる。 When the azimuth spectrum shift unit 115 shifts (k' rg , k az ) to (k' rg , k' az ), a spectrum as illustrated in the lower part of FIG. 8 is obtained. Note that when C 2 =0, the center of the azimuth band becomes 0, making it easier to avoid aliasing in the azimuth direction.
　なお、（１）式におけるtanθsqおよび（４）式におけるsinθsqは、tanθsqに近い値およびsinθsqに近い値であってもよい。すなわち、理想的には衛星に搭載された測位システムやアンテナの制御情報等に基づいて厳密なスクイント角を用いるが、例えば正確な測位システム情報が利用できない場合に地上から反射された電磁波のドップラーシフトから逆算して用いてもよい。また、画像化の処理においては曲線の軌道を直線として近似したり曲面の地上を平面として近似する場合があるが、その近似された幾何におけるスクイント角相当のものとして、例えば、θsqとして、実効スクイント角を用いてもよい。また、θsqとして、地上から見た反射波の入射角を用いてもよい。 Note that tanθ sq in equation (1) and sinθ sq in equation (4) may be values close to tanθ sq and values close to sinθ sq . That is, ideally, a precise squint angle is used based on the control information of the positioning system and antenna on board the satellite, but for example, when accurate positioning system information is not available, the Doppler shift of electromagnetic waves reflected from the ground is used. You may use it by calculating backwards from In addition, in imaging processing, the trajectory of a curved line may be approximated as a straight line, or the ground of a curved surface may be approximated as a plane, but the equivalent of the squint angle in the approximated geometry is, for example, θ sq , which is the effective The Squint angle may also be used. Furthermore, the angle of incidence of the reflected wave as seen from the ground may be used as θ sq .
　その後、２Ｄ逆フーリエ変換部１１６は、２次元逆フーリエ変換を行う（ステップＳ１０６）。 After that, the 2D inverse Fourier transform unit 116 performs two-dimensional inverse Fourier transform (step S106).
　第３の実施形態では、図８における下段に例示されるようなスペクトルが得られる。すなわち、不要な信号が低減される。したがって、レーダ画像のデータ量の増大が抑制される。 In the third embodiment, a spectrum as illustrated in the lower part of FIG. 8 is obtained. That is, unnecessary signals are reduced. Therefore, an increase in the amount of radar image data is suppressed.
　なお、第３の実施形態でも、実質的に、アンテナ方向とそれに直交する方向とを２軸のいずれかに平行な格子によって形成される複数のメッシュを含む領域に、レーダ画像が生成される。 Note that in the third embodiment as well, a radar image is substantially generated in a region including a plurality of meshes formed by a lattice parallel to either of the two axes, the antenna direction and the direction perpendicular thereto.
実施形態４．
　図９は、第４の実施形態の信号処理装置の構成例を示すブロック図である。図９に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０とを備えている。第４の実施形態では、傾斜画像生成部１００は、アップサンプル部１１７、ゼロドップラー結像処理部１１８、回転処理部１１９、およびダウンサンプル部１２０を含む。第４の実施形態では、傾斜画像生成部１００は、画像化アルゴリズムとして、一般的なゼロドップラーアルゴリズムを使用する。ゼロドップラーアルゴリズムは、ゼロドップラー方向と衛星軌道方向との二軸で画像化する画像化方法一般を意味する。 Embodiment 4.
FIG. 9 is a block diagram showing a configuration example of a signal processing device according to the fourth embodiment. The signal processing device shown in FIG. 9 includes an inclined image generation section 100 and a satellite observation data storage section 130. In the fourth embodiment, the tilted image generation section 100 includes an up-sampling section 117, a zero-Doppler imaging processing section 118, a rotation processing section 119, and a down-sampling section 120. In the fourth embodiment, the tilt image generation unit 100 uses a general zero Doppler algorithm as an imaging algorithm. The zero Doppler algorithm refers to a general imaging method that images in two axes: the zero Doppler direction and the satellite orbit direction.
　アップサンプル部１１７は、画素数を増やす処理を行う。ゼロドップラー結像処理部１１８は、ゼロドップラーアルゴリズムに基づく画像化処理すなわち結像処理としてのゼロドップラー処理を行う。回転処理部１１９は、画像化処理結果のスペクトルを回転させる処理を行う。ダウンサンプル部１２０は、スペクトルの周囲の画素数を減らす処理を行う。 The up-sampling unit 117 performs processing to increase the number of pixels. The zero Doppler imaging processing unit 118 performs imaging processing based on a zero Doppler algorithm, that is, zero Doppler processing as imaging processing. The rotation processing unit 119 performs processing to rotate the spectrum of the imaging processing result. The down-sampling unit 120 performs processing to reduce the number of pixels around the spectrum.
　図１０は、ゼロドップラーを用いた画像化処理を説明するための説明図である。ゼロドップラー処理が用いられる場合には、ゼロドップラー時刻と呼ばれる時刻情報が保存がされる。ゼロドップラー時刻は、レーダが実際に信号を受信する時刻とは異なっている。スクイント角θsqが小さい場合には、受信時刻とゼロドップラー時刻との乖離は少ない。よって、ゼロドップラー時刻に補間した衛星位置で地上投影しても、レーダ画像においてずれは生じない。しかし、高スクイントの場合には、受信時刻とゼロドップラー時刻とが大きく異なるので、ずれが生じる。 FIG. 10 is an explanatory diagram for explaining imaging processing using zero Doppler. When zero Doppler processing is used, time information called zero Doppler time is saved. The zero Doppler time is different from the time when the radar actually receives the signal. When the squint angle θ sq is small, the deviation between the reception time and the zero Doppler time is small. Therefore, even if the radar image is projected onto the ground using a satellite position interpolated at zero Doppler time, no deviation will occur in the radar image. However, in the case of high squint, the reception time and the zero Doppler time are significantly different, so a shift occurs.
　なお、ゼロドップラー処理が用いられる場合に、観測信号に基づいて画像が生成されるときに、図１７に例示されたように、スペクトルが傾く。その結果、エイリアシングが生じやすくなる。 Note that when zero Doppler processing is used and an image is generated based on the observed signal, the spectrum is tilted as illustrated in FIG. 17. As a result, aliasing is more likely to occur.
　第４の実施形態では、ゼロドップラー処理が用いられる場合でも、エイリアシングの発生が回避される。 In the fourth embodiment, the occurrence of aliasing is avoided even when zero Doppler processing is used.
　図１１は、ゼロドップラー処理を説明するための説明図である。図１１における上段の左側に例示されるように、観測信号に基づいて画像が生成されるときにスペクトルが傾く。そこで、アップサンプル部１１７は、スペクトル全体がサンプリング可能になるように、実際のスペクトルの周囲に画素値０の画素を追加する（図１１における上段の右側参照）。 FIG. 11 is an explanatory diagram for explaining zero Doppler processing. As illustrated on the left side of the upper row in FIG. 11, the spectrum is tilted when an image is generated based on the observation signal. Therefore, the up-sampling unit 117 adds pixels with a pixel value of 0 around the actual spectrum so that the entire spectrum can be sampled (see the upper right side of FIG. 11).
　ゼロドップラー結像処理部１１８は、ゼロドップラー処理を実行する。ゼロドップラー処理によって、レーダ画像が得られる。しかし、図１１における下段の左側に例示されるように、スペクトルが傾く。回転処理部１１９は、スペクトルの傾きがなくなるように、画像に回転処理を施す。スペクトルの傾きを是正する。回転処理部１１９による回転処理が実行されると、図１１における下段の中央に例示されるように、スペクトルの傾きがなくなる。ダウンサンプル部１２０は、スペクトルが存在しない部分の画素を削除する（図１１における下段の右側参照）。 The zero Doppler imaging processing unit 118 executes zero Doppler processing. Radar images are obtained by zero Doppler processing. However, as illustrated on the left side of the lower row in FIG. 11, the spectrum is tilted. The rotation processing unit 119 performs rotation processing on the image so that the tilt of the spectrum is eliminated. Correct the spectral tilt. When the rotation processing by the rotation processing unit 119 is executed, the slope of the spectrum disappears, as illustrated in the center of the lower row in FIG. 11 . The down-sampling unit 120 deletes pixels in a portion where no spectrum exists (see the lower right side in FIG. 11).
　第４の実施形態の信号処理装置は、アップサンプルによってエイリアシングを回避できる。また、信号処理装置は、回転処理を行った後に実行されるダウンサンプルによってレーダ画像のデータ量の増大を抑制できる。 The signal processing device of the fourth embodiment can avoid aliasing by upsampling. Further, the signal processing device can suppress an increase in the amount of data of the radar image by down-sampling performed after rotation processing.
　なお、上記の各実施形態は、送信アンテナと受信アンテナとが異なる位置に存在するバイスタティック構成にも適用可能である。バイスタティック構成の場合には、送信アンテナの対象物体に対する方向と、受信アンテナの対象物体に対する方向とがなす角の二等分線方向を１つの軸とし、その直交方向をもう１つの軸とすればよい。 Note that each of the above embodiments is also applicable to a bistatic configuration in which the transmitting antenna and the receiving antenna are located at different positions. In the case of a bistatic configuration, one axis is the direction of the bisector of the angle formed by the direction of the transmitting antenna with respect to the target object and the direction of the receiving antenna with respect to the target object, and the other axis is the direction perpendicular thereto. Bye.
　また、複数軌道で撮影を行って立体的な合成開口処理をおこなうトモグラフィに対して、上記の各実施形態を適用可能である。トモグラフィの場合には、例えば、２次元のスクイント画像同様に、１つの軸をアンテナ方向とし、もう１つの軸を、アンテナ方向に垂直で、かつ、衛星軌道とアンテナ方向がなす面内の方向とする。そして、そのような２軸が構成する面に対して法線方向をエレベーション方向として三次元格子を作成すると、エイリアシングの発生を効果的に防ぐことができる。 Furthermore, each of the above embodiments can be applied to tomography that performs three-dimensional synthetic aperture processing by performing imaging in multiple trajectories. In the case of tomography, for example, as with two-dimensional squint images, one axis is the antenna direction, and the other axis is a direction perpendicular to the antenna direction and within the plane formed by the satellite orbit and the antenna direction. shall be. If a three-dimensional lattice is created with the normal direction to the plane constituted by such two axes as the elevation direction, aliasing can be effectively prevented from occurring.
　バイスタティックトモグラフィ（送信機衛星が１台であるが、複数の受信機衛星が飛行する形態）では、アンテナ方向の代わりに送信機アンテナ方向と受信機アンテナ方向の角の二等分線方向を用いることによって、上記の各実施形態を適用できる。 In bistatic tomography (a form in which there is one transmitter satellite but multiple receiver satellites fly), the direction of the bisector of the angle between the transmitter antenna direction and the receiver antenna direction is used instead of the antenna direction. By using this, each of the above embodiments can be applied.
　なお、第４の実施形態でも、実質的に、アンテナ方向とそれに直交する方向とを２軸のいずれかに平行な格子によって形成される複数のメッシュを含む領域に、レーダ画像が生成される。 Note that in the fourth embodiment as well, a radar image is substantially generated in a region including a plurality of meshes formed by a lattice parallel to either of the two axes, the antenna direction and the direction perpendicular thereto.
実施形態５．
　第５の実施形態の信号処理装置は、高解像度モードまたは広域モードに効果的に適用される。例えば、ＳＡＲ画像を高解像度化するために、人工衛星に搭載されているレーダのアンテナを長期間に亘って撮影領域に向けることによって合成開口長を長くすることが考えられる。ＳＡＲ画像を高解像度化するための処理が実行されるモードを、高解像度モードとする。 Embodiment 5.
The signal processing device of the fifth embodiment is effectively applied to high resolution mode or wide area mode. For example, in order to increase the resolution of SAR images, it is conceivable to increase the synthetic aperture length by directing a radar antenna mounted on an artificial satellite toward the imaging area for a long period of time. A mode in which processing for increasing the resolution of a SAR image is executed is referred to as a high resolution mode.
　また、例えば、アンテナのスクイント角を変化させながら撮影を行うことによって、撮影領域を広げることができる。広い範囲を撮影領域とするモードを、広域モードとする。以下、アンテナのスクイント角を変化させることを、アンテナを振ると表現することがある。 Furthermore, for example, by performing photography while changing the squint angle of the antenna, the photographing area can be expanded. A mode in which a wide range is photographed is called a wide-area mode. Hereinafter, changing the squint angle of the antenna may be expressed as shaking the antenna.
　図１２に示す信号処理装置は、傾斜画像生成部１０１と、衛星観測データ記憶部１３０と、位相変調推定部２００とを備えている。 The signal processing device shown in FIG. 12 includes a tilt image generation section 101, a satellite observation data storage section 130, and a phase modulation estimation section 200.
　第５の実施形態では、傾斜画像生成部１０１は、第１の実施形態における傾斜画像生成部１００と同じ機能を有する。ただし、傾斜画像生成部１０１は、アンテナを振ったことによる影響を考慮して画像化処理を行う。例えば、画像化結果に、各時刻のアンテナの方向に依存した位相変調を表す位相変調情報が含まれる。したがって、画像における画像の位置に依存した帯域の変化を、位相変調情報から算出したり、その影響を取り除いたりすることができる。 In the fifth embodiment, the tilted image generation unit 101 has the same function as the tilted image generation unit 100 in the first embodiment. However, the tilted image generation unit 101 performs the imaging process in consideration of the influence of swinging the antenna. For example, the imaging results include phase modulation information representing the phase modulation dependent on the direction of the antenna at each time. Therefore, it is possible to calculate a change in the band depending on the position of the image from the phase modulation information, and to remove the influence thereof.
　第５の実施形態では、傾斜画像生成部１０１がレーダ画像を出力するとともに、位相変調推定部２００が、位相変調情報を出力する。位相変調推定部２００は、アンテナ方向に直交する方向の各座標における位相変調量を算出する。なお、アンテナ方向では、位相変調量は、ほぼ一定である。 In the fifth embodiment, the tilt image generation unit 101 outputs a radar image, and the phase modulation estimation unit 200 outputs phase modulation information. The phase modulation estimation unit 200 calculates the amount of phase modulation at each coordinate in a direction orthogonal to the antenna direction. Note that in the antenna direction, the amount of phase modulation is approximately constant.
　撮影時に人工衛星が散乱体に近づく時には、ドップラー周波数が高い。人工衛星と散乱体との距離がほほ一定の状態で撮影が行われるときには、人工衛星は散乱体に近づきもせず遠ざかりもしないので、ドップラー周波数は０である。アンテナが振られると、人工衛星が散乱体に近づく状態と人工衛星と散乱体との距離がほほ一定の状態との双方が繰り返し現れる。 When the satellite approaches the scatterer during photography, the Doppler frequency is high. When photography is performed with the distance between the satellite and the scatterer being almost constant, the satellite neither approaches nor moves away from the scatterer, so the Doppler frequency is 0. When the antenna is swung, a state in which the satellite approaches the scatterer and a state in which the distance between the satellite and the scatterer remains almost constant appear repeatedly.
　すなわち、アンテナが振られると、画像化後の各々の画素に対応する散乱体に対して電磁波が当たる時刻が異なるので、電磁波が当たった時刻のアンテナ方向に依存した帯域の変化が起こる。その結果、画像全体において位相変調が現れる。画素位置が異なると帯域が異なるので、例えば、画像の左端に対してエイリアシングしないようなサンプリングを行ったとしても、画像の右端に対してエイリアシングを起こしてしまうおそれがある。 That is, when the antenna is swung, the time at which the electromagnetic waves hit the scatterer corresponding to each pixel after imaging differs, so a change in the band occurs depending on the direction of the antenna at the time when the electromagnetic waves hit. As a result, a phase modulation appears throughout the image. Since different pixel positions have different bands, for example, even if sampling is performed to avoid aliasing to the left end of the image, aliasing may occur to the right end of the image.
　第５の実施形態では、信号処理装置は、信号処理装置の出力を利用する画像処理装置などの装置に、位相変調情報を提供する。以下、画像処理装置などの装置を、他の装置という。 In the fifth embodiment, the signal processing device provides phase modulation information to a device such as an image processing device that uses the output of the signal processing device. Hereinafter, a device such as an image processing device will be referred to as another device.
　十分に遠方を撮影している条件下では、画素位置に依存した帯域の変化は帯域中心のシフトとして生じ、帯域幅の変化はかなり小さい。そのことを利用して、例えば、各画素およびその近傍から得られる帯域中心に対して０からシフトさせる位相変調を算出し、算出した位相変調をレーダ画像から除去することによってエイリアシングを回避しつつ、平行移動等の画像処理を行うことができる。 Under conditions where a sufficiently far distance is photographed, changes in the band depending on pixel position occur as a shift in the center of the band, and changes in the band width are quite small. Taking advantage of this, for example, by calculating a phase modulation that shifts from 0 with respect to the band center obtained from each pixel and its vicinity, and removing the calculated phase modulation from the radar image, aliasing can be avoided. Image processing such as parallel movement can be performed.
　また、他の装置が干渉処理等を実行する場合、干渉処理等で、位相変調をレーダ画像から除去する処理を行った後に、互いに画像の移動による位置合わせ処理し、その後、位相変調を再付加してから干渉処理を行うことができる。また、他の装置は、位置合わせされた画像同士の干渉処理と、各々の画像に付加される位相変調同士の干渉処理とを行い、画像同士の干渉処理結果に位相変調同士の干渉処理結果を付加することによって、エイリアシングの発生を防止しつつ、正確に位相を保持した干渉処理を行える。 In addition, when another device performs interference processing, etc., the phase modulation is removed from the radar image by interference processing, etc., and then the images are aligned with each other by movement, and then the phase modulation is re-added. After that, interference processing can be performed. In addition, other devices perform interference processing between aligned images and interference processing between phase modulations added to each image, and add the interference processing results between phase modulations to the interference processing results between images. By adding this, it is possible to perform interference processing that accurately maintains the phase while preventing the occurrence of aliasing.
　また、他の装置は、位相変調情報を利用することによって、エイリアシングの発生を防止しつつ、位相情報を失わずに画像を変形できる。特に、上記の各実施形態のレーダ処置装置のように斜交した座標系で画像化結果を得る場合には、以下のような効果も得られる。 In addition, other devices can transform images without losing phase information while preventing aliasing by using phase modulation information. In particular, when obtaining imaging results using oblique coordinate systems as in the radar treatment apparatus of each of the embodiments described above, the following effects can also be obtained.
　すなわち、他の装置が、斜交した座標系で画像化結果について位相変調情報を計算する場合、アンテナ方向の画素位置依存性がなく、アンテナ方向に垂直な方向に二次の関数で位相変調情報を近似できるので、変形による伸縮等の処理を多項式の変形処理として簡単に行える。 That is, when another device calculates phase modulation information for the imaging result in an oblique coordinate system, there is no pixel position dependence in the antenna direction, and the phase modulation information is calculated by a quadratic function in the direction perpendicular to the antenna direction. can be approximated, processing such as expansion/contraction by deformation can be easily performed as polynomial deformation processing.
　また、他の装置が、干渉ＳＡＲ（Synthetic Aperture Radar Interferometry）によって画像生成する場合などに、第５の実施形態の信号処理装置を利用するときに、位相変調を除去した状態で互いに位置合わせして２つのレーダ画像を干渉させることができる。他の装置は、干渉に、位相変調同士での干渉結果を付加し直す。そのような処理を実行することによって、他の装置は、処理中のエイリアシング等を回避しながら干渉処理を実行できる。 Also, when using the signal processing device of the fifth embodiment, such as when another device generates an image by interference SAR (Synthetic Aperture Radar Interferometry), it is possible to align them with each other with phase modulation removed. Two radar images can be made to interfere. Other devices re-add the interference results between phase modulations to the interference. By performing such processing, other devices can perform interference processing while avoiding aliasing and the like during processing.
　なお、位相変調推定部２００は、位相変調を、画像化アルゴリズムにおいて使用される係数の組み合わせで算出することができる。また、位相変調推定部２００は、位相変調を、衛星軌道とスクイント角と注視点位置とのみから計算することもできる。位相変調推定部２００は、位相変調を、衛星軌道と撮影対象の位置と注視点位置とのみから計算することもできる。 Note that the phase modulation estimation unit 200 can calculate the phase modulation using a combination of coefficients used in the imaging algorithm. Further, the phase modulation estimating unit 200 can also calculate the phase modulation only from the satellite orbit, the squint angle, and the position of the gaze point. The phase modulation estimating unit 200 can also calculate the phase modulation only from the satellite orbit, the position of the object to be photographed, and the position of the gaze point.
実施形態６．
　図１３は、第６の実施形態の信号処理装置の構成例を示すブロック図である。図１３に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０と、画像処理部３００と、地上投影部３０１とを備えている。傾斜画像生成部１０２は、第１の実施形態における傾斜画像生成部１００と同じ機能を有する。 Embodiment 6.
FIG. 13 is a block diagram showing a configuration example of a signal processing device according to the sixth embodiment. The signal processing device shown in FIG. 13 includes an inclined image generation section 100, a satellite observation data storage section 130, an image processing section 300, and a ground projection section 301. The tilted image generation section 102 has the same function as the tilted image generation section 100 in the first embodiment.
　第６の実施形態の信号処理装置の構成は、第１の実施形態の信号処理装置に、画像処理部３００と地上投影部３０１とが追加された構成である。なお、第１の実施形態以外の実施形態の信号処理装置に、画像処理部３００と地上投影部３０１とが追加されてもよい。 The configuration of the signal processing device of the sixth embodiment is such that an image processing unit 300 and a ground projection unit 301 are added to the signal processing device of the first embodiment. Note that the image processing section 300 and the ground projection section 301 may be added to the signal processing apparatus of embodiments other than the first embodiment.
　ただし、傾斜画像生成部１０２は、傾斜画像生成部１００の機能に加えて、斜交座標情報を作成する機能も有する。 However, in addition to the function of the tilted image generation unit 100, the tilted image generation unit 102 also has a function of creating oblique coordinate information.
　画像処理部３００は、傾斜画像生成部１０２が生成したデータすなわちレーダ画像に対して画像処理を行う。地上投影部３０１は、画像処理結果を地上投影する地上投影処理を行う。 The image processing unit 300 performs image processing on the data generated by the tilted image generation unit 102, that is, the radar image. The ground projection unit 301 performs ground projection processing to project the image processing result onto the ground.
　絶対値画像への変換や変化検知結果など、空間周波数が狭くなる画像処理が行われることがある。画像処理部３００が、そのような画像処理を行うときに、傾斜画像生成部１０２が生成したデータをそのまま使用して画像処理を行い、次いで、地上投影部３０１が地上投影処理を行うことによって、処理の計算量を削減できる。 Image processing that narrows the spatial frequency may be performed, such as conversion to an absolute value image or change detection results. When performing such image processing, the image processing unit 300 performs image processing using the data generated by the tilted image generation unit 102 as is, and then the ground projection unit 301 performs ground projection processing. The amount of calculation required for processing can be reduced.
　斜交座標情報は、衛星軌道からのシフト量や座標軸方向等を含む。ただし、斜交座標情報が、例えば図１４に示すような情報、すなわち、レンジ方向、レンジ方向に対して垂直な方向、画像中心距離を含んでいれば、地上投影部３０１は、衛星軌道に基づく投影処理を行える。なお、レンジ方向およびレンジ方向に対して垂直な方向が傾斜画像生成部１０２から出力されるように構成されているのは、それらが必ずしも厳密な情報でなくてよいためである。 The oblique coordinate information includes the amount of shift from the satellite orbit, the coordinate axis direction, etc. However, if the oblique coordinate information includes information as shown in FIG. 14, for example, the range direction, the direction perpendicular to the range direction, and the image center distance, the ground projection unit 301 Can perform projection processing. Note that the range direction and the direction perpendicular to the range direction are configured to be output from the tilted image generation unit 102 because these do not necessarily have to be exact information.
　地上投影部３０１は、例えば、以下のように、地上投影処理を実行する。 The terrestrial projection unit 301 executes terrestrial projection processing, for example, as follows.
　地上投影部３０１は、レーダ画像における各々の画素が、どの衛星時刻で受信され、衛星軌道に対してどの距離にあるかを、画素番号と斜交座標情報に基づいて算出する。そして、地上投影部３０１は、地上投影を行う。例えば、地上投影部３０１は、地上の立体形状に基づいて、衛星軌道から等距離にある円と地上の立体との交差を算出する。地上投影部３０１は、より簡便に、撮影対象地点の中心における地球楕円体の接面との交差を算出してもよい。 The ground projection unit 301 calculates at what satellite time each pixel in the radar image is received and at what distance from the satellite orbit, based on the pixel number and oblique coordinate information. Then, the terrestrial projection unit 301 performs terrestrial projection. For example, the ground projection unit 301 calculates the intersection of a circle equidistant from the satellite orbit and a solid object on the ground based on the three-dimensional shape on the ground. The ground projection unit 301 may more simply calculate the intersection of the center of the imaging target point with the tangent surface of the earth ellipsoid.
　例えば、接面を平面とし、小規模な領域における投影を行う場合には、地上投影部３０１は、特許文献２に記載された方法を若干改変することによって、Ground Control Pointすなわち地上位置とＳＡＲ画素位置を確実に整合させられる点の位置合わせと、簡単な変形によって、投影処理や位置合わせの補正処理を実現できる。なお、特許文献２に記載された方法ではアンテナ方向と衛星進行方向との２軸による座標系が用いられているのに対して、第６の実施形態では、アンテナ方向とアンテナ直交方向の２軸が使用されるように改変される。 For example, when the tangential surface is a plane and projection is performed in a small area, the ground projection unit 301 uses the Ground Control Point, that is, the ground position and the SAR pixel, by slightly modifying the method described in Patent Document 2. Projection processing and alignment correction processing can be realized by alignment of points that can reliably align the positions and simple deformation. Note that while the method described in Patent Document 2 uses a coordinate system with two axes: the antenna direction and the satellite traveling direction, in the sixth embodiment, a coordinate system with two axes: the antenna direction and the direction perpendicular to the antenna is used. be modified so that it is used.
　また、特許文献２に記載された方法では、画像中の軸を表すベクトルが先に投影される。そして、各画素の投影位置が、画像中心位置に対して先に投影されたベクトルが加算された相対位置として計算される。 Furthermore, in the method described in Patent Document 2, vectors representing the axes in the image are projected first. Then, the projected position of each pixel is calculated as a relative position obtained by adding the previously projected vector to the image center position.
実施形態７．
　図１５は、第７の実施形態の信号処理装置の構成例を示すブロック図である。図１５に示す信号処理装置は、傾斜画像生成部１００と、衛星観測データ記憶部１３０と、ベクトルデータ抽出部３０２と、地上投影部３０１とを備えている。傾斜画像生成部１０２は、第１の実施形態における傾斜画像生成部１００と同じ機能を有する。 Embodiment 7.
FIG. 15 is a block diagram showing a configuration example of a signal processing device according to the seventh embodiment. The signal processing device shown in FIG. 15 includes an inclined image generation section 100, a satellite observation data storage section 130, a vector data extraction section 302, and a ground projection section 301. The tilted image generation section 102 has the same function as the tilted image generation section 100 in the first embodiment.
　第７の実施形態の信号処理装置の構成は、第１の実施形態の信号処理装置に、ベクトルデータ抽出部３０２と地上投影部３０３とが追加された構成である。なお、第１の実施形態以外の実施形態の信号処理装置に、ベクトルデータ抽出部３０２と地上投影部３０３とが追加されてもよい。第７の実施形態の信号処理装置の構成は、第６の実施形態の信号処理装置における画像処理部３００に代えて、ベクトルデータ抽出部３０２が設けられた構成である。なお、地上投影部３０３は、地上投影部３０１と同様に地上撮影処理を行うが、地上投影部３０３の入力はベクトルデータである。 The configuration of the signal processing device of the seventh embodiment is such that a vector data extraction section 302 and a ground projection section 303 are added to the signal processing device of the first embodiment. Note that the vector data extraction section 302 and the ground projection section 303 may be added to the signal processing apparatus of embodiments other than the first embodiment. The configuration of the signal processing apparatus according to the seventh embodiment is such that a vector data extraction section 302 is provided in place of the image processing section 300 in the signal processing apparatus according to the sixth embodiment. Note that the terrestrial projection unit 303 performs terrestrial photographing processing similarly to the terrestrial projection unit 301, but the input to the terrestrial projection unit 303 is vector data.
　第６の実施形態と同様に、傾斜画像生成部１０２は、傾斜画像生成部１００の機能に加えて、斜交座標情報を作成する機能も有する。 Similarly to the sixth embodiment, the tilted image generation unit 102 has the function of creating oblique coordinate information in addition to the function of the tilted image generation unit 100.
　ベクトルデータ抽出部３０２は、例えば、レーダ画像に画像処理が施された画像から、ベクトルデータを取得する。一例として、画像処理としてセマンティックセグメンテーションが実行される場合には、画素や画素群を接続したポリゴンを取得できる。地上投影部３０１は、ベクトルデータに基づいて地上投影処理を行う。 The vector data extraction unit 302 obtains vector data from, for example, an image obtained by performing image processing on a radar image. As an example, when semantic segmentation is performed as image processing, polygons connecting pixels or pixel groups can be obtained. The terrestrial projection unit 301 performs terrestrial projection processing based on vector data.
　ベクトルデータに基づく地上投影処理の処理負荷は比較的小さい。すなわち、第７の実施形態の信号処理装置は、エイリアシングを防止しつつ、短期間で地上投影処理を実行できる。 The processing load of terrestrial projection processing based on vector data is relatively small. That is, the signal processing device of the seventh embodiment can perform terrestrial projection processing in a short period of time while preventing aliasing.
　なお、ベクトルデータ抽出部３０２は、干渉データ解析機能を含んでいてもよい。 Note that the vector data extraction unit 302 may include an interference data analysis function.
　上記の実施形態における各構成要素は、１つのハードウェアで構成可能であるが、１つのソフトウェアでも構成可能である。また、各構成要素は、複数のハードウェアでも構成可能であり、複数のソフトウェアでも構成可能である。また、各構成要素のうちの一部をハードウェアで構成し、他部をソフトウェアで構成することもできる。 Each component in the above embodiment can be configured with one piece of hardware, but can also be configured with one piece of software. Further, each component can be configured with a plurality of pieces of hardware, and can also be configured with a plurality of pieces of software. Further, some of the components can be configured with hardware, and the other parts can be configured with software.
　上記の実施形態における各機能を、ＣＰＵ（Central Processing Unit）等のプロセッサやメモリ等を有するコンピュータで実現可能である。例えば、記憶装置に上記の実施形態における方法を実施するためのプログラムを格納し、各機能を、記憶装置に格納されたプログラムをＣＰＵで実行することによって実現してもよい。 Each function in the above embodiment can be realized by a computer having a processor such as a CPU (Central Processing Unit), memory, and the like. For example, a program for implementing the method in the above embodiment may be stored in a storage device, and each function may be realized by executing the program stored in the storage device with a CPU.
　図１６は、ＣＰＵを有するコンピュータの一例を示すブロック図である。コンピュータは、信号処理装に実装される。ＣＰＵ１０００は、記憶装置１００１に格納された信号処理プログラムに従って処理を実行することによって、上記の実施形態における信号処理装置の機能を実現する。 FIG. 16 is a block diagram showing an example of a computer having a CPU. The computer is implemented in a signal processing device. The CPU 1000 implements the functions of the signal processing device in the above embodiment by executing processing according to the signal processing program stored in the storage device 1001.
　具体的には、第１の実施形態の場合には、コンピュータは、傾斜画像生成部１００の機能を実現する。第２の実施形態の場合には、コンピュータは、格子生成部１１１および逆投影部１１２の機能を実現する。第３の実施形態の場合には、コンピュータは、２Ｄフーリエ変換部１１３、レンジスペクトルシフト部１１４、アジマススペクトルシフト部１１５、および２Ｄ逆フーリエ変換部１１６の機能を実現する。第４の実施形態の場合には、コンピュータは、アップサンプル部１１７、ゼロドップラー結像処理部１１８、回転処理部１１９、およびダウンサンプル部１２０の機能を実現する。第５の実施形態の場合には、コンピュータは、傾斜画像生成部１００および位相変調推定部２００の機能を実現する。第６の実施形態の場合には、コンピュータは、傾斜画像生成部１０２、画像処理部３００、および地上投影部３０１の機能を実現する。第７の実施形態の場合には、コンピュータは、傾斜画像生成部１０２、ベクトルデータ抽出部３０２、および地上投影部３０３の機能を実現する。 Specifically, in the case of the first embodiment, the computer realizes the function of the tilted image generation section 100. In the case of the second embodiment, the computer implements the functions of the grid generation section 111 and the back projection section 112. In the case of the third embodiment, the computer realizes the functions of a 2D Fourier transform section 113, a range spectrum shift section 114, an azimuth spectrum shift section 115, and a 2D inverse Fourier transform section 116. In the case of the fourth embodiment, the computer implements the functions of an up-sampling section 117, a zero-Doppler imaging processing section 118, a rotation processing section 119, and a down-sampling section 120. In the case of the fifth embodiment, the computer realizes the functions of the tilt image generation section 100 and the phase modulation estimation section 200. In the case of the sixth embodiment, the computer realizes the functions of the tilted image generation section 102, the image processing section 300, and the ground projection section 301. In the case of the seventh embodiment, the computer realizes the functions of the tilted image generation section 102, the vector data extraction section 302, and the ground projection section 303.
　記憶装置１００１は、例えば、非一時的なコンピュータ可読媒体（non-transitory computer readable medium）である。非一時的なコンピュータ可読媒体は、様々なタイプの実体のある記録媒体（tangible storage medium）を含む。非一時的なコンピュータ可読媒体の具体例として、磁気記録媒体（例えば、ハードディスク）、光磁気記録媒体（例えば、光磁気ディスク）、ＣＤ－ＲＯＭ（Compact Disc-Read Only Memory）、ＣＤ－Ｒ（Compact Disc-Recordable）、ＣＤ－Ｒ／Ｗ（Compact Disc-ReWritable）、半導体メモリ（例えば、マスクＲＯＭ、ＰＲＯＭ（Programmable ROM）、ＥＰＲＯＭ（Erasable PROM）、フラッシュＲＯＭ）がある。 The storage device 1001 is, for example, a non-transitory computer readable medium. Non-transitory computer-readable media include various types of tangible storage media. Specific examples of non-transitory computer-readable media include magnetic recording media (e.g., hard disks), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Compact Disc-Read Only Memory), and CD-Rs (Compact Disc-Recordable), CD-R/W (Compact Disc-ReWritable), and semiconductor memories (for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), and flash ROM).
　衛星観測データ記憶部１３０は、記憶装置１００１で実現可能である。 The satellite observation data storage unit 130 can be realized by the storage device 1001.
　また、プログラムは、様々なタイプの一時的なコンピュータ可読媒体（transitory computer readable medium ）に格納されてもよい。一時的なコンピュータ可読媒体には、例えば、有線通信路または無線通信路を介して、すなわち、電気信号、光信号または電磁波を介して、プログラムが供給される。 The program may also be stored on various types of transitory computer readable medium. The program is supplied to the temporary computer-readable medium, for example, via a wired or wireless communication channel, ie, via an electrical signal, an optical signal, or an electromagnetic wave.
　メモリ１００２は、例えばＲＡＭ（Random Access Memory）で実現され、ＣＰＵ１０００が処理を実行するときに一時的にデータを格納する記憶手段である。メモリ１００２に、記憶装置１００１または一時的なコンピュータ可読媒体が保持するプログラムが転送され、ＣＰＵ１０００がメモリ１００２内のプログラムに基づいて処理を実行するような形態も想定しうる。 The memory 1002 is realized by, for example, RAM (Random Access Memory), and is a storage means that temporarily stores data when the CPU 1000 executes processing. It is also conceivable that a program held in the storage device 1001 or a temporary computer-readable medium is transferred to the memory 1002, and the CPU 1000 executes processing based on the program in the memory 1002.
　信号処理装置は、アンテナ方向に直交する方向の各座標における位相変調量を算出する位相変調推定手段（実施形態では、位相変調推定部２００で実現される。）を備えていてもよい。 The signal processing device may include a phase modulation estimating means (in the embodiment, realized by the phase modulation estimating section 200) that calculates the amount of phase modulation at each coordinate in a direction orthogonal to the antenna direction.
　信号処理装置は、レーダ画像に対して画像処理を施す画像処理手段（実施形態では、画像処理部３００で実現される。）と、画像処理の結果を地上投影する処理を行う地上投影手段（実施形態では、地上投影部３０１で実現される。）とを備えていてもよい。 The signal processing device includes an image processing unit (implemented by the image processing unit 300 in the embodiment) that performs image processing on a radar image, and a ground projection unit (implemented) that performs processing to project the result of the image processing on the ground. In some embodiments, it may be realized by the ground projection unit 301.)
　信号処理装置は、レーダ画像に画像処理が施された画像から、ベクトルデータを取得するベクトルデータ抽出手段（実施形態では、ベクトルデータ抽出部３０２で実現される。）と、ベクトルデータに基づく地上投影処理を行う地上投影手段（実施形態では、地上投影部３０３で実現される。）とを備えていてもよい。 The signal processing device includes a vector data extraction unit (in the embodiment, realized by a vector data extraction unit 302) that acquires vector data from an image obtained by performing image processing on a radar image, and a ground projection unit based on the vector data. It may also include a terrestrial projection means (in the embodiment, realized by the terrestrial projection unit 303) that performs processing.
　以上、実施形態を参照して本願発明を説明したが、本願発明は上記実施形態に限定されるものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。 Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. The configuration and details of the present invention can be modified in various ways that can be understood by those skilled in the art within the scope of the present invention.
　１００，１０１，１０２　傾斜画像生成部
　１１１　　格子生成部
　１１２　　逆投影部
　１１３　　２Ｄフーリエ変換部
　１１４　　レンジスペクトルシフト部
　１１５　　アジマススペクトルシフト部
　１１６　　２Ｄ逆フーリエ変換部
　１１７　　アップサンプル部
　１１８　　ゼロドップラー結像処理部
　１１９　　回転処理部
　１２０　　ダウンサンプル部
　１３０　　衛星観測データ記憶部
　１３１　　観測信号
　１３２　　衛星情報
　２００　　位相変調推定部
　３００　　画像処理部
　３０１，３０３　地上投影部
　３０２　　ベクトルデータ抽出部
　１０００　ＣＰＵ
　１００１　記憶装置
　１００２　メモリ 100, 101, 102 Tilt image generation section 111 Grid generation section 112 Back projection section 113 2D Fourier transformation section 114 Range spectrum shift section 115 Azimuth spectrum shift section 116 2D inverse Fourier transformation section 117 Up sample section 118 Zero Doppler imaging processing section 119 Rotation processing section 120 Down sampling section 130 Satellite observation data storage section 131 Observation signal 132 Satellite information 200 Phase modulation estimation section 300 Image processing section 301, 303 Ground projection section 302 Vector data extraction section 1000 CPU
1001 Storage device 1002 Memory

Claims (6)

  1. 　衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、前記進行方向および前記直交方向がなす平面において前記第１方向に直交する第２方向とに沿って表すデータ形式にて、前記信号に対する反射信号を表す情報を作成する
    　信号処理装置。     A first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction that is orthogonal to the traveling direction of the satellite, and a plane that is orthogonal to the first direction in a plane formed by the traveling direction and the orthogonal direction. A signal processing device that creates information representing a reflected signal with respect to the signal in a data format represented along a second direction.
  2. 　前記第２方向の各座標における位相変調量を算出する位相変調推定手段を備えた
    　請求項１に記載の信号処理装置。     The signal processing device according to claim 1, further comprising phase modulation estimating means for calculating the amount of phase modulation at each coordinate in the second direction.
  3. 　前記第１方向と、前記第２方向とを軸とする複数の格子を生成する格子生成手段と、
    　逆投影法によって、前記複数の格子の間に画素を生成する逆投影手段とを備えた
    　請求項１または請求項２に記載の信号処理装置。     lattice generating means for generating a plurality of lattices with axes in the first direction and the second direction;
    The signal processing device according to claim 1 or 2, further comprising a back projection unit that generates pixels between the plurality of grids by a back projection method.
  4. 　スペクトルの周囲に画素を追加するアップサンプル手段と、
    　画像化アルゴリズムとしてのゼロドップラーアルゴリズムに基づいて画像化処理を行うゼロドップラー結像処理手段と、
    　前記画像化処理の結果のスペクトルを回転させる回転処理手段と、
    　スペクトルの周囲の画素数を減らす処理を行うダウンサンプル手段とを含む
    　請求項１または請求項２に記載の信号処理装置。     an upsampling means for adding pixels around the spectrum;
    Zero Doppler imaging processing means that performs imaging processing based on a zero Doppler algorithm as an imaging algorithm;
    rotation processing means for rotating the spectrum resulting from the imaging process;
    3. The signal processing device according to claim 1, further comprising: down-sampling means that performs processing to reduce the number of pixels around a spectrum.
  5. 　衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、前記進行方向および前記直交方向がなす平面において前記第１方向に直交する第２方向とに沿って表すデータ形式にて、前記信号に対する反射信号を表す情報を、コンピュータが作成する
    　信号処理方法。     A first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction that is orthogonal to the traveling direction of the satellite, and a plane that is orthogonal to the first direction in a plane formed by the traveling direction and the orthogonal direction. A signal processing method, wherein a computer creates information representing a reflected signal with respect to the signal in a data format represented along a second direction.
  6. 　衛星の進行方向に直交する直交方向とは異なる方向に信号を照射する衛星が該信号を照射する方向を表す第１方向と、前記進行方向および前記直交方向がなす平面において前記第１方向に直交する第２方向とに沿って表すデータ形式にて、前記信号に対する反射信号を表す情報を作成する処理
    　をコンピュータに実行させるプログラムが格納された
    　コンピュータ読み取り可能な記録媒体。     A first direction representing a direction in which a satellite emits a signal in a direction different from an orthogonal direction that is orthogonal to the traveling direction of the satellite, and a plane that is orthogonal to the first direction in a plane formed by the traveling direction and the orthogonal direction. A computer-readable recording medium storing a program that causes a computer to execute a process of creating information representing a reflected signal with respect to the signal in a data format represented along a second direction.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011169869A (en) * 2010-02-22 2011-09-01 Mitsubishi Electric Corp Apparatus for processing radar signal
JP2015215257A (en) * 2014-05-12 2015-12-03 株式会社東芝 Synthetic aperture radar device and image processing method thereof
KR102028324B1 (en) * 2019-02-26 2019-11-04 엘아이지넥스원 주식회사 Synthetic Aperture Radar Image Enhancement Method and Calculating Coordinates Method
US20200025855A1 (en) * 2017-08-08 2020-01-23 U.S. Army Research Laboratory Attn: Rdrl-Loc-I Method and apparatus for providing a passive transmitter based synthetic aperture radar

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011169869A (en) * 2010-02-22 2011-09-01 Mitsubishi Electric Corp Apparatus for processing radar signal
JP2015215257A (en) * 2014-05-12 2015-12-03 株式会社東芝 Synthetic aperture radar device and image processing method thereof
US20200025855A1 (en) * 2017-08-08 2020-01-23 U.S. Army Research Laboratory Attn: Rdrl-Loc-I Method and apparatus for providing a passive transmitter based synthetic aperture radar
KR102028324B1 (en) * 2019-02-26 2019-11-04 엘아이지넥스원 주식회사 Synthetic Aperture Radar Image Enhancement Method and Calculating Coordinates Method

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