On-orbit real-time processing device and method for AIS-guided SAR imaging

Abstract

The present invention provides an on-orbit real-time processing device and method for AIS-guided SAR imaging, which can realize AIS-guided satellite-borne SAR payload to perform positive and side-view imaging of the selected target area, thereby realizing high-resolution detailed inspection and imaging monitoring of distant sea ship targets. The present invention receives AIS messages in real time, performs matching analysis on the messages, monitors whether there are targets of interest in the observation area, and guides the SAR payload to work, thereby realizing high-resolution detailed inspection and imaging monitoring of distant sea ship targets; based on the AIS information of time-sensitive ship targets, on-orbit real-time imaging task planning is performed, and by designing and optimizing the processing flow, the on-orbit SAR payload on the satellite is guided to detect and image the selected ship target, meeting the high real-time, high efficiency, and high reliability requirements of on-orbit applications.

Description

Technical Field

[0001] The present invention relates to the technical field of signal and information processing, and in particular to an on-orbit real-time processing device and method for AIS-guided SAR imaging. Background Art

[0002] Satellite-borne AIS refers to a radio communication system that uses an AIS receiver on one or more low-orbit satellites (orbital altitude between 400 and 1000 km) to detect and receive ship AIS signals in orbit. Due to the high and long-range characteristics of satellites, it overcomes the shortcomings of the traditional AIS system in terms of small ship-to-ship and ship-to-shore communication range, and can achieve large-scale detection of AIS information transmitted by ships under the satellite. Satellite-borne AIS has a wide detection range, usually up to thousands of nautical miles; at the same time, the ship's AIS signal reporting rate is relatively high, so it can meet actual application needs.

[0003] Beijing Space Vehicle General Department CN201811280751.8 discloses a SAR autonomous imaging workflow based on the guidance of satellite-borne AIS real-time information. This method selects the ship target of interest based on the real-time demodulation information of AIS and GPS real-time information on the satellite, and calculates various parameters required for SAR imaging in real time, generates satellite attitude adjustment instructions and SAR power-on imaging instructions, and realizes the imaging task planning from target discovery to SAR image acquisition on the satellite in a fully autonomous manner. Based on the workflow design of satellite-borne AIS guiding SAR imaging, the satellite-borne SAR system accurately images the targets confirmed by AIS, completes real-time monitoring and imaging of non-cooperative ship targets, and improves the timeliness and accuracy of sea surface ship target identification.

[0004] CN202010324490.6.9 of the Institute of Space Information Innovation of the Chinese Academy of Sciences discloses a method and device for calculating and refocusing the position of a ship in a SAR image based on AIS, the method comprising: obtaining first GPS data and second GPS data; obtaining the spatial coordinates of the ship and the spatial coordinates of the SAR platform; obtaining a first distance course, a first speed and a first acceleration of the ship according to the spatial coordinates of the ship and the spatial coordinates of the SAR platform; obtaining the imaging time according to the first distance course; obtaining the stationary spatial coordinates of the ship at the imaging time according to the first GPS data; obtaining the second distance course, a second speed and a second acceleration of the ship according to the stationary spatial coordinates and the spatial coordinates of the SAR platform; obtaining the position offset of the ship according to the first speed and the second speed; compensating for the azimuth motion of the ship according to the first acceleration and the second acceleration to obtain a focused image of the ship; moving the focused image of the ship by the position offset to obtain the true position of the ship.

[0005] CN201610317235.2 of the Third Institute of Oceanography of the State Oceanic Administration discloses a data fusion method based on multi-source ship automatic identification system data, which involves a ship automatic identification system. It includes: obtaining multi-source AIS data for a continuous period of time; uniformly standardizing and quality controlling the obtained multi-source AIS data; using programming software to process the standardized data, and calculating the position and navigation status of each ship at each moment according to the time, azimuth, ship speed, heading angle and other information in the obtained multi-source AIS data; performing batch calculation processing to draw a ship distribution map and a ship trajectory map. By fusing multi-source AIS data, the distribution of ships in the target sea area at any moment or the navigation trajectory curve of a certain ship can be calculated. In hot spots, the detection probability of satellite-borne AIS can be increased from 20% to 80%, solving the problem of low detection probability of satellite-borne AIS in hot spots. It can restore the real distribution of ocean ships to the greatest extent, and can also restore the trajectory of a single ship more accurately.

[0006] However, the above methods mainly have the following problems:

[0007] (1) It does not take into account that on-orbit processing devices are different from ground or other platforms. For on-orbit processing devices, they have distinct characteristics such as high reliability, high efficiency, high real-time, radiation resistance, and strong tolerance / error correction capabilities. The design ideas of the above method only consider the logical process of applying AIS information, which is difficult to meet the needs of aerospace applications.

[0008] (2) It does not take into account that for time-sensitive targets, the timeliness and continuity of on-orbit processing of AIS information and mission planning are very important. Therefore, the reliability of on-orbit processing equipment and the rationality of the processing process become the main concerns.

[0009] (3) No specific consideration is given to the engineering implementation issues of on-orbit processing. Summary of the invention

[0010] In view of this, the present invention provides an on-orbit real-time processing device and method for AIS-guided SAR imaging, which can enable AIS-guided satellite-borne SAR payload to perform positive and side-view imaging of the selected target area, thereby realizing high-resolution detailed inspection and imaging monitoring of offshore ship targets.

[0011] To achieve the above-mentioned purpose, an on-orbit real-time processing device for AIS-guided SAR imaging of the present invention comprises an AIS receiving module, a central processing unit module, a navigation enhancement module, an intelligent information processing module, an attitude orbit control module and a payload control module; wherein the central processing unit module completes the matching and selection of the target of interest according to the ship AIS information, sends the determined ship of interest information to the intelligent information processing module, and sends an instruction to the navigation enhancement module to start orbit extrapolation; after receiving the instruction of the central processing unit module, the navigation enhancement module completes the orbit extrapolation calculation of the specified start time, and sends the extrapolation result to the intelligent information processing module; the intelligent information processing module calculates the imaging angle, the imaging start and end time according to the ship of interest information and the orbit extrapolation data, and sends the result to the central processing unit module; the central processing unit module sends the imaging angle to the attitude orbit control module, and the attitude orbit control module completes the attitude adjustment of the satellite specified side swing angle according to the received parameters; the central processing unit module sends the imaging angle, the imaging start and end time to the payload control module, and the payload control module completes the calculation of the SAR payload beam pointing, and controls the SAR payload to complete the imaging monitoring of the target of interest.

[0012] The navigation enhancement module completes 10 minutes of orbit extrapolation calculation.

[0013] Among them, the central processing unit module is implemented by FPGA, which is responsible for collecting orbit extrapolation data and AIS guidance information and sending them to DSP through EMIFB bus for imaging parameter calculation; the intelligent information processing module is implemented by DSP.

[0014] Among them, after receiving the AIS data, the navigation enhancement module parses the link layer protocol, encapsulates it into a PUS telemetry protocol packet and sends it to the intelligent information processing module through the CAN bus. At the same time, the navigation enhancement module sends an instruction to start orbit extrapolation, and forwards 600s of orbit extrapolation data to the intelligent information processing module through the 422 bus. It is triggered by the AIS and orbit extrapolation data packets, and starts to execute the track prediction AIS guidance algorithm after receiving all the data. If the data is incomplete or illegal, or the AIS result has been sent, the intelligent information processing module will no longer execute the AIS task this time.

[0015] Among them, after receiving the data packet, the DSP first holds the timer; the track prediction AIS guidance algorithm determines the starting time of track planning and the time difference compensation of track planning according to the AIS message time, the current on-board time at the trigger time, and the start time of orbit extrapolation, and calculates the optimal imaging time and the corresponding lower viewing angle according to the starting time of track planning and the time difference compensation of track planning, and outputs the imaging time to be unified to the on-board time axis; if the algorithm obtains that the imaging lower viewing angle is not within the satellite maneuvering range, the planning fails; if the algorithm obtains the imaging time less than 90s, the satellite cannot maneuver in place on time, and the planning fails; if the algorithm obtains the imaging time of 90-210s, the data is sent immediately, the payload is turned on and maneuvered, and the planning task is completed; if the algorithm obtains the imaging time greater than 210s, the DSP starts the timer and enters the waiting action; the DSP timer Inertial CLK is set to 1 / 8CPU CLK, each beat counts 8 CPU clock cycles; the timer triggers the timer interrupt every 0.5s, and when the timer interrupts, the DSP obtains the current on-board time. If the current time is within 210s from the best imaging moment, the data is sent immediately, the payload is turned on and maneuvered, and the planned task is completed; if the current time is beyond 210s from the best imaging moment, the timer GO mode continues to wait.

[0016] The present invention also provides an on-orbit real-time processing method for AIS-guided SAR imaging, which uses the device of the present invention and includes the following steps:

[0017] Step 1: Receive, process and extract the AIS signal transmitted by the ship's AIS equipment through the AIS receiving module, and parse the AIS message in real time;

[0018] Step 2: The central processing unit module selects target information from the AIS receiving module information according to the target location ID information, sends it to the intelligent information processing module, and sends the track extrapolation information instruction to the navigation enhancement module;

[0019] Step 3: After receiving the instruction, the navigation enhancement module forwards the orbit extrapolation data of the specified time to the intelligent information processing module through the central processing module;

[0020] Step 4: After receiving the target information and orbit extrapolation data, the intelligent information processing module performs imaging feasibility analysis, calculates the viewing angle and time under imaging, and sends them to the central processing unit module;

[0021] Step 5. The central processing unit module compares the received imaging time with the current star time and performs an imaging feasibility analysis. If the planned imaging time is 90 seconds less than the current star time, imaging is not feasible, subsequent operations are terminated, and this planning ends. If the planned imaging time is 90 seconds greater than the current star time and less than 210 seconds, the imaging viewing angle and time are sent to the payload control module. If the planned imaging time is 210 seconds greater than the current star time, planning continues until the difference between the planned imaging time and the current star time is between 90 seconds and 210 seconds, and this planning ends.

[0022] Step 6: The payload control module selects beam parameters according to the imaging viewing angle and time to complete payload imaging control.

[0023] Beneficial effects:

[0024] 1. The on-orbit real-time processing device for AIS-guided SAR imaging designed by the present invention receives AIS messages in real time, performs matching analysis on the messages, monitors whether there are targets of interest in the observation area, and guides the SAR payload to work, thereby achieving high-resolution detailed imaging monitoring of offshore ship targets.

[0025] 2. The device of the present invention performs on-orbit real-time imaging task planning based on the AIS information of time-sensitive ship targets. By designing and optimizing the processing flow, the on-board SAR payload is guided on-orbit to detect and image the selected ship targets, thus meeting the high real-time, high efficiency and high reliability requirements of on-orbit applications.

[0026] 3. The method of the present invention receives AIS messages in real time, performs matching analysis on the messages, monitors whether there are targets of interest in the observation area, and guides the SAR payload to work, thereby achieving high-resolution detailed imaging monitoring of offshore ship targets.

[0027] 4. The method of the present invention performs on-orbit real-time imaging task planning based on the AIS information of time-sensitive ship targets. By designing and optimizing the processing flow, the on-board SAR payload is guided on-orbit to detect and image the selected ship targets, thus meeting the high real-time, high efficiency and high reliability requirements of on-orbit applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A block diagram of the AIS-guided SAR imaging data flow design of the present invention.

[0029] Figure 2 This is the basic flow chart of AIS-guided SAR imaging of the present invention.

[0030] Figure 3 This is a hardware block diagram for implementing the AIS-guided SAR imaging core algorithm of the present invention.

[0031] Figure 4 The software flow chart of the AIS-guided SAR imaging core algorithm of the present invention is provided. DETAILED DESCRIPTION

[0032] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0033] The block diagram of the AIS guided SAR imaging data flow design of the present invention is as follows Figure 1 As shown, the present invention provides an on-orbit real-time processing device for AIS-guided SAR imaging, including an AIS receiving module, a central processing unit module, a navigation enhancement module, an intelligent information processing module, an attitude and orbit control module, and a payload control module.

[0034] Among them, the AIS receiving module extracts the ship's identity, position and speed information based on the real-time demodulation signal of the onboard AIS system and sends it to the central processing unit module.

[0035] The central processing unit module matches and analyzes the message, monitors whether there are targets of interest in the observation area, and guides the SAR payload to work, thereby realizing imaging monitoring of offshore ship targets. Specifically, after the central processing unit completes the matching and selection of targets of interest based on the ship's AIS information, it sends the determined ship information of interest to the intelligent information processing module, and at the same time issues a command to the navigation enhancement module to start orbit extrapolation.

[0036] After receiving the instruction from the central processing unit module, the navigation enhancement module completes the orbit extrapolation calculation for the specified start time and sends the extrapolation result to the intelligent information processing module; in this embodiment, the orbit extrapolation calculation for 10 minutes is completed.

[0037] The intelligent information processing module calculates parameters such as imaging angle, imaging start and end time based on the ship information of interest and orbit extrapolation data, and sends the results to the central processing unit module.

[0038] The central processing unit module sends the imaging angle to the attitude orbit control module, and the attitude orbit control module completes the attitude adjustment of the satellite's specified side swing angle based on the received parameters.

[0039] In addition, the central processing unit module sends the imaging angle, imaging start and end time to the payload control module, which calculates imaging parameters such as SAR payload beam pointing and controls the SAR payload to complete imaging monitoring of the target of interest.

[0040] The basic process of AIS guided SAR imaging of the present invention is as follows: Figure 2 As shown, the on-orbit real-time processing method of AIS-guided SAR imaging of the present invention, using the device of the present invention, comprises the following steps:

[0041] Step 1: Receive, process and extract the AIS signal transmitted by the ship's AIS equipment through the AIS receiving module, and parse the AIS message in real time;

[0042] Step 2: The central processing unit module selects target information (including navigation status, turning rate, speed over the ground, longitude, latitude, and heading over the ground) from the AIS receiving module information according to the target position ID information (which can be recorded through the ground measurement and control channel), sends it to the intelligent information processing module, and sends the orbit extrapolation information instruction to the navigation enhancement module;

[0043] Step 3: After receiving the instruction, the navigation enhancement module forwards the 10-minute orbit extrapolation data to the intelligent information processing module through the central processing module;

[0044] Step 4: After receiving the target information and orbit extrapolation data, the intelligent information processing module performs imaging feasibility analysis, calculates the viewing angle and time under imaging, and sends them to the central processing unit module;

[0045] Step 5. The central processing unit module compares the received imaging time with the current star time and performs an imaging feasibility analysis. If the planned imaging time is 90 seconds less than the current star time, imaging is not feasible, subsequent operations are terminated, and this planning ends. If the planned imaging time is 90 seconds greater than the current star time and less than 210 seconds, the imaging viewing angle and time are sent to the payload control module. If the planned imaging time is 210 seconds greater than the current star time, it means that the current time is still far from the optimal imaging time (more than 210 seconds), and planning can continue until the difference between the planned imaging time and the current star time is between 90 seconds and 210 seconds, and this planning ends.

[0046] Step 6: The payload control module selects beam parameters according to the imaging viewing angle and time to complete payload imaging control.

[0047] The hardware block diagram of the AIS guided SAR imaging core algorithm of the present invention is as follows: Figure 3 As shown in the figure. The core algorithm function software of AIS-guided SAR imaging is mainly implemented by FPGA and DSP. Among them, the central processing unit module is implemented by FPGA, which is responsible for collecting orbit extrapolation data and AIS guidance information and sending them to DSP through EMIFB bus for imaging parameter calculation. The intelligent information processing module is implemented by DSP. DSP uses TI's TMS320C6414T, which runs at a main frequency of 800MHz and has a computing power of 6400MIPS. It has powerful computing power to ensure the real-time calculation of imaging parameters.

[0048] The software flow chart of the core algorithm for AIS guided SAR imaging of the present invention is shown in Figure 4As shown. AIS calculation is based on the target longitude and latitude and satellite orbit parameters, and the imaging position and the downward viewing angle are obtained through orbit extrapolation calculation. According to different models, it is divided into autonomous AIS calculation and fast AIS calculation. Autonomous AIS calculation performs autonomous orbit extrapolation based on the self-built model, and uses its results to calculate the imaging time and the downward viewing angle; in order to better meet the real-time requirements of system functions, the fast AIS calculation obtains the orbit extrapolation data of the satellite in the WGS84 coordinate system from the attitude and orbit control module through the EMIF interface for fast calculation; after receiving the AIS data, the navigation enhancement module parses the link layer protocol, encapsulates it into a PUS telemetry protocol package and sends it to the intelligent information processing module through the CAN bus. At the same time, the navigation enhancement module sends a command to start orbit extrapolation, and forwards the 600s orbit extrapolation data to the intelligent information processing module through the 422 bus; triggered by the AIS and orbit extrapolation data packets, the track prediction AIS guidance algorithm is executed after receiving all the data. If the data is incomplete or illegal, or the AIS result has been sent, the intelligent information processing module will no longer perform the AIS task this time. After receiving the data packet, the DSP first HOLDs the timer to prevent interference or abnormal results from being sent during the processing process; the track prediction AIS guidance algorithm determines the starting time of track planning and the time difference compensation of track planning according to the AIS message time, the current time on the satellite at the trigger time, and the start time of orbit extrapolation, and calculates the optimal imaging time and the corresponding lower viewing angle according to the starting time of track planning and the time difference compensation of track planning, and outputs the imaging time to the satellite time axis; if the algorithm obtains that the imaging lower viewing angle is not within the satellite maneuvering range, the current planning fails; if the algorithm obtains that the imaging time is close (less than 90s), the satellite cannot maneuver in place on time, and the current planning fails; if the algorithm obtains that the imaging time is appropriate (90-210s), the data is sent immediately, the payload is powered on and maneuvered, and the planning task is completed; if the algorithm obtains that the imaging time is far away (greater than 210s), the DSP starts the timer and enters the waiting action. The DSP timer Inertial CLK is set to 1 / 8CPU CLK, and each beat counts 8CPU clock cycles (counting PRD45M / CPU720M). The timer triggers a timer interrupt every 0.5s. When the timer interrupts, the DSP obtains the current on-board time. If the current time is suitable for the best imaging moment (within 210s), the data is sent immediately, the payload is powered on and maneuvered, and the planned task is completed. If the current time is still far from the best imaging moment (outside 210s), the timer GO mode is entered to wait. While the DSP is executing the waiting action, it can also be triggered by new AIS data to execute the guidance algorithm. The guidance result output strategy is the same as the above strategy.

[0049] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An on-orbit real-time processing device for AIS-guided SAR imaging, characterized in that: It includes an AIS receiving module, a central processing unit module, a navigation enhancement module, an intelligent information processing module, an attitude orbit control module and a payload control module; wherein the central processing unit module completes the matching and selection of the target of interest according to the ship AIS information, sends the determined ship of interest information to the intelligent information processing module, and sends an instruction to the navigation enhancement module to start orbit extrapolation; after receiving the instruction from the central processing unit module, the navigation enhancement module completes the orbit extrapolation calculation of the specified start time, and sends the extrapolation result to the intelligent information processing module; The intelligent information processing module calculates the imaging angle, imaging start and end time according to the information of the ship of interest and the orbit extrapolation data, and sends the result to the central processing unit module; the central processing unit module sends the imaging angle to the attitude orbit control module, and the attitude orbit control module completes the attitude adjustment of the satellite's specified side swing angle according to the received parameters; the central processing unit module sends the imaging angle, imaging start and end time to the payload control module, and the payload control module completes the calculation of the SAR payload beam pointing, and controls the SAR payload to complete the imaging monitoring of the target of interest; The navigation enhancement module completes 10 minutes of orbit extrapolation calculation; The central processing unit module is implemented by FPGA, which is responsible for collecting orbit extrapolation data and AIS guidance information and sending them to DSP through EMIFB bus for imaging parameter calculation; the intelligent information processing module is implemented by DSP; After receiving the AIS data, the navigation enhancement module parses the link layer protocol, encapsulates it into a PUS telemetry protocol packet and sends it to the intelligent information processing module through the CAN bus. At the same time, the navigation enhancement module sends an instruction to start orbit extrapolation, and forwards 600s of orbit extrapolation data to the intelligent information processing module through the 422 bus. It is triggered by the AIS and orbit extrapolation data packets, and starts to execute the track prediction AIS guidance algorithm after receiving all the data. If the data is incomplete or illegal, or the AIS result has been sent, the intelligent information processing module will no longer execute the AIS task this time; after receiving the data packet, the DSP first HOLDs the timer; the track prediction AIS guidance algorithm determines the starting time of track planning and the time difference of track planning according to the AIS message time, the current on-board time at the trigger time, and the starting time of orbit extrapolation, and calculates the optimal imaging time and the corresponding downward viewing angle according to the starting time of track planning and the time difference of track planning, and outputs the imaging time to be unified to the on-board time axis; If the algorithm obtains that the viewing angle under imaging is not within the satellite maneuvering range, the current planning fails; if the algorithm obtains that the imaging time is less than 90s, the satellite cannot maneuver to the position on time, and the current planning fails; if the algorithm obtains that the imaging time is 90-210s, the data is sent immediately, the payload is powered on and maneuvered, and the current planning task is completed; If the imaging time obtained by the algorithm is greater than 210s, the DSP starts the timer and enters the waiting action; the DSP timer Inertial CLK is set to 1 / 8CPU CLK, and each beat counts 8 CPU clock cycles; the timer triggers the timer interrupt every 0.5s, and when the timer interrupts, the DSP obtains the current on-board time. If the current time is within 210s from the best imaging time, the data is sent immediately, the payload is turned on and maneuvered, and the planned task is completed; if the current time is beyond 210s from the best imaging time, the timer GO mode continues to wait.

2. An on-orbit real-time processing method for AIS-guided SAR imaging, characterized in that: The device as claimed in claim 1 comprises the following steps: Step 1: Receive, process and extract the AIS signal transmitted by the ship's AIS equipment through the AIS receiving module, and parse the AIS message in real time; Step 2: The central processing unit module selects target information from the AIS receiving module information according to the target location ID information, sends it to the intelligent information processing module, and sends the track extrapolation information instruction to the navigation enhancement module; Step 3: After receiving the instruction, the navigation enhancement module forwards the orbit extrapolation data of the specified time to the intelligent information processing module through the central processing module; Step 4: After receiving the target information and orbit extrapolation data, the intelligent information processing module performs imaging feasibility analysis, calculates the viewing angle and time under imaging, and sends them to the central processing unit module; Step 5, the central processing unit module compares the received imaging time with the current star time and performs imaging feasibility analysis. If the planned imaging time is less than 90 seconds than the current star time, imaging is not feasible, subsequent operations are terminated, and this planning ends; if the planned imaging time is greater than 90 seconds and less than 210 seconds than the current star time, the imaging viewing angle and time are sent to the payload control module; if the planned imaging time is greater than 210 seconds than the current star time, the planning continues until the difference between the planned imaging time and the current star time is between 90 seconds and 210 seconds, and this planning ends; Step 6: The payload control module selects beam parameters according to the imaging viewing angle and time to complete payload imaging control.

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