JP7629192B2 - Signal processing device, signal processing method, and program - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Website posting date: September 21, 2020, website address: https://igarss2020.org/view_paper.php? PaperNum=1350 (2020 IEEE International Geoscience and Remote Sensing Symposium Proceedings), Publisher: IEEE Website posting date: September 21, 2020, website address: https://igarss2020.org/view_paper.php? PaperNum=1350 (Presentation materials from the 2020 IEEE International Geoscience and Remote Sensing Symposium), Publisher: IEEE, Date: September 29, 2020, Name of meeting: 2020 IEEE International Geoscience and Remote Sensing Symposium, Venue: Virtual Symposium (online oral presentation)

The present invention relates to a signal processing device, a signal processing method, and a program.

Synthetic aperture radar (SAR) and its synthetic aperture processing have been known for some time (see, for example, Patent Document 1). Synthetic aperture processing technology is efficient, revolutionary, and widely used. To further improve convenience and performance, there is a method of synthesizing the imaging results of multiple satellites if the observation frequency allows for miniaturization, and when miniaturization is difficult, consideration is being given to using a single satellite with a larger antenna or using multiple frequencies. However, development costs and the load on platform resources are issues. In addition, observations using multiple satellites with a time lag are not suitable for detecting moving objects.

JP 2021-47019 A

Conventional solutions include digital beamforming (DBF) processing and compressed sensing technology. With digital beamforming processing, the benefit of resolution in the direction of the platform's movement is limited because it is synthetic aperture processing. With compressed sensing technology, it is possible to maintain resolution by thinning out the observation points (reducing the amount of data), but this is premised on sparsity in the frequency components of the observation data, and the conditions under which thinning can be performed are also limited.

The present invention has been made in consideration of these circumstances, and one of its objectives is to provide a signal processing device, a signal processing method, and a program that can improve the freedom and resolution of sensing.

One aspect of the present invention is a signal processing device that includes a processing unit that performs synthetic aperture processing based on an observation signal received by the antenna in each observation when a moving object equipped with an antenna moves among multiple observation positions, when an observation point equipped with the antenna rotates, or when a target to be observed is a moving object and is observed multiple times, and the processing unit virtually sets the observation position at a non-observation position by performing Khatri-Rao product expansion on the observation position in the synthetic aperture processing.

According to one aspect of the present invention, it is possible to improve the freedom and resolution of sensing. In addition, the number of observations can be reduced and interpolated, allowing for further system trade-offs.

1 is a conceptual diagram of a remote sensing system 1 according to an embodiment. 1 is a diagram showing a schematic diagram of ground observation by an artificial satellite M. 1 is a configuration diagram of a radar device 100 according to an embodiment. FIG. 2 is a configuration diagram of a signal processing device 200 according to an embodiment. 10 is a flowchart showing the flow of a series of processes of a synthetic aperture processing unit 232 according to the embodiment. FIG. 1 is a schematic diagram showing Khatri-Rao product expansion. 1 is a diagram showing a schematic diagram of an artificial satellite M traveling along an orbit OR.

Below, an embodiment of the signal processing device, signal processing method, and program of the present invention will be described with reference to the drawings.

[Remote Sensing System]
FIG. 1 is a conceptual diagram of a remote sensing system 1 according to an embodiment. As shown in the figure, the remote sensing system 1 includes, for example, at least one mobile object M and one or more ground stations G. The mobile object M is a type of platform, and is typically an artificial satellite. This artificial satellite may form a cluster, such as a satellite megaconstellation or a cluster satellite group. When the mobile object M, such as an artificial satellite, has an autonomous function and a control function for other observation systems, etc., the ground station G is not necessarily required.

The moving body M is not limited to an artificial satellite, but may be a space probe or a flying object that travels above the ground, such as an airplane or a drone. The moving body M may be any moving body capable of performing synthetic aperture processing, and may be, for example, a vehicle or other object that moves on land. In the following, as an example, the moving body M will be described as an "artificial satellite."

The artificial satellite M, for example, observes the ground (including the ocean) while traveling on a predetermined orbit OR, and transmits a signal representing the observation results (hereinafter referred to as an observation signal) to a ground station G. The orbit OR is, for example, an orbit around the Earth.

Ground station G is a radio station installed on the ground. Ground station G receives observation signals from satellite M and transmits observation-related instructions (such as the timing of observation and the location to be observed) to satellite M.

Figure 2 is a schematic diagram showing ground observation by an artificial satellite M. As shown in the figure, the artificial satellite M travels along an orbit OR, irradiating a microwave beam toward the ground where a target T is located, and receiving the reflected wave (echo) of the beam, thereby performing ground observation. The target T may be, for example, a ship on the ocean. The method of collecting data while scanning a strip of the observation range as a platform such as the artificial satellite M moves is called strip mapping.

A position (hereinafter referred to as the observation position) from which the ground should be observed is determined on the orbit OR of the artificial satellite M, and when the artificial satellite M reaches the observation position, observation of the ground is performed. In this embodiment, a position that is not an observation position, i.e., a non-observation position, is treated as a virtual observation position (hereinafter referred to as a "virtual position") and synthetic aperture processing is performed. The elliptical area shown in the figure represents the area irradiated with the microwave beam. Synthetic aperture processing can improve the resolution to an area narrower than the irradiation area of the beam (elliptical area).

[Radar device]
3 is a configuration diagram of a radar device 100 according to the embodiment. The radar device 100 is mounted on an artificial satellite M. For example, the radar device 100 includes an antenna 110, a transceiver 120, a transmission/reception control unit 130, and a storage unit 140.

The antenna 110 is, for example, a phased array antenna in which multiple antenna elements are arranged. It may also be a large deployable antenna, and the received data for each observation position that is stored may be analog-synthesized or digitally synthesized.

The transceiver 120 supplies a pulse signal of a specific frequency (e.g., a PRF (Pulse Repetition Frequency) signal) to the antenna 110, and irradiates pulsed microwaves in a desired direction via the antenna 110. Furthermore, the transceiver 120 receives reflected waves of the irradiated radio waves (i.e., observation signals) via the antenna 110.

The transmission/reception control unit 130 causes the transceiver 120 to transmit and receive microwaves so that observations are made at each observation position on the orbit OR. The transmission/reception control unit 130 also stores the results of encoding the observation signal received by the antenna 110 in the memory unit 240. When synthetic aperture processing is performed on the ground system side, the observation signal may be transmitted to the ground station G and encoded at the ground station G side. When synthetic aperture processing is performed on the satellite system side, the observation signal may be encoded on the artificial satellite M side before being transmitted to the ground station G.

The transmission/reception control unit 130 is realized by, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit) executing a program or an API (Application Programming Interface) stored in the storage unit 140. The transmission/reception control unit 130 may be realized by hardware (circuits) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array), or may be realized by collaboration between software and hardware. The program referenced by the processor may be stored in the storage unit 140 in advance, or may be stored in a removable storage medium such as a DVD or CD-ROM, and installed from the storage medium to the storage unit 140. Each functional unit of the radar device 100 is not limited to being provided in the artificial satellite M, but may also be provided in a ground station G or other ground facilities different from the ground station G (for example, a data center where servers are aggregated).

The storage unit 140 is realized by, for example, a hard disk drive (HDD), a flash memory, an electrically erasable programmable read only memory (EEPROM), a read only memory (ROM), a random access memory (RAM), etc. The storage unit 140 stores, for example, orbit information 142. The orbit information 142 is information that represents the orbit OR of the artificial satellite M, and includes the above-mentioned information on the observation position (observation time).

[Signal Processing Device]
4 is a configuration diagram of a signal processing device 200 according to an embodiment. The signal processing device 200 may be installed in any ground facility such as a ground station G or a data center. For example, the signal processing device 200 includes an antenna 210, a transceiver 220, a processing unit 230, and a storage unit 240. The combination of the antenna 210 and the transceiver 220 is an example of a "receiving unit."

The antenna 210 is, for example, a parabolic antenna or a phased array antenna.

The transceiver 220 irradiates microwaves toward the satellite M via the antenna 210. Furthermore, the transceiver 120 receives an observation signal from the satellite M via the antenna 110.

The processing unit 230 includes, for example, a synthetic aperture processing unit 232, a navigation interpolation unit 234, and a transmission/reception control unit 236.

The components of the processing unit 230 are realized, for example, by a processor such as a CPU or GPU executing a program stored in the storage unit 240. Some or all of the components of the processing unit 230 may be realized by hardware (circuits) such as an LSI, ASIC, or FPGA, or by a combination of software and hardware. The programs referenced by the processor may be stored in advance in the storage unit 240, or may be stored on a removable storage medium such as a DVD or CD-ROM and installed into the storage unit 240 from that storage medium.

The storage unit 240 is realized by, for example, a HDD, a flash memory, an EEPROM, a ROM, a RAM, etc. The storage unit 240 stores, for example, programs, etc.

The synthetic aperture processing unit 232 performs synthetic aperture processing on the observation signal received from the artificial satellite M. A detailed explanation of the synthetic aperture processing according to this embodiment will be given later.

The navigation interpolation unit 234 interpolates the satellite M navigation information at the virtual observation position for azimuth compression using navigation information from the selected effective actual observation position. More specifically, the navigation interpolation unit 234 determines the interval and number of actual observation positions on the orbit OR, or thins out the observed observation data so as to reduce redundancy by being able to interpolate the observed observation data at the virtual observation position.

When the satellite M needs to communicate with the ground station G, the transmission/reception control unit 236 controls the transceiver 220 so that uplink and downlink are performed.

[flowchart]
5 is a flowchart showing a series of processing steps of the synthetic aperture processing unit 232 according to the embodiment. For example, when the signal processing device 200 is installed in an arbitrary terrestrial data center, the processing of this flowchart may be executed when the transceiver 220 of the ground station G receives an observation signal from the satellite M via the antenna 210 and transmits the signal to the data center by terrestrial transmission. When the radar device 100 mounted on the satellite M has some or all of the functions of the signal processing device 200, the processing of this flowchart may be executed by the radar device 100.

First, the synthetic aperture processing unit 232 performs level 0 (L0) processing (step S1000). For example, as level 0 processing, the synthetic aperture processing unit 232 decodes the observation signal received from the satellite M (i.e., the downlinked observation signal) and acquires the original observation signal (raw data) before being encoded in the satellite M. At this time, the synthetic aperture processing unit 232 separates unnecessary packets from the raw data. Hereinafter, the observation signal that has undergone level 0 processing will be referred to as "L0 data".

Next, the synthetic aperture processing unit 232 performs level 1 (L1) processing (step S1100). Level 1 processing includes level 1.0 processing (S1110 in the figure), level 1.1 processing (S1120 in the figure), and level 1.5 processing (S1130 in the figure). Level 1.0 processing is an example of "first processing". Level 1.1 processing is an example of "second processing".

Level 1.0 processing (L1.0) is processing that extracts data for each scene from one L0 data. The observation signals that are the source of the L0 data are time-series data in which observation signals corresponding to each of multiple observation positions are linked in the order in which the satellite M arrived. Therefore, the L0 data is also time-series data. For example, the synthetic aperture processing unit 232 extracts the L0 data, which is time-series data, for each observation position, that is, for each scene, and reduces the data size to a size that is easy to handle in subsequent processing. Level 1.0 processing is an example of "first processing".

Level 1.1 processing (L1.1) is processing that compresses the pulses of data for each scene. For example, the synthetic aperture processing unit 232 performs pulse compression in the azimuth direction, which is the direction of travel of the artificial satellite M on the ground, and also performs pulse compression in the ground range direction perpendicular to the azimuth direction.

More specifically, the synthetic aperture processor 232 decodes the data of each scene as a level 1.1 process, and further performs pulse compression in the ground range direction (step S1122). Note that if decoding is performed in the L0 process, the decoding in S1122 may be omitted.

Next, the synthetic aperture processing unit 232 performs Khatri-Rao product expansion (step S1124).

Figure 6 is a diagram that shows a schematic representation of Khatri-Rao product expansion. For example, as shown in Figure 6, the synthetic aperture processing unit 232 sets (interpolates or expands) a virtual observation position (virtual position) at a non-observation position where no observation signal is obtained, based on the interval between the observation positions where an actual observation signal is obtained. The virtual position may be interpolated between multiple observation positions according to the actual observation position, or may be extrapolated outside the observation position.

Since no observations are made at the virtual positions, no observation signals are present. Therefore, the synthetic aperture processing unit 232 performs Khatri-Rao product extension on the observation signals at each observation position to interpolate the observation signals at non-observation positions. This Khatri-Rao product extension increases the number of targets for compression processing in the azimuth direction at the subsequent stage, improving the resolution in the azimuth direction. In addition, the number of observations can be reduced, which can alleviate the onboard resources of the satellite.

When performing the Khatri-Rao product extension, the synthetic aperture processing unit 232 may thin out or expand the multiple observation positions actually obtained so as to satisfy a specified condition. The thinned observation positions are the targets for which virtual positions are set during the Khatri-Rao product extension.

For example, the synthetic aperture processing unit 232 selects one observation position from among multiple observation positions where the Doppler shift between the ground target T to be observed and the artificial satellite M is zero, and thins out or expands the observation positions so that the redundancy of the observation positions is the lowest when the selected observation position is used as the basis for the Khatri-Rao product expansion. More specifically, it determines the thinning interval and the number to be thinned out, or the expansion interval and the number to be expanded so that the array has the lowest redundancy when a method such as a nested array is used.

The synthetic aperture processing unit 232 may also thin out or expand the observation signal instead of the observation position. The thinned observation signal is subject to estimation as a virtual signal during Khatri-Rao product expansion.

For example, the synthetic aperture processing unit 232 may select, from among multiple observation signals, an observation signal corresponding to an observation position where the Doppler transition with the target T is zero, and thin out or expand the observation signal so that redundancy is minimized when the selected observation signal is used as the basis for the Khatri-Rao product expansion.

Furthermore, when performing the Khatri-Rao product expansion, the synthetic aperture processing unit 232 may thin out the observation positions based on the positions of virtual images that appear on the SAR image. For example, when multiple observation positions are arranged in the azimuth direction, the observation position where the Doppler transition between the target T and the artificial satellite M is zero is located at the center of the observation positions. Some users who provide SAR images do not care about the resolution of other areas as long as the target T can be confirmed with high resolution on the SAR image. In such a case, the observation position (center) where the Doppler transition is zero is used as a reference, and the closer the observation position is to the reference observation position (center), the narrower the thinning interval and the fewer the number of thinned positions, and the farther the observation position is from the reference observation position (center), the wider the thinning interval and the more the number of thinned positions. If it is possible to ignore virtual images that may appear due to the thinning process in this way, it is possible to thin out even more observation positions (or their observation signals).

Returning to the explanation of the flowchart in FIG. 5, the synthetic aperture processing unit 232 then performs pulse compression in the azimuth direction on the observation signal (L0 data) that has been subjected to the Khatri-Rao product extension (step S1126). When a virtual position is interpolated or extended by the Khatri-Rao product extension and an observation signal at the virtual position is estimated, the observation signal at the virtual position is also pulse compressed in addition to the observation signal at the observation position. Navigation information for the virtual position required during pulse compression is created by the navigation interpolation unit 234.

Next, the synthetic aperture processing unit 232 generates a SAR image and/or an interferogram (step S1128).

Next, the synthetic aperture processing unit 232 performs geometric correction of the SAR image and interferogram as level 1.5 processing (step S1130). For example, the synthetic aperture processing unit 232 may correct the SAR image and interferogram using the speed and acceleration of the satellite M, or may perform multi-look processing to reduce noise in the SAR image and interferogram. Furthermore, the synthetic aperture processing unit 232 may map the SAR image and interferogram so as to overlay them on a map using techniques such as georeferencing based on the azimuth direction or geocoding based on a map.

Next, the synthetic aperture processing unit 232 performs higher-dimensional processing such as level 2.0 or 3.0 (step S1200). For example, the synthetic aperture processing unit 232 may perform orthorectification as level 2.0 processing. Also, for example, the synthetic aperture processing unit 232 may perform noise reduction processing and pulse compression in the dynamic range direction as level 3.0 processing. In addition, various corrections such as standby correction, slope gradient correction, and reflectance correction may also be performed. This completes the series of synthetic aperture processing steps shown in this flowchart.

The above-mentioned navigation interpolation unit 234 may optimize the pulse transmission/reception timing for the transmission/reception control unit 130 of the artificial satellite M on the orbit OR based on the results of past synthetic aperture processing so as to minimize redundancy for the target T. Alternatively, it may thin out the information on the observation positions that can be interpolated, and further optimize it repeatedly to improve the observation performance for the target T using an expanded virtual observation position. The transmission/reception control unit 236 transmits the observation conditions optimized by the navigation interpolation unit 234 to the artificial satellite M on the orbit OR via the transceiver 220.

By determining the observation position in this way, the number of times that the satellite M transmits and receives pulse signals can be reduced during the next revolution of the orbit OR, and therefore the power consumption within the satellite M can be reduced. In addition, since the number of times that the satellite M transmits and receives pulse signals can be reduced, the amount of data downlinked from the satellite M to the ground station G can also be reduced.

According to the embodiment described above, in synthetic aperture processing, the observation position is virtually set (interpolated) by performing Catri-Rao product extension on the observation position, and the observation signal is virtually increased and extended by performing Catri-Rao product extension on the observation signal. This makes it possible to improve the freedom and resolution of sensing.

In addition, according to the above-described embodiment, when expanding the Khatri-Rao product, the observation positions or observation signals are thinned out to create the minimum redundant array, which further improves the freedom of sensing.

Furthermore, according to the above-described embodiment, if it is possible to ignore the artifacts that may appear on the SAR image due to the thinning process when performing Khatri-Rao product extension, it is possible to thin out even more observation positions (or their observation signals).

In addition, according to the above-described embodiment, since the thinned observation positions are removed from the orbit OR of the satellite M, the number of times the satellite M transmits and receives pulse signals can be reduced in the next orbit, etc. As a result, it is possible to reduce power consumption within the satellite M and to reduce the amount of data downlinked from the satellite M to the ground station G.

In addition, according to the above-described embodiment, thinning processing is applied to the artificial satellite M traveling in an orbit OR such as an Earth orbit, which simplifies the calculation of the Khatri-Rao product expansion and further reduces redundancy.

Figure 7 is a schematic diagram showing how an artificial satellite M travels along an orbit OR. As shown in the figure, the orbit OR of the artificial satellite M traveling far above the Earth's surface draws a slight curve (arc shape). It is generally known that when calculating the Khatri-Rao product expansion on a straight line, thinning out the observation positions irregularly (randomly) rather than at equal intervals reduces redundancy and makes it less likely for a false image to occur. In contrast, in this embodiment, since the observation positions are on a curved orbit OR, even if the observation positions are thinned out at equal intervals, the interpolated virtual observation positions are irregularly positioned in the azimuth direction, so that the calculation of the Khatri-Rao product expansion can be simplified compared to when thinning out regularly, and furthermore, redundancy can be reduced to make it less likely for a false image to occur.

Other Embodiments
Other embodiments will be described below. When thinning out the observation positions so as to minimize the redundancy of the observation positions, the navigation interpolation unit 234 of the above-mentioned signal processing device 200 may create a database of the correspondence between the relative positions of the multiple targets T and the multiple observation positions, and store the database in the storage unit 240. Furthermore, the navigation interpolation unit 234 may update the database stored in the storage unit 240. This allows the satellite M equipped with an antenna to always perform optimal observation when navigating multiple observation positions.

Furthermore, if the above-mentioned navigation interpolation unit 234 can tolerate the appearance of other virtual images for the target T identified by the synthetic aperture processing (if the appearance of a virtual image other than the target T on the SAR image can be tolerated), it may irregularly interpolate the observation positions so that the Khatri-Rao product expansion has the minimum redundancy, and perform synthetic aperture processing again using the interpolated irregular observation positions. This can improve the resolution of a portion of the observation area.

In the above-described embodiment, the artificial satellite M observes the target T while moving, that is, the artificial satellite M moves relative to the target T, but the present invention is not limited to this. For example, assume that the radar device 100 is mounted on a ground station G. In this case, the ground station G performs fixed-point observation of the target T. Even if the ground station G observes the target T multiple times as the target T moves relative to the ground station G, the Khatri-Rao product extension may be applied to the moving direction of the target T, which is a moving object, during synthetic aperture processing. Even if the artificial satellite M is a quasi-zenith satellite or the like that is capable of fixed-point observation, the Khatri-Rao product extension may be applied to the moving direction of the target T, which is a moving object, during synthetic aperture processing.

In addition, when the radar device 100 is mounted on a ship or the like and the antenna 110 rotates all around while observing the target T, the Khatri-Rao product extension may be applied to the direction of movement of the target T, which is a moving object, during synthetic aperture processing. In other words, when a platform equipped with the radar device 100 performs fixed-point observation of the target T, if the relative positional relationship between the direction of emission of radio waves from the antenna 110 of the radar device 100 and the direction in which the target T exists (the direction in which the target T exists as seen from the platform) fluctuates, the Khatri-Rao product extension may be applied to the direction of movement of the target T, which is a moving object, during synthetic aperture processing.

[Additional Notes]
The above-described embodiment can be expressed as follows.
a processor that performs synthetic aperture processing based on observation signals received by the antenna at each of a plurality of observation positions when a platform equipped with the antenna observes a target;
the processing unit, when (i) the relative positional relationship between the platform and the target fluctuates, or (ii) when the relative positional relationship between the radiation direction of the radio waves from the antenna and the direction in which the target exists as viewed from the platform fluctuates when the platform observes the target from a fixed position, performs Khatri-Rao product expansion on the observation position in the synthetic aperture processing to virtually set the observation position at a non-observation position;
Signal processing device.

The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made without departing from the spirit of the present invention.

1...Remote sensing system, S...Satellite, G...Ground station, 100...Radar device, 110...Antenna, 120...Transmitter/receiver, 130...Transmission/reception control unit, 140...Storage unit, 200...Signal processing device, 210...Antenna, 220...Transmitter/receiver, 230...Processing unit, 232...Synthetic aperture processing unit, 234...Navigation interpolation unit, 236...Transmission/reception control unit, 240...Storage unit

Claims (9)

a processing unit that performs synthetic aperture processing based on an observation signal received by the antenna at each observation position when a moving body equipped with an antenna moves among a plurality of observation positions, when an observation point equipped with the antenna rotates, or when a target to be observed is a moving body and is observed multiple times;
The processing unit includes:
In the synthetic aperture processing, a Khatri-Rao product expansion is performed on the observation position to virtually set the observation position at a non-observation position;
selecting an observation position from the plurality of observation positions where a Doppler shift between the target and the moving body is zero;
thinning out the observation positions or expanding the virtual observation positions so that redundancy of the observation positions is minimized when the selected observation positions are used as a reference for the Khatri-Rao product expansion;
Signal processing device. The processing unit includes:
generating an image of the target observed from the observation position based on the observation signal that has been subjected to the synthetic aperture processing;
thinning out the observation positions based on positions of virtual images appearing on the image;
The signal processing device according to claim 1 . the processing unit creates a database of positional relationships between the plurality of targets and the plurality of observation positions when thinning out the observation positions so as to minimize redundancy of the observation positions.
The signal processing device according to claim 1 . The processing unit reprocesses the target identified by the synthetic aperture processing using irregular observation positions so that the Khatri-Rao product expansion is minimally redundant, while allowing other virtual images.
A signal processing device according to any one of claims 1 to 3 . the synthetic aperture processing includes a first process of extracting data corresponding to each scene from an observation signal at each of the observation positions, and a second process of compressing the data extracted for each of the scenes;
The processing unit performs the Khatri-Rao product extension during the second processing.
A signal processing device according to any one of claims 1 to 4 . a receiving unit that receives an observation signal from a moving object equipped with an antenna at each observation position when the moving object moves between a plurality of observation positions;
a processing unit that performs synthetic aperture processing based on the observation signal received by the receiving unit,
The processing unit virtually increases an observation signal at a non-observation position by performing a Khatri-Rao product extension on the observation signal in the synthetic aperture processing.
Signal processing device. a processor that performs synthetic aperture processing in a moving direction of the observation target based on observation signals received by the antenna at each of a plurality of observation positions when the platform equipped with the antenna observes the moving observation target a plurality of times;
The processing unit includes:
In the synthetic aperture processing, a Khatri-Rao product expansion is performed on the observation position to virtually set the observation position at a non-observation position;
selecting an observation position from the plurality of observation positions where a Doppler shift with respect to the moving observation target is zero;
performing the Khatri-Rao product extension in the moving direction of the observation target using the selected observation position as a reference for the Khatri-Rao product extension, thinning out the observation positions so that the redundancy of the observation positions is minimized, or extending virtual observation positions;
Signal processing device. The computer
When a moving object equipped with an antenna moves among a plurality of observation positions, when an observation point equipped with the antenna rotates, or when a target to be observed is a moving object and is observed multiple times, a synthetic aperture process is performed based on an observation signal received by the antenna at each observation position;
In the synthetic aperture processing, a Khatri-Rao product expansion is performed on the observation position to virtually set the observation position at a non-observation position;
selecting an observation position from the plurality of observation positions where a Doppler shift between the target and the moving body is zero;
thinning out the observation positions or expanding the virtual observation positions so that redundancy of the observation positions is minimized when the selected observation positions are used as a reference for the Khatri-Rao product expansion;
Signal processing methods. On the computer,
performing synthetic aperture processing based on an observation signal received by the antenna at each observation position when a moving object equipped with the antenna moves among a plurality of observation positions, when an observation point equipped with the antenna rotates, or when a target to be observed is a moving object and is observed multiple times;
in the synthetic aperture processing, performing Khatri-Rao product expansion on the observation position to virtually set the observation position at a non-observation position;
selecting an observation position from the plurality of observation positions where a Doppler shift between the target and the moving body is zero;
thinning out the observation positions or expanding the virtual observation positions so that redundancy of the observation positions is minimized when the selected observation positions are used as a reference for the Khatri-Rao product expansion;
A program for executing.

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