Signal processing device and signal processing method

Abstract

A signal processing device 100 comprises: a cutout unit 102 for cutting out, from a first signal representing a reflection of a signal emitted from a radar, a second signal in a signal-existing region including a reflection signal reflected by a scattering body; and a diffraction process unit 103 for changing, for the cut-out second signal, a time period from a timing at which the second signal is emitted to a time at which the reflection signal is received.

Description

Signal processing device and signal processing method

[0001] The present invention relates to a signal processing device and a signal processing method.

[0002] Synthetic aperture radar (SAR) technology is a technology in which an antenna in a radar mounted on a flying object (such as an artificial satellite or an airplane) transmits and receives electromagnetic waves while the flying object is moving, and an aperture is artificially synthesized so that an image (SAR image) equivalent to that obtained by an antenna with a large aperture can be obtained. Hereinafter, an artificial satellite (SAR satellite) will be used as an example of the flying object. An artificial satellite will also be referred to as a SAR satellite.

[0003] There is an increasing demand for high-resolution SAR images capturing a wide area. Research into video SAR is also progressing. To increase the resolution of SAR images, it is conceivable to lengthen the synthetic aperture length by pointing the antenna toward the capture area for a long period of time. A mode in which processing for increasing the resolution of SAR images is executed is referred to as high-resolution mode. It is also conceivable to widen the capture area by increasing the squint angle of the antenna when performing squint imaging (see, for example, Patent Document 1). In squint imaging, the capture area is captured by tilting the antenna in the azimuth direction or the opposite direction. In squint imaging, the antenna tilt may also fluctuate.

[0004] JP 2012-093257 A

[0005] When squint photography is performed, the bandwidth of signal data indicating reflection from an object widens in the range direction as the squint angle increases. As a result, the amount of signal data indicating reflection increases. In particular, when squint photography is performed at a high squint, the amount of signal data increases even more. When the amount of signal data increases, for example, a problem arises in that a memory with a large capacity is required when storing the signal data.

[0006] An object of the present invention is to suppress an increase in the amount of signal data indicating reflection.

[0007] The signal processing device according to the present invention includes an extraction means for extracting a second signal in a signal-containing region including a reflected signal from a scatterer from a first signal representing a reflection of a signal emitted from a radar, and a return processing means for changing the time from the emission of the second signal to the reception of the reflected signal for the extracted second signal.

[0008] The signal processing method according to the present invention extracts a second signal from a first signal representing a reflection of a signal emitted from a radar in a signal-containing region including a reflected signal from a scatterer, and changes the time from the time the second signal is emitted to the time the reflected signal is received for the extracted second signal.

[0009] The signal processing program according to the present invention causes a computer to execute the following processes: extracting a second signal from a first signal representing a reflection of a signal emitted from a radar in a signal-containing region that includes a reflected signal from a scatterer; and changing the time from the time the second signal is emitted until the reflected signal is received for the extracted second signal.

[0010] According to the present invention, an increase in the amount of signal data indicating reflections is suppressed.

[0011] FIG. 1 is an explanatory diagram for explaining a general method for suppressing the amount of signal data. FIG. 1 is an explanatory diagram for explaining signal data when squint photography is performed with a high squint. FIG. 1 is a diagram for explaining a method for suppressing the amount of signal data in an embodiment. FIG. 2 is a block diagram showing an example of the configuration of a signal processing device of a first embodiment. FIG. 3 is a flowchart showing the operation of the signal processing device of the first embodiment. FIG. 4 is a block diagram showing an example of the configuration of a signal processing device of a second embodiment. FIG. 5 is a flowchart showing the operation of the signal processing device of the second embodiment. FIG. 6 is a block diagram showing an example of the configuration of a signal processing device of a third embodiment. FIG. 7 is a flowchart showing the operation of the signal processing device of the third embodiment. FIG. 8 is a block diagram showing an example of the configuration of a signal processing device of a fourth embodiment. FIG. 9 is a flowchart showing the operation of the signal processing device of the fourth embodiment. FIG. 10 is a block diagram showing an application example including a signal processing device. FIG. 11 is a block diagram showing another application example including a signal processing device. FIG. 12 is an explanatory diagram for explaining signal data when squint photography is performed with a long period of time with a high squint. FIG. 13 is a block diagram showing an example of an implementation of a signal processing device in a satellite. FIG. 14 is a block diagram showing another implementation example of an implementation of a signal processing device in a satellite. FIG. 15 is a block diagram showing an example of a computer having a CPU.

[0012] FIG. 1 is an explanatory diagram for explaining a method for suppressing the amount of signal data. A radar mounted on a satellite successively irradiates (or emits) electromagnetic pulses (pulse signals) onto an observation area (photography area). In FIG. 1, the horizontal axis represents the emission time of each pulse (i.e., the timing of emitting each pulse signal). Hereinafter, the pulse emission time will be referred to as azimuth time. The vertical axis represents the delay time from when a pulse is emitted until the reflected wave is received. The vertical axis can also be said to represent the elapsed time from when a signal is emitted until the reflected signal representing the reflection of that signal is received. Hereinafter, the time from when a pulse is emitted until the reflected wave is received will be referred to as range time.

[0013] In Fig. 1, each elongated rectangle A extending in the vertical direction, i.e., in the range-time direction, indicates, for example, the intensity of a reflected signal representing a reflection from a pulse. In the example shown in Fig. 1, only one rectangle is labeled A. As shown in Fig. 1, there are many rectangles indicating the intensity of the reflected signal received after a pulse is emitted once. The rectangles do not necessarily have to represent the intensity of the reflected signal, as long as they are values ​​that allow reflections from a reflector to be distinguished from other objects. Hereinafter, the received reflected signal will be referred to as a "received signal" or "signal data."

[0014] The crescent-shaped region B is a portion where reflections (backscattering) caused by point reflectors (scatterers) in the photographed region are recorded. Hereinafter, the point reflectors will be simply referred to as reflectors. In FIG. 1, only one of the crescent-shaped regions is designated by the symbol B. FIG. 1 shows an example in which there are five regions where reflections from reflectors are recorded. Hereinafter, each region will be referred to as region B. Furthermore, in FIG. 1, region B exists across multiple rectangles A. In reality, the portion where reflections from reflectors are recorded exists only in the portion that overlaps with rectangle A.

[0015] 2, 3 and 14, rectangle A is the signal received after a pulse has been emitted once, area B is the area where reflections from the reflector are recorded, and the area where reflections from the reflector are actually recorded is only present in the area that overlaps with rectangle A.

[0016] As illustrated in FIG. 1 , the received reflected signal contains portions where no reflection from a reflector is observed (no-signal portions, no-signal regions). Such portions correspond to regions where no reflected signal from a reflector is recorded. Saving the received signal from the no-signal portions is pointless. Therefore, as shown on the right side of FIG. 1 , it is possible to exclude the received signal from the no-signal portions. Specifically, for example, the received signal is extracted so that the range time falls within a certain range based on the depth of the imaging area when measuring the reflected signal. In other words, the signal-containing portion (or signal-containing region) is extracted. Hereinafter, the signal-containing region is also referred to as the "extracted region." A signal-containing region is, for example, a region having a certain range time width in signal data represented on the axes of azimuth time and range time, as illustrated in FIG. 1 , and which includes reflection from a reflector. A signal-containing region may include not only portions where reflection from a reflector is observed, but also portions where reflection from a reflector is not observed. A no-signal region does not include portions where reflection from a reflector is observed.

[0017] FIG. 2 is an explanatory diagram illustrating signal data when squint photography is performed with a high squint angle. A high squint, for example, refers to a squint angle of 5° or greater. The squint angle is the angle between the direction perpendicular to the azimuth direction and the direction of electromagnetic radiation. When squint photography is performed with a high squint angle, particularly in high-resolution mode, the signal reflected from the photography area is recorded in a highly tilted form. As a result, as shown on the right side of FIG. 2, a large area is recorded where no reflections are recorded. In other words, when a high squint angle and high resolution are used, the effect of focusing on a single point is added, causing the time at which reflections from reflectors begin to shift sequentially. As a result, reflections from an obliquely tilted band-like area C are recorded. Note that high resolution is, for example, less than 2 meters in ground resolution.

[0018] In the case of high squint and high resolution, when a rectangular portion is set as shown in Fig. 1, some of the no-signal areas are also saved, resulting in a large amount of data including no-signal areas.

[0019] FIG. 3 is a diagram illustrating a method for suppressing (or reducing) the amount of signal data in the following embodiment. FIG. 3 shows an example of a high squint and high resolution image. In the following embodiment, the signal processing device cuts out a signal-containing portion as shown in the center of FIG. 3. In the case of a high squint (or high resolution) image, the signal-containing portion is inclined obliquely with respect to the coordinate axes. In this case, when an area in which a reflected signal is recorded is cut out with a constant range time width, a parallelogram-shaped area is cut out as the cut-out area, as shown in the center of FIG. 3. Alternatively, the cut-out area can be described as an area in which the starting point of the range time (i.e., the range time corresponding to the base of the parallelogram shown in the center of FIG. 3) changes as the azimuth time transitions, and further, the cut-out area has a constant range time width. The non-signal portion is a region shown in the left diagram of FIG. 3 that is different from the region cut out as described above.

[0020] For example, the cut-out region is a region that includes all the reflected signals from the reflector in the azimuth time direction and the largest number of reflected signals from the reflector in the range time direction. By cutting out such a region, the amount of data in the signal-containing portion can be further reduced.

[0021] The signal processing device performs clipping and wraparound processing. For example, JIS (Japanese Industrial Standards) X 0013 (ISO (International Organization for Standardization) / IEC (International Electrotechnical Commission) 2382-13 "Information Processing Terms (Graphic Processing)" defines wraparound processing as displaying an image portion that extends beyond one edge of a display space on the opposite edge of the space. The signal processing device sets a set region and moves data within the cutout region but outside the set region to a blank portion within the set region. The set region is a region to be processed by the wraparound process. Alternatively, the set region can be considered a storage region that is different from the signal-present region and represents a storage region in which signals from the signal-present region can be stored in the wraparound process. The set region may represent a region in which the starting point of the range time is constant and the range time width is constant for each azimuth time. The set region may be a predetermined set region, or may be a region determined to have the same time width as the range time width of the signal-present region. In the following embodiment, the set region corresponds to the rectangular region shown on the right side of Figure 3. The blank portion within the set region corresponds to the no-signal regions D and E shown in the center of Figure 3. The rectangle may be rectangular or square. In the cut-out process, the signal processing device cuts out no-signal portions and performs wraparound processing to move signal-containing portions not included in the set region to no-signal portions in the set region in the range time direction. Alternatively, the cut-out process can be said to identify signal-containing regions including reflected signals from reflectors from signal regions showing received signals and perform processing to change the elapsed time for signal data in signal-containing regions not included in the set region. Alternatively, the cut-out process can be said to identify signal-containing regions including reflected signals from reflectors from signal regions showing received signals and perform processing to change the elapsed time for some of the signal-containing regions that do not overlap with the set region.Alternatively, the region in which the elapsed time for a portion of the signal-present region has been changed as described above can also be referred to as a set region. In this case, the signal processing device can be said to identify a signal-present region including a reflected signal from a reflector from a signal region representing a received signal in the cutout process, and create a set region in which the elapsed time for a portion of the signal-present region has been changed. For example, in the cutout process, the signal processing device performs a process of moving the portion of the parallelogram region above the set region to region E. This process can also be said to be a process of moving a signal-present region at azimuth time to a no-signal region at that azimuth time. In the cutout process, the signal processing device performs a process of moving the portion of the parallelogram region below the set region to region D. Hereinafter, performing the wraparound process may be referred to as wraparounding the received signal (reflected signal) in the range time direction.

[0022] It should be noted that a received signal corresponding to a pixel value of 0 may be inserted into the signal data among a set of received signals. The right side of Fig. 3 shows an example in which a received signal with a pixel value of 0 is inserted diagonally (see portion F in Fig. 3). The presence of portion F, in which a received signal with a pixel value of 0 is inserted, makes it possible to suppress the influence of side lobes, particularly side lobes at the edges of an image, when imaging processing is performed based on the output of the signal processing device.

[0023] Specific embodiments will be described below with reference to the drawings.

[0024] 4 is a block diagram showing an example of the configuration of a signal processing device according to a first embodiment. The signal processing device 100 shown in FIG. 4 includes a clipping region calculation unit 101, a clipping unit 102, and a wraparound processing unit 103.

[0025] The imaging conditions for measuring the reflected signals are input to the cutout region calculation unit 101. The signals acquired by the radar of the artificial satellite (SAR satellite), i.e., the reflected signals, are input to the cutout unit 102. The reflected signals are input to the cutout unit 102, for example, directly from the artificial satellite or from a storage device in which the signals acquired by the radar of the artificial satellite are stored. Then, a set of received signals that have been cut out from the set of reflected signals and further subjected to coupling processing is output from the coupling processing unit 103.

[0026] The imaging conditions for measuring the reflected signal include information for determining the size of the cutout area. The size of the cutout area is determined by the width in the azimuth time direction and the width of the range time and direction. Alternatively, the size of the cutout area is determined by the width in the azimuth time direction and the start point and length of the range time at each azimuth time. Alternatively, the size of the cutout area is determined by the width in the azimuth time direction and the end point and length of the range time at each azimuth time. The imaging conditions include the squint angle, satellite orbit, satellite speed, antenna rotation angle, pulse interval, sampling rate of the reflected wave received by the satellite radar, shape of the imaging area, antenna characteristics, etc.

[0027] The clipping area calculation unit 101 calculates a clipping area based on the imaging conditions. The clipping unit 102 clips the received signal in the clipping area from the received signal. The loop processing unit 103 performs loop processing on the clipped received signal. The above processing can also be expressed as follows: The clipping unit 102 identifies a signal-containing area containing a reflected signal from a reflector from a signal area in which signal data for the reflected signal is displayed, using the elapsed time and timing from when the signal is emitted from the radar until when a reflected signal representing a reflection of the signal is received. The loop processing unit 103 performs loop processing to change the elapsed time for a portion of the signal-containing area.

[0028] Next, the operation of the signal processing device 100 will be described with reference to the flowchart of FIG.

[0029] The clipping region calculation unit 101 calculates a clipping region based on the imaging conditions (step S101). Specifically, the clipping region calculation unit 101 calculates a time range to be clipped from the set of received signals based on the imaging conditions.

[0030] The cutout unit 102 cuts out the cutout region from the received signal (step S102). Specifically, the cutout region is extracted from the set of received signals.

[0031] The loop processing unit 103 performs loop processing on the extracted received signal (step S103). That is, the loop processing unit 103 sets, for example, a rectangular area that partially overlaps with the extracted area. Next, the loop processing unit 103 moves the received signal that is included in the extracted area but not the rectangular area to a no-signal area within the rectangular area (see FIG. 3).

[0032] The loop processing unit 103 outputs a set of received signals that have been extracted from a set of received signals acquired by the radar of the artificial satellite and further subjected to loop processing. The output is input to, for example, an imaging device or a storage device.

[0033] Signal processing device 100 may delete non-signal portions through clipping processing. In this case, signal processing device 100 deletes unnecessary signals. This prevents an increase in the amount of signal data. When squint photography is performed with a high squint, the signal indicating reflection from one target point spreads in the range direction according to the squint angle, increasing the amount of signal data. Therefore, in this embodiment, when squint photography is performed with a high squint, the effect of preventing an increase in the amount of signal data through clipping processing is enhanced.

[0034] Furthermore, when a wide range (for example, a target area about three times larger than the target area observed by a general SAR satellite) is targeted, the amount of signal data increases, but even in such a case, the signal processing device 100 of this embodiment is effective. In other words, when using a storage device with a predetermined capacity, the signal processing device 100 of this embodiment can reduce the amount of signal data compared to observation by a general SAR satellite, and as a result, it is possible to observe a wider range.

[0035] Furthermore, the signal processing device 100 performs a wraparound process in the range time direction. The amount of the reflected signal based on the reflection caused by the reflector after the wraparound process is substantially the same as the amount of the reflected signal based on the reflection caused by the reflector before the wraparound process is performed.

[0036] Furthermore, when imaging is performed by an imaging device that uses the output of the signal processing device 100, a Fourier transform in the range-time direction or a Fourier transform in the range-time direction and the azimuth time direction may be used. The result of the Fourier transform in the range-time direction or the Fourier transform in the range-time direction and the azimuth time direction based on the signal data after the wraparound processing is performed is the same as the result of the Fourier transform based on the signal data before the wraparound processing is performed. Therefore, when an imaging algorithm that uses a Fourier transform in the range-time direction or a Fourier transform in the range-time direction and the azimuth time direction is used, this embodiment can be applied without changing the algorithm.

[0037] An imaging device that uses the output of signal processing device 100 can use a common algorithm, such as the OmegaK algorithm or the Wavenumber Domain Algorithm, as an imaging algorithm. In order to enable an imaging device that uses such an imaging algorithm to perform imaging without changing the algorithm and to maximize the area that is accurately imaged, signal processing device 100 preferably has an accompanying information output means that supplies the following accompanying information to the imaging device:

[0038] For example, the accompanying information may include the reference azimuth time at which a reference point (e.g., the center of the imaging area) is captured directly in front of the antenna, the reference range time required for electromagnetic waves to travel back and forth between the satellite and the reference point, the range bin number corresponding to the reference range time, the azimuth bin number corresponding to the reference azimuth time, the sampling rate of the range bin, and the rate of the azimuth bin (PRF: Pulse Repetition Frequency).

[0039] In addition, instead of supplying accompanying information such as the reference range time and the reference azimuth time to the imaging device, the accompanying information output unit may supply other types of information, such as those described below, to the imaging device as accompanying information.

[0040] In this embodiment, the signal processing device 100 supplies signal data in a two-dimensional raster format to the imaging device. That is, the signal processing device 100 supplies signal data defined by a column direction (the direction along the columns, i.e., the vertical direction) and a row direction (the direction along the rows, i.e., the horizontal direction) to the imaging device. For example, the column direction corresponds to the range direction. Also, the row direction corresponds to the azimuth direction. In this case, time information corresponding to each bin may be used as the associated information. Furthermore, the range time and azimuth time based on the 0th range bin and the 0th azimuth bin may be used as the associated information.

[0041] Furthermore, circular shifts may be performed in the range direction and the azimuth direction. Furthermore, the signal processing device 100 may include information that can identify the cut-out position in the accompanying information, but even without such information, the imaging device can perform imaging processing.

[0042] Embodiment 2 Fig. 6 is a block diagram showing an example of the configuration of a signal processing device according to a second embodiment. The signal processing device 200 shown in Fig. 6 includes a clipping region calculation unit 101, a clipping unit 102, a wraparound processing unit 103, and a pulse compression unit 201. The configuration of the signal processing device 200 is the same as that of the signal processing device 100 according to the first embodiment, except that the pulse compression unit 201 is added.

[0043] The pulse compression unit 201 executes pulse compression processing. The pulse compression processing narrows the pulse width of the received signal pulse by performing a predetermined cross-correlation process (a process that evaluates the degree to which two time-series signals are interdependent or similar) on the shapes of the transmitted signal and the received signal. In the cross-correlation process, a cross-correlation function is calculated using the transmitted signal and the received signal. When calculating the cross-correlation, a method of calculating the similarity of vectors can also be used.

[0044] Next, the operation of the signal processing device 200 will be described with reference to the flowchart of FIG.

[0045] The pulse compressor 201 executes the pulse compression process described above (step S201). The pulse compressor 201 outputs the received signal that has been subjected to the pulse compression process to the extractor 102. The other processes are the same as those in the first embodiment.

[0046] In this embodiment, the cutout unit 102 performs cutout processing on a received signal that has been subjected to pulse compression processing, so the cutout area can be narrower than when cutout processing is performed on a signal acquired by a radar on an artificial satellite, which further improves the effect of suppressing an increase in the amount of signal data compared to the first embodiment.

[0047] In the field of synthetic aperture radar, LFM (Linear Frequency Modulation) signals are often used, but in ground-based radar systems such as body scanners, stepped signals called stepped continuous waves are often used as transmission signals. When stepped continuous waves are used, pulse compression processing is completed by performing an inverse Fourier transform. The concept of this embodiment may also be applied when stepped continuous waves are used.

[0048] Embodiment 3. Fig. 8 is a block diagram showing an example of the configuration of a signal processing device according to a third embodiment. The signal processing device 300 shown in Fig. 8 includes a clipping region calculation unit 101, a clipping unit 102, a wraparound processing unit 103, a pulse compression unit 201, a conversion unit 301, and a reference multiplication unit 302. The configuration of the signal processing device 300 is the same as that of the signal processing device 200 according to the second embodiment, except that the conversion unit 301 and the reference multiplication unit 302 are added.

[0049] The signal processing device 300 may have a configuration in which the transform unit 301 and the reference multiplication unit 302 are added to the signal processing device 100 of the first embodiment.

[0050] The conversion unit 301 performs conversion processing on the received signal output from the loop interference processing unit 103. The conversion processing is, for example, processing to convert signal data into signal data in the frequency domain. The reference multiplication unit 302 multiplies the converted received signal by a reference signal.

[0051] Next, the operation of the signal processing device 300 will be described with reference to the flowchart of Fig. 9. The processes of step S201 and steps S101 to S103 are the same as those in the second embodiment.

[0052] In this embodiment, the transform unit 301 performs a transform process on the received signal output by the loop processing unit 103 (step S301). In step S301, the transform unit 301 performs, for example, a Fourier transform. Note that the target of the Fourier transform is the received signal after the loop processing has been performed, but the result of the Fourier transform is the same as the result of the Fourier transform when zero-padding is performed. Therefore, when an imaging process using a Fourier transform is performed, it is not necessary to modify the imaging algorithm.

[0053] The reference multiplication unit 302 multiplies the Fourier-transformed received signal by a reference signal as a correlation function (step S302). The reference signal is, for example, the complex conjugate of the Fourier transform of a response (ideal response) from a scatterer when the scatterer is assumed to be present at the above-mentioned reference point (e.g., the center of the imaging area). In step S302, the reference multiplication unit 302 calculates a reference signal and multiplies the Fourier-transformed frequency-domain received signal by the complex conjugate reference signal.

[0054] In imaging processing using a Fourier transform, an inverse Fourier transform is also performed. If the reference multiplication unit 302 is not present, the inverse Fourier transform is performed based on the Fourier transform result of the received signal after the wraparound processing is performed, and an image that appears to have undergone wraparound processing is reproduced.

[0055] When the reference multiplication unit 302 performs the above processing as in this embodiment, a clear image can be obtained around the reference point. Also, whereas the portion in which the reflection (response) caused by the scatterer is recorded is distributed in an oblique direction (see FIGS. 2 and 3), the response is now contained within a certain range. Therefore, when the signal processing device 300 of this embodiment is used, it is possible to perform imaging processing without increasing the memory capacity.

[0056] Fourth Embodiment Fig. 10 is a block diagram showing an example of the configuration of a signal processing device according to a fourth embodiment. The signal processing device 400 shown in Fig. 10 includes a clipping region calculation unit 101, a clipping unit 102, a loop processing unit 103, a pulse compression unit 201, and a division unit 401. The configuration of the signal processing device 400 is the same as that of the signal processing device 200 according to the second embodiment, except that the division unit 401 is added. The division unit 401 divides a set of received signals output by the loop processing unit 103.

[0057] The signal processing device 400 may have a configuration in which a dividing unit 401 is added to the signal processing device 100 of the first embodiment.

[0058] Next, the operation of the signal processing device 400 will be described with reference to the flowchart of Fig. 11. The processes of step S201 and steps S101 to S103 are the same as those in the second embodiment.

[0059] In this embodiment, the dividing unit 401 divides the set of received signals output by the wraparound processing unit 103 into a plurality of sub-blocks in the azimuth time direction (step S401). Note that the dividing unit 401 may divide the set of received signals into sub-blocks if two adjacent sub-blocks overlap, or may divide the set of received signals so that two adjacent sub-blocks have an overlapping portion.

[0060] In this embodiment, since the signal processing device 400 outputs a plurality of sub-blocks, the imaging device can easily reproduce a high-resolution image using the plurality of sub-blocks, and the processing load of the imaging device that reproduces a moving image using the output of the signal processing device 400 is reduced.

[0061] Note that a transform unit and a reference multiplication unit that perform Fourier transform or the like in the third embodiment, and an inverse transform unit that performs inverse Fourier transform or the like may be provided between the wraparound processing unit 103 and the division unit 401 .

[0062] An application example of the above embodiment will be described below.

[0063] The output of the signal processing device of the above embodiment can be used as input to an imaging device that executes a process that combines the Omega K algorithm, which is one of the imaging algorithms and processes on a two-dimensional spectrum, and Baseband Azimuth Scaling, which is one of the high-resolution processes.

[0064] Furthermore, as an imaging algorithm in the imaging device, for example, the following method can be used.

[0065] Wavenumber Domain Algorithm (Stolt may be applied) which is a process on a two-dimensional spectrum other than the Omega K algorithm. Range Doppler algorithm which is a process in the range time domain and azimuth frequency domain. Chirp Scaling algorithm which is a process in the range time domain and azimuth frequency domain, but performs some transformations in the range frequency domain. Back Projection which is a process in the range time domain and azimuth time domain.

[0066] Furthermore, as the imaging algorithm, an algorithm obtained by modifying the above algorithm can also be used.

[0067] 12 is a block diagram showing an example of an application including the signal processing device 300 of the third embodiment. The output of the signal processing device 300 is supplied to an imaging device 500 that performs imaging processing based on a predetermined imaging algorithm.

[0068] Application Example 1. Assume that the imaging algorithm is the Omega K algorithm, which includes a two-dimensional Fourier transform process, a reference multiplication process, a transformation process for performing spectral transformation, and an inverse two-dimensional Fourier transform process.

[0069] The two-dimensional Fourier transform processing and reference multiplication processing in the Omega K algorithm can be performed by the transform unit 301 and the reference multiplication unit 302 in the signal processing device 300. Therefore, in Application Example 1, the imaging device 500 only needs to perform the transformation processing and the inverse two-dimensional Fourier transform processing.

[0070] In addition, when the signal processing device 100 of the first embodiment or the signal processing device 200 of the second embodiment is combined with the imaging device 500, the imaging device 500 performs two-dimensional Fourier transform processing, reference multiplication processing, transformation processing, and inverse two-dimensional Fourier transform processing.

[0071] When imaging processing based on the Omega K algorithm, which performs processing in the frequency domain, is performed using the output of the signal processing device according to the above embodiment, there is no need to modify the Omega K algorithm. For example, an image based on squint photography with a high squint can be reproduced without modifying a program that executes an existing Omega K algorithm and without increasing the memory capacity for storing data.

[0072] Application Example 2: Assume that the imaging algorithm is a range-Doppler algorithm, which includes two-dimensional Fourier transform processing, reference multiplication processing, inverse Fourier transform processing in the range direction, deformation processing (RCMC: Range Cell Migration Correction), imaging multiplication processing, and inverse Fourier transform processing in the azimuth direction.

[0073] The two-dimensional Fourier transform processing and reference multiplication processing in the range Doppler algorithm can be performed by the transform unit 301 and the reference multiplication unit 302 in the signal processing device 300. Therefore, in Application Example 2, the imaging device 500 only needs to perform the inverse Fourier transform processing in the range direction, the deformation processing, the imaging multiplication processing, and the inverse Fourier transform processing in the azimuth direction.

[0074] When the signal processing device 100 of the first embodiment or the signal processing device 200 of the second embodiment is combined with the imaging device 500, the imaging device 500 performs two-dimensional Fourier transform processing, reference multiplication processing, inverse Fourier transform processing in the range direction, deformation processing, imaging multiplication processing, and inverse Fourier transform processing in the azimuth direction.

[0075] When imaging processing based on a range-Doppler algorithm that performs processing in the time domain is performed using the output of the signal processing device according to the above embodiment, there is no need to modify the range-Doppler algorithm. For example, images based on squint photography with a high squint can be reproduced without modifying a program that executes an existing range-Doppler algorithm and without increasing the memory capacity for storing data.

[0076] Application Example 3: Assume that the imaging algorithm is a chirp scaling algorithm, which includes two-dimensional Fourier transform processing, reference multiplication processing, inverse Fourier transform processing in the range direction, chirp processing for multiplying a chirp signal, Fourier transform processing in the range direction, second chirp processing, inverse Fourier transform processing in the range direction, imaging multiplication processing, and inverse Fourier transform processing in the azimuth direction.

[0077] The two-dimensional Fourier transform processing and reference multiplication processing in the chirp scaling algorithm can be performed by the transform unit 301 and the reference multiplication unit 302 in the signal processing device 300. Therefore, in Application Example 3, the imaging device 500 only needs to perform inverse Fourier transform processing in the range direction, chirp processing for multiplying by a chirp signal, Fourier transform processing in the range direction, second chirp processing, inverse Fourier transform processing in the range direction, imaging multiplication processing, and inverse Fourier transform processing in the azimuth direction.

[0078] When the signal processing device 100 of the first embodiment or the signal processing device 200 of the second embodiment is combined with the imaging device 500, the imaging device 500 executes two-dimensional Fourier transform processing, reference multiplication processing, inverse Fourier transform processing in the range direction, chirp processing for multiplying a chirp signal, Fourier transform processing in the range direction, second chirp processing, inverse Fourier transform processing in the range direction, imaging multiplication processing, and inverse Fourier transform processing in the azimuth direction.

[0079] When imaging processing based on a chirp scaling algorithm that performs processing in the time domain is performed using the output of the signal processing device according to the above embodiment, there is no need to modify the chirp scaling algorithm. For example, images based on squint photography with a high squint can be reproduced without modifying a program that executes an existing chirp scaling algorithm and without increasing the memory capacity for storing data.

[0080] 13 is a block diagram showing an example of an application including the signal processing device 400 of the fourth embodiment. The output of the signal processing device 400 is supplied to an imaging device 600 that performs imaging processing based on a predetermined imaging algorithm.

[0081] Application Example 4: The imaging algorithm is assumed to be a baseband azimuth scaling algorithm, which includes division processing, processing similar to the above-described chirp scaling for each sub-block (including at least two-dimensional Fourier transform processing and reference multiplication processing), and processing for combining the processed sub-blocks.

[0082] The division processing in the Baseband Azimuth Scaling algorithm can be performed by the division unit 401 in the signal processing device 400. As described above, when the signal processing device 400 also includes a transform unit and a reference multiplication unit, the division processing, two-dimensional Fourier transform processing, and reference multiplication processing can be performed by the division unit 401, transform unit, and reference multiplication unit in the signal processing device 400. Therefore, in Application Example 4, the imaging device 600 only needs to perform processing that is performed after the division processing in the Baseband Azimuth Scaling algorithm, or processing that is performed after the division processing, two-dimensional Fourier transform processing, and reference multiplication processing.

[0083] When imaging processing (in this example, imaging processing based on the Baseband Azimuth Scaling algorithm) is performed using the output of the signal processing device of the above embodiment, there is no need to modify the Baseband Azimuth Scaling algorithm. For example, an image based on squint photography with a high squint can be reproduced without modifying a program that executes an existing Baseband Azimuth Scaling algorithm and without increasing the memory capacity for storing data.

[0084] Application Example 5. Figure 14 is an explanatory diagram for explaining signal data when squint imaging is performed at a high squint angle for a long period of time. When squint imaging of a target area is performed at a high squint angle for a long period of time, the orientation of the antenna mounted on the satellite is controlled so that the squint angle changes as the satellite moves, so that the antenna is always pointed toward the target area. As a result, as shown on the left side of Figure 14, for example, there are multiple types of inclinations in the portion of the imaging area where reflections caused by scatterers are recorded (crescent-shaped region B). In the example shown in Figure 14, there is region B pointing downward to the right and region B pointing upward to the right.

[0085] In such a case, the cropping unit 102 in the above embodiment does not set a parallelogram cropping region (see the central part of FIG. 3 ), but sets a cropping region having a curved portion that matches the inclination of region B. Then, the wraparound processing unit 103 executes wraparound processing in the same manner as in the above embodiment.

[0086] The cut-out region having a curved portion that matches the slope of region B is a region that includes the reflection signals of all reflectors in the azimuth time direction and includes the reflection signals of the most reflectors in the range time direction.

[0087] That is, even when squint photography is performed at a high squint for a long period of time, the effect of increasing the amount of signal data can be maintained by simply changing the shape of the cutout region from a parallelogram.

[0088] The signal processing device can generate a video with a playback time corresponding to the observation time of the target region. In practice, the playback time of the video can be determined by the capacity of the storage device for storing the SAR images.

[0089] The signal processing device of the above embodiment may be installed on the ground, but can also be mounted on an artificial satellite.

[0090] Fig. 15 is a block diagram showing an example in which a signal processing device is mounted on an artificial satellite. In the example shown in Fig. 15, the signal processing device 100 of the first embodiment shown in Fig. 4 is mounted on an artificial satellite. That is, a satellite-mounted unit 801 includes the components of the signal processing device 100.

[0091] The satellite-mounted unit 801 further includes an AD converter 111 that performs AD conversion on the received signal of the cut-out region, and a transmitting unit 112 that transmits the received signal after loop processing to the ground. The transmitting unit 112 includes a wireless communication unit that performs wireless communication. In addition to the wireless communication unit, the transmitting unit 112 may also include an encoding unit that encodes the received signal after loop processing.

[0092] If the satellite is equipped with a means for performing the cutout process by hardware, that means may be used as the cutout unit 102. In that case, the cutout region calculation unit 101 and the wraparound processing unit 103 are realized by software, for example.

[0093] Fig. 16 is a block diagram showing another example in which a signal processing device is mounted on an artificial satellite. In the example shown in Fig. 16, the signal processing device 200 of the second embodiment shown in Fig. 6 is mounted on an artificial satellite. That is, a satellite-mounted unit 802 includes the components of the signal processing device 200.

[0094] The satellite-mounted unit 802 further includes an AD converter 111 for AD-converting the received signal, and a transmitting unit 112 for transmitting the received signal after loopback processing to the ground.

[0095] If the satellite has a function for performing pulse compression, that function may be used as the pulse compressor 201. In that case, the cutout region calculation unit 101, the cutout unit 102, and the wraparound processing unit 103 are realized, for example, by software.

[0096] According to the configurations shown in Figures 15 and 16, the amount of data transmitted from an airborne object such as an artificial satellite to the ground is reduced compared to a general configuration that does not use the signal processing device of the above embodiment.

[0097] When the signal processing device of the above embodiment is installed on the ground, for example, when the signal processing device of the above embodiment is incorporated into a ground imaging device, the capacity of the storage device in the ground device is reduced.

[0098] The signal processing device of the above embodiment can be applied to synthetic aperture technologies other than synthetic aperture radar technology that uses flying objects, such as synthetic aperture sonar, etc. The signal processing device of the above embodiment can also be applied to ISAR (Inverse Synthetic Aperture Radar).

[0099] Each component in the above embodiment can be configured as a single piece of hardware, or as a single piece of software. Each component can also be configured as multiple pieces of hardware, or as multiple pieces of software. Furthermore, some of the components can be configured as hardware, and the other parts can be configured as software.

[0100] For example, in the configurations shown in FIGS. 15 and 16, the functions of the cutout section 102 and pulse compression section 201 can be realized by hardware, and the other functions can be configured by software.

[0101] Each function (each process) in the above-described embodiments can be realized by a computer having a processor such as a CPU (Central Processing Unit), a memory, etc. For example, a program for implementing the method in the above-described embodiments may be stored in a storage device, and each function may be realized by having the CPU execute the program stored in the storage device.

[0102] 17 is a block diagram showing an example of a computer having a CPU. The computer is implemented in a signal processing device. The CPU 1000 executes processing in accordance with a signal processing program stored in a storage device 1001, thereby realizing the functions of the clipping region calculation unit 101, clipping unit 102, wraparound processing unit 103, pulse compression unit 201, conversion unit 301, reference multiplication unit 302, and division unit 401 in the above-described embodiment.

[0103] The storage device 1001 is, for example, a non-transitory computer readable medium. Non-transitory computer readable media include various types of tangible storage media. Specific examples of non-transitory computer readable media include magnetic recording media (for example, hard disks), magneto-optical recording media (for example, magneto-optical disks), CD-ROMs (Compact Disc-Read Only Memory), CD-Rs (Compact Disc-Recordable), CD-R / Ws (Compact Disc-ReWritable), and semiconductor memories (for example, mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), and flash ROMs).

[0104] The program may also be stored in various types of transitory computer-readable media, to which the program is supplied, for example, via a wired or wireless communication path, i.e., via an electrical signal, an optical signal, or an electromagnetic wave.

[0105] The memory 1002 is realized by, for example, a RAM (Random Access Memory), and is a storage means for temporarily storing data when the CPU 1000 executes processing. A configuration is also conceivable in which a program held in the storage device 1001 or a temporary computer-readable medium is transferred to the memory 1002, and the CPU 1000 executes processing based on the program in the memory 1002.

[0106] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0107] 100, 200, 300, 400 Signal processing device 101 Cutout region calculation unit 102 Cutout unit 103 Loop processing unit 201 Pulse compression unit 301 Conversion unit 302 Reference multiplication unit 401 Division unit 500, 600 Imaging device 801, 802 Satellite-mounted unit 1000 CPU 1001 Storage device 1002 Memory

Claims

1. an extracting means for extracting a second signal in a signal-containing region including a reflected signal from a scatterer from a first signal representing a reflection of a signal emitted from a radar; a wraparound processing means for changing a time from a timing at which the second radar emits the extracted second signal to a timing at which the reflected signal is received by the second radar; A signal processing device comprising:

2. the extraction means extracts the second signal from a region in which the first signal is represented by a timing at which the first radar emits the signal and an elapsed time until a reflected signal of the first signal is received; The wraparound processing means transfers the second signal, which does not overlap with a storage area representing a storage destination area capable of storing the second signal, from the signal-present area to the storage area. The signal processing device according to claim 1 .

3. A region calculation means for identifying the signal-containing region based on the imaging conditions when the reflected signal is measured. The signal processing device according to claim 1 or 2, further comprising:

4. The signal area is defined in an azimuth time direction and a range time direction, The area calculation means determines the signal area having a boundary that is inclined in the azimuth time direction.

4. The signal processing device according to claim 3.

5. and an associated information output means for outputting associated information including at least an azimuth time, a range time, a range bin number corresponding to the range time, and an azimuth bin number corresponding to the azimuth time, for a reference point in a photographing area.

2. The signal processing device according to claim 1.

6. and an associated information output unit that outputs associated information including a range bin number and an azimuth bin number for a reference point in an imaging area based on the 0th range bin and the 0th azimuth bin.

2. The signal processing device according to claim 1.

7. a pulse compression means for performing a pulse compression process on the signal and the reflected signal; The extraction means extracts the second signal using the signal that has been subjected to the pulse compression processing. The signal processing device according to claim 1 .

8. a conversion means for converting the output of the wraparound processing means into data in the frequency domain; a reference multiplication means for multiplying an output of the conversion means by a reference signal serving as a correlation function; The signal processing device according to claim 1 , further comprising:

9. The information processing device extracts a second signal in a signal-present region including a reflected signal from a scatterer from a first signal representing a reflection of a signal emitted from a radar, and changes a time from a timing at which the second radar emits the signal to a timing at which the reflected signal is received for the extracted second signal. Signal processing methods.

10. A computer comprising: A process of extracting a second signal in a signal-present region including a reflected signal from a scatterer from a first signal representing a reflection of a signal emitted from a radar; a process of changing a time from a timing at which the second radar emits the extracted second signal to a timing at which the second radar receives the reflected signal; A computer-readable recording medium on which a signal processing program for causing a computer to execute the above is recorded.