JP6011746B1 - Synthetic aperture radar apparatus and signal processing apparatus - Google Patents

Synthetic aperture radar apparatus and signal processing apparatus Download PDF

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JP6011746B1
JP6011746B1 JP2016526365A JP2016526365A JP6011746B1 JP 6011746 B1 JP6011746 B1 JP 6011746B1 JP 2016526365 A JP2016526365 A JP 2016526365A JP 2016526365 A JP2016526365 A JP 2016526365A JP 6011746 B1 JP6011746 B1 JP 6011746B1
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synthetic aperture
radar
chirp
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JPWO2017094157A1 (en
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正芳 土田
正芳 土田
啓 諏訪
啓 諏訪
照幸 原
照幸 原
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三菱電機株式会社
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO 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
    • G01S13/00Systems 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
    • G01S13/88Radar or analogous systems specially adapted for specific applications
    • G01S13/89Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques

Abstract

Due to the movement of the synthetic aperture radar device during observation, the frequency of the received signal changes from the frequency at the time of transmission. Such a Doppler has a problem that azimuth ambiguity is generated in the synthetic aperture radar image. The synthetic aperture radar device of the present invention includes an antenna unit that radiates a transmission signal and receives a transmission signal reflected by a target, a transmission unit that generates a transmission signal by pulse-to-pulse modulation and transmits the transmission signal to the antenna unit, and an antenna unit And a radar control unit for controlling the chirp plate of the transmission signal generated by the transmission unit based on the directivity direction of the radar beam radiated from the antenna unit. Thereby, in the received signal subjected to the range compression process, the peak shift in the range direction that occurs according to the influence of Doppler can be compensated, and the azimuth ambiguity generated in the synthetic aperture radar image can be suppressed.

Description

  The present invention relates to a synthetic aperture radar apparatus that radiates radio waves modulated between pulses toward a target and receives radio waves reflected by the target, and a signal that performs image reproduction processing of a received signal received by the synthetic aperture radar apparatus The present invention relates to a processing apparatus.

  Conventional Synthetic Aperture Radar (SAR) devices and signal processing devices switch between up-chirp and down-chirp when transmitting a pulse signal according to an autocorrelation code string such as a Barker code, and at a desired observation point. By making it possible to distinguish between a reflected transmission pulse and a transmission pulse reflected at other observation points, range ambiguity suppression that is unavoidable in observation by a synthetic aperture radar apparatus has been performed (for example, Patent Document 1). ).

Japanese Patent Laid-Open No. 2003-167052

I. G. Cumming and F.M. W. Wong, Digital Processing of Synthetic Aperture Radar Data Algorithms and Implementation, Arttech House, 2005.

  In conventional synthetic aperture radar devices and signal processing devices, stop-and-go approximation generally used in signal processing of synthetic aperture radar observations, that is, assuming that the radar is stationary while the radar transmits and receives pulses. Signal processing was performed on the premise.

  However, in actual observation, the radar moves while transmitting and receiving pulses, and the frequency of the received signal changes from the frequency at the time of transmission due to the influence of the movement of the radar. Due to such Doppler during observation, there is a problem that azimuth ambiguity is generated in the synthetic aperture radar image. A synthetic aperture radar image is an image obtained by image reproduction processing of observation data.

  The present invention has been made to solve the above-described problems, and is a synthetic aperture that performs observation while changing the pointing direction of a radar beam while switching between up-chirp and down-chirp of a transmission signal by inter-pulse modulation. An object of the present invention is to obtain a synthetic aperture radar device and a signal processing device that suppress azimuth ambiguity generated in a synthetic aperture radar image after image reproduction in radar observation.

The synthetic aperture radar apparatus according to the present invention obtains a reception signal used for reproducing a synthetic aperture radar image by switching between up-chirp and down-chirp of a transmission signal and observing while changing the direction of the radar beam. Synthetic aperture radar device, comprising: an antenna unit that radiates a transmission signal and receives a transmission signal reflected by a target; a transmission unit that generates a transmission signal by pulse-to-pulse modulation and transmits the transmission signal to the antenna unit; A reception unit that outputs the received transmission signal as a reception signal, and a radar control unit that controls the chirp plate of the transmission signal generated by the transmission unit based on the directivity direction of the radar beam radiated from the antenna unit.

In addition, the signal processing apparatus according to the present invention switches the reception signal up-chirp and down-chirp and changes the direction of the radar beam and observes the received signal used for reproducing the synthetic aperture radar image. A synthetic aperture radar device for obtaining an antenna unit that radiates a transmission signal and receives a transmission signal reflected by a target, a transmission unit that generates a transmission signal by inter-pulse modulation and transmits the transmission signal to the antenna unit, and an antenna unit A receiver that outputs the transmission signal received in step 1 as a reception signal, and a radar control unit that controls the chirp plate of the transmission signal generated by the transmission unit based on the directivity direction of the radar beam emitted from the antenna unit a signal processing apparatus for obtaining processed to synthetic aperture radar image signals received aperture radar device, chirp of a transmission signal corresponding to the received signal Based on the orientation of the over bets and the radar beam, and a compensation unit for compensating the peak shift of the range direction generated due to the radar movement upon receiving a received signal.

  According to the synthetic aperture radar device and the signal processing device according to the present invention, the configuration as described above can suppress the occurrence of azimuth ambiguity in the synthetic aperture radar image after image reproduction.

It is explanatory drawing explaining arrangement | positioning of a radar and a point target. It is a block diagram which shows an example of a structure of the synthetic aperture radar apparatus in Embodiment 1 of this invention. It is a figure which shows an example of the hardware constitutions of the synthetic aperture radar apparatus in Embodiment 1 of this invention. It is a block diagram which shows an example of a structure of the signal processing apparatus in Embodiment 1 of this invention. It is a figure which shows an example of the hardware constitutions of the signal processing apparatus in Embodiment 1 of this invention. It is a flowchart which shows the flow of a process of the signal processing apparatus in Embodiment 1 of this invention. It is explanatory drawing explaining the peak position after the range compression of observation data.

Embodiment 1 FIG.
The present invention relates to a synthetic aperture radar device that controls the chirp plate of a transmission signal based on the directivity direction of the radar beam, and the direction of the radar beam and the transmission signal relative to the reception signal received by the synthetic aperture radar device. The present invention relates to a signal processing apparatus that performs Doppler compensation based on a chirp plate. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same numerals indicate the same or corresponding parts.

In the first embodiment, spotlight observation that changes the directivity direction of a radar beam during observation will be described as an example. FIG. 1 is a schematic diagram showing a geometrical arrangement of a synthetic aperture radar device (also simply referred to as “radar”) and a point target to be observed. In the figure, the velocity in the azimuth direction of the synthetic aperture radar apparatus is Vs, and the beam steering angle is θ. Further, the distance between the synthetic aperture radar apparatus and the point target is R, and the closest distance between the synthetic aperture radar apparatus and the point target is R 0 . The radar beam footprint is indicated by an ellipse, and the direction orthogonal to the azimuth direction is indicated by a one-dot chain line.

  FIG. 2 is a block diagram showing an example of the configuration of the synthetic aperture radar apparatus according to Embodiment 1 of the present invention. FIG. 3 is a diagram illustrating an example of a hardware configuration of the synthetic aperture radar apparatus according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing an example of the configuration of the signal processing apparatus according to Embodiment 1 of the present invention. FIG. 5 is a diagram illustrating an example of a hardware configuration of the signal processing device according to Embodiment 1 of the present invention.

  First, the configuration of the synthetic aperture radar device in the present embodiment will be described with reference to FIG. In the figure, a synthetic aperture radar apparatus 100 includes a transmission / reception unit 118 that transmits / receives a signal, a processing unit 119 that digitally processes a signal received by the transmission / reception unit, a radar control unit 112 that controls the transmission / reception unit 118 and the processing unit 119, and digital processing. The data transmission unit 117 transmits the transmitted signal. The transmission / reception unit 118 includes an antenna unit 111, a transmission unit 114, and a reception unit 113. The processing unit 119 includes a digital processing unit 115 and a data recording unit 116.

  The antenna unit 111 radiates the transmission signal supplied from the transmission unit 114 to the space as a radio wave, receives the radio wave in the space, and outputs it to the reception unit 113. Further, the antenna unit 111 receives a transmission signal that is reflected by the observation target and reaches the antenna unit 111. The transmission unit 114 generates a transmission signal and transmits it to the antenna unit 111. The transmission signal is a pulse signal composed of a plurality of pulses, and is a chirp signal in which the frequency of the pulse changes with time. The transmission unit 114 performs inter-pulse modulation to switch between chirp up and down (up chirp and down chirp) of the transmission signal. For example, as in Patent Document 1, the inter-pulse modulation may be a method of switching up-chirp and down-chirp according to an autocorrelation code string such as a Barker code, or a method of switching up-chirp and down-chirp alternately. The receiving unit 113 receives the signal output from the antenna unit 111, amplifies and detects the phase, and then outputs the received signal.

  The digital processing unit 115 digitizes the reception signal output from the reception unit 113 and performs digital signal processing such as data compression processing and packetization on the digitized reception signal. The data recording unit 116 stores the reception signal processed by the digital processing unit 115. The data transmission unit 117 reads the reception signal processed by the digital processing unit 115 from the data recording unit 116 and transmits it to the ground.

  The radar control unit 112 controls the operation of the devices that make up the synthetic aperture radar device 100. Specifically, the radar control unit 112 controls the transmission / reception unit 118 and the processing unit 119, that is, the antenna unit 111, the reception unit 113, the transmission unit 114, the digital processing unit 115, and the data recording unit 116. . Under the control of the radar control unit 112, the synthetic aperture radar apparatus 100 performs a series of operations for transmitting and receiving radio waves and recording received signals. Specifically, the radar control unit 112 controls the antenna unit 111 to change the directivity direction of the radar beam and also controls the transmission unit 114 to change the chirp plate of the transmission signal generated. Further, the digital processing unit 115 is controlled to store the received signal subjected to the digital signal processing in the data recording unit 116. A detailed method for changing the chirp plate will be described later.

  The configuration of the synthetic aperture radar device 100 is an example assuming a synthetic aperture radar device mounted on a satellite, and is not necessarily the same configuration. For example, in a synthetic aperture radar apparatus mounted on an aircraft, a data transmission unit 117 is often omitted because a hard disk in which a received signal is recorded can be taken out from the data recording unit 116. In the following description, the received signal obtained by observation is also referred to as observation data.

  Next, a hardware configuration of the synthetic aperture radar device 100 according to the present embodiment will be described with reference to FIG. The synthetic aperture radar device 100 includes hardware such as an antenna 101, a receiver 103, a transmitter 104, a processing circuit 102, a recording device 106, a data transmitter 107, and a memory 108. The processing circuit 102 controls the antenna 101, the receiver 103, the transmitter 104, the recording device 106, and the memory 108.

  The transmission unit 114 is realized by the transmitter 104. The antenna unit 111 is realized by the antenna 101. The receiving unit 113 is realized by the receiver 103. The data transmission unit 117 is realized by the data transmitter 107.

  A processing circuit (Processing Circuit) 102 is a general-purpose central processing unit (CPU), a digital signal processor (DSP), or the like that reads a program and performs digital signal processing. The processing circuit 102 may be dedicated hardware such as ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). The processing circuit 102 may be configured by a single piece of hardware or a combination of a plurality of pieces of hardware. The radar control unit 112 and the digital processing unit 115 are realized by the processing circuit 102.

  The recording device 106 is a recording medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk, a DVD (Digital Versatile Disc), an HDD (Hard Disk Drive), or an SSD (Solid State Drive). The data recording unit 116 is realized by the recording device 106.

  The memory 108 is a nonvolatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), and a flash memory, and is connected to the processing circuit 102 to temporarily record a digital signal. Note that programs that implement the functions of the radar control unit 112 and the digital processing unit 115 are stored in the recording device 106 or the memory 108.

  Next, the configuration of the signal processing apparatus according to the present embodiment will be described with reference to FIG. In the figure, the signal processing device 200 includes a DFT unit 210, a compensation unit 211, a pulse width equalization unit 212, an IDFT unit 213, and an image reproduction unit 214. The signal processing device 200 processes observation data obtained by the observation of the synthetic aperture radar device 100.

  The DFT unit 210 performs DFT (Discrete Fourier Transform) processing of observation data, that is, performs a range direction Fourier transform of the received signal. The compensation unit 211 compensates for the influence of Doppler on observation data due to the movement of the radar under observation. A pulse width equalization unit (also referred to as an equalization unit) 212 equalizes the pulse width of observation data. The IDFT unit 213 processes the observation data by an IDFT (Inverse Discrete Fourier Transform). The image reproduction unit 214 performs image reproduction processing on the observation data. Note that DFT and IDFT represent Fourier transform and inverse Fourier transform for discrete signals.

  Next, with reference to FIG. 5, the hardware configuration of the signal processing device 200 in the present embodiment will be described. The signal processing device 200 includes a processing circuit 201, a memory 202, and a data recording device 203.

  The processing circuit 201 is a general-purpose central processing unit or a digital signal processor that reads a program and performs digital signal processing. The processing circuit 201 may be configured by a single piece of hardware or a combination of a plurality of pieces of hardware. The DFT unit 210, the compensation unit 211, the pulse width equalization unit 212, the IDFT unit 213, and the image reproduction unit 214 are realized by the processing circuit 201.

  The memory 202 is a nonvolatile or volatile semiconductor memory such as a RAM, a ROM, or a flash memory, and is connected to the processing circuit 201 to temporarily record a digital signal.

  The data recording device 203 is a recording medium such as a magnetic disk, a flexible disk, an optical disk, a compact disk, a DVD, and an HDD. The observation data obtained by the observation by the synthetic aperture radar apparatus 100 and the digital signal processed by the processing circuit 201 are used. Record. Note that programs that realize the functions of the DFT unit 210, the compensation unit 211, the pulse width equalization unit 212, the IDFT unit 213, and the image reproduction unit 214 are stored in the memory 202 or the data recording device 203.

  Next, operations of the synthetic aperture radar apparatus 100 and the signal processing apparatus 200 in the first embodiment will be described with reference to the drawings. FIG. 6 is a flowchart showing a processing flow of the synthetic aperture radar device 100 and the signal processing device 200 according to the first embodiment.

  First, in step ST100, observation by the synthetic aperture radar device 100 is performed. The transmission / reception unit 118 switches between up-chirp and down-chirp, transmits a pulse signal while changing the direction of the radar beam as the radar moves, and observes the point target. In this observation, the radar control unit 112 controls the transmission unit 114 to change the absolute value of the chirp plate of the transmission signal to be generated in accordance with the control of the antenna unit 111 so as to change the directivity direction of the radar beam. To do. Specifically, the radar control unit 112 controls the transmission unit 114 so that the chirp plate of the transmission signal increases as the beam steering angle of the radar beam emitted from the antenna unit 111 increases.

  Here, a method for controlling the chirp plate according to the directivity direction of the radar beam will be described. In the following description, first, the shift of the peak position obtained by the range compression including the correlation processing between the transmission signal and the reception signal will be described, and then the chirp plate control method for reducing the shift of the peak position will be described.

  FIG. 7 is a schematic diagram showing how the position of the peak appearing after range compression changes according to the distance between the synthetic aperture radar device and the point target. The horizontal axis is the position of the peak that appears due to the range compression processing of the observation data, and corresponds to the distance between the radar and the point target. The vertical axis indicates the position of the synthetic aperture radar device in the azimuth direction. The white circles in the figure indicate peak positions when the movement of the radar during pulse transmission / reception is not considered, and the black circles indicate the peak positions when the movement of the radar during pulse transmission / reception is considered. Also, the alternate long and short dash line in the figure corresponds to the locus of the distance R between the synthetic aperture radar apparatus and the point target, that is, the change in the distance R. “Down” represents that the transmission signal has been down-chirp modulated, and “up” represents that the transmission signal has been up-chirp modulated.

  When the radar moves during observation, the observation data shifts in the direction indicated by the arrow in the figure due to the influence of Doppler. As a result, the peak position after the range compression is shifted from the position of the white circle indicating the original target position to the position of the black circle. Since this shift depends on the chirp plate and Doppler frequency at the time of transmission, the chirp code (up-chirp or down-chirp) is used when switching between up-chirp and down-chirp at the time of pulse transmission for the purpose of suppressing range ambiguity. The shift direction is reversed in response to. In addition, in an observation method such as a spotlight, a sliding spotlight, or TOPS (Terrain Observing by Progressive Scan) that changes the direction of the radar beam during observation, the absolute value of this shift amount is large because the Doppler frequency during observation is large. growing.

The distance R between the synthetic aperture radar apparatus and the point target draws a parabolic trajectory with R 0 as the minimum, as shown by a one-dot chain line in the figure. The peak positions after range compression when approximated by stop-and-go are arranged on a parabolic locus as indicated by white circles. However, if the radar moves during pulse transmission / reception, the peak position after range compression shifts in the range direction from the parabolic locus due to the influence. In the observation in which the chirp code is switched alternately, the shift direction is reversed according to the chirp code. Furthermore, the shift direction is reversed as the Doppler frequency changes from positive to negative at the position P 0 in the azimuth direction. Also, the absolute value of the shift amount increases in proportion to the absolute Doppler frequency.

  The absolute value of this shift amount is usually less than the sampling interval in the range direction, but in the arrangement in the azimuth direction along the trajectory of the distance R, amplitude modulation in the azimuth direction is generated. Due to the amplitude modulation in the azimuth direction, azimuth ambiguity is generated in the synthetic aperture radar image. However, the synthetic aperture radar apparatus of the first embodiment suppresses the shift of the peak position after range compression by controlling the chirp plate in accordance with the direction of the radar. As a result, azimuth ambiguity generated in the synthetic aperture radar image can be suppressed.

  Next, a method for controlling the chirp plate in the synthetic aperture radar apparatus according to the first embodiment will be described.

When the char plate of a pulse transmitted with an azimuth time (or also called a slow time) η is K r [η], the change of the absolute value | K r [η] | S is performed so that S becomes a minimum value. However, the change of the absolute value of the chirp plate is performed while satisfying the hardware performance and the parameter setting range restricted by the observation conditions such as the desired observation width and resolution.

  Here, θ [η] is a beam steering angle at the azimuth time η. The absolute value of the chirp plate is a value obtained by dividing the transmission bandwidth by the transmission pulse width. However, during observation, the transmission bandwidth is fixed so that the range resolution is constant. Therefore, the absolute value of the chirp plate is changed by changing the transmission pulse width. The change of the absolute value of the chirp plate according to the equation (1) is to shorten the pulse width when the beam steering angle θ [η] is large (increase the char plate), and lengthen the pulse width when θ [η] is small ( This is equivalent to making the chirp plate smaller.

  When the pulse width is shortened, the signal power per pulse is lowered, and when the pulse width is lengthened, the signal power is improved. Since the signal power of the synthetic aperture radar image is determined by the integration of multiple pulses, the synthetic aperture time is required to make the signal power equivalent to the case where the char plate is fixed even if the absolute value of the chirp plate is changed. Is set so that the average of the absolute value of the chirp plate is equivalent to the absolute value of the chirp plate before the change.

  Next, the reason why the radar control unit 112 changes the absolute value of the char plate according to the beam steering angle at the azimuth time η will be described.

The peak position τ peak [η] after range compression when considering the movement of the radar during pulse transmission / reception is given by equation (2).

Here, τ 0 [η] is the round-trip time of the radio wave between the radar and the point target at the azimuth time η when approximated by stop and go, and corresponds to the one-dot chain line in FIG. f 0 is the transmission center frequency, K r [η] is the transmission pulse chirp at the azimuth time η, V s is the radar moving speed, θ [η] is the beam steering angle at the azimuth time η, and c is the speed of light.

  In Equation (2), the second term represents the amount of peak shift that occurs due to the effect of radar movement during pulse transmission / reception. This shift amount is proportional to the value S shown in Equation (1), and the sign is inverted according to the sign of the chirp. Therefore, by changing the absolute value of the chirp plate so as to minimize S, it is possible to suppress a peak shift caused by the influence of the radar moving during pulse transmission / reception.

  Returning to the description of the operation using the flowchart again. In step ST100, the received signal received by the synthetic aperture radar device 100 is digitally processed by the digital processing unit 115 and stored in the data recording unit 116. The data recording unit 116 also records a transmission signal corresponding to the reception signal, a chirp plate of the transmission signal, and a beam steering angle at the time of transmission of the transmission signal. The data transmission unit 117 reads out the data recorded in the data recording unit 116 and transmits it to the ground.

  Next, in step ST <b> 200, the signal processing device 200 receives the data transmitted from the data transmission unit 117 and stores it in the data recording device 203.

  In step ST201, the DFT unit 210 reads the data stored in the data recording device 203 and performs DFT processing on the received signal in the range direction.

  In step ST202, the compensation unit 211 multiplies the reception signal that has undergone Fourier transform in the range direction by a complex function given by Equation (3). Expression (3) is a complex function generated based on the direction of the chirp plate and the radar beam according to the azimuth time. This compensates for a peak shift in the range time that occurs with radar movement during pulse transmission / reception, that is, a peak shift in the range direction.

Here, represents a range frequency, and R [η] represents a distance between the radar beam pointing center point and the radar set to determine the radar beam pointing direction at the azimuth time η. In Equation (3), the first term compensates for the peak shift that occurs as the radar moves during pulse transmission and reception, and the second term compensates for the phase change. Here, although the function for compensating for the peak shift accompanying the radar movement during pulse transmission / reception is given by Expression (3), the function is not limited to this, and any function having an equivalent function may be used.

  In step ST203, the pulse width equalization unit 212 multiplies the signal after the peak shift compensation by the complex function given by the equation (4) to remove the chirp in the range direction. The complex function given by Equation (4) is a complex function based on a chirp rate corresponding to the azimuth time.

Here, B w is a transmission bandwidth, rect [f / B] is a rectangular function given by Equation (5).

  Here, in order to remove the chirp in the range direction, the complex function given by Equation (4) is used. However, the present invention is not limited to this. For example, a function obtained by performing a Fourier transform on the replica signal in the range direction. Any function having an equivalent function may be used. When a function obtained by performing Fourier transform on the replica signal of the transmission signal in the range direction is used, in step ST201, the DFT unit 210 may perform range direction Fourier transform on the replica signal of the transmission signal.

  In step ST204, the pulse width equalization unit 212 further multiplies the signal after removing the chirp in the range direction by the complex function given by Equation (6), and adds the chirp fixed in the range direction.

Here , Kr and uni are predetermined char plates. By the multiplication of this function, the pulse width that has changed according to the azimuth time η is changed to a constant value (B w / K r, uni ). Here, in order to add the chirp in the range direction, the complex function given by Equation (6) is used, but the present invention is not limited to this, and any function having an equivalent function may be used.

  In step ST205, the IDFT unit 213 performs IDFT processing on the signal to which the chirp in the range direction is added in the range direction. The signal subjected to IDFT processing is a signal equivalent to that observed with a fixed chirp plate.

  In step ST206, the image reproduction unit 204 performs image reproduction processing on the signal subjected to IDFT processing. For this image reproduction processing, for example, a general image reproduction algorithm such as a range Doppler algorithm, a chirp scaling algorithm, or an omega K algorithm as shown in Non-Patent Document 1 may be used.

In step ST207, when the image reproduction unit 204 stores the synthetic aperture radar image obtained as a result of the image reproduction processing in the data recording device 203, the series of processing ends.

  As described above, the synthetic aperture radar device 100 according to the first embodiment radiates a transmission signal, receives the transmission signal reflected by the target, and generates a transmission signal by inter-pulse modulation to generate an antenna. A transmission unit 114 that transmits to the unit 111, a reception unit 113 that outputs a transmission signal received by the antenna unit 111 as a reception signal, and a transmission unit 114 that is generated based on the directivity direction of the radar beam radiated from the antenna unit 111. And a radar control unit 112 for controlling the chirp plate of the transmission signal. With such a configuration, the synthetic aperture radar apparatus 100 changes the chirp plate in accordance with the beam steering angle during observation, so that it is possible to suppress a peak shift after range compression that occurs due to radar movement during pulse transmission / reception. As a result, it is possible to prevent the amplitude modulation accompanying the occurrence of the peak shift and reproduce the synthetic aperture radar image without generating the azimuth ambiguity.

  The signal processing device 200 according to the first embodiment is a device that processes the reception signal received by the synthetic aperture radar device 100, and is based on the chirp plate of the transmission signal corresponding to the reception signal and the pointing direction of the radar beam. And a compensation unit 211 that compensates for the peak shift in the range direction that occurs with the movement of the radar when the received signal is received. The compensation unit 211 performs compensation processing of the peak shift after range compression caused by radar movement during pulse transmission / reception by multiplying a complex function in the range frequency space, thereby preventing the occurrence of azimuth ambiguity without increasing the calculation load. be able to. Furthermore, even if the peak shift cannot be completely suppressed by changing the chirp plate according to the beam steering angle in the synthetic aperture radar apparatus 100, the compensation processing based on the chirp plate of the transmission signal and the directivity direction of the radar beam The remaining peak shift can be compensated.

  Further, according to the signal processing apparatus 200 of the first embodiment, the observation data chirp plate is fixed to a fixed value, that is, the pulse width is set to a fixed value only by multiplication of the complex function in the range frequency space, and the observation data is converted into a general char. Use observation data equivalent to that obtained by observation with a fixed plate. This makes it possible to use an existing image reproduction process as it is without requiring any change in the image reproduction algorithm.

  Furthermore, according to the signal processing device 200 of the first embodiment, since the peak shift after range compression due to radar movement during pulse reception is compensated for every azimuth time, any rangeture plate for every azimuth time due to inter-pulse modulation. Can handle switching.

  100 Synthetic Aperture Radar Device, 101 Antenna, 102 Processing Circuit, 103 Receiver, 104 Transmitter, 106 Recording Device, 107 Data Transmitter, 108 Memory, 111 Antenna Unit, 112 Radar Controller, 113 Receiver, 114 Transmitter, 115 digital processing unit, 116 data recording unit, 117 data transmission unit, 118 transmission / reception unit, 119 processing unit, 200 signal processing device, 201 processing circuit, 202 memory, 203 data recording device, 210 DFT unit, 211 compensation unit, 212 pulse Width equalization unit, 213 IDFT unit, 214 image reproduction unit.

Claims (6)

  1. A synthetic aperture radar apparatus for obtaining a reception signal used for reproduction of a synthetic aperture radar image by switching between up-chirp and down-chirp of a transmission signal and observing while changing the directivity direction of the radar beam,
    An antenna unit in which the transmission signal is radiated, receives the transmission signal reflected by the target,
    A transmission unit that generates the transmission signal by inter-pulse modulation and transmits the transmission signal to the antenna unit;
    A receiving unit which outputs the transmission signal received by the antenna portion as said received signal,
    A synthetic aperture radar apparatus comprising: a radar control unit configured to control a chirp plate of the transmission signal generated by the transmission unit based on a directivity direction of a radar beam radiated from the antenna unit.
  2.   2. The synthetic aperture radar apparatus according to claim 1, wherein the radar control unit controls the chirp plate of the transmission signal to increase as the beam steering angle of the radar beam emitted from the antenna unit increases. .
  3. A signal processing device for processing a received signal of the synthetic aperture radar device according to claim 1 or 2 to obtain a synthetic aperture radar image ,
    A signal processing apparatus including a compensation unit that compensates for a peak shift in a range direction that occurs due to radar movement when receiving the reception signal, based on a chirp plate of a transmission signal corresponding to the reception signal and a pointing direction of the radar beam. .
  4.   The compensation unit multiplies the reception signal Fourier-transformed in the range direction by a complex function generated based on the direction of the radar plate and the chirp plate corresponding to the azimuth time to compensate for the peak shift in the range direction. The signal processing apparatus according to claim 3, wherein:
  5.   5. The signal processing apparatus according to claim 3, further comprising an equalization unit that equalizes chirp in a range direction of the reception signal compensated by the compensation unit.
  6.   The equalization unit multiplies the reception signal compensated by the compensation unit by a complex function generated based on the chirp plate according to the azimuth time to remove the chirp in the range direction, and to fix the fixed chirp. The signal processing apparatus according to claim 5, wherein the signal processing apparatus is added.
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