A method for judging validity of spaceborne AIS guiding imaging data based on position revision

Abstract

A kind of satellite-based AIS guiding imaging data validity discrimination method based on position revision, first, the message type of AIS message is obtained in a certain time period, whether the message belongs to position report type is judged according to message format, if it belongs to, continue to extract MMSI, latitude and longitude information according to message format, and store record AIS message receiving UTC time and message receiving frequency, then according to the frequency information of AIS message measured multiple times, the rough position estimation information of ship is obtained using Doppler positioning algorithm, the latitude and longitude position information carried by Doppler positioning result and AIS message are compared, if they are not consistent, output warning, and give the position correction value of ship, then the latest effective position information of target ship after correction is used, the imaging calculation of ship position and SAR system is started, and the validity of the position message is judged according to the angle and time of SAR guiding imaging.The present application improves the effectiveness of satellite-based AIS message data used for guiding SAR imaging in AIS signal deception environment.

Description

Technical Field

[0001] This invention relates to a method for determining the validity of spaceborne AIS-guided imaging data based on location revision, which is mainly used for determining the location validity of spaceborne AIS messages used to guide SAR imaging. Background Technology

[0002] AIS messages are susceptible to data loss and errors during transmission due to obstacles and electromagnetic interference. Since the location information in AIS messages originates from GPS or BeiDou positioning devices, location errors may occur due to equipment malfunctions. Incorrect location information cannot provide accurate data support for maritime traffic condition prediction and maritime accidents, thus compromising safe navigation. Furthermore, abnormal vessels may falsely report their geographical locations, resulting in unpredictable tracks and position deception; therefore, AIS messages cannot be directly used to guide SAR imaging calculations.

[0003] Furthermore, for moving ship targets, on the one hand, the difference in data acquisition time will cause errors between the position data obtained by the satellite AIS demodulation and the actual position data of the ship. On the other hand, considering the Doppler displacement between the ship target and the satellite SAR, there are differences in Doppler between the position observations of the satellite SAR and AIS.

[0004] Currently, the main methods for detecting and repairing abnormal points in AIS message data locations are:

[0005] (1) The method based on a single ship and a single track uses data such as the position, speed and heading of a single ship to identify and repair position anomalies, but the identification of position anomalies depends on the discrimination model.

[0006] (2) The method based on track clustering relies on a large number of historical ship track clustering results. It mainly uses machine learning and data mining techniques to detect anomalies, identify abnormal points in ship position trajectories and repair them. This method requires a large amount of historical track data as support and cannot detect anomalies in newly arrived position trajectories.

[0007] (3) The Doppler information-based positioning method uses electromagnetic information in the radiation or reflection space of the target to locate and track the target. Compared with active positioning, it has the advantages of wide operating frequency band, long detection range, strong concealment, strong anti-interference and strong survivability.

[0008] Ship target surveillance technology based on spaceborne SAR and AIS has become a research hotspot in the field of marine surveillance, and is widely used in marine environmental governance, territorial sea management, and other fields, making large-scale marine ship target surveillance a reality. The accuracy and validity of AIS message location data directly affect the results of spaceborne SAR surveillance of marine ships. Therefore, the correct detection and validity of spaceborne AIS message location data are of paramount importance. Summary of the Invention

[0009] The technical problem solved by the present invention is to overcome the shortcomings of the prior art and provide a method for determining the validity of spaceborne AIS guided imaging data based on position revision. The technical problem solved is to improve the validity of spaceborne AIS message data used for guiding SAR imaging in the context of AIS signal deception.

[0010] The technical solution of this invention is:

[0011] A method for determining the validity of spaceborne AIS-guided imaging data based on location revision includes:

[0012] (1) Demodulate the AIS messages acquired within a certain time period, extract the message ID of the AIS message according to the AIS message format, and obtain the message type message that can be used for location reporting;

[0013] (2) Based on the message type message obtained in step (1), extract and calculate the ship's MMSI identification code, longitude, and latitude information to obtain the location information used for the location report message;

[0014] (3) Using the Doppler frequency shift positioning principle, the ship's position is calculated to obtain the ship's beacon position;

[0015] (4) Associate the latitude and longitude location information demodulated from the AIS message itself in step (2) with the ship beacon location calculated using Doppler frequency shift in step (3);

[0016] (5) Perform multiple correlation comparisons, eliminate false location information in AIS messages, retain messages with correct location information, and select the AIS message with the latest location as the valid guidance message;

[0017] (6) Based on the valid guidance message obtained in step (5), and in accordance with the guidance SAR imaging calculation process, start the imaging calculation mode.

[0018] (7) Based on the imaging calculation results in step (6), determine the validity of the location message-guided imaging, that is, determine whether it is a valid message for AIS-guided imaging.

[0019] Furthermore, step (3) utilizes the Doppler frequency shift positioning principle to calculate the AIS ship's position, specifically as follows:

[0020] (3.1) Calculate the location of ship beacons using the Doppler measurement equation;

[0021] (3.2) Introduce surface elevation constraints and repeat the positioning calculation N times to improve the positioning accuracy of the ship.

[0022] Furthermore, the Doppler measurement equations are used to calculate the location of the ship's beacon, specifically as follows:

[0023]

[0024] Where: FOA j f is the frequency signal measured by satellite at time j; f is the transmitted frequency signal; v s j r is the velocity of the satellite at time j. s j The position of satellite at time j; r b The position of the ship is ε; the measurement noise is c; the speed of light is c.

[0025] Assuming the frequency f of the ship's transmitted signal is a fixed value, then according to the Doppler positioning principle, we only need to obtain the ship's position information r at time j. b .

[0026] Furthermore, a surface elevation constraint is introduced, and the positioning calculation is repeated N times. Specifically, after obtaining the ship's latitude and longitude information in the geodetic coordinate system, the digital elevation constraint method is used to constrain the ship's height in the geodetic coordinate system. The ship's position in the geodetic coordinate system is updated using the new ship position in the geodetic coordinate system. This process is repeated multiple times until the accuracy requirements are met.

[0027] Furthermore,

[0028] Given the initial values ​​of the beacon and the initial value of the transmission frequency, the target is located. After obtaining the position, the latitude and longitude (B, L) are calculated, and the H is given using digital elevation.

[0029] The calculation process is as follows: Let Y = (B, L, f) T For the quantity to be estimated in the geodetic coordinate system, the linearized equation obtained by the nonlinear parameter estimation algorithm is as follows: In the formula, O represents the measured value, and C represents the theoretically calculated value of the observed quantity. Let be the partial derivative matrix of the observed theoretical values ​​with respect to (x, y, z). Let (x,y,z) be the partial derivative matrix of (B,L,f); given (B,L,H,f) T Initial values ​​are obtained by solving the linearized equations to calculate corrections and updating (B,L,f). T , by (B,L) T Using digital elevation data to determine H, iterate until the required accuracy is met.

[0030] Furthermore, step (5) involves comparing the two information, removing false location information from AIS messages, and retaining messages with correct location information. Specifically:

[0031] The ship position information extracted from AIS message parsing is correlated with the ship position information obtained by Doppler frequency shift positioning. The correlation calculation is performed twice in a row, and the position accuracy assessment and position correction value are given based on the calculation results.

[0032] Furthermore, the location data obtained by the two methods must be correlated and compared to satisfy |FOA-f AIS |<f T And |r s -r b |<r T Where FOA is the frequency of the signal measured by the satellite, f AIS f is the frequency at which the ship transmits signals. T To measure the threshold value of the frequency difference between the transmitted and transmitted signals, r s For the satellite's position, r b For the location of the AIS vessel, r T The radial distance threshold between the two is denoted as .

[0033] Furthermore, step (7), which determines the validity of the location message and whether it is a valid message for AIS-guided imaging, specifically involves:

[0034] (7.1) Upon receiving an instruction packet containing the target ship's MMSI identification code, the system enters the imaging calculation mode;

[0035] (7.2) After parsing and extracting the MMSI identification code from the message and matching it with the MMSI identification code of the target ship, the calculation of the relative position between the ship and the SAR is started, and the azimuth and elevation angles of the satellite pointing to the target ship at time Tc in the satellite's own system are obtained; time Tc is defined as the time when the SAR scanning angle can cover the ship.

[0036] (7.3) Determine whether the ship is within the SAR imaging area based on the relative position calculated in (7.2);

[0037] (7.4) When the ship's position is within the SAR imaging area, determine whether the imaging time difference Tc-Tp satisfies the AIS-guided SAR imaging time limit A≤Tc-Tp≤B; where Tp is the current time, and A and B are the minimum and maximum time thresholds, respectively.

[0038] (7.5) If the judgment condition in (7.4) is not met, the current position message is invalid. Obtain new message information, match the MMSI identification code of the new message with the MMSI identification code of the ship's injection package, and continue to guide the calculation of the imaging relationship.

[0039] (7.6) If the ship's position is not within the SAR imaging area in (7.3), and the target ship does not fall within the SAR imaging scanning angle range within the effective lock duration T1 of the ship's position information, then it is determined that the current relative position of the ship on the satellite does not meet the guidance imaging conditions, the currently locked ship position information is invalidated, and the message is reacquired for MMSI identification code matching.

[0040] Furthermore, this invention also proposes a position-corrected spaceborne AIS-guided imaging data validity determination system, comprising:

[0041] AIS message validity monitoring module: Demodulates AIS messages acquired within a certain time period, extracts the message ID of the AIS message according to the AIS message format, and obtains message types that can be used for location reporting; based on the acquired message types, it extracts and calculates the ship's MMSI identification code, longitude, and latitude information to obtain the location information used for location reporting messages;

[0042] Auxiliary positioning correction module: Utilizes the Doppler frequency shift positioning principle to perform positioning calculations on the ship's position and obtain the ship's beacon position;

[0043] The message location validity judgment module: associates the latitude and longitude location information demodulated from the AIS message itself with the ship beacon location calculated using Doppler frequency shift; performs multiple association comparisons, eliminates false location information in AIS messages, retains messages with correct location information, and selects the AIS message with the latest location as the valid guidance message;

[0044] Guided SAR Imaging Module: Based on the obtained valid guidance message, the module starts the imaging calculation mode according to the guided SAR imaging calculation process; based on the imaging calculation results, it determines the validity of the message guidance imaging at that location, that is, whether it is a valid message for AIS guided imaging.

[0045] The beneficial effects of this invention compared to the prior art are:

[0046] (1) The method of the present invention adopts the signal Doppler frequency shift positioning principle, which avoids the situation where AIS messages are deliberately defrauded and incorrect data is used to guide imaging;

[0047] (2) This invention improves the accuracy of Doppler measurement and positioning by using multiple iterations of elevation constraints;

[0048] (3) This invention combines the implementation process of specific engineering projects and designs multiple processes such as antenna coverage area, satellite attitude, satellite extrapolation orbit and imaging guidance process timing control in a unified manner, and provides an available implementation plan for engineering implementation.

[0049] (4) This invention uses the Doppler frequency shift positioning principle and the method of multiple iterations of elevation constraints to improve the accuracy of Doppler measurement positioning. The location information obtained by this method is compared with the location information obtained from AIS message parsing to eliminate false messages, thereby improving the effectiveness of AIS message data used to guide SAR imaging. Attached Figure Description

[0050] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0051] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0052] The challenge in determining the validity of spaceborne AIS-guided SAR imaging data lies in improving the accuracy and validity of the spaceborne AIS message data used for guiding SAR imaging, especially in situations involving location spoofing by abnormal vessels, data loss errors during AIS message transmission, and discrepancies between the acquired and actual positions due to rapid vessel movement. Doppler-based positioning utilizes electromagnetic information radiated or reflected in space to locate and track targets. Compared to active positioning, it offers advantages such as a wider operating frequency band, longer reconnaissance range, stronger concealment, and greater resistance to interference and survivability.

[0053] The technical principle of this invention is to determine the specific position information of a ship within a certain time using the Doppler frequency shift measurement principle, introduce a digital elevation constraint method, update the ship's position in the Earth-fixed coordinate system, and iterate multiple times until the accuracy requirements are met. The ship's position information obtained by this method is correlated with the ship's position information obtained by demodulating spaceborne AIS messages, and the results are calculated twice consecutively to determine the validity of the results. Then, based on the calculation results, a position accuracy assessment and a corrected value for the true position are given. Using the corrected position information, guided SAR imaging calculations are initiated. When all the different criteria of the guided imaging process are met, the position message is determined to be a valid spaceborne AIS message that can be used for guided imaging.

[0054] like Figure 1 As shown, this invention proposes a method for determining the validity of spaceborne AIS-guided imaging data based on position revision, comprising:

[0055] (1) Demodulate the AIS messages acquired within a certain time period, extract the message ID of the AIS message according to the AIS message format, and obtain the message type message that can be used for location reporting;

[0056] (2) Based on the message type message obtained in step (1), extract and calculate the ship's MMSI identification code, longitude, and latitude information to obtain the location information used for the location report message;

[0057] (3) Using the Doppler frequency shift positioning principle, the ship's position is calculated to obtain the ship's beacon position;

[0058] Specifically:

[0059] (3.1) Calculate the location of ship beacons using the Doppler measurement equation;

[0060]

[0061] Where: FOA j f is the frequency signal measured by satellite at time j; f is the transmitted frequency signal; v s j r is the velocity of the satellite at time j. s j The position of satellite at time j; r b The position of the ship is ε; the measurement noise is c; the speed of light is c.

[0062] Assuming the frequency f of the ship's transmitted signal is a fixed value, then according to the Doppler positioning principle, we only need to obtain the ship's position information r at time j. b .

[0063] (3.2) Introduce surface elevation constraints and repeat the positioning calculation N times to improve the positioning accuracy of the ship.

[0064] By introducing surface elevation constraints, the positioning calculation is repeated N times. Specifically, after obtaining the ship's latitude and longitude information in the geodetic coordinate system, the digital elevation constraint method is used to constrain the ship's height in the geodetic coordinate system. The ship's position in the geodetic coordinate system is updated using the new ship position in the geodetic coordinate system. This process is repeated multiple times until the accuracy requirements are met.

[0065] The specific calculations are as follows:

[0066] Given the initial values ​​of the beacon and the initial value of the transmission frequency, the target is located. After obtaining the position, the latitude and longitude (B, L) are calculated, and the H is given using digital elevation.

[0067] The calculation process is as follows: Let Y = (B, L, f) T For the quantity to be estimated in the geodetic coordinate system, the linearized equation obtained by the nonlinear parameter estimation algorithm is as follows: In the formula, O represents the measured value, and C represents the theoretically calculated value of the observed quantity. Let be the partial derivative matrix of the observed theoretical values ​​with respect to (x, y, z). Let (x,y,z) be the partial derivative matrix of (B,L,f); given (B,L,H,f) T Initial values ​​are obtained by solving the linearized equations to calculate corrections and updating (B,L,f). T , by (B,L) TUsing digital elevation data to determine H, iterate until the required accuracy is met.

[0068] (4) Associate the latitude and longitude location information demodulated from the AIS message itself in step (2) with the ship beacon location calculated using Doppler frequency shift in step (3);

[0069] (5) Perform multiple correlation comparisons, eliminate false location information in AIS messages, retain messages with correct location information, and select the AIS message with the latest location as the valid guidance message;

[0070] The two are compared and contrasted to remove messages with false location information from AIS messages and retain messages with correct location information. Specifically:

[0071] The ship position information extracted from AIS message parsing is correlated with the ship position information obtained by Doppler frequency shift positioning. The correlation calculation is performed twice in a row, and the position accuracy assessment and position correction value are given based on the calculation results.

[0072] The location data obtained by the two methods must be correlated and compared to satisfy |FOA-f AIS |<f T And |r s -r b |<r T Where FOA is the frequency of the signal measured by the satellite, f AIS f is the frequency at which the ship transmits signals. T To measure the threshold value of the frequency difference between the transmitted and transmitted signals, r s For the satellite's position, r b For the location of the AIS vessel, r T The radial distance threshold between the two is denoted as .

[0073] (6) Based on the valid guidance message obtained in step (5), and in accordance with the guidance SAR imaging calculation process, start the imaging calculation mode.

[0074] (7) Based on the imaging calculation results in step (6), determine the validity of the location message-guided imaging, that is, determine whether it is a valid message for AIS-guided imaging.

[0075] Specifically:

[0076] (7.1) Upon receiving an instruction packet containing the target ship's MMSI identification code, the system enters the imaging calculation mode;

[0077] (7.2) After parsing and extracting the MMSI identification code from the message and matching it with the MMSI identification code of the target ship, the calculation of the relative position between the ship and the SAR is started, and the azimuth and elevation angles of the satellite pointing to the target ship at time Tc in the satellite's own system are obtained; time Tc is defined as the time when the SAR scanning angle can cover the ship.

[0078] (7.3) Determine whether the ship is within the SAR imaging area based on the relative position calculated in (7.2);

[0079] (7.4) When the ship's position is within the SAR imaging area, determine whether the imaging time difference Tc-Tp satisfies the AIS-guided SAR imaging time limit A≤Tc-Tp≤B; where Tp is the current time, and A and B are the minimum and maximum time thresholds, respectively.

[0080] (7.5) If the judgment condition in (7.4) is not met, the current position message is invalid. Obtain new message information, match the MMSI identification code of the new message with the MMSI identification code of the ship's injection package, and continue to guide the calculation of the imaging relationship.

[0081] (7.6) If the ship's position is not within the SAR imaging area in (7.3), and the target ship does not fall within the SAR imaging scanning angle range within the effective lock duration T1 of the ship's position information, then it is determined that the current relative position of the ship on the satellite does not meet the guidance imaging conditions, the currently locked ship position information is invalidated, and the message is reacquired for MMSI identification code matching.

[0082] Example:

[0083] This invention provides a method for determining the validity of spaceborne AIS-guided imaging data based on location revision, the steps of which are as follows:

[0084] (1) Demodulate the AIS messages acquired within a certain time period and extract the ship static parameter message ID number according to the AIS message message format. Obtain messages of types 1, 2, 3, 18, 19, and 27 that can be used for position reporting, and save the ID messages of types 1, 2, and 3 for guiding imaging.

[0085] (2) In the location report message ID type message obtained in step (1), extract the ship's static parameters such as MMSI identification code, longitude, latitude and other information to obtain the location information used for the location report message. In specific implementation, the extracted MMSI is set to 413381260, longitude B046.9° and latitude L00.4°.

[0086] (3) The position of the AIS ship is calculated by using the Doppler frequency shift positioning principle.

[0087] In practice, it is assumed that the frequency f of the ship's transmitted signal at time j is fixed at 156.780MHz and the satellite speed v is... s =[v sx v sy v sz ] T Satellite position r s =[Xs Y s Z s ] T c = 2.99792458 × 10 8 m / s, the signal frequency FOA measured by the satellite at time j j =157.0MHz, find the position r of the ship in the geocentric coordinate system at time j. b =[r bx r by r bz ] T The ship's latitude and longitude in the geodetic coordinate system (B) are obtained by conversion. c ,L c H is calculated using digital elevation data and linear equations, and the process is iterated until the positioning error is within ±10km (positioning is limited to single-satellite single-orbit data).

[0088] (4) Combine the latitude and longitude location information (B0, L0) obtained from the AIS message demodulation in step (2) with the ship beacon location (B0, L0) calculated using Doppler frequency shift in step (3). c ,L c To link;

[0089] (5) Repeat the location information comparison in step (4) twice, discard false location information in the AIS message, retain the message with correct location information, and select the AIS message with the latest location as the valid guidance message. The location data comparison obtained by the two methods must meet |FOA sat -f AIS |<f T 、|r s -r b |<r T f T =25KHz, r T =1000km. After two comparisons, the location message obtained from demodulation was selected as the guidance message, with latitude and longitude of (B0, L0).

[0090] (6) Based on the valid location message obtained in step (5) and the guided SAR imaging calculation process, start the guided SAR imaging calculation mode.

[0091] (7) Based on the calculation results in step (6), determine the validity of the location message for guided imaging and whether it is a valid message for AIS guided imaging.

[0092] The specific steps are as follows:

[0093] (7.1) Upon receiving a command packet containing the target ship's MMSI number 413381260, the imaging calculation mode is activated;

[0094] (7.2) Parse and extract the MMSI in the message, which can be matched with the MMSI of the target ship. Start the calculation of the relative position relationship between the ship and the SAR, and obtain the azimuth angle θ = 0.279 and the elevation angle φ = -7.09 of the vector pointing to the target ship by the satellite at time Tc (time Tc is defined as the time when the SAR scanning angle can cover the ship).

[0095] (7.3) Determine whether the ship is located in the SAR imaging area based on the relative position calculated in (7.2); limit the SAR imaging azimuth angle range [θ1,θ2]=[-15.17,12.10]°, and the elevation angle range [φ1,φ2]=[-0.48,0.48]°, and determine whether the azimuth angle and elevation angle satisfy θ∈[θ1,θ2] and φ∈[φ1,φ2] respectively;

[0096] (7.4) In (7.3), when the ship's position is within the SAR imaging area, determine whether the imaging time difference Tc-Tp (Tp is the current time) satisfies the AIS-guided SAR imaging time limit A≤Tc-Tp≤B; let A=82s, B=91s.

[0097] (7.5) When (7.3) the ship is located within the SAR imaging area and (7.4) the time limit is met, the location message is a valid message for guiding imaging; in specific implementation, the azimuth angle θ = 0.279 and the elevation angle φ = -7.09 meet the angle range, and Tc-Tp = 85s meet the time limit, the message is a valid message for guiding imaging.

[0098] (7.6) If the time limit in (7.4) is not met, check if a new message is received; if a new message is received, repeat steps (7.2) to (7.5) to determine the validity of the message guidance; in specific implementation, if Tc-Tp=80s does not meet the time limit, repeat the steps to calculate from two angles to determine the validity of the new message.

[0099] (7.7) If the ship in (7.3) is not located within the SAR imaging area, and the target ship still does not fall within the SAR imaging angle range within the effective lock-on time T1, then it is determined that the current relative position of the ship on the satellite does not meet the guidance imaging conditions, the current locked ship position message is invalid, and a new message is acquired for MMSI matching. In specific implementation, T1 = 360s. If the two angles do not meet the imaging angle range, the message is invalidated, and a new ship position message is waited for for guidance imaging matching calculation. The longest guidance mission time T0 = 1h. If the two angles still do not meet the imaging angle range, the guidance imaging mode is exited.

[0100] By comparing and contrasting data, the validity of positioning messages suitable for guiding imaging is determined, preventing imaging failures due to AIS positioning errors and improving the success rate of guided imaging.

[0101] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A method for judging the validity of spaceborne AIS guiding imaging data based on position revision, characterized in that The method comprises the following steps: (1) demodulating AIS messages obtained in a certain time period, extracting message IDs of the AIS messages according to the message format of the AIS messages, and obtaining message type messages available for position reporting; (2) extracting the MMSI identification code, longitude and latitude information of a ship from the message type messages obtained in step (1) to obtain position information of the position reporting message; (3) performing positioning calculation on the position of the ship by using the Doppler frequency shift positioning principle to obtain the position of the ship beacon; (4) correlating the longitude and latitude position information demodulated from the AIS message in step (2) with the position of the ship beacon calculated by using the Doppler frequency shift in step (3); (5) performing multiple correlation comparisons, eliminating false position information of the AIS message, retaining the message with correct position information, and selecting the AIS message with the latest position as the effective guiding message; (6) starting the imaging calculation mode according to the effective guiding message obtained in step (5) and the guiding SAR imaging calculation process; (7) judging the effectiveness of the position message for guiding imaging, i.e., judging whether the position message is an effective message for guiding imaging according to the imaging calculation result in step (6); The step (3) utilizes the Doppler frequency shift positioning principle to perform positioning calculation on the position of the AIS ship, and specifically comprises the following steps: (3.1) performing positioning calculation on the ship beacon by using the Doppler measurement equation; (3.2) introducing a ground elevation constraint condition, and repeatedly performing positioning calculation N times to improve the positioning accuracy of the position of the ship; The step (3.1) utilizes the Doppler measurement equation to perform positioning calculation on the ship beacon, and specifically comprises the following steps: where: FOA j is the frequency signal measured at time for satellite j; f is the transmitted frequency signal; v s j is the velocity at time for satellite j; r s j is the position at time for satellite j; r b is the position of the vessel; ε is the measurement noise; c is the speed of light; If the frequency f of the signal emitted by the ship is a fixed value, then according to the Doppler positioning principle, only the position information r of the ship at time j is required b ; The step (3.2) introduces a ground elevation constraint condition, and repeatedly performs positioning calculation N times, and specifically comprises the following steps: after the longitude and latitude information of the ship in the geodetic coordinate system is obtained, the height of the ship in the geodetic coordinate system is constrained by using a digital elevation constraint method, the position of the ship in the new geodetic coordinate system is used to update the position of the ship in the earth-fixed coordinate system, and multiple iterations are performed until the accuracy requirement is met; The initial value of the beacon and the initial value of the transmission frequency are given to the target positioning, the longitude and latitude (B, L) are calculated after the position is obtained, and the H is given by using the digital elevation; The calculation process is: Y = (B, L, f) T The to-be-estimated quantity is in the earth coordinate system, and a linearization equation obtained by a nonlinear parameter estimation algorithm is In the formula, O is a measurement value, C is a theoretical calculation value of an observation value, is a partial derivative matrix of the observation value theoretical value with respect to (x, y, z), is a partial derivative matrix of (x, y, z) with respect to (B, L, f); given (B, L, H, f) T An initial value is obtained, a correction amount is calculated from the linearization equation, and (B, L, f) is updated T (B, L) T H is given by using a digital elevation, and iteration is performed until a precision requirement is met; The step (5) correlates and compares the two, eliminates the false position information of the AIS message, and retains the message with correct position information, and specifically comprises the following steps: The ship position information extracted from the AIS message analysis is correlated with the ship position information obtained by using the Doppler frequency shift positioning, and continuous correlation measurement is performed twice, and the position accuracy evaluation and position correction value are given according to the measurement result; The position data obtained by the two methods need to be correlated and compared, and the correlation comparison needs to satisfy |FOA-f AIS |<f T and |r s -r b |<r T where FOA is the frequency of the signal measured by the satellite, f AIS is the frequency of the signal transmitted by the ship, f T is the threshold of the difference between the measured signal and the transmitted signal frequency, r s is the position of the satellite, r b is the position of the AIS ship, r T is the threshold of the radial distance between the two; The step (7) judges the effectiveness of the position message, and judges whether the position message is an effective message for guiding imaging, and specifically comprises the following steps: (7.1) entering the imaging calculation mode after receiving the instruction packet containing the MMSI identification code of the target ship; (7.2) analyzing and extracting the MMSI identification code in the message, and after the matching of the MMSI identification code with the target ship MMSI identification code is completed, the relative position calculation between the ship and the SAR is started, and the azimuth and pitch angle of the satellite pointing vector to the target ship in the satellite body at the time Tc is obtained; Tc is defined as the time when the SAR scanning angle can cover the ship; (7.3) judging whether the ship is located in the SAR imaging area according to the relative position calculated in step (7.2); (7.4) When the ship position is located in the SAR imaging area, it is judged whether the imaging time difference Tc-Tp satisfies the AIS guided SAR imaging time limit A≤Tc-Tp≤B; wherein Tp is the current time, and A and B are the minimum and maximum values of the time threshold, respectively; (7.5) If the judgment condition in (7.4) is not satisfied, the current position message is invalid, new message information is obtained, the MMSI identification code of the new message is matched with the MMSI identification code of the ship on the package, and the calculation of the guided imaging relationship is continued; (7.6) When the ship position is not in the SAR imaging area in (7.3), the target ship does not fall into the SAR imaging scanning angle range within the effective time T1 of the ship position information locking, it is judged that the current satellite ship relative position does not satisfy the guided imaging condition, the current locked ship position information is invalid, and the message is reacquired for MMSI identification code matching.

2. A discrimination system based on the position revision satellite AIS guiding imaging data validity discrimination method of claim 1, characterized in that It includes: AIS message validity monitoring module: demodulate the AIS message obtained within a certain time period, extract the message ID of the AIS message according to the AIS message format, and obtain the message type message that can be used for position reporting; according to the obtained message type message, the ship MMSI identification code, longitude and latitude information are extracted, and the position information of the position reporting message is obtained; Auxiliary positioning position correction module: using the Doppler frequency shift positioning principle, the ship position is calculated to obtain the ship beacon position; Message position validity judgment module: associate the latitude and longitude position information demodulated by the AIS message with the ship beacon position calculated by the Doppler frequency shift; Multiple correlation comparison is carried out, false position information of the AIS message is eliminated, correct position information of the AIS message is retained, the latest position AIS message is selected as the effective guide message; Guided SAR imaging module: according to the obtained effective guide message, the imaging calculation mode is started according to the guided SAR imaging calculation process; according to the imaging calculation result, it is judged whether the position message is an effective guide image, that is, whether it is an effective AIS guide image.

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