KR102654879B1 - Spaceborne multistatic synthetic aperture radar(SAR) system and method of generating high-resolution SAR image using the same - Google Patents

Abstract

The 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 on the same orbit and spaced apart by a preset baseline distance, and their 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 observation target area and generate radar reflection signal data.

Description

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

The present invention relates to a multistatic synthetic aperture radar system mounted on a satellite to acquire high-resolution radio images of an observation target area. More specifically, it relates to a satellite-based multistatic synthetic aperture radar system consisting of a single transmitter and multiple receivers; This relates to a method of generating high-resolution SAR images of an observation target area using this.

Synthetic Aperture Radar (SAR) is a technology that forms multi-purpose radio images, especially SAR images, based on electromagnetic wave signals acquired from radar sensors mounted on flying platforms such as satellites and aircraft. Compared to optical image sensors, SAR's image resolution is not determined by sensor hardware but depends on the geometry of collecting information, so the image resolution can be flexibly adjusted according to situations and requirements. Because the resolution of the video is independent of distance, performance can be maintained consistently regardless of the distance/altitude of the platform. Because these advantages make SAR suitable for obtaining high-resolution images of wide-area areas of interest, satellite-mounted SAR remote sensing systems are being widely developed regardless of the nature of the mission, such as civil or military.

As with other imaging sensors, the most important performance measure 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 that makes up the system. Generally, in satellite-based systems, the speed of the platform is determined depending on the operating altitude, so the Doppler bandwidth of the signal must be adjusted to meet the resolution requirements for the system. The range of the Doppler bandwidth within the signal is proportional to the length of the synthetic aperture, more precisely, the size of the integration angle formed by the target and 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 conducting observations for a longer period of 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 of several centimeters to tens of centimeters, but currently the most advanced satellite-based SAR remote sensing system has a 3m, high-resolution Spotlight mode in the standard stripmap observation mode. Since succeeding in achieving a resolution of less than 1m, it has remained at a standstill.

The bottleneck in improving video resolution 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 wider Doppler bandwidth at the current level.

The first limitation of the current design method is that arbitrary expansion of the antenna beam width is impossible. The frequency response of the signal acquired from the platform moving along the synthetic aperture is formed during the aperture time when the target is exposed to the radar beam width. However, since the aperture time is determined as a constant when the design of the antenna hardware and the setting of the platform operating altitude are completed, a bandwidth exceeding this cannot be obtained in general strip map observations. Therefore, when attempting 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. However, since the antenna inherently has a direct/indirect effect on the design elements of various SAR systems, its arbitrary change is not possible. requires a complete redesign of the system, and the result is likely not to meet the system requirements. For example, as the aperture size decreases, problems such as image sensitivity and an increase in ambiguity response within the signal occur. To solve this problem, a spotlight mode observation has been developed and is in operation, which extends the aperture time by adjusting the attitude of the satellite during the observation time instead of changing the antenna hardware. However, this cannot be a complete solution for the following reasons.

The second problem is that the power burden on the radar due to the increase in observation time is enormous. While satellites have limited energy sources represented by solar cells, SAR payloads are high-power equipment with high power consumption. Therefore, the time that SAR remote sensing satellites can maneuver for each orbital cycle is extremely limited. All satellite-based SAR remote sensing systems are premised on securing global imaging capability (global coverage). Therefore, the satellite SAR remote sensing system must be designed to secure the widest possible observation area with limited resources, but since the amount of power that can be acquired while the satellite is orbiting is limited, it is natural to increase the observation time to improve resolution. Reduces the size of the image area that the radar can secure for a period of time. This leads to an increase in the revisit cycle, and in various SAR applications, it is desirable to reduce the time baseline interval, which can be seen as deteriorating the quality of the image.

For the above reasons, it is very difficult to improve the resolution of SAR images beyond current levels 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 multistatic synthetic aperture radar system that can improve resolution by securing a wider synthetic aperture length in a limited operation time by overcoming the limitations of the monostatic, single channel design, and This provides a method of generating high-resolution SAR images.

As a technical means for achieving the above-mentioned technical problems, a satellite-based multistatic synthetic aperture radar system according to one 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 on the same orbit and spaced apart by a preset baseline distance, and their 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 observation target area and generate radar reflection signal data.

According to one 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 transmit beam steering information at this time to the plurality of slave satellites. The plurality of slave satellites may synchronize the beam center with the master satellite by steering beams 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 the ground station enters the coverage of its data link, the radar reflection signal data is transmitted to the ground station. can be transmitted 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 multistatic high-resolution synthetic aperture radar (SAR) image based on the plurality of radar reflection signal data.

A method of generating a high-resolution synthetic aperture radar image according to one 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, preprocessing the plurality of radar reflection signal data to generate a plurality of SAR raw data, and regarding 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. It includes the step of generating a multistatic high-resolution synthetic aperture radar (SAR) image by image matching the plurality of SAR image data.

According to one example, the step of preprocessing the plurality of radar reflection signal data to generate a plurality of SAR raw data is based on the radar reflection signal data of the center channel received from the master satellite, each of the plurality of slave satellites. It may include correcting the residual phase error component of the radar reflection signal data of the received peripheral channel and the response imbalance between channels.

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

According to another example, the step of generating a plurality of SAR image data respectively corresponding to the plurality of distance profile data includes monostatic SAR for the distance profile data of the 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 generating a bistatic SAR image for distance profile data of peripheral channels corresponding to the plurality of slave satellites among the plurality of distance profile data. It may include generating SAR image data of peripheral channels from among the plurality of SAR image data by processing.

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

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

The computer program according to one 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 high-resolution SAR images by overcoming the limitations of the monostatic SAR system and securing a wider synthetic aperture length in a limited operation time.

Figure 1a shows a swarm configuration method of a multistatic SAR system according to the present invention.
Figure 1b is a schematic block diagram of a master satellite constituting a multistatic SAR system according to the present invention.
Figure 1c is a schematic block diagram of a slave satellite constituting a multistatic SAR system according to the present invention.
Figure 2 is a flowchart explaining the observation process using the multistatic SAR system of the present invention.
Figure 3 is a diagram for explaining a method of generating a high-resolution SAR image based on radar reflection signal data for each channel acquired using the multistatic SAR system of the present invention.
Figure 4 is a diagram for explaining the effect of the satellite formation configuration of the multistatic SAR system according to the present invention.
Figure 5 is a diagram for explaining the effect of the 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.

Below, various embodiments will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement them. However, since the technical idea of the present disclosure can be modified and implemented in various forms, it is not limited to the embodiments described in this specification. In describing the embodiments disclosed in this specification, if it is determined that detailed description of related known technologies may obscure the gist of the technical idea of the present disclosure, detailed descriptions of the known technologies will be omitted. Identical or similar components will be assigned the same reference number 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 in between. When an element is said to “include” another element, this means that it does not exclude another element in addition to the other element, but may further include another element, unless specifically stated to the contrary.

Some embodiments may be described in terms of functional block configurations and various processing steps. Some or all of these functional blocks may be implemented as any number of hardware and/or software configurations that perform specific functions. For example, the functional blocks of the present disclosure may be implemented by one or more microprocessors, or may be implemented by circuit configurations for certain functions. Functional blocks of the present disclosure may be implemented in various programming or scripting languages. The functional blocks of this disclosure may be implemented as algorithms running on one or more processors. Functions performed by a functional block in the present disclosure may be performed by a plurality of functional blocks, or functions performed by a plurality of functional blocks in the present disclosure may be performed by a single functional block. Additionally, the present disclosure may employ conventional technologies for electronic environment setup, signal processing, and/or data processing.

In order to solve the above-described technical problem, the present invention provides a multistatic SAR system consisting of a plurality of satellites arranged in the same orbit. The present invention relates to the configuration of a satellite formation of a multistatic SAR system for generating high-resolution SAR images, their observation process, and a method for generating high-resolution SAR images using a plurality of raw SAR data generated in this way, so that the minimum unit is Descriptions of individual hardware elements and related procedures below the satellite are omitted.

Figure 1a shows a swarm configuration method 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 equipped with both a transmitter 112 and a receiver 114, and the slave satellites 120 are SAR satellites that independently operate the receiver 124.

The master satellite 110 and the plurality of slave satellites 120 constitute one satellite formation and can maneuver in the x direction while being spaced apart by the same baseline distance 130. The orbit 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 size corresponding to the baseline distance 130 in the same orbit.

When the master satellite 110 and a plurality of slave satellites 120 exist in the same orbit, the master satellite 110 is composed of a master satellite 110 and a plurality of slave satellites 120 in consideration of the symmetry of the SAR data spectrum. It may be located in the center of the satellite formation, that is, in 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 1st to nth slave satellites 120 are arranged in the direction from the master satellite 110, and the (n+1)th to 2nth slave satellites 120 may be 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 be located at another location within the array formed by the satellite formation.

Figure 2 is a flowchart explaining the observation process using the multistatic SAR system of the present invention.

Referring to FIG. 2 along with FIGS. 1A and 1B, the master satellite 110 and the plurality of slave satellites 120 of the multistatic SAR system 100 fly along an orbit spaced apart by a baseline distance 130. The master satellite 110 and the plurality of slave satellites 120 approach the observation target area (S201). An observation plan using the multistatic SAR system 100 is pre-specified, and the master satellite 110 and a plurality of slave satellites 120 flying along the orbit are located 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 to maintain the target observation geometry with respect to the reference point 140 within the observation target area. At this time, 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 beam steering to each of the slave satellites 120 for situational awareness.

The slave satellites 120 synchronize the beam center with the master satellite 110 (S211). Once the line-of-sight direction of the master satellite 110 is determined according to beam steering, the slave satellites 120 may steer the beam to form a constant squint angle with respect to the reference point 140, respectively. Through this, the slave satellites 120 can synchronize the beam center with the master satellite 110.

The master satellite 110 transmits a radar observation signal (S205). For the observation target area, 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 entering 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 can initiate transmission of a synchronization reference signal through a direct channel to each slave satellite 120 through a synchronization link, and can maintain this until the end of the observation event. At this time, the transmission event of the synchronization reference signal may be synchronized with the transmission event of the radar observation signal.

Slave satellites 120 attempt to detect a transmission event of a synchronization reference signal through a 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 a synchronization reference signal from the master satellite 110 and recognize the occurrence of a reception event of the synchronization channel, they begin to receive a radar reflection signal 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 reflection signal.

After completing the transmission event of the radar observation signal and the synchronization reference signal, the master satellite 110 determines the necessity of beam steering and synchronization according to the observation plan and the current state of the master satellite 110 (S206). If additional beam steering is necessary, the master satellite 110 proceeds to step S202 and further steers the beam according to the observation plan. If additional beam steering is not required, the master satellite 110 determines whether to end observation (S207). The master satellite 110 may decide whether to end observation or not depending on the observation plan and the status of the master satellite 110. For example, if the antenna footprint of the reference channel begins to enter the reference point 140 and before completely leaving, the master satellite 110 proceeds to steps S204 and S205 and transmits a synchronization reference signal and a radar observation signal. there is. If the antenna's footprint deviates from the reference point 140, the master satellite 110 may decide to end the observation.

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 completed, the slave satellites 120 and the master satellite 110 record various observation metadata such as received radar reflection signal data and ephemeris, and the ground station records the data link. Once in coverage, observation metadata can be transmitted for processing.

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

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

1A to 3, the procedure for generating a high-resolution SAR image may consist of three steps: a signal pre-processing process 310, a SAR image generation process for each channel 330, and an image matching process 340. One high-resolution SAR image 350 can be finally generated from the radar reflection signal data set acquired from n channels. The high-resolution SAR image 350 may be generated, for example, in a signal processor of a ground station. n is the total number of master satellites 110 and slave satellites 120, the signal pre-processing process 310 and the SAR image generation process 330 for each channel are performed for each n channel, 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 digitize the received analog radar reflection signals to generate radar reflection signal data 302a. The 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 can transmit radar reflection signal data 302a to the ground station when the ground station enters 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.

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

The radar reflection signal data 302a received from the ground station may be tailored to be suitable for multi-channel image formation processing by the signal pre-processing process 310. The radar reflection signal data 302a received from the slave satellites 120 may have a residual phase error component and inter-channel response imbalance caused by bistatic asynchrony. The signal pre-processing processor 310 determines the residual phase error component of the radar reflection signal data 302a and the response imbalance between channels based on the radar reflection signal data 311 of the center channel received from the receiver 114 of the master satellite 110. 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 are displayed as images of the corresponding SAR raw data 312a.

Distance compression may be performed on the SAR raw data 312a by a distance compression process. Distance compression is achieved by duplicating the radar observation signal acquired from the master satellite 120 to generate duplicate data 322, and performing matched filtering on each of the SAR raw data 312a with the duplicate data 322. As a result of matched 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 images.

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. Transmitter elements such as the transmitter 112 of the master satellite 110 constituting the multistatic SAR imaging system 100 and receiver elements such as the receiver 124 of the slave satellites 120 each have a bistatic structure, so the channel The star SAR image generation process 330 is performed by a bistatic image forming kernel rather than a typical monostatic SAR image forming kernel, and the state vector 331a of the master satellite 110 and the state vectors 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 can be generated by performing monostatic SAR image processing on the distance profile data of the center channel using a typical monostatic SAR image forming kernel. SAR image data 341a of the peripheral channel may be generated by performing bistatic SAR image processing on the distance profile data of the peripheral channel by a bistatic SAR image forming kernel. Independent SAR image data 341a for each channel includes SAR image data 341a of the 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 are no restrictions on the type of image forming kernel that can be selected in the step of performing the SAR image generation process 330 for each channel, but additional procedures may be required when selecting a specific algorithm. For example, when using 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 any additional procedures. can do. However, in the case of the Range-Doppler-based image formation kernel, since the SAR image is presented in the data space, after generating the SAR image, each pixel in the image area of the target coordinate space is aligned to determine the specific size 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 channel-specific SAR image data 341a generated in the channel-specific SAR image generation process 330 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 registration process 340 creates a high-resolution SAR image 350 by complex summing the SAR image data 341a for each channel. can be created.

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 it is an area where the entire signal response can be effectively added, such as the distance-Doppler spectrum space. Additionally, an area suitable for performing the image registration process 340 may vary depending on which image forming kernel is used in the SAR image generation process 330 for each channel.

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

According to the present invention, the master satellite 110 and the slave satellites 120 form one multistatic satellite formation, so that 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 this information in one final SAR image, the multistatic SAR system according to the present invention generates high-resolution SAR images more efficiently than the monostatic system. It is possible.

FIG. 4 is a diagram for explaining the effect of the satellite formation configuration of the multistatic SAR system according to the present invention, and FIG. 5 is a diagram for explaining the effect of the 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.

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

Referring to FIG. 4, the 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 function as a slave satellite (110 in FIG. 1). 120). The first satellite 410a, the second satellite 410b, and the third satellite 410c are arranged to be spaced apart by the same baseline distance, and may rotate in the same orbit at the same speed. Satellite constellation 410 may include four or more satellites.

In the satellite formation 410, the speeds of all satellites 410a, 410b, and 410c are the same, and the composite antenna footprint formed by the transmitter beam and receiver beam is also almost uniform, so the Doppler spectrum 420a, 420b secured in each channel , 420c), the size of the bandwidth is determined in the same way.

Since the Doppler spectrum 420b acquired from the reception 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, and 420c of each channel itself is It is no different from the bandwidth of a monostatic spectrum. However, excluding the monostatic channel of the second satellite 410b, each receiver in the bistatic channels of the first satellite 410a and the third satellite 410c has a squint different from the second satellite 410b for the observation area. Since the angle is occupied, the diversity of composite angles is secured. 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 Doppler centroids 421a, 421b, and 421c that occur differently for each channel, and the range of Doppler frequencies referenced 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 SAR raw data acquired from the computer simulation of Figure 6b.

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

Referring to FIG. 5, specific pixels of sub-images 501, 511, and 521 formed for each receiving 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 distance between the target and the sensor, the point intensity distribution functions (502a, 512a, 522a) formed by the point referenced by the corresponding pixel in the target coordinate space during the infinite aperture time are the same. However, since the actual observation time is finite, given the geometries (500, 510, 520) of the transmitter (T) and receiver (R), the target response observed in the actual data is a portion 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.

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

The above explanation was written based on the strip map mode, which is a standard SAR observation mode, but if dynamic beam steering synchronization can be achieved between the transmitter and receiver, it can also be applied to improve resolution in wide-area imaging modes such as ScanSAR and TOPS. It is possible. At this time, a correction routine for additional phase error generated by beam steering may be added in the signal processing step. The wide-area imaging mode has the characteristic of improving the observation range by taking resolution as a trade-off, so when the configuration proposed in the present invention is adopted, the inseparable performance indicators of wide-area observation and high resolution can be satisfied at the same time.

The various embodiments described above are illustrative and should not be distinguished from each other and should be implemented independently. Embodiments described herein may be implemented in combination with each other.

The various embodiments described above may be implemented in the form of a computer program that can be executed through various components on a computer, and such a computer program may be recorded on a computer-readable medium. At this time, the medium may continuously store a computer-executable program, or temporarily store it for execution or download. In addition, the medium may be a variety of recording or storage means in the form of a single or several pieces of hardware combined. It is not limited to a medium directly connected to a computer system and may be distributed over a network. Examples of media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, And there may be something configured to store program instructions, including ROM, RAM, flash memory, etc. Additionally, examples of other media include recording or storage media managed by app stores that distribute applications, sites or servers that supply or distribute various other software, etc.

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

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

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

Claims (10)

Master satellite containing transmitter and receiver; and
a plurality of slave satellites each including a receiver;
The master satellite and the plurality of slave satellites are arranged on the same orbit and spaced apart by a preset baseline distance, and their 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 the observation target area to generate radar reflection signal data, and the ground station determines the coverage of its data link. Upon entering, the radar reflection signal data is transmitted to the ground station,
The ground station is,
Receiving the radar reflection signal data from the plurality of slave satellites and the master satellite, respectively,
Generating a plurality of SAR raw data by pre-processing the plurality of radar reflection signal data,
Performing distance compression on the plurality of SAR raw data to generate a plurality of distance profile data,
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,
A satellite-based multistatic synthetic aperture radar system that generates a multistatic high-resolution synthetic aperture radar (SAR) image by image matching the plurality of SAR image data. In claim 1,
The master satellite steers 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 transmits beam steering information to the plurality of slave satellites,
A satellite-based multistatic synthetic aperture radar system in which the plurality of slave satellites synchronize the beam center with the master satellite by steering the beam to form a squint angle corresponding to the baseline distance, respectively, based on the beam steering information. In claim 1,
A satellite-based multistatic synthetic aperture radar system in which the plurality of slave satellites and the master satellite digitize the radar reflection signal to generate the radar reflection signal data. 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;
Preprocessing the plurality of radar reflection signal data to generate a plurality of SAR raw 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 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 multistatic high-resolution synthetic aperture radar (SAR) image by image matching the plurality of SAR image data. In claim 4,
The step of preprocessing the plurality of radar reflection signal data to generate a plurality of SAR raw data,
Comprising the step of correcting the residual phase error component and inter-channel response imbalance of radar reflection signal data of peripheral channels received from each of the plurality of slave satellites, based on the radar reflection signal data of the center channel received from the master satellite. A method of generating high-resolution synthetic aperture radar images. In 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 replicating radar observation signals obtained from the master satellite; and
A method of generating a high-resolution synthetic aperture radar image comprising the step of performing matched filtering on each of the SAR raw data and the duplicate data. In claim 4,
The step of generating a plurality of SAR image data respectively corresponding to the plurality of distance profile data,
generating SAR image data of a center channel 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 among the plurality of distance profile data; and
Generating SAR image data of a peripheral channel among the plurality of SAR image data by performing bistatic SAR image processing on the distance profile data of a peripheral channel corresponding to the plurality of slave satellites among the plurality of distance profile data. How to generate high-resolution synthetic aperture radar images. In claim 4,
A method of generating a high-resolution synthetic aperture radar image in which pixels at the same location in the plurality of SAR image data refer to the same target coordinate space. In 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 of the plurality of SAR image data for each pixel. A computer program stored in a medium to execute the 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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