KR20230089920A - Spaceborne multistatic synthetic aperture radar(SAR) system and method of generating high-resolution SAR image using the same - Google Patents

Abstract

A satellite-based multistatic synthetic aperture radar system according to the present invention includes a master satellite including a transmitter and a receiver, and a plurality of slave satellites each including a receiver. The master satellite and the plurality of slave satellites are arranged spaced apart from each other by a preset baseline distance on the same orbit, and beam centers are synchronized with each other. The transmitter of the master satellite transmits a radar observation signal and a synchronization reference signal. The plurality of slave satellites are synchronized with the master satellite by receiving the synchronization reference signal. The receiver of the plurality of slave satellites and the receiver of the master satellite receive a radar reflection signal obtained by reflecting the radar observation signal in an observation target area and generate radar reflection signal data.

Description

Spaceborne multistatic synthetic aperture radar (SAR) system and method of generating high-resolution SAR image using the same}

The present invention relates to a multi-static synthetic aperture radar system mounted on a satellite to obtain a high-resolution radio image of an area to be observed, and more specifically, to a satellite-based multi-static synthetic aperture radar system composed of a single transmitter and a plurality of receivers, and It relates to a method of generating a high-resolution SAR image for an observation target region using this.

Synthetic Aperture Radar (SAR) is a technology that forms a multi-purpose radio wave image, especially a SAR image, based on an electromagnetic wave signal acquired from a radar sensor mounted on a flying platform such as a satellite or an aircraft. Compared to optical image sensors, SAR can flexibly adjust the image resolution according to the situation and requirements because the image resolution is not determined by the sensor hardware but depends on the geometry that collects information. Since the resolution of the video is independent of the distance, performance can be maintained consistently regardless of the distance/altitude of the platform. Since these advantages make SAR suitable for obtaining high-resolution images of a wide area of interest, satellite-mounted SAR remote sensing systems are being widely developed regardless of the nature of missions such as civilian and military.

As with other imaging sensors, the most important performance metric for SAR is resolution. The resolution of the SAR image is determined by the bandwidth of the Doppler frequency formed by the signal acquired from the system and the speed of the platform constituting the system. In general, since the speed of a platform in a satellite-based system is determined depending on the operating altitude, the Doppler bandwidth of a signal must be adjusted to meet the resolution condition required for the system. The range of the Doppler bandwidth in the signal is proportional to the length of the synthesis aperture, more precisely, the size of the integration angle formed by the target and the platform at the start and end points of observation. Therefore, in order to secure a wider Doppler bandwidth, it is necessary to form a long synthetic aperture by performing observations for a longer time.

As the applications of SAR have expanded, the demand for missions such as identification and recognition of small moving targets and targets of interest has increased significantly. These missions require high image resolution on the order of several centimeters (cm) to tens of centimeters (cm), but the current most advanced satellite-based SAR remote sensing system is 3 m in standard stripmap observation mode and high-resolution spotlight mode. It has been at a standstill since it succeeded in achieving sub-1m resolution in .

The bottleneck in image resolution improvement is due to the physical and technical limitations of the current monostatic, single-channel design structure. The following reasons dominate the difficulty in securing a wider synthetic aperture length and a wider Doppler bandwidth at the current level.

The first limitation of the current design method is that it is impossible to arbitrarily expand the antenna beam width. The frequency response of the signal obtained from the platform traveling along the synthetic aperture is formed during the aperture time when the target is exposed to the beam width of the radar. However, since the aperture time is determined as a constant at the time when the design of the antenna hardware and the setting of the operating altitude of the platform are completed, it is impossible to obtain a bandwidth exceeding this in general strip map observation. Therefore, in order to increase the aperture time, the beam width must be expanded, that is, the size of the physical aperture of the payload antenna must be reduced. requires a complete redesign of the system, which is also likely to not meet system requirements. Representatively, problems such as an increase in image sensitivity and an ambiguity response within a signal may occur as the size of the aperture decreases. In order to solve this problem, a spotlight mode observation that extends the aperture time by adjusting the attitude of the satellite during the observation time instead of changing the antenna hardware has been developed and is in operation, but this cannot be a complete solution for the following reasons.

The second problem is that the power burden of the radar is enormous due to the increase in observation time. While artificial satellites have a limited energy source represented by solar cells, SAR payloads are high-output equipment with high power consumption. For this reason, the time that SAR remote sensing satellites can start for each orbit period is extremely limited. All satellite-based SAR remote sensing systems are premised on securing global coverage. Therefore, the satellite SAR remote sensing system should be designed to secure the widest possible observation area with limited resources, but since the amount of power that can be obtained while the satellite orbits is limited, it is natural to increase the observation time to improve resolution. It reduces the size of the image area that the radar can secure during time. This leads to an increase in the revisit period, and since it is desirable to reduce the time baseline interval in various SAR applications, it can be seen that the quality of the image deteriorates.

For the above reasons, it is very difficult to improve the resolution of SAR images beyond the current level while maintaining global imaging capabilities through standard and wide-area observation modes.

The problem to be solved by the present invention is a satellite-based multi-static synthetic aperture radar system capable of improving resolution by overcoming the limitations of the above-mentioned monostatic and single-channel design and securing a wider synthetic aperture length in a limited operating time, and It is to provide a method for generating a high-resolution SAR image using this.

As a technical means for achieving the above technical problems, a satellite-based multi-static synthetic aperture radar system according to an aspect of the present invention includes a master satellite including a transmitter and a receiver; and a plurality of slave satellites each including a receiver. The master satellite and the plurality of slave satellites are arranged spaced apart from each other by a preset baseline distance on the same orbit, and beam centers are synchronized with each other. The transmitter of the master satellite transmits a radar observation signal and a synchronization reference signal. The plurality of slave satellites are synchronized with the master satellite by receiving the synchronization reference signal. The receiver of the plurality of slave satellites and the receiver of the master satellite receive a radar reflection signal obtained by reflecting the radar observation signal in an observation target area and generate radar reflection signal data.

According to an example, the master satellite may steer a beam to maintain a target observation geometry with respect to a reference point within the observation target area according to an observation plan, and may transmit beam steering information to the plurality of slave satellites. The plurality of slave satellites may synchronize a beam center with the master satellite by steering a beam to form a squint angle corresponding to the baseline distance, respectively, based on the beam steering information.

According to another example, the plurality of slave satellites and the master satellite digitize the radar reflection signal to generate the radar reflection signal data, and when a ground station comes within the coverage of its own data link, the radar reflection signal data is converted to the ground station. can be sent to The ground station may receive the radar reflection signal data from the plurality of slave satellites and the master satellite, respectively, and generate a multi-static high-resolution synthetic aperture radar (SAR) image based on the plurality of radar reflection signal data.

A method for generating a high resolution synthetic aperture radar image according to an aspect of the present invention is performed by a computing device. The method includes receiving a plurality of radar reflection signal data from a master satellite and a plurality of slave satellites, generating a plurality of SAR raw data by pre-processing the plurality of radar reflection signal data, and using the plurality of SAR raw data. Generating a plurality of distance profile data by performing distance compression, generating a plurality of SAR image data respectively corresponding to the plurality of distance profile data using the state vector of the master satellite and the state vectors of the plurality of slave satellites and generating a multi-static high-resolution synthetic aperture radar (SAR) image by image matching the plurality of SAR image data.

According to an example, the step of generating a plurality of SAR raw data by pre-processing the plurality of radar reflection signal data is performed in each of the plurality of slave satellites based on the radar reflection signal data of the center channel received from the master satellite. The method may include correcting residual phase error components of received radar reflection signal data of neighboring channels and response imbalance between channels.

According to another example, the generating of a plurality of distance profile data by performing distance compression on the plurality of SAR raw data includes generating duplicate data by replicating a radar observation signal obtained from the master satellite, and the SAR and performing matching filtering on each of the original data and the replicated data.

According to another example, the generating of a plurality of SAR image data respectively corresponding to the plurality of distance profile data may include monostatic SAR for distance profile data of a center channel corresponding to the master satellite among the plurality of distance profile data. Generating SAR image data of a center channel among the plurality of SAR image data by image processing, and bistatic SAR image of distance profile data of peripheral channels corresponding to the plurality of slave satellites among the plurality of distance profile data. and generating SAR image data of neighboring channels from among the plurality of SAR image data by processing.

According to another example, pixels at the same position in the plurality of SAR image data may refer to the same target coordinate space.

According to another example, the multi-static high-resolution SAR image may be generated by performing complex summation on each pixel of the plurality of SAR image data.

A computer program according to an aspect of the present invention is stored in a medium to execute a method of generating a high-resolution synthetic aperture radar image using a computing device.

According to the present invention, it is possible to generate a high-resolution SAR image by overcoming the limitations of the monostatic SAR system and securing a wider synthesis aperture length in a limited operation time.

Figure 1a shows a scheme for constructing a cluster of a multistatic SAR system according to the present invention.
1b is a schematic block diagram of a master satellite constituting a multistatic SAR system according to the present invention.
1c is a schematic block diagram of a slave satellite constituting a multistatic SAR system according to the present invention.
Figure 2 is a flow chart for explaining the observation process using the multi-static SAR system of the present invention.
3 is a diagram for explaining a method of generating a high-resolution SAR image based on radar reflection signal data for each channel obtained using the multi-static SAR system of the present invention.
Figure 4 is a diagram for explaining the effect of the satellite formation configuration of the multi-static SAR system according to the present invention.
5 is a diagram for explaining the effect of a method for generating a high-resolution SAR image according to the present invention.
6a to 6d show computer simulation results of a multistatic SAR system according to the present invention.

Hereinafter, various embodiments will be described in detail so that those skilled in the art can easily implement the present disclosure with reference to the accompanying drawings. However, since the technical spirit of the present disclosure may be implemented in various forms, it is not limited to the embodiments described herein. In describing the embodiments disclosed in this specification, if it is determined that a detailed description of a related known technology may obscure the gist of the technical idea of the present disclosure, a detailed description of the known technology will be omitted. The same or similar components are assigned the same reference numerals, and duplicate descriptions thereof will be omitted.

In this specification, when an element is described as being “connected” to another element, this includes not only the case of being “directly connected” but also the case of being “indirectly connected” with another element intervening therebetween. When an element "includes" another element, this means that it may further include another element without excluding another element in addition to the other element unless otherwise stated.

Some embodiments may be described as functional block structures and various processing steps. Some or all of these functional blocks may be implemented with any number of hardware and/or software components that perform a particular function. For example, functional blocks of the present disclosure may be implemented by one or more microprocessors or circuit configurations for a predetermined function. The functional blocks of this disclosure may be implemented in a variety of programming or scripting languages. The functional blocks of this disclosure may be implemented as an algorithm running on one or more processors. The functions performed by the function blocks of the present disclosure may be performed by a plurality of function blocks, or the functions performed by the plurality of function blocks in the present disclosure may be performed by one function block. In addition, the present disclosure may employ prior art for electronic environment setting, signal processing, and/or data processing.

In order to solve the above technical problem, the present invention provides a multi-static SAR system composed of a plurality of satellites arranged on the same orbit. The present invention relates to a configuration of satellite formations of a multi-static SAR system for generating high-resolution SAR images, an observation process thereof, and a method for generating high-resolution SAR images using a plurality of SAR raw data generated in this way, Descriptions of individual hardware elements and related procedures below artificial satellites are omitted.

Figure 1a shows a scheme for constructing a cluster of a multistatic SAR system according to the present invention.

1b and 1c are schematic block diagrams of a master satellite and a slave satellite constituting a multistatic SAR system according to the present invention.

Referring to FIGS. 1A and 1B , the multistatic SAR system 100 is a satellite-based multistatic SAR system and includes one master satellite 110 and a plurality of slave satellites 120 .

The master satellite 110 is a SAR satellite having both a transmitter 112 and a receiver 114, and the slave satellites 120 are SAR satellites that operate the receiver 124 alone.

The master satellite 110 and the plurality of slave satellites 120 constitute one satellite formation, and may be spaced apart by the same baseline distance 130 and maneuver in the x direction. The orbits of the master satellite 110 and the orbits of the slave satellites 120 may be designed to have the same orbit element. The master satellite 110 and the slave satellites 120 may have a true anomaly offset of a magnitude corresponding to the baseline distance 130 on the same orbit.

When the master satellite 110 and the plurality of slave satellites 120 exist on the same orbit, the master satellite 110 consists of the master satellite 110 and the plurality of slave satellites 120 in consideration of the symmetry of the SAR data spectrum. It may be located at the center of the satellite formation, that is, at the center of the plurality of slave satellites 120. The number of slave satellites 120 may be an even number. For example, when there are 2n slave satellites 120, the first to nth slave satellites 120 are arranged in a traveling direction from the master satellite 110, and the (n+1)th to 2nth slave satellites 120 is arranged in the opposite direction from the master satellite 110, so that the master satellite 110 may be arranged between the nth slave satellite 120 and the (n+1)th slave satellite 120. However, the present invention is not limited to this arrangement, and the master satellite 110 may exist at another position within the ranks formed by the satellite formations.

Figure 2 is a flow chart for explaining the observation process using the multi-static SAR system of the present invention.

Referring to FIG. 2 together with FIGS. 1A and 1B , a master satellite 110 and a plurality of slave satellites 120 of the multistatic SAR system 100 fly apart from each other by a baseline distance 130 along an orbit. The master satellite 110 and the plurality of slave satellites 120 are close to the observation target area (S201). An observation plan using the multistatic SAR system 100 is specified in advance, and the master satellite 110 and the plurality of slave satellites 120 flying along the orbit are in an area where the observation target area according to the observation plan can be observed. enter

The master satellite 110 steers the beam according to the observation plan (S202). The master satellite 110 may steer the beam so as to maintain a target observation geometry with respect to the reference point 140 within the observation target area. In this case, the beam steering may be static steering such as Broadside observation or dynamic steering such as scan mode or zero-Doppler steering. The line of sight direction of the master satellite 110 is determined according to beam steering.

The master satellite 110 transmits beam steering information (S203). The master satellite 110 may transmit information about its own beam steering to each of the slave satellites 120 for situational awareness.

The slave satellites 120 synchronize beam centers with the master satellite 110 (S211). When the gaze distance direction of the master satellite 110 is determined according to the beam steering, the slave satellites 120 may steer the beam to form a constant squint angle with respect to the reference point 140 . Through this, the slave satellites 120 may synchronize the beam centers with the master satellite 110 .

The master satellite 110 transmits a radar observation signal (S205). With respect to the area to be observed, the transmitter 112 of the master satellite 110 may transmit a radar observation signal during the maximum aperture time when the antenna footprint of the reference channel starts to rush to the reference point 140 and completely departs.

At the same time, the master satellite 110 transmits a synchronization reference signal (S204). The master satellite 110 may initiate transmission of a synchronization reference signal through a direct channel to each slave satellite 120 through a synchronization link, and may maintain it until an observation event ends. At this time, the transmission event of the synchronization reference signal may be synchronized with the transmission event of the radar observation signal.

The slave satellites 120 attempt to detect the transmission event of the synchronization reference signal through the synchronization link (S212). If the receivers 124 of the slave satellites 120 succeed in receiving the synchronization reference signal from the master satellite 110 through the synchronization link, the slave satellites 120 transmit the synchronization reference signal from the master satellite 110. It is determined that an event has occurred (S213). When the slave satellites 120 succeed in receiving the synchronization reference signal from the master satellite 110 and recognize the occurrence of the reception event of the synchronization channel, the slave satellites 120 start receiving radar reflection signals using the receiver 124. The receivers 124 of the slave satellites 120 each receive radar reflection signals (S214). The receiver 114 of the master satellite 110 also receives the radar return signal.

After completing the transmission event of the radar observation signal and the synchronization reference signal, the master satellite 110 determines the need for beam steering and synchronization according to the observation plan and the current state of the master satellite 110 (S206). If additional beam steering is required, the master satellite 110 proceeds to step S202 to additionally steer the beam according to the observation plan. If additional beam steering is not required, the master satellite 110 determines whether to terminate observation (S207). The master satellite 110 may determine whether to terminate the observation according to the observation plan and the state of the master satellite 110 . For example, if the antenna footprint of the reference channel starts rushing to the reference point 140 and before completely departing, the master satellite 110 proceeds to steps S204 and S205 to transmit a synchronization reference signal and a radar observation signal. there is. If the footprint of the antenna deviates from the reference point 140, the master satellite 110 may determine the end of the observation.

The slave satellites 120 determine whether an additional transmission event has occurred (S215). The slave satellites 120 and the master satellite 110 may repeat the reception process using the receivers 124 and 114 until the transmission event of the radar observation signal and the synchronization reference signal ends.

When the observation according to the observation plan is completely finished, the slave satellites 120 and the master satellite 110 record various observation metadata such as the received radar reflection signal data and ephemeris, and the ground station establishes the data link. When it comes into coverage, it can transmit observation metadata for processing.

The ground station may receive observation metadata from the slave satellites 120 and the master satellite 110, respectively, and a signal processor of the ground station may generate a high-resolution SAR image using radar reflection signal data for each channel.

3 is a diagram for explaining a method of generating a high-resolution SAR image based on radar reflection signal data for each channel obtained using the multi-static SAR system of the present invention.

1A to 3, a procedure for generating a high-resolution SAR image may consist of three steps: a signal pre-processing process 310, a SAR image generation process 330 for each channel, and an image matching process 340, One high-resolution SAR image 350 may be finally generated from the data set of radar reflection signals obtained from n channels. The high-resolution SAR image 350 may be generated, for example, by a signal processor of a ground station. n is the total number of master satellites 110 and slave satellites 120, the signal preprocessing process 310 and the SAR image generation process 330 for each channel are performed for each n number of channels, and the image matching process 340 One high-resolution SAR image is generated from n pieces of SAR image data 341a.

The receiver front ends 301 each digitize the received analog radar reflection signal to generate radar reflection signal data 302a. Receiver front ends 301 are included in the receiver 124 of the slave satellites 120 and the receiver 114 of the master satellite 110, respectively. Each of the slave satellites 120 and the master satellite 110 may transmit radar reflection signal data 302a to the ground station when the ground station comes within the coverage of the data link. Each of the radar reflection signal images 302b displays the corresponding radar reflection signal data 302a as an image.

In the receiver front end 301 of each of the slave satellites 120 and the master satellite 110, various signal processing including digitization of analog radar reflection signals is performed. Since the present invention does not focus on hardware characteristics, a detailed description of signal processing performed in the receiver front end 301 is omitted in this specification.

The radar return signal data 302a received from the ground station may be cut to be suitable for multi-channel image formation processing by a signal pre-processing process 310. In the radar reflection signal data 302a received from the slave satellites 120, there may be residual phase error components and response imbalance between channels caused by bistatic asynchrony. The signal pre-processing processor 310 is based on the radar reflection signal data 311 of the center channel received by the receiver 114 of the master satellite 110, and the residual phase error component of the radar reflection signal data 302a and the response imbalance between the channels. can be corrected. The radar return signal data 302a preprocessed through the signal preprocessing process 310 is referred to as SAR raw data 312a. The SAR raw images 312b represent the corresponding SAR raw data 312a as an image.

SAR raw data 312a may be subjected to distance compression by a distance compression process. The radar observation signal obtained from the master satellite 120 is copied to generate duplicate data 322, and distance compression is performed by performing matched filtering on each of the SAR raw data 312a with the duplicate data 322. As a result of matching filtering with the duplicate data 322 , distance profile data 321a for each channel may be generated. The distance profile images 321b display the corresponding distance profile data 321a as an image.

The SAR image generation process 330 for each channel is a process of generating independent SAR image data 341a for each channel using the corresponding distance profile data 321a. Since the transmitter element such as the transmitter 112 of the master satellite 110 and the receiver element such as the receiver 124 of the slave satellites 120 constituting the multistatic SAR imaging system 100 are individually bistatic, the channel The star SAR image generation process 330 is performed by a bistatic image formation kernel rather than a conventional monostatic SAR image formation kernel, and the state vector 331a of the master satellite 110 and the state vector of the slave satellites 120 By calculating using (331b), independent SAR image data 341a for each channel can be generated from the distance profile data 321a for each channel.

The plurality of distance profile data 321a includes distance profile data of a center channel corresponding to the master satellite 110 and distance profile data of peripheral channels corresponding to the slave satellites 120 . SAR image data 341a of the center channel may be generated by performing monostatic SAR image processing on the distance profile data of the center channel using a conventional monostatic SAR image formation kernel. SAR image data 341a of an adjacent channel may be generated by performing bistatic SAR image processing by a bistatic SAR image forming kernel on distance profile data of an adjacent channel. The independent SAR image data 341a for each channel includes SAR image data 341a of a center channel and SAR image data 341a of peripheral channels.

The independent SAR image data 341a for each channel is Single-Look Complex (SLC) SAR image data. The SAR images 341b for each channel are images of the corresponding SAR image data 341a for each channel.

There is no restriction on the type of image formation kernel that can be selected in the step of performing the SAR image generation process 330 for each channel, but an additional procedure may be required when a specific algorithm is selected. For example, in the case of adopting a back-projection kernel and a spatial frequency-based kernel in which the synthesized SAR image is reconstructed into the target coordinate space, the SAR image generation process 330 for each channel is completed without a separate additional procedure. can do. However, in the case of the Range-Doppler based image formation kernel, since the SAR image is presented on the data space, after generating the SAR image, each pixel of the image area of the target coordinate space is aligned to specify the specificity of all channels. Additional processes may be performed to ensure that pixels refer to the same target coordinate space.

The image matching process 340 is a process of matching the SAR image data 341a for each channel generated in the SAR image generation process 330 for each channel into a single multistatic high-resolution SAR image 350 . Since the SAR image data 341a for each channel refers to the same target coordinate space, the image matching process 340 complex sums the SAR image data 341a for each channel to obtain a high-resolution SAR image 350. can create

The method according to the present invention described with reference to FIG. 3 can be performed in areas other than the image area as long as the entire signal response can be effectively added, such as a range-Doppler spectral space. In addition, an area suitable for performing the image matching process 340 may vary depending on which image formation kernel is used in the SAR image generation process 330 for each channel.

When image registration process 340 is complete, one multistatic high-resolution SAR image 350 is generated from the multistatic SAR raw data set consisting of n SAR raw data 312a.

According to the present invention, since the master satellite 110 and the slave satellites 120 form one multi-static satellite formation, the amount of information contained in SAR raw data can be greatly improved. Since the multistatic multi-channel image generation process can fully reflect the diversity of such information in one finally generated SAR image, the multistatic SAR system according to the present invention generates a high-resolution SAR image more efficiently than a monostatic system. it is possible

FIG. 4 is a diagram for explaining the effect of configuring a satellite formation in a multi-static SAR system according to the present invention, and FIG. 5 is a diagram for explaining the effect of a method for generating a high-resolution SAR image according to the present invention. 6a to 6d show computer simulation results of a multistatic SAR system according to the present invention.

FIG. 6A shows a computer simulation simulating a multistatic SAR system 600 constituting an observation geometry with a baseline distance of about 5 km and an altitude of 550 km from three satellites (TX/RX1, RX2, and RX3).

Referring to FIG. 4 , a satellite formation 410 includes a first satellite 410a, a second satellite 410b, and a third satellite 410c. The second satellite 410b includes both a transmitter and a receiver and functions as a master satellite (110 in FIG. 1 ), and the first satellite 410a and the third satellite 410c include only a receiver and functions as a slave satellite (110 in FIG. 1 ). 120) can function. The first satellite 410a, the second satellite 410b, and the third satellite 410c are spaced apart from each other by the same baseline distance and can rotate in the same orbit at the same speed. A satellite formation 410 may include four or more satellites.

Since the speed of all satellites 410a, 410b, and 410c in the satellite formation 410 is the same, and the combined antenna footprint formed by the transmitter beam and the receiver beam is also almost uniform, the Doppler spectrum 420a, 420b obtained for each channel , the size of the bandwidth of 420c) is determined identically.

Since the Doppler spectrum 420b obtained from the receiving channel of the second satellite 410b, that is, the master satellite, is the same as the monostatic spectrum under equivalent conditions, the bandwidth of the Doppler spectrum 420a, 420b, 420c of each channel itself is It is not different from the bandwidth of the monostatic spectrum. However, except for the monostatic channel of the second satellite 410b, each receiver in each bistatic channel of the first satellite 410a and the third satellite 410c has a squint different from that of the second satellite 410b for the observation area. Since angles are occupied, diversity of composite angles is ensured. This appears as a change in the position of the Doppler Centroid on the spectrum.

Accordingly, the Doppler frequency response of each channel is formed around the Doppler centroids 421a, 421b, and 421c that occur differently for each channel, and the range of Doppler frequencies referred to by the entire multistatic data set is up to n times the monostatic bandwidth. It appears as a huge spectrum 430 reaching . This can also be confirmed in the Doppler bandwidth measurement result 610 formed from the SAR raw data acquired in the computer simulation of FIG. 6B.

Therefore, according to the present invention, a high-resolution SAR image can be generated by securing a wide bandwidth through a formation of satellites.

Referring to FIG. 5 , specific pixels of sub-images 501, 511, and 521 formed for each receive channel refer to the same point in the target coordinate space where the actual target is located. Under the condition that the baseline distance is very small compared to the target-sensor distance, the point intensity distribution functions 502a, 512a, and 522a formed by points referenced by corresponding pixels in the target coordinate space for infinite aperture time are the same. However, since the actual observation time is finite, given the geometry (500, 510, 520) of the transmitter (T) and receiver (R), the target response observed in the actual data is a part of the point intensity distribution function (502b, 512b, 522b) am. This can also be confirmed through the distance history record 620 of the computer simulation of FIG. 6C.

In the image generation process for each channel, the distribution responses 502b, 512b, and 522b recorded in the data are accumulated as one pixel. Therefore, when pixel matching of sub-images for each channel is perfectly completed according to the concept of the image generation procedure, the corresponding pixel 430 of the matched image generated by adding each sub-image overlaps (431) the distribution response for each channel. Therefore, it is possible to produce the same effect as forming an image from a signal obtained from a longer aperture. This can be confirmed by comparing the azimuth resolution of the monostatic SAR image 630a generated by the reference channel of the master satellite in FIG. 6D alone and the multistatic SAR image 630b generated by matching all channels according to the present invention.

The above description is based on the stripmap mode, which is a standard SAR observation mode. it is possible In this case, a correction routine for an additional phase error caused by beam steering may be added in the signal processing step. The wide-area imaging mode has a feature of improving the observation range by making a trade-off between the resolution and, when the configuration proposed in the present invention is adopted, it is possible to simultaneously satisfy incompatible performance indicators of wide-area observation and high resolution.

The various embodiments described above are illustrative, and should not be discriminated from each other and independently implemented. The embodiments described in this specification may be implemented in a combination with each other.

Various embodiments described above may be implemented in the form of a computer program that can be executed on a computer through various components, and such a computer program may be recorded on a computer-readable medium. In this case, the medium may continuously store a program executable by a computer or temporarily store the program for execution or download. In addition, the medium may be various recording means or storage means in the form of a single or combined hardware, but is not limited to a medium directly connected to a certain computer system, and may be distributed on a network. Examples of the medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical recording media such as CD-ROM and DVD, magneto-optical media such as floptical disks, and ROM, RAM, flash memory, etc. configured to store program instructions. In addition, examples of other media include recording media or storage media managed by an app store that distributes applications, a site that supplies or distributes various other software, and a server.

In this specification, “unit”, “module”, etc. may be a hardware component such as a processor or a circuit, and/or a software component executed by a hardware component such as a processor. For example, "unit", "module", etc. may refer to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, It can be implemented by procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays and variables.

The above description of the present invention is for illustrative purposes, and those skilled in the art can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be construed as being included in the scope of the present invention. do.

Claims (10)

a master satellite comprising a transmitter and a receiver; and
a plurality of slave satellites each including a receiver;
The master satellite and the plurality of slave satellites are arranged spaced apart from each other by a preset baseline distance on the same orbit, and beam centers are synchronized with each other;
The transmitter of the master satellite transmits a radar observation signal and a synchronization reference signal,
The plurality of slave satellites are synchronized with the master satellite by receiving the synchronization reference signal;
The receiver of the plurality of slave satellites and the receiver of the master satellite receive a radar reflection signal in which the radar observation signal is reflected from an area to be observed and generate radar reflection signal data. The method of claim 1,
The master satellite steers a beam to maintain a target observation geometry with respect to a reference point in the observation target area according to an observation plan, transmits beam steering information at this time to the plurality of slave satellites,
The plurality of slave satellites synchronize beam centers with the master satellite by steering beams to form squint angles corresponding to the baseline distances, respectively, based on the beam steering information. The method of claim 1,
The plurality of slave satellites and the master satellite digitize the radar reflection signal to generate the radar reflection signal data, and transmit the radar reflection signal data to the ground station when the ground station comes within the coverage of its own data link,
The ground station receives the radar reflection signal data from the plurality of slave satellites and the master satellite, respectively, and generates a multistatic high-resolution synthetic aperture radar (SAR) image based on the plurality of radar reflection signal data. Synthetic aperture radar system. A method performed by a computing device, comprising:
Receiving a plurality of radar reflection signal data from a master satellite and a plurality of slave satellites;
generating a plurality of raw SAR data by pre-processing the plurality of radar reflection signal data;
generating a plurality of distance profile data by performing distance compression on the plurality of SAR raw data;
generating a plurality of SAR image data respectively corresponding to the plurality of distance profile data by using the state vector of the master satellite and the state vectors of the plurality of slave satellites; and
A method of generating a high-resolution synthetic aperture radar image comprising the step of generating a multi-static high-resolution synthetic aperture radar (SAR) image by image matching the plurality of SAR image data. The method of claim 4,
The step of generating a plurality of SAR raw data by preprocessing the plurality of radar reflection signal data,
Correcting a response imbalance between channels and a residual phase error component of radar reflection signal data of peripheral channels respectively received from the plurality of slave satellites, based on the radar reflection signal data of the central channel received from the master satellite. A method for generating high-resolution synthetic aperture radar images. The method of claim 4,
The step of generating a plurality of distance profile data by performing distance compression on the plurality of SAR raw data,
generating duplicate data by duplicating the radar observation signal obtained from the master satellite; and
A method of generating a high-resolution synthetic aperture radar image comprising performing matched filtering on each of the SAR raw data and the replicated data. The method of claim 4,
Generating a plurality of SAR image data respectively corresponding to the plurality of distance profile data,
generating SAR image data of a center channel from among the plurality of SAR image data by performing monostatic SAR image processing on distance profile data of a center channel corresponding to the master satellite from among the plurality of distance profile data; and
Generating SAR image data of an adjacent channel from among the plurality of SAR image data by performing bistatic SAR image processing on distance profile data of an adjacent channel corresponding to the plurality of slave satellites from among the plurality of distance profile data A method for generating high-resolution synthetic aperture radar images. The method of claim 4,
A method of generating a high-resolution synthetic aperture radar image in which pixels at the same position in the plurality of SAR image data refer to the same target coordinate space. The method of claim 4,
The multi-static high-resolution SAR image is a method of generating a high-resolution synthetic aperture radar image generated by performing complex summation on each pixel of the plurality of SAR image data. A computer program stored in a medium to execute a method of generating a high-resolution synthetic aperture radar image according to any one of claims 4 to 9 using a computing device.

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