CN113238226A - Synthetic aperture radar - Google Patents

Synthetic aperture radar Download PDF

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Publication number
CN113238226A
CN113238226A CN202110503616.0A CN202110503616A CN113238226A CN 113238226 A CN113238226 A CN 113238226A CN 202110503616 A CN202110503616 A CN 202110503616A CN 113238226 A CN113238226 A CN 113238226A
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moving target
baseline
satellite
signal
clutter
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CN113238226B (en
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杜志贵
杨峰
任维佳
陈险峰
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Changsha Tianyi Space Technology Research Institute Co Ltd
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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
    • G01S13/9021—SAR image post-processing techniques
    • G01S13/9029—SAR image post-processing techniques specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time
    • 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
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G01S13/581—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of interrupted pulse modulated waves and based upon the Doppler effect resulting from movement of targets
    • G01S13/582—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of interrupted pulse modulated waves and based upon the Doppler effect resulting from movement of targets adapted for simultaneous range and velocity measurements
    • 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
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G01S13/589—Velocity or trajectory determination systems; Sense-of-movement determination systems measuring the velocity vector
    • 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
    • G01S13/9021—SAR image post-processing techniques
    • G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/023—Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/36—Means for anti-jamming, e.g. ECCM, i.e. electronic counter-counter measures
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/414—Discriminating targets with respect to background clutter
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/415—Identification of targets based on measurements of movement associated with the target

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention relates to a synthetic aperture radar, comprising a moving target detection system, wherein the moving target detection system comprises a baseline compensation module, a clutter suppression module and a moving target detection module, wherein the moving target detection module is configured to: after the echo signal is subjected to clutter suppression processing through a clutter suppression module and is prevented from being reduced in coherence of an obtained image through a baseline compensation module, phase difference caused by clutter is eliminated based on prior information, so that only phase difference caused by a moving target remains in the echo signal. The invention can utilize the space-time adaptive processing technology to inhibit the non-stationary clutter and set the period of the pulse repetition periodic signal at the same time to avoid the moving target signal from being eliminated in the process of inhibiting the clutter by the space-time adaptive processing technology, thereby reducing the probability of detection failure.

Description

Synthetic aperture radar
The invention has the application number of CN201910787400.4, the application date of 08-23.2019 and the application type of invention, and the application name is divisional application of a moving target detection system based on a distributed synthetic aperture radar.
Technical Field
The invention relates to the technical field of radars, in particular to a synthetic aperture radar.
Background
The Synthetic Aperture Radar (Synthetic Aperture Radar) ground moving target monitoring technology can perform high-resolution imaging on an observation scene and complete detection and positioning of a ground target at the same time, and is widely applied to the fields of urban traffic monitoring and military reconnaissance and early warning.
At present, research aiming at the ground moving target detection technology of the synthetic aperture radar is mainly divided into three types, namely amplitude monitoring, phase monitoring and amplitude and phase joint detection. And the amplitude detection is to detect the target of the synthetic aperture radar image subjected to the adaptive clutter suppression by using the amplitude information of the synthetic aperture radar image. The phase detection is mainly to perform interference processing on the synthetic aperture radar image data of two channels of the radar, and realize ground target detection based on the interference phase information of the signal after extracting the interference phase. The amplitude and phase joint detection is realized by jointly taking the amplitude information of the self-adaptive clutter suppressed synthetic aperture laser radar image and the two-channel interference phase of the synthetic aperture laser radar image as a judgment criterion.
For example, chinese patent publication No. CN106249219B discloses a method for detecting a moving target of a synthetic aperture radar based on adaptive matched filtering, which mainly solves the problems of difficulty in detecting a slow moving target on the ground and unstable detection performance in the prior art. The method comprises the following implementation steps: (1) generating a data vector; (2) amplitude detection is carried out on each pixel point to obtain a potential target; (3) estimating a radial velocity value for each potential target; (4) estimating energy loss of the potential target; (5) determining a detection threshold of the energy loss amount; (6) removing false alarms; (7) and determining a monitoring result, and taking the moving target as a final monitoring result. However, the patent does not consider the problem of suppression of blurred strong clutter in a non-uniform scene with obvious strong and weak contrast.
For example, chinese patent publication No. CN103217677A discloses a single-channel synthetic aperture radar moving target detection method based on joint detection quantity, which is to obtain sub-apertures corresponding to sub-images based on division of synthetic aperture radar images in the azimuth spectrum, and then correct the errors in amplitude and phase between different sub-images by combining a two-dimensional adaptive method to realize registration between the sub-apertures; and then, the time target detection is jointly detected by using a second eigenvalue obtained by the covariance matrix between the adjacent sub-images and the independent normalized phase. The method has good clutter suppression capability and high robustness, so that the detection of the moving target can be efficiently realized, and the method is used for detecting the moving target of a single-channel synthetic aperture radar image. However, the actual monitoring scene often cannot meet the distance stability, and when the ground fluctuates severely, targets in the same distance ring have different distance characteristics, the space-time adaptive processing method of the joint time provided by the patent is based on the stability that the clutter has a better distance, and the clutter suppression method provided by the patent cannot effectively suppress the non-stable clutter.
For example, chinese patent publication No. CN104515980A discloses a ground moving object detection method and apparatus based on In synthetic aperture radar configuration, wherein the method includes: establishing a sliding bunching synthetic aperture radar echo model according to an original echo signal received by a scene irradiation area, and performing two-dimensional sliding bunching on a single radar in the model to obtain an initial synthetic aperture radar image; forming a three-dimensional matrix by the imaged initial synthetic aperture radar images of the plurality of radars, and performing compressed sensing processing on a three-dimensional matrix slice to obtain a synthetic aperture radar image; registering the synthetic aperture radar images, wherein the same pixel in different synthetic aperture radar images corresponds to the same ground unit; performing space-time adaptive processing on the registered synthetic aperture radar image, and performing elevation phase compensation on the synthetic aperture radar image subjected to the space-time adaptive processing; and performing target detection on the synthetic aperture radar image after the elevation phase compensation by using a constant false alarm rate detection technology. The method adopts the elevation phase compensation method to obviously improve the speed measurement precision. However, the moving target detection method provided by the patent does not consider that the formation configuration of the distributed small satellites cannot meet the requirement of uniform arrangement actually, and the actual monitoring scene often cannot meet the requirement of distance stability, so that clutter cannot be effectively suppressed by space-time adaptive processing. Furthermore, the method disclosed in this patent requires compensation for elevation phase, but in practice the distributed microsatellites provide a baseline that is a hybrid with an along-track baseline that requires decoupling of the hybrid baseline.
For example, chinese patent publication No. CN1066842143A discloses a filtering-based radar target fast CFAR detection method, which mainly includes: acquiring synthetic aperture radar imaging data; recording the synthetic aperture radar imaging data as an amplitude matrix I of an image to be detected, wherein the I comprises an interested moving target and a background clutter of the interested moving target, the number of pixels occupied by the interested moving target in the I is then sequentially calculated to obtain an X multiplied by Y dimensional energy matrix S of the image to be detected and an M multiplied by N dimensional statistical matrix of the image to be detected, and calculating a dimensional frequency domain matrix to be filtered of the image to be detected, thereby calculating a dimensional statistical matrix after filtering the background clutter; sequentially calculating an R multiplied by G dimension clutter energy matrix of an image to be detected and an R 'multiplied by G' dimension judgment matrix of an interested moving target; calculating an X 'multiplied by Y' dimension effective judgment matrix of the interested moving target; and obtaining the X 'X Y' dimension effective judgment matrix of the interested moving object, wherein the X 'row and Y' column elements in the effective judgment matrix correspond to the interested moving object in the interested object. However, this method can only be used when the background clutter is weak and the echo energy of the moving target is strong, and the echo energy of the moving target is drowned when the background echo energy is strong, so that the moving target cannot be detected effectively. Furthermore, for high resolution wide swath imaging, typical distributed synthetic aperture radar systems use low-periodicity pulse repetition period signals for sampling. The spacing along the track baseline of the distributed synthetic aperture radar system determines a maximum unambiguous range of radial velocities. Spatial blurring occurs when the radial velocity of a moving object exceeds the maximum unambiguous radial velocity range. The spatial domain ambiguity not only affects the estimation and positioning of the ground moving target speed, but also affects the guide vector of the ambiguity clutter component. After the airspace fuzzy occurs, when the equivalent radial velocity of the moving target is close to the equivalent radial velocity of the fuzzy clutter component, the moving target is also inhibited. Therefore, the period of the pulse repetition period signal needs to be set to avoid the moving target signal being eliminated in the process of suppressing the clutter by the space-time adaptive processing technology.
In summary, it is necessary to improve the prior art to set the period of the pulse repetition periodic signal while suppressing the non-stationary clutter by using the space-time adaptive processing technique in the distributed synthetic aperture radar imaging system, so as to prevent the moving target signal from being eliminated in the process of suppressing the clutter by using the space-time adaptive processing technique, thereby reducing the probability of detection failure and obtaining the speed information and the position information of the moving target.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a moving target detection system based on a distributed synthetic aperture radar, which is characterized in that a clutter suppression module can suppress clutter by utilizing the multi-degree-of-freedom characteristic of the distributed synthetic aperture radar based on a signal reconstruction mode, the signal-to-noise ratio of an output signal can be maximized so as to improve the detection probability of a ground moving target, and then the signal output by the clutter suppression module is fed back to a pulse transmitting module to adjust the pulse period, so that the moving target signal is prevented from being eliminated in the process of suppressing the clutter by a space-time adaptive processing technology, and the probability of detection failure is reduced; in addition, the invention can also carry out baseline decoupling and phase compensation through the baseline compensation module to avoid the reduction of the image coherence of the synthetic aperture radar, thereby improving the clutter suppression performance of the clutter suppression module and improving the speed measurement precision.
According to a preferred embodiment, the moving target detection system based on the distributed synthetic aperture radar comprises at least one main satellite and at least one auxiliary satellite which take the synthetic aperture radar as a payload. The system also comprises a clutter suppression module and a pulse transmitting module which are arranged on the primary/secondary satellite. The main satellite transmits signals through the pulse transmitting module, and the clutter suppression module reconstructs an echo signal reconstructor which returns based on the transmitted signals to generate virtual uniform sampling signals and then maximizes the signal-to-noise-and-noise ratio of output signals. And after the speed information of the moving target in the echo signal is obtained, the period of the pulse transmitting module is adjusted to enable the generated clutter equivalent radial speed to fall outside the preset range of the speed of the moving target.
According to a preferred embodiment, the clutter suppression module comprises a signal reconstructor and a space-time adaptive processor. The signal reconstructor describes coordinates of a spatially sampled signal of the echo signal based on an orientation dimension, a distance dimension, and a pitch dimension. And the signal reconstructor calculates an interpolation matrix under the corresponding dimensionality according to a proximity principle. The signal reconstructor performs signal reconstruction on the space sampling signal to obtain a virtual uniform sampling signal determined by the guide vector.
According to a preferred embodiment, the space-time adaptive processor further comprises at least a weight generator and a data training unit. The weight generator acts on the virtual uniform sampling signal based on the virtual uniform sampling signal and the weight learned by the data training unit so as to maximize the signal-to-noise-ratio of the signal output of the moving target. And the data training unit is used for learning to obtain a weight value after eliminating the data of the ground moving target and the data of the unit adjacent to the ground moving target from the echo data.
According to a preferred embodiment, the system further comprises a moving object detection module. The moving target detection module is configured to: after the echo signals are subjected to clutter suppression processing through the clutter suppression module, phase differences caused by the clutter are eliminated based on the prior information, and a moving target speed preset range is selected. And the moving target detection module constructs a speed vector function related to the moving target in the selected moving target speed range, and realizes moving target detection based on the speed vector function and the moving target speed preset range.
According to a preferred embodiment, the system is further provided with a baseline compensation module. Before the echo signal is detected by the moving target detection module, the echo signal is compensated into a fixed baseline along the track by the baseline compensation module based on the motion trail parameters of the primary satellite and the spatial position relationship between the primary satellite and the secondary satellite, so as to avoid the decrease of the coherence of the obtained image.
According to a preferred embodiment, the baseline compensation module comprises a time-varying baseline compensator. The time-varying baseline compensator is configured to: and constructing at least one new auxiliary satellite track parallel to the track of the main satellite based on the track of the main satellite in a synthetic aperture imaging time period, wherein the polynomial equation with time as a variable compensates the phase difference caused by the wave path difference value of the echo. Thus obtaining the echo signal which is equivalent to the echo signal along the new auxiliary satellite track and under the fixed track base line.
According to a preferred embodiment, the baseline compensation module further comprises a decoupler. The decoupler is configured to: and obtaining a vector mode equation of the effective along-track baseline by projecting the time-varying baseline to the track direction of the auxiliary satellite to obtain a geometric relationship between the velocity vector of the auxiliary satellite and the unit vector of the central sight line direction of the antenna beam of the main satellite, and generating the time-varying along-track baseline by the central sight line vector of the antenna beam under the front side view of the main satellite to improve the speed measurement precision.
According to a preferred embodiment, the pulse transmitting module adjusts a pulse period based on the moving target speed information obtained by the target detecting module to avoid a blind speed within a preset range of the moving target speed.
According to a preferred embodiment, the moving target detection method based on the distributed synthetic aperture radar uses a system which is composed of at least one main satellite and at least one auxiliary satellite with the synthetic aperture radar as a payload, and a clutter suppression module and a pulse transmitting module which are arranged on the main/auxiliary satellites to carry out moving target detection. And the main satellite transmits signals through the pulse transmitting module. The clutter suppression module generates a virtual uniform sampling signal based on the echo signal reconstruction returned by the transmitting signal and then maximizes the signal-to-noise ratio of the output signal. And the clutter suppression module adjusts the period of the pulse emission module after obtaining the speed information of the moving target in the echo signal so that the generated clutter equivalent radial speed is out of the preset range of the speed of the moving target.
According to a preferred embodiment, the clutter suppression module comprises a signal reconstructor and a space-time adaptive processor. The signal reconstructor describes coordinates of a spatially sampled signal of the echo signal based on an orientation dimension, a distance dimension, and a pitch dimension. And the signal reconstructor calculates an interpolation matrix under the corresponding dimensionality according to a proximity principle, so that the spatial sampling signal is subjected to signal reconstruction to obtain a virtual uniform sampling signal determined by the guide vector.
The beneficial technical effects of the invention comprise one or more of the following:
1. because the space-time adaptive technology needs to acquire training samples from adjacent range units to estimate a covariance matrix to realize effective suppression of clutter, when a distributed synthetic aperture radar system is in a non-uniform space configuration, non-uniform sampling signals can be generated, and the frequency spectrum of the signals can generate very strong side lobes, so that the distributed synthetic aperture radar system in the non-uniform space configuration cannot effectively suppress ground clutter through the space-time adaptive technology, the invention reconstructs the non-uniform sampling echo signals into virtual uniform sampling signals in the distance direction, the azimuth direction and the pitching direction respectively through a signal reconstructor, thereby obtaining virtual uniform sampling signals, wherein the virtual uniform sampling signals not only retain necessary information in real signals, but also meet the requirements of a space-time adaptive processor on the configuration, and the space-time adaptive processor can fully utilize the space freedom degrees of the pitching direction and the distance direction of the non-uniform space configuration, the method can effectively inhibit non-stationary clutter and maximize the signal-to-noise ratio of the output signal so as to improve the detection probability of the moving target;
2. the obtained virtual uniform sampling signal can be combined with a space-time adaptive technology to suppress clutter, and the space freedom degree in the pitching direction can be effectively utilized to suppress non-stationary clutter, so that the detection probability of a moving target is improved;
3. the data training unit is used for obtaining a weight value after the data training unit eliminates the ground moving target and the data of the unit adjacent to the ground moving target from the echo data, so that the situation that the clutter and the moving target cannot be distinguished by the obtained weight value due to performance loss can be avoided;
4. the moving target detection module respectively carries out threshold detection on the maximum value of the velocity vector function of the moving target and the square of the complex amplitude of the moving target, so that the probability of detection failure can be greatly reduced, and the velocity information and the position information of the moving target can also be obtained;
5. when the synthetic aperture radar high-resolution and wide swath imaging needs sampling of a pulse repetition period signal in a low direction, the pulse transmitting module sets the period of the pulse repetition period signal through moving target speed information fed back by the moving target detecting module so as to avoid the moving target signal from being eliminated in the process of suppressing clutter by the space-time adaptive processing technology, thereby reducing the probability of detection failure.
Drawings
FIG. 1 is a simplified block diagram of a preferred embodiment of the present invention; and
FIG. 2 is a geometric schematic of a preferred distributed synthetic aperture radar of the present invention along a track baseline.
List of reference numerals
100: the main star 200: auxiliary star
210: the new assistant satellite 300: baseline compensation module
310: time-varying baseline compensator 320: decoupling device
400: the clutter suppression module 410: signal reconstructor
420: space-time adaptive processor 421: weight generator
422: data training unit 500: moving target detection module
600: pulse transmitting module O1: spatial location points of the Master Star 100
O22: sky after movement of the satellite 200Intermediate position point P: area illuminated by the main star 100
N1: 100 track N of the Master Star2: master satellite and auxiliary satellite 200 track
θ: main star 100 antenna squint angle F: n is a radical of1And b1Plane of formation
O2: spatial location points of the satellite 200
A: spatial location point O of the dominant star 1001At the satellite 200 track N2Projected point on
Figure BDA0003056331500000071
: assistant 200 track N2Flight path obtained by projection to plane F
b1: unit vector of central sight line direction of 100 antenna beams of main satellite
b2: auxiliary satellite 200 antenna beam center line-of-sight direction unit vector
b3: unit vector of beam center line of sight direction under front view of primary star 100
Figure BDA0003056331500000072
：O2In that
Figure BDA0003056331500000073
Upper corresponding projected point
Figure BDA0003056331500000074
：O22In that
Figure BDA0003056331500000075
Upper corresponding projected point
Figure BDA0003056331500000076
: a is at
Figure BDA0003056331500000077
Upper corresponding projected point
Detailed Description
The following description is made with reference to fig. 1 and 2.
Example 1
The invention discloses a moving target detection system based on a distributed synthetic aperture radar, which comprises at least one main satellite 100 and at least one auxiliary satellite 200 which take the synthetic aperture radar as a payload according to a preferred embodiment. The system also includes a clutter suppression module 400 and a pulse transmit module 600 disposed on the primary/secondary satellite. The dominant star 100 transmits signals through the pulse transmitting module 600, and the clutter suppression module 400 reconstructs an echo signal reconstructor based on the returned transmitted signals to generate a virtual uniform sampling signal and then maximizes the signal-to-noise ratio of the output signal. After the speed information of the moving target in the echo signal is obtained, the period of the pulse transmitting module 600 is adjusted so that the generated clutter equivalent radial speed falls outside the preset range of the speed of the moving target. Preferably, the distributed synthetic aperture radar system of the present invention may be in a non-uniform spatial configuration. Non-uniform spatial configuration refers to linear and/or area arrays where the position between the primary/secondary stars is not uniform. For example, the interference Cartheel configuration, Helix configuration, Pendulum configuration, etc. are all non-uniform spatial configurations. Non-uniform spatial configurations may result in unequal lengths of the baseline between the primary/secondary stars (i.e., the connection between antennas on the primary/secondary stars), and may result in time-varying and mixed characteristics of the baseline between the primary/secondary stars as the relative positions of the primary and secondary stars change. Preferably, the time-varying characteristic refers to a change in direction and length of the baseline over time. The hybrid characteristic means that the direction of the baseline is not purely in the direction of travel of the satellite (i.e., along the track baseline) or in the direction perpendicular to the satellite travel (i.e., the tangent track baseline), but rather is a hybrid of an along-track baseline component and a tangent-track baseline component. The speed information of the ground moving target is carried along the track base line. The track cutting baseline carries ground elevation information.
Preferably, the synthetic aperture radar system on the primary satellite 100 transmits radar signals for imaging to ground. The transmitted radar signal may be a pulse repetition periodic signal, for example, a chirp pulse repetition signal. Preferably, the synthetic aperture radar systems on the primary satellite 100 and the secondary satellite 200 generate two synthetic aperture radar complex images based on the received ground echo signals, and perform interference imaging processing on the two synthetic aperture radar complex images. The ground echo signals include phase information from the baseline between the transmitting primary satellite and the receiving secondary satellite. Preferably, since the ground clutter in the echo signal may obscure the echo signal of the ground moving target, the prior art generally employs a space-time adaptive processing technique to suppress the ground clutter echo signal to avoid burying the signal of the slow moving target with the clutter signal. The space-time adaptive technology is to sample echo signals to form a three-dimensional matrix form of time correlation, distance correlation and satellite number correlation, and detect whether moving targets exist or not by filtering out clutter through impulse response in a time dimension, namely, in signals of a two-dimensional matrix (distance multiplied by the number of satellites) in the three-dimensional matrix. The invention can at least realize the following beneficial technical effects by reconstructing the echo signal into the virtual uniform sampling signal: firstly, because the space-time adaptive technology needs to acquire training samples from adjacent range units to estimate a covariance matrix to realize effective suppression of clutters, when a distributed synthetic aperture radar system is in a non-uniform space configuration, a non-uniform sampling signal can be generated, and a very strong side lobe can be generated in a frequency spectrum of the signal, so that the distributed synthetic aperture radar system in the non-uniform space configuration cannot effectively suppress ground clutters through the space-time adaptive technology, the non-uniform sampling echo signal is respectively reconstructed into a virtual uniform sampling signal in a distance direction, an azimuth direction and a pitching direction through a signal reconstructor 410, so that a virtual uniform sampling signal is obtained, the virtual uniform sampling signal not only retains necessary information in a real signal, but also meets the requirements of a space-time adaptive processor 420 on the configuration; secondly, the space-time adaptive processor 420 can fully utilize the spatial degrees of freedom in the pitch direction and the distance direction of the non-uniform spatial configuration, can effectively suppress non-stationary clutter, and maximizes the signal-to-noise ratio of the output signal to improve the detection probability of the moving target.
Preferably, the pulse transmitting module 600 transmits a pulse repetition period signal. As shown in fig. 1, the pulse transmitting module 600 adjusts the pulse period by enabling the moving object detecting module 500 to obtain the speed information of the moving object. Preferably, in the time period of high-resolution and wide swath imaging of the synthetic aperture radar system, in the process that the echo signal after being repeatedly sampled by the pulse repetition period signal suppresses clutter through the clutter suppression module 400, the equivalent radial velocity generated based on the period of the pulse repetition period signal falls outside the preset range of the moving target velocity, so that the moving target signal within the preset range of the moving target velocity is prevented from being eliminated in the process that the clutter suppression module 400 suppresses clutter.
According to a preferred embodiment, the clutter suppression module 400 comprises a signal reconstructor 410 and a space-time adaptive processor 420. The signal reconstructor 410 describes coordinates of the spatially sampled signals of the echo signals based on the azimuth dimension, the distance dimension, and the pitch dimension. The signal reconstructor 410 calculates interpolation matrices in the respective dimensions according to the proximity principle. The signal reconstructor 410 thereby performs signal reconstruction on the spatial sampled signal to obtain a virtual uniformly sampled signal determined by the steering vector. Preferably, the signal reconstructor 410 is configured to: describing coordinates of the space sampling signal based on an orientation dimension, a distance dimension and a pitching dimension, and calculating the distance between the space sampling signal and each signal of the virtual uniform sampling signal according to a proximity principle; under the condition that the azimuth dimension, the distance dimension and the pitch dimension are respectively taken as reference surfaces, an azimuth interpolation matrix, a distance interpolation matrix and a pitch interpolation matrix under the corresponding dimensions are obtained through calculation; and performing signal reconstruction on the space sampling signals based on the azimuth interpolation matrix, the distance interpolation matrix and the pitch interpolation matrix to obtain virtual uniform sampling signals determined by the guide vectors. Preferably, the distributed synthetic aperture radar system can provide multiple functions of ground detection for the radar due to the combination of the base line components with different directions and the base lines with different lengths. In most cases, the distributed synthetic aperture radar system cannot satisfy the uniform distribution of the satellite, either in the direction of motion along the satellite or in the pitch direction of the antenna. However, space-time adaptive techniques require that the satellites must be spatially distributed strictly at uniform intervals, otherwise non-uniform sampling of the echo signals may result due to the non-uniform configuration of the satellites. Non-uniform sampling can cause the frequency spectrum of the sampled signal to produce very strong side lobes, thereby reducing the ability to suppress clutter. Therefore, the distributed synthetic aperture radar system with the non-uniform spatial configuration cannot directly use the space-time adaptive technology. In this way, the signal reconstructor 410 can reconstruct the non-uniform sampling signal with the non-uniform spatial configuration into a virtual uniform sampling signal, and overcome the spatial under-sampling problem, so that the distributed synthetic aperture radar system with the non-uniform spatial configuration meets the requirements of the space-time adaptive processing technology.
Preferably, since the energy distribution of the ground clutter is distributed not only with the time doppler frequency and the space doppler frequency, but also due to the difference of the pitch angle of the antenna, the distance characteristics of two clutter points located in the same distance band are also different, and the clutter is non-stationary. Preferably, the distributed synthetic aperture radar system has satellite antennas distributed along the elevation direction, and can provide the frequency information of the elevation direction of the echo signal. And the distributed synthetic aperture radar system with the non-uniform spatial configuration has the spatial degree of freedom in the pitching direction, and provides conditions for inhibiting non-stationary clutter.
Preferably, since the intervals between the satellites are different due to non-uniform sampling of the echo signals compared to uniform sampling, spatial undersampling of the echo signals is caused, and correlation between the sampled signals is also reduced. The signal reconstructor 410 reconstructs the actual non-uniform signal into a virtual uniformly sampled signal according to the array interpolation. Preferably, the non-uniform spatial sampling signal can be described based on an azimuth dimension, a distance dimension and a pitch dimension, i.e. by the azimuth dimension, the distance dimension and the pitch dimension as coordinates of the echo spatial sampling signal. The actual non-uniformly sampled signal with N receiving synthetic aperture radar antennas has the coordinate x1,y1,z1]…[xN,yN,zN]And the coordinates of M virtual uniform sampling signals existing after reconstruction are x'1,y’1,y‘1]…[x’M,y‘M,z’M]. The distance before and after signal reconstruction can be calculated according to the coordinates as:
Figure BDA0003056331500000101
wherein N is 1,2, N and M is 1,2, … M. Preferably, m is fixed, and the spatial position of the sampled signal in the non-uniformly sampled signal is tested to be closest to the spatial position of the mth virtual uniformly sampled signal. Sampling signal x with shortest distance after testnAnd x'mAnd correspondingly. Then the position relation of other sampling signals is determined according to the method. After the corresponding relation is established, the guide vector E of the non-uniform sampling signal and the guide vector of the virtual uniform sampling signal are obtained
Figure BDA0003056331500000102
Thus, an interpolation matrix B is obtained to reconstruct the signal. Because the coordinates have three variables, the interpolation matrixes corresponding to the azimuth dimension, the distance dimension and the pitch dimension need to be calculated respectively. After the interpolation matrix is obtained, the non-uniform sampling signal can be reconstructed to obtain a virtual uniform sampling signal. Through the method, the reconstructed virtual uniform sampling signal not only retains necessary information in the non-uniform sampling signal, but also meets the requirement of the space-time self-adaptive clutter suppression technology on uniform configuration.
According to a preferred embodiment, the space-time adaptive processor 420 further includes at least a weight generator 421 and a data training unit 422. The weight generator 421 acts on the virtual uniform sampling signal based on the virtual uniform sampling signal and the weight learned by the data training unit 422 to maximize the signal-to-noise ratio of the signal output of the moving object. The data training unit 422 gets the weight value by learning after eliminating the data of the ground moving target and the unit adjacent to the ground moving target from the echo data. Preferably, after the spatial sampling signal is reconstructed into a virtual uniform sampling signal, the weight generator 421 learns a weight based on the virtual uniform sampling signal and the data training unit 422, and applies the weight to the virtual uniform sampling signal to maximize the signal-to-noise-and-noise ratio of the signal output by the moving object. The data training unit 422 culls ground motion from echo dataAnd learning the data of the target and the unit adjacent to the ground moving target to obtain the weight. Preferably, the clutter of the distributed synthetic aperture radar system may be expressed as a Kronecker product of a temporal steering vector with respect to the normalized doppler frequency and a spatial steering vector with respect to the spatial frequency of the clutter source point, in case the clutter source satisfies the independent co-distribution condition. There is a coupling relationship between the normalized doppler frequency and the spatial frequency in a distributed synthetic aperture radar system, and this coupling relationship accurately describes the energy distribution of the clutter. The clutter distribution is defined, and the corresponding weight generator 421 can effectively suppress the clutter. The coupling relationship between the normalized doppler frequency and the spatial frequency can be represented by β. The physical meaning of β is the number of times that the satellite 200 or the satellite 100 flies half the baseline length within a coherent integration time. In the case of the positive side view, most of the energy of the clutter is concentrated on a straight line with a slope of β, and the weight of the weight generator 421 can be set according to this rule. Under the condition that the clutter sources satisfy the independent same distribution condition, the weight of the weight generator 421 acts on the virtual uniform sampling signal, so that the output signal-to-noise ratio of the moving target which is located at the oblique angle θ relative to the secondary star 200 and/or the primary star 100 and has the radial velocity vector is maximized. The weight of the weight generator 421 is related to the estimated value of the covariance matrix of the clutter
Figure BDA0003056331500000111
Estimation of covariance matrix
Figure BDA0003056331500000112
The virtual uniform sampling signal to be detected can be obtained, and the virtual uniform sampling signal can also be obtained through the data training unit 422. Data training unit 422 and
Figure BDA0003056331500000113
the relationship of (a) is shown as follows:
Figure BDA0003056331500000114
wherein P is the amount of training data. smIs training data, i.e. a virtually uniformly sampled signal, except to be detected.
Figure BDA0003056331500000115
Is s ismThe conjugate transpose of (c). Preferably, the weight generator 421 has a performance loss due to the difference between the estimated covariance matrix and the actual covariance matrix. The performance loss may be accumulated over time as the data training unit 422 learns. In order to avoid that the obtained weight cannot distinguish the clutter and the moving target due to performance loss, the data training unit 422 needs to learn to obtain the weight after eliminating the data of the ground moving target and the unit adjacent to the ground moving target from the echo data. By adopting the technical scheme, the invention can at least obtain the following beneficial technical effects: firstly, clutter can be suppressed by combining the obtained virtual uniform sampling signal with a space-time adaptive technology, and nonstationary clutter can be effectively suppressed by utilizing the space freedom in the pitching direction, so that the detection probability of a moving target is improved; secondly, the data training unit 422 gets the weight value by learning after eliminating the ground moving target and the data of the unit adjacent to the ground moving target from the echo data, so that the condition that the clutter and the moving target cannot be distinguished by the obtained weight value due to performance loss can be avoided.
According to a preferred embodiment, the system further comprises a moving object detection module 500. The moving object detection module 500 is configured to: after the echo signal is subjected to clutter suppression processing by the clutter suppression module 400, the phase difference caused by the clutter is cancelled based on the prior information, and a moving target speed preset range is selected. The moving target detection module 500 constructs a velocity vector function related to the moving target within the selected moving target velocity range, and realizes moving target detection based on the velocity vector function and the moving target velocity preset range. Preferably, the moving object detection module 500 is configured to: after the echo signal is processed by the clutter suppression module 400 for clutter suppression and compensated for phase by the baseline compensation module 300, the moving target detection module 500 cancels out the phase difference caused by the clutter based on the prior information so that only the phase difference caused by the moving target remains in the echo signal; base ofSelecting a moving target speed preset range from the prior information, and selecting enough sample observation values in the target speed range to construct a speed vector function related to the moving target; when the maximum value of the velocity vector function of the moving target exceeds a preset threshold value and the estimated value of the velocity vector of the moving target is within a preset range of the velocity of the moving target, amplitude information of the moving target is obtained through calculation to carry out threshold detection, so that the detection of the moving target is realized; when the maximum value of the velocity vector function of the moving target is smaller than a preset threshold and/or the velocity vector of the moving target is not in the preset range of the velocity of the moving target, another preset range of the velocity of the moving target is selected based on the prior information to construct the velocity vector function related to the moving target, and the steps are repeated. Preferably, the target detection module 500 constructs an inverse matrix of the vector for the clutter frequency item based on the prior information such as the baseline formed by the secondary satellite 200 with respect to the primary satellite 100, the flight velocity vector of the secondary satellite 200, and the like, and the matrix with 1 element is obtained after the inverse matrix is multiplied by the vector for the clutter frequency item, so as to eliminate the frequency change caused by clutter. Preferably, the phase difference caused by the clutter frequency is canceled out, so that only the phase difference caused by the moving target remains in the echo signal. Preferably, the information related to the moving object is not known in the actual situation. But the motion speed ranges of different types of moving objects can be known according to the existing prior information. For example, the tank has a traveling speed of about 48-72 km/h, and the military jeep has a traveling speed of about 70-120 km/h. Thus, sufficient sample observations can be taken at these velocity ranges to obtain the desired velocity vector function by a suitable estimation algorithm, such as maximum likelihood. The significance of the velocity vector function is that when the velocity vector function reaches the maximum value, the velocity vector estimation value closest to the real velocity value of the moving target is obtained through solving. Preferably, when the maximum value of the velocity vector function of the moving target exceeds a preset threshold value and the estimated value of the velocity vector of the moving target is within a preset range of the velocity of the moving target, the amplitude information of the moving target is determined by an algorithm such as a least square method. Preferably, the preset threshold value may be set according to a moving speed range of the moving object. Preferably based on the results obtainedAnd carrying out constant false alarm threshold detection by the square of the complex amplitude of the moving target. Preferably, the value of the constant false alarm threshold is determined by the false alarm probability
Figure BDA0003056331500000121
Determining, wherein ThIs a threshold value. When the square of the complex amplitude of the moving target is greater than ThWhen, a moving target exists. When the square of the complex amplitude of the moving target is less than ThWhen there is no moving object. In this way, the moving target detection module 500 performs threshold detection on the maximum value of the velocity vector function of the moving target and the square of the complex amplitude of the moving target, so as to greatly reduce the probability of detection failure, and obtain the velocity information and the position information of the moving target.
According to a preferred embodiment, the pulse transmitting module 600 adjusts the pulse period based on the moving target speed information obtained by the target detecting module 500 to avoid the occurrence of blind speed within a preset range of the moving target speed. Preferably, when the synthetic aperture radar system receives echo signals through the primary satellite 100 and the secondary satellite 200 and performs sampling with pulse repetition periodic signals in the azimuth direction to form a high-resolution and wide swath image, the product of the frequency of the pulse repetition periodic signals and half of the working wavelength is greater than the maximum value of the preset range of the moving target speed, so that the blind speed in the preset range of the moving target speed is avoided. Preferably, the ground moving target has the same multi-channel steering vector as the stationary clutter due to Doppler center ambiguity, so that echoes returned by the ground moving target are also suppressed in the clutter suppression process. Accordingly, a notch, i.e., a blind speed, may appear on the speed response curve. The output signal-to-noise ratio of the moving target close to the blind speed is greatly reduced, and the detectable speed range is greatly influenced. Preferably, for high resolution wide swath imaging, the sampling is performed using a low period pulse repetition period signal. However, the smaller the period of the pulse repetition periodic signal is, the more frequently the blind speed appears within the preset range of the moving target speed. In order to avoid the occurrence of blind speed within the preset range of the moving target speed, the frequency of the pulse repetition periodic signal needs to meet the requirement
Figure BDA0003056331500000131
Wherein v ismaxRepresenting the maximum moving target preset speed. v. ofPRFRepresenting the speed of the pulse repetition period signal. PRF denotes the frequency of the pulse repetition period signal. λ represents the wavelength at which the radar operates. Preferably, the spacing of the multi-satellite azimuth platforms along the track baseline determines a maximum unambiguous radial velocity range. Spatial blurring occurs when the radial velocity of a moving object exceeds the maximum unambiguous radial velocity range. The spatial domain ambiguity not only affects the estimation and positioning of the ground moving target path speed, but also affects the guide vector of the ambiguity clutter component. The spurious suppression module 400 has a band-pass band rejection-like characteristic due to the weight generator 421. The bandstops of the clutter suppression module 400 are aligned to the equivalent radial velocity of each blurred clutter component. After the airspace fuzzy occurs, when the equivalent radial velocity of the moving target is close to the equivalent radial velocity of the fuzzy clutter component, the moving target is also inhibited. Therefore, the equivalent radial velocity generated by the period of the pulse repetition period signal falls outside the preset range of the moving target velocity, thereby preventing the moving target signal within the preset range of the moving target velocity from being eliminated in the process of clutter suppression by the clutter suppression module 400. By the method, when the synthetic aperture radar high-resolution and wide swath imaging needs the pulse repetition period signal of the low azimuth to be sampled, the frequency of the pulse repetition period signal is set to meet the requirement
Figure BDA0003056331500000141
And the equivalent radial velocity generated by the pulse repetition period signal falls outside the moving target velocity preset range, so that the blind velocity in the moving target velocity preset range can be avoided, and the echo signal is prevented from being eliminated in the process of clutter suppression by the clutter suppression module 400.
Example 2
This embodiment may be a further improvement and/or a supplement to embodiment 1, and repeated contents are not described again. The preferred embodiments of the present invention are described in whole and/or in part in the context of other embodiments, which can supplement the present embodiment, without resulting in conflict or inconsistency.
According to a preferred embodiment, the system is further provided with a baseline compensation module 300. Before the echo signal is detected by the moving object detection module 500, the echo signal is compensated by the baseline compensation module 300 to a fixed along-track baseline based on the motion trajectory parameters of the primary satellite 100 and the spatial position relationship of the primary satellite 100 and the secondary satellite 200 to avoid the decrease in coherence of the obtained image. Preferably, the baseline compensation module 300 compensates the echo signals received at the time-varying, mixed baseline to the echo signals received at the fixed along-track baseline based on the ephemeris data and the spatial position relationship of the primary/secondary satellites during the imaging period of the synthetic aperture radar system. The invention can at least realize the following beneficial technical effects by adopting the mode: firstly, because the non-uniform spatial configuration can cause the inter-satellite baseline to be continuously changed at the transmitting time of each chirp repeated signal, a high-order variation factor is added to the phase information of the synthetic aperture radar image during interference imaging, and after the method and the device are adopted, the baseline compensation module 300 reconstructs a time-varying baseline into a fixed baseline and compensates based on a wave path difference value between the time-varying baseline and the fixed baseline to eliminate the high-order variation factor, so that the coherence of the synthetic aperture radar image pair is prevented from being reduced, and the clutter suppression performance of the clutter suppression module 400 is improved; secondly, because the mixed base line has a track cutting base line component and an along track base line component, the phase information is mixed with the ground elevation information of the track cutting base line, and a large approximate error exists in the effective along track base line directly calculated according to the mixed base line, so that the speed measuring precision of the ground moving target is influenced.
According to a preferred embodiment, the baseline compensation module 300 includes a time-varying baseline compensator 310. The time-varying baseline compensator 310 is configured to: and constructing at least one new auxiliary satellite 210 track parallel to the track of the main satellite 100 based on the track of the main satellite 100 in a synthetic aperture imaging time period by using a polynomial equation with time as a variable to compensate the phase difference caused by the wave path difference value of the echo. Thereby obtaining an echo signal equivalent to a constant along-track baseline along the new satellite 210 track. Preferably, the time-varying baseline compensator 310 is configured to: generating a polynomial approximation equation with time as a variable according to the flight path of the main satellite 100 in a synthetic aperture imaging time period; constructing at least one polynomial equation which is parallel to the flight path of the main satellite 100 and takes time as a variable for the flight path of the new auxiliary satellite 210 based on the fitting result of the generated polynomial approximation equation; obtaining the value of the time by the repetition period of the azimuth pulse based on the polynomial equation of the flight paths of the satellite 200 and the new satellite 210 about the time variable, and obtaining the wave path difference value of the echo on the satellite 200 flight path and the new satellite 210 flight path at the emission moment of each azimuth pulse; based on the wave path difference of the echo, the echo signal of the satellite 200 at the receiving time of each azimuth pulse compensates the phase difference caused by the wave path difference of the echo, so that the echo signal which is equivalent to the echo signal under the new satellite 210 track and is under the fixed track base line is obtained. Preferably, the flight path equations of the primary and secondary stars 100, 200 are fitted by parameter estimation from the position measurement data of the primary and secondary stars 100, 200. According to the gaussian-markov theorem, for example, the least square method, the total least square method, is used as the fitting algorithm. Preferably, the value of the repetition period of the azimuth pulse is taken with respect to time in the imaging time period, and the trajectory equations of the satellite 200 and the new satellite 210 are taken in, so as to obtain the position coordinates of each azimuth pulse transmission time on the trajectories of the satellite 200 and the new satellite 210. The position coordinates can be used to calculate the difference between the upper echoes of the satellites 200 and the new satellite 210 at each azimuth pulse transmission time. Preferably, the wave path difference of the echo can be obtained according to the position coordinates, and is the cosine value of the included angle between the new satellite 210 and the undersatellite point connecting line and the beam sight line, and the length of the auxiliary satellite 200 and the new satellite 210 corresponding point connecting line. The satellite 200 echo signals are preferably compensated by computing the antenna beam center line of sight direction unit vector to obtain the path difference between the satellite 200 and the new satellite 210. Preferably, the wave path difference can be approximately expressed as a polynomial of the same order as the parametric equation. The constant term does not affect the imaging result, the primary term of the time variable can cause the azimuth spectrum of the echo signal to generate offset, and the influence on small-amplitude imaging is small. The higher order terms of the time variables can cause the azimuth response of the echo to be mismatched with the reference signal of the matched filter, and the coherence of the satellite imaging is reduced. Preferably, the compensation of the echo signal of the satellite 200 can avoid the influence of the high-order term of the time variable. By the method, the spectrum domain of the echo signal after the time-varying baseline compensation can be more concentrated, the standard deviation of the interference phase becomes small, the coherence of the synthetic aperture radar image pair can be effectively improved, especially the improvement in the area where the interference phase is close to the clutter is obvious, and the clutter suppression performance of the clutter suppression module 400 can be improved.
According to a preferred embodiment, the baseline compensation module 300 further includes a decoupler 320. The decoupler 320 is configured to: and obtaining a vector mode equation of the effective track-following baseline based on the projection of the time-varying baseline to the track direction of the auxiliary satellite 200 to obtain a geometric relationship between the velocity vector of the auxiliary satellite 200 and the unit vector of the central sight line direction of the antenna beam of the main satellite 100, and generating the time-varying track-following baseline for the central sight line vector of the antenna beam under the front side view of the main satellite 100 so as to improve the speed measurement accuracy. Preferably, the decoupler 320 is configured to: under the condition that the time-varying baseline is mixed with the components of the along-track baseline and the components of the track-cutting baseline and the track-cutting baseline, the time-varying baseline is projected to the track direction of the satellite 200 to obtain a vector mode equation of the effective along-track baseline; the vector mode equation of the effective along-track baseline obtains a time-varying baseline, a velocity vector of the auxiliary satellite 200 and a unit vector of the central sight line direction of the antenna beam of the main satellite 100 based on ephemeris measurement data, and generates the time-varying along-track baseline based on the central sight line vector of the antenna beam of the main satellite 100 under the front side view, which is obtained based on the geometric relationship between the velocity vector of the auxiliary satellite 200 and the unit vector of the central sight line direction of the antenna beam of the main satellite 100, so as to improve the speed measurement accuracy. Preferably, as shown in FIG. 2, N1、N2The flight path of the primary 100 and secondary 200 stars, respectively. O is1And O2The spatial location points of the primary satellite 100 and the secondary satellite 200 at the same time, respectively. b1、b2The unit vectors of the antenna beam center line of sight directions of the primary satellite 100 and the secondary satellite 200, respectively. N is a radical of1And b1Constituting the F-plane. P is the area illuminated by the primary star 100. When the satellite 200 is along N2Move to O22When in position, can be connected with the masterThe same beam of the star is pointed to observe the P region. Thus, the along-track baseline of the hybrid baseline formed by the secondary star 200 with respect to the primary star 100 is
Figure BDA0003056331500000161
A is the spatial location point O of the primary star 1001At the satellite 200 track N2The projected point of (a). Theta is b of the main star 1001The angle between the antenna and the moving direction of the main satellite 100 is the squint angle of the main satellite 100. When the satellite 200 track N2Projecting to a plane F to obtain a flight path
Figure BDA0003056331500000162
And
Figure BDA0003056331500000163
are each O2、O22And A is at
Figure BDA0003056331500000164
And (4) the corresponding projection point. b3Is the unit vector of the beam center line of sight direction for the front view of the primary star 100 in the F plane. b3And
Figure BDA0003056331500000165
is intersected at
Figure BDA0003056331500000166
And (4) point. When O is present2With b2When the light is irradiated to the region P,
Figure BDA0003056331500000167
can simultaneously use b1The region P is irradiated. Along the track baseline D may be of the form:
Figure BDA0003056331500000168
due to the fact that
Figure BDA0003056331500000169
Is composed of
Figure BDA00030563315000001610
In that
Figure BDA00030563315000001611
Is projected onto, and
Figure BDA00030563315000001612
is composed of
Figure BDA00030563315000001613
In that
Figure BDA00030563315000001614
Thereby according to the motion vector of the satellite 200
Figure BDA00030563315000001615
Equation (1) can be obtained and can be expressed as:
Figure BDA00030563315000001616
preferably, considering that an error in antenna installation may cause an error in the squint angle in the wave position parameters compared to the true squint angle, the squint angle θ may be calculated by accurately estimating the doppler center frequency of the echo signal.
Figure BDA00030563315000001617
And
Figure BDA00030563315000001618
can be measured from ephemeris or from satellite-mounted measurement means. Preferably, the solution b can be obtained from the geometrical relationship shown in fig. 23The system of equations of (1). The system of equations is shown below:
Figure BDA0003056331500000171
preferably, the above equation set has a unique solution. Preferably, root ofAccording to the solved squint angles theta and b3Values along the track baseline can be obtained. In this way, compared with an approximate method of directly projecting the mixed spatial baseline formed by the satellite 200 with respect to the main satellite 100 to the track of the satellite 200, under the condition that the tracks of the main satellite 100 and the satellite 200 and the beam sight of the antenna are not on the same plane, the along-track baseline including the speed information of the ground moving target can be decomposed, and the track-cutting baseline with the ground elevation information mixed with the base line processed in the baseline compensation module 300 is avoided. And the mixed base line is decomposed in the mode without being influenced by the configuration of the distributed synthetic aperture radar system and the view angle of the radar antenna.
Preferably, the time-varying baseline is independent of the time-varying along-the-track baseline by the decoupler 320 before the time-varying baseline formed by the secondary satellite 200 with respect to the primary satellite 100 is compensated by the time-varying baseline compensator 310, thereby avoiding that the time-varying baseline mixed with the along-track baseline component and the tangential-track baseline component introduces an approximation error for the phase compensation of the time-varying baseline compensator 310.
Example 3
The embodiment also discloses a moving target detection method, which can also be a moving target detection method of the satellite-borne synthetic aperture radar, a moving target detection method of the distributed synthetic aperture radar, or a moving target detection method of a system of the distributed satellite-borne synthetic aperture radar, and the method can be realized by the system and/or other replaceable parts. For example, the method of the present invention may be implemented using various components of the system of the present invention. This embodiment may be a further improvement and/or a supplement to embodiments 1 and 2, and repeated contents are not described again. The preferred embodiments of the present invention are described in whole and/or in part in the context of other embodiments, which can supplement the present embodiment, without resulting in conflict or inconsistency.
According to a preferred embodiment, the moving target detection is performed by using a system consisting of at least one primary satellite 100 and at least one secondary satellite 200 which take a synthetic aperture radar as a payload, and a clutter suppression module 400 and a pulse transmission module 600 which are arranged on the primary/secondary satellites. The master satellite 100 transmits signals through the pulse transmission module 600. The clutter suppression module 400 maximizes the signal-to-noise ratio of the output signal after generating the virtual uniform sampling signal based on the echo signal reconstruction returned by the transmit signal. The clutter suppression module 400 adjusts the period of the pulse transmission module 600 after obtaining the speed information of the moving target in the echo signal so that the generated clutter equivalent radial speed falls outside the preset range of the moving target speed.
According to a preferred embodiment, the clutter suppression module 400 comprises a signal reconstructor 410 and a space-time adaptive processor 420. The signal reconstructor 410 describes coordinates of the spatially sampled signals of the echo signals based on the azimuth dimension, the distance dimension, and the pitch dimension. The signal reconstructor 410 calculates an interpolation matrix in a corresponding dimension according to a proximity principle, thereby performing signal reconstruction on the spatial sampling signal to obtain a virtual uniform sampling signal determined by the steering vector.
The word "module" as used herein describes any type of hardware, software, or combination of hardware and software that is capable of performing the functions associated with the "module".
It should be noted that the above-mentioned embodiments are exemplary, and that those skilled in the art, having benefit of the present disclosure, may devise various arrangements that are within the scope of the present disclosure and that fall within the scope of the invention. It should be understood by those skilled in the art that the present specification and figures are illustrative only and are not limiting upon the claims. The scope of the invention is defined by the claims and their equivalents.

Claims (10)

1. A synthetic aperture radar comprising a moving target detection system, characterized in that the moving target detection system comprises a baseline compensation module (300), a clutter suppression module (400) and a moving target detection module (500), wherein,
the moving object detection module (500) is configured to: after echo signals are subjected to clutter suppression processing by the clutter suppression module (400) and are subjected to baseline compensation module (300) to avoid coherence reduction of the obtained image, phase difference caused by clutter is eliminated based on prior information, so that only phase difference caused by moving targets remains in the echo signals.
2. The radar of claim 1, wherein the moving object detection module (500) performs constant false alarm threshold detection based on the square of the complex amplitude of the moving object, the constant false alarm threshold value being defined by a false alarm probability
Figure FDA0003056331490000011
Determining, wherein ThAs a threshold value, when the square of the complex amplitude of the moving target is greater than ThWhen, a moving target exists; when the square of the complex amplitude of the moving target is less than ThWhen there is no moving object.
3. A radar according to any preceding claim wherein, when the synthetic aperture radar system receives the echo signals via the primary (100) and secondary (200) satellites and samples them in the azimuth direction with a pulse repetition period signal to form a high resolution, wide swath image, the product of the frequency of the pulse repetition period signal times half the operating wavelength is greater than the maximum of a preset range of moving target speeds, thereby avoiding blind speed within the preset range of moving target speeds.
4. The radar of one of the preceding claims, wherein the baseline compensation module (300) comprises a decoupler (320), the decoupler (320) being configured to: under the condition that the time-varying baseline is mixed with an along-track baseline component and a track-cutting baseline component, the time-varying baseline is projected to the track direction of the satellite (200) to obtain a vector mode equation of the effective along-track baseline; the vector mode equation of the effective along-track baseline obtains a time-varying baseline, a velocity vector of the auxiliary satellite (200) and a unit vector of the central sight line direction of the antenna beam of the main satellite (100) based on ephemeris measurement data, and generates the time-varying along-track baseline based on the central sight line vector of the antenna beam of the main satellite (100) under the front side view, which is obtained by the geometric relationship between the velocity vector of the auxiliary satellite (200) and the unit vector of the central sight line direction of the antenna beam of the main satellite (100), so as to improve the speed measurement accuracy.
5. Radar according to one of the preceding claims, wherein the time-varying baseline is capable of being derived by the decoupler (320) as an independent time-varying along-track baseline, thereby avoiding approximation errors of the phase compensation of the time-varying baseline compensator (310) due to the time-varying baseline mixed with the along-track baseline component and the off-track baseline component.
6. Radar according to any one of the preceding claims wherein the frequency of the pulse repetition periodic signal is such that
Figure FDA0003056331490000021
Wherein v ismaxIndicating the maximum moving target preset speed, vPRFIndicating the speed of the pulse repetition period signal, PRF indicating the frequency of the pulse repetition period signal, and λ indicating the wavelength at which the radar operates.
7. A radar as claimed in any preceding claim wherein the equivalent radial velocity generated by the period of the pulse-repetition periodic signal falls outside a preset range of moving target velocities to avoid moving target signals within the preset range of moving target velocities being cancelled during clutter suppression by the clutter suppression module (400).
8. Radar according to one of the preceding claims, characterised in that the echo signals are reconstructed as virtual uniformly sampled signals based on a space-time adaptive technique.
9. Radar according to one of the preceding claims, characterised in that the moving object detection system comprises at least one primary satellite (100) and at least one secondary satellite (200), the primary satellite (100) transmitting a signal via a pulse transmission module (600).
10. A moving target detection method based on a synthetic aperture radar is characterized in that echo signals returned by radar transmitting signals can be compensated into a fixed along-track baseline through a baseline compensation module (300) so as to avoid coherent reduction of obtained images, a clutter suppression module (400) performs clutter suppression processing, and then phase differences caused by clutter are eliminated based on prior information, and only phase differences caused by moving targets are left through a moving target detection module (500).
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