GNSS MEOSAR positioning enhancement method and system based on calibration station

Abstract

The invention relates to a GNSS MEOSAR positioning enhancement method and system based on a calibration station. The method comprises the following steps: establishing a networked calibration station; a satellite communication link is established between each calibration station and a medium-orbit satellite of the MEOSAR system, and a search and rescue calibration signal is transmitted to the medium-orbit satellite; the distress beacon sends a search and rescue beacon signal to a medium orbit satellite of the MEOSAR system; the medium orbit satellite forwards the received search and rescue beacon signal and the search and rescue calibration signal to a ground central station; the ground center station receives the search and rescue beacon signals and the search and rescue calibration signals forwarded by the multiple satellites to carry out combined positioning processing; in the combined positioning processing, a calibration station is matched for the distress beacon, and an error correction factor for positioning the distress beacon is calculated by matching a search and rescue calibration signal of the calibration station. According to the invention, the differential positioning enhancement of the calibration station data in the GNSS MEOSAR system is realized, and the positioning precision and reliability of medium-orbit satellite search and rescue are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of global navigation satellite system positioning, and more particularly to a GNSS MEOSAR positioning enhancement method and system based on a calibration station. Background Art

[0002] The COSPAS-SARSAT system is a global public welfare satellite distress alarm system jointly developed by the United States, the Soviet Union, France and Canada in 1979. Its purpose is to provide accurate, timely and reliable distress alarm and positioning services to help search and rescue agencies assist people in distress to receive timely and effective rescue. It is the main satellite communication means of the Global Aircraft Distress and Safety System (GADSS) advocated by the International Civil Aviation Organization (ICAO).

[0003] In recent years, in order to better serve the search and rescue needs of human beings in emergency situations, various countries have developed the Medium Earth Orbit Search and Rescue System (MEOSAR). The MEOSAR system combines traditional satellite navigation technology with search and rescue applications to improve the efficiency and response speed of search and rescue operations. When encountering an emergency, such as a plane crash, a ship in distress, or getting lost in the mountains, MEOSAR can quickly locate the accident site, thereby speeding up rescue.

[0004] However, the traditional MEOSAR system may have positioning errors in some cases, which may be due to interference in signal propagation, the influence of the atmosphere on the signal, or various other reasons. To solve this problem, researchers began to explore how to improve the positioning accuracy of MEOSAR. Summary of the invention

[0005] In view of the above analysis, the present invention aims to disclose a GNSS MEOSAR positioning enhancement method and system based on a calibration station to improve the accuracy and reliability of search and rescue signal beacon positioning.

[0006] The present invention discloses a GNSS MEOSAR positioning enhancement method based on a calibration station, comprising:

[0007] Establishing a networked calibration station; each of the calibration stations establishes a satellite communication link with a medium-orbit satellite of the MEOSAR system and transmits a search and rescue calibration signal to the medium-orbit satellite;

[0008] The distress beacon sends a search and rescue beacon signal to the medium-orbit satellite of the MEOSAR system;

[0009] The medium-orbit satellite forwards the received search and rescue beacon signal and search and rescue calibration signal to the ground center station;

[0010] The ground center station receives the search and rescue beacon signals and search and rescue calibration signals forwarded by multiple satellites for joint positioning processing;

[0011] In the joint positioning process, a calibration station is matched for the distress beacon, and the error correction factor used for the distress beacon positioning is calculated by matching the search and rescue calibration signal of the calibration station.

[0012] Furthermore, it also includes:

[0013] Track and process the search and rescue beacon signals of the same distress beacon received continuously to improve the positioning accuracy of the distress beacon;

[0014] In the search and rescue beacon signal tracking process, the ground central station continuously tracks the search and rescue beacon signal of the calibration station matched with the distress beacon and updates the error correction factor.

[0015] Furthermore, the calibration stations are set up at key geographical locations required for rescue; low-latency and stable communication links are established between each calibration station and the ground central station;

[0016] The communication link transmits the operating status of each calibration station, timestamp, precise geometric distance between each calibration station and the satellite, and clock advance of the calibration station relative to the ground central station to the ground central station in real time.

[0017] Furthermore, the calibration station is equipped with a high-precision GNSS receiver and a transmitting device capable of sending beacon signals to medium-orbit satellites; and the calibration station transmits search and rescue calibration signals to medium-orbit satellites regularly or as needed;

[0018] The search and rescue calibration signal of each calibration station encodes information including the station's precise geographic coordinate location and transmission timestamp.

[0019] Furthermore, the joint positioning process includes:

[0020] 1) The ground center station uses the search and rescue beacon signals forwarded by multiple medium-orbit satellites to obtain the rough positioning coordinates of the distress beacon using the arrival time positioning method;

[0021] 2) The ground center station calculates the distance between the search and rescue beacon and each calibration station based on the rough positioning coordinates of the search and rescue beacon and the position coordinates of each calibration station demodulated from the search and rescue calibration signal received from the medium-orbit satellite;

[0022] 3) The ground center station selects a calibration station that meets the matching distance threshold range and is closest to the search and rescue beacon location, and matches it with the distress beacon;

[0023] 4) The ground center station calculates the error correction factor for pseudo-range calculation of each medium-orbit satellite participating in the joint positioning process;

[0024] 5) The ground central station uses the error correction factor to perform error correction in the distress beacon joint positioning processing, and adopts the arrival time positioning method to obtain the precise position coordinates of the distress beacon; in the error correction process, the error correction factor closest to the distress beacon transmission time is used for correction.

[0025] Furthermore, the matching distance threshold range satisfies that: within the range, the distress beacon and the calibration station establish communication links with at least four identical medium-orbit satellites, and each medium-orbit satellite establishes a communication link with a ground central station.

[0026] Furthermore, the medium-orbit satellite S i The error correction factor PRC i (T 0 ):

[0027]

[0028] Among them, TOA i is the i-th medium orbit satellite S i The observed value of the arrival time of the forwarded rescue calibration signal, i = 1, 2, ..., n, indicating that there are n medium-orbit satellites forwarding the rescue signal sent by the beacon; δ T L i It's TOA i The error of the observed quantity; c is the speed of light; (X i ,Y i ,Z i ) is a medium orbit satellite S i Coordinates in the Earth-fixed coordinate system; (X g ,Y g ,Z g ) is the coordinate of the site of the ground central station in the ground-fixed coordinate system; (X b ,Y b ,Z b ) is the coordinate of the calibration station in the earth-fixed coordinate system; T 0 is the transmission time of the search and rescue calibration signal, ΔT b is the advance of the calibration station clock relative to the ground station clock; ε i is the correction amount.

[0029] Furthermore, the ground central station uses the error correction factor to perform error correction on the distress beacon joint positioning process, and the differential pseudorange of the distress beacon is calculated. for:

[0030]

[0031] in, For distress beacons at t 0The search and rescue beacon signal transmitted at any time is transmitted from the distress beacon to the medium-orbit satellite S i , and then from the medium orbit satellite S i Pseudorange transmitted to the ground central station; PRC i (T 0 ) is a medium orbit satellite S i In T 0 Error correction factor PRC at time i (T 0 );T 0 The time is close to the time t 0 ; (X, Y, Z) are the position coordinates of the distress beacon, and ΔT is the advance of the distress beacon clock relative to the ground station clock.

[0032] Furthermore, in the arrival time positioning method, the end of the same bit position of the search and rescue calibration signal and the search and rescue beacon signal is used as the reference point of the time of arrival to calculate the time of arrival at the ground central station.

[0033] The present invention also discloses a positioning enhancement system for implementing the GNSS MEOSAR positioning enhancement method based on a calibration station as described above, comprising: a ground central station, a distress beacon and a calibration station arranged in a network;

[0034] Each of the calibration stations establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and transmits a search and rescue calibration signal to the medium-orbit satellite;

[0035] The distress beacon establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and sends a search and rescue beacon signal to the medium-orbit satellite;

[0036] The ground central station receives and performs joint positioning processing based on the search and rescue beacon signals and search and rescue calibration signals received and forwarded by multiple medium-orbit satellites; in the joint positioning processing, the distress beacon is matched with the calibration station, and the error correction factor used for locating the distress beacon is calculated by matching the search and rescue calibration signal of the calibration station.

[0037] The present invention can achieve one of the following beneficial effects:

[0038] The GNSS MEOSAR positioning enhancement method and system based on calibration stations disclosed in the present invention realize the differential positioning enhancement of calibration station data in the GNSS MEOSAR system, greatly improving the positioning accuracy and reliability of medium-orbit satellite search and rescue. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0040] Figure 1 The figure is a flow chart of a GNSS MEOSAR positioning enhancement method based on a calibration station in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used to illustrate the principles of the present invention together with the embodiments of the present invention.

[0042] Embodiment 1

[0043] An embodiment of the present invention discloses a GNSS MEOSAR positioning enhancement method based on a calibration station, such as Figure 1 As shown, including:

[0044] Step S1, setting up a networked calibration station; each of the calibration stations establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system, and transmits a search and rescue calibration signal to the medium-orbit satellite;

[0045] Step S2, the distress beacon sends a search and rescue beacon signal to the medium-orbit satellite of the MEOSAR system;

[0046] Step S3: The medium-orbit satellite forwards the received search and rescue beacon signal and search and rescue calibration signal to the ground center station;

[0047] Step S4: The ground central station receives the search and rescue beacon signals and the search and rescue calibration signals forwarded by multiple satellites to perform joint positioning processing;

[0048] In the joint positioning process, the distress beacon is matched with a calibration station, and the error correction factor for the distress beacon positioning is calculated by matching the search and rescue calibration signal of the calibration station;

[0049] Step S5, tracking and processing the search and rescue beacon signals of the same distress beacon received continuously to improve the positioning accuracy of the distress beacon;

[0050] Step S6: In the search and rescue beacon signal tracking process, the ground central station continuously tracks the search and rescue beacon signal of the calibration station matched with the distress beacon and updates the error correction factor.

[0051] Furthermore, the calibration station is set up at a key geographical location required for rescue; areas with open terrain and clear vision are preferentially selected as the construction location of the calibration station to ensure unobstructed communication with the medium-orbit satellite.

[0052] Specifically, the calibration station is equipped with a high-precision GNSS receiver and a transmitting device capable of sending beacon signals to medium-orbit satellites; and the calibration station transmits search and rescue calibration signals to medium-orbit satellites regularly or as needed.

[0053] The calibration station can provide high-precision location information to the calibration station through a high-precision GNSS receiver (X b ,Y b ,Z b ) The transmitting equipment establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system, using the unified frequency specified by the International Search and Rescue Association for beacons, namely 406MHz; and transmits search and rescue calibration signals regularly or as needed.

[0054] The search and rescue calibration signal of each calibration station encodes the station's precise geographic coordinates, transmission timestamp and other related information.

[0055] In the calibration station, an atomic clock or other high-precision clock is used to add a timestamp to the signal to ensure that the time is accurately synchronized with the ground central station. This ensures that the receiving end can accurately obtain the signal's transmitting source information.

[0056] Preferably, a low-latency and stable communication link is established between each calibration station and the ground central station; the communication link transmits the calibration station operating status, timestamp, the precise geometric distance between each calibration station and the satellite, and the clock advance of the calibration station relative to the ground central station to the ground central station in real time, so that the central station can perform joint positioning processing.

[0057] Through the communication link, the ground central station can also regularly calibrate the equipment of the calibration station to ensure that the beacon signals sent are accurate.

[0058] In step S2, the distress beacon sends a search and rescue beacon signal to an orbiting satellite in the MEOSAR system;

[0059] The distress beacon is a MEOSAR system beacon; when a ship, vehicle, aircraft, etc. equipped with a MEOSAR system beacon is in distress, the MEOSAR system beacon can be activated by a trigger device to become a distress beacon that transmits a distress signal, and the search and rescue beacon signal is sent to a medium-orbit satellite using the unified frequency of 406MHz specified by the International Search and Rescue Association for beacons;

[0060] In step S3, after receiving the 406MHz beacon signal transmitted by the calibration station or the distress beacon, the search and rescue payload carried by the medium-orbit satellite will forward the signal to the L or S band through the search and rescue payload carried by it, and send it to the central station via the downlink channel.

[0061] Specifically, the joint positioning process in step S4 includes the following sub-steps:

[0062] 1) The ground center station uses the search and rescue beacon signals forwarded by multiple medium-orbit satellites to obtain the rough positioning coordinates (X c ,Y c ,Zc ); The influence of error terms including atmospheric delay is not considered in the process of coarse positioning;

[0063] In the process of coarse positioning, the ground center station uses the i-th medium orbit satellite S i The observed time of arrival of the forwarded rescue beacon signal TOA i ', and the transmission time T of the rescue signal obtained by demodulating the rescue beacon signal 0 ', obtain the rescue beacon signal transmitted from the distress beacon to the medium orbit satellite S i The time to receive at the central station; the coordinates of the ground central station (ME0LUT) in the ground-fixed coordinate system (X g ,Y g ,Z g ) It is known that the i-th medium orbit satellite S i The coordinates in the Earth-fixed coordinate system (X i ,Y i ,Z i ) can be obtained by demodulating the search and rescue beacon signal.

[0064] Based on the above known information, the arrival time positioning method (TOA) is used to obtain the rough positioning coordinates (X c ,Y c ,Z c Since the atmospheric delay error information is not processed during the coarse positioning process, the position coordinate (X c ,Y c ,Z c ) are the approximate coordinates of the distress beacon, but the location is not precise.

[0065] 2) The ground center station calculates the distance between the search and rescue beacon and each calibration station based on the rough positioning coordinates of the search and rescue beacon and the position coordinates of each calibration station demodulated from the search and rescue calibration signal received from the medium-orbit satellite;

[0066] 3) The ground center station selects a calibration station that meets the matching distance threshold range and is closest to the search and rescue beacon location, and matches it with the distress beacon;

[0067] The matching distance threshold range satisfies: within the range, the distress beacon and the calibration station can establish communication links with at least four identical medium-orbit satellites, and each medium-orbit satellite can establish a communication link with a ground central station.

[0068] 4) The ground center station calculates the error correction factor for pseudo-range calculation of each medium-orbit satellite participating in the joint positioning process;

[0069] The medium-orbit satellites participating in the joint positioning processing select at least four medium-orbit satellites from the medium-orbit satellites that simultaneously establish communication links with the distress beacon, the calibration station and the ground central station.

[0070] The search and rescue calibration signal is transmitted from the calibration station to the medium-orbit satellite S i , and then from the medium orbit satellite S i The distance equation for propagation to the ground central station can be described as:

[0071]

[0072] The equation combines the transmission time of the search and rescue signal, the position of the satellite and the calibration station, and other corrections such as atmospheric delay and clock error. i is the i-th medium orbit satellite S i The observed value of the arrival time of the forwarded rescue calibration signal, i = 1, 2, ..., n, indicating that there are n medium-orbit satellites forwarding the rescue signal sent by the beacon; δ T L i It's TOA i The error of the observed quantity. Generally, the physical quantity measured by instruments and equipment usually has errors; c is the speed of light; (X i ,Y i ,Z i ) is a medium orbit satellite S i The coordinates of the medium-orbit satellite use the earth-fixed coordinate system; (X g ,Y g ,Z g ) is the coordinate of the site of the ground center station ME0LUT of the medium-orbit satellite search and rescue system in the ground-fixed coordinate system; (X b ,Y b ,Z b ) is the coordinate of the calibration station in the earth-fixed coordinate system; T 0 is the transmission time of the search and rescue calibration signal, ΔT b is the advance of the calibration station clock relative to the ground station clock; ε i It is a correction factor, which mainly includes the correction factor of ionospheric and tropospheric delay, channel calibration correction and relativistic effect correction. The correction factor of ionospheric and tropospheric delay includes two parts: from the ground center station to the satellite and from the beacon to the satellite.

[0073] By transforming equation (1), we can get the satellite S expressed by equation (2): i The error correction factor PRC i (T 0 ):

[0074]

[0075] Satellite position (Xi ,Y i ,Z i ) can be obtained from the broadcast ephemeris, the calibration station position (X b ,Y b ,Z b ) and T 0 Obtained from the decoded information of the search and rescue calibration signal; the ground center station position (X g ,Y g ,Z g ) is known;

[0076] The clock advance ΔT can be obtained by establishing a low-delay stable communication link between the central station and each calibration station; TOA i Through observation, the signal transmission time T can be calculated 0 For medium orbit satellite S i Error correction factor for pseudorange calculations.

[0077] Preferably, the precise geometric distance between each calibration station and the satellite can be obtained through a low-latency and stable communication link. Then, the geometric distance can be substituted into formula (2) to calculate the error correction factor.

[0078] In special circumstances, when the quality of the communication link between the satellite and the calibration station is poor, a low-latency and stable communication link is used to enable the ground central station to obtain data to calculate the error correction factor, thereby ensuring the accuracy of the error correction factor.

[0079] 5) The ground central station uses the error correction factor to perform error correction in the distress beacon joint positioning processing, and adopts the arrival time positioning method to obtain the precise position coordinates of the distress beacon; in the error correction process, the error correction factor closest to the distress beacon transmission time is used for correction.

[0080] Distress beacon at t 0 The search and rescue beacon signal transmitted at any time is transmitted from the distress beacon to the medium-orbit satellite S i , and then from the medium orbit satellite S i The distance equation for propagation to the ground central station can be described as:

[0081]

[0082] in, is the i-th medium orbit satellite S i Observation of the arrival time of the forwarded rescue beacon signal, i = 1, 2, ..., n, indicating that there are n medium-orbit satellites that forwarded the rescue signal sent by the beacon; (X, Y, Z) is the position coordinates of the distress beacon; yes The error of the observation, is the correction amount; c is the speed of light.

[0083] Since the distance between the distress beacon and the matching calibration station is close, and the transmission time of the beacon signal is close, the distress beacon The error of the observation and correction amount and error correction factor PRC i (T 0 ) i The error of the observed quantity δ T L i and the correction value ε i Approximately equal. Then PRC i (T 0 ) as the differential term to eliminate the differential pseudorange of the distress beacon after the difference for:

[0084]

[0085] So far, the differential pseudorange The only unknowns are the position coordinates (X, Y, Z) of the distress beacon and ΔT. When performing joint positioning, the differential pseudoranges of at least four satellites are required. The position of the distress beacon can be accurately located.

[0086] Preferably, in the arrival time positioning method, the end of the same bit (for example, the 24th bit) is used as the reference point of the time of arrival for both the rescue calibration signal and the rescue beacon signal, and the time TOA of the search and rescue calibration signal and the search and rescue beacon signal arriving at the ground central station is calculated. i and

[0087] When n medium-orbit satellites are visible, the n positioning equations obtained are shown in equation (5):

[0088]

[0089] Where X = (x 1 ,...,x m ) is an unknown vector, which is 4 unknown numbers, representing the beacon coordinates (X, Y, Z) and the above-mentioned ΔT. is the multivariate error vector.

[0090] Preferably, the least squares Newton iteration method is used to solve the problem. By approaching the optimal solution one by one in this method, the positioning accuracy can be further improved, especially in the case of complex signal environment or large signal interference.

[0091] Specifically, in step S5, the search and rescue beacon signals of the same distress beacon that are continuously received are tracked and processed;

[0092] The ground center station continuously tracks the forwarding signal of the medium-orbit satellite that forwards the search and rescue beacon signal of the same distress beacon to the ground center station, thereby achieving continuous positioning of the distress beacon and tracking of the position of the distress beacon; during the tracking process, the use of existing satellite positioning and tracking algorithms can further improve the positioning accuracy.

[0093] Specifically, the error correction factor in the updating of the search and rescue beacon signal tracking process in step S6 includes:

[0094] The ground center station continuously tracks the calibration station, and forms a closed-loop transmission mechanism for the search and rescue calibration signal through the communication link from the calibration station to the medium-orbit satellite and then to the ground center station, as well as the low-latency and stable communication link from the calibration station to the ground center station; the error correction factor is continuously updated to make the error correction factor closer to the distress beacon positioning error term, thereby ensuring high reliability and positioning accuracy. In the algorithm part, an adaptive filtering mechanism can be introduced. The system automatically selects the best positioning algorithm and parameters according to the quality of the received signal to ensure the overall optimization of positioning accuracy.

[0095] In summary, the GNSS MEOSAR positioning enhancement method based on calibration stations in the embodiment of the present invention realizes the differential positioning enhancement of calibration station data in the GNSS MEOSAR system, greatly improving the positioning accuracy and reliability of medium-orbit satellite search and rescue.

[0096] Embodiment 2

[0097] An embodiment of the present invention discloses a positioning enhancement system for implementing the GNSS MEOSAR positioning enhancement method based on calibration stations as described in Embodiment 1, comprising: a ground central station, a distress beacon, and a calibration station arranged in a network;

[0098] Each of the calibration stations establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and transmits a search and rescue calibration signal to the medium-orbit satellite;

[0099] The distress beacon establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and sends a search and rescue beacon signal to the medium-orbit satellite;

[0100] The ground central station receives and performs joint positioning processing based on the search and rescue beacon signals and search and rescue calibration signals received and forwarded by multiple medium-orbit satellites; in the joint positioning processing, the distress beacon is matched with the calibration station, and the error correction factor used for locating the distress beacon is calculated by matching the search and rescue calibration signal of the calibration station.

[0101] The specific technical details and beneficial effects of this embodiment are the same as those in Embodiment 1. Please refer to them for details and will not be described in detail here.

[0102] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A GNSS MEOSAR positioning enhancement method based on calibration stations. It is characterized in that include: Establish a networked calibration station; Each of the calibration stations establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and transmits a search and rescue calibration signal to the medium-orbit satellite; The distress beacon sends a search and rescue beacon signal to the medium-orbit satellite of the MEOSAR system; The medium-orbit satellite forwards the received search and rescue beacon signal and search and rescue calibration signal to the ground center station; The ground center station receives the search and rescue beacon signals and search and rescue calibration signals forwarded by multiple satellites for joint positioning processing; In the joint positioning process, a calibration station is matched for the distress beacon, and the error correction factor used for the distress beacon positioning is calculated by matching the search and rescue calibration signal of the calibration station.

2. The GNSS MEOSAR positioning enhancement method based on the calibration station according to claim 1, It is characterized in that Also includes: Track and process the search and rescue beacon signals of the same distress beacon received continuously to improve the positioning accuracy of the distress beacon; The ground center station continuously tracks the search and rescue beacon signal of the matching calibration station; and updates the error correction factor in the search and rescue beacon signal tracking process.

3. The GNSS MEOSAR positioning enhancement method based on the calibration station according to claim 1 or 2, It is characterized in that A low-latency and stable communication link is established between the ground central station and each calibration station; the communication link transmits the operating status of each calibration station, timestamp, precise geometric distance between each calibration station and the satellite, and clock advance of the calibration station relative to the ground central station to the ground central station in real time.

4. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 3, It is characterized in that The networked calibration stations are equipped with high-precision GNSS receivers and transmitters capable of sending beacon signals to medium-orbit satellites; The calibration station transmits search and rescue calibration signals to the medium-orbit satellite regularly or as needed; The search and rescue calibration signal of each calibration station encodes information including the station's precise geographic coordinate location and transmission timestamp.

5. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 3, It is characterized in that The joint positioning process comprises: 1) The ground center station uses the search and rescue beacon signals forwarded by multiple medium-orbit satellites to obtain the rough positioning coordinates of the distress beacon using the arrival time positioning method; 2) The ground center station calculates the distance between the search and rescue beacon and each calibration station based on the rough positioning coordinates of the search and rescue beacon and the position coordinates of each calibration station demodulated from the search and rescue calibration signal received from the medium-orbit satellite; 3) The ground center station selects the calibration station closest to the search and rescue beacon that meets the matching distance threshold range and matches it with the distress beacon; 4) The ground center station calculates the error correction factor for pseudo-range calculation of each medium-orbit satellite participating in the joint positioning process; 5) The ground central station uses the error correction factor to perform error correction in the distress beacon joint positioning processing, and adopts the arrival time positioning method to obtain the precise position coordinates of the distress beacon; in the error correction process, the error correction factor closest to the distress beacon transmission time is used for correction.

6. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 5, It is characterized in that The matching distance threshold range satisfies: within the range, the distress beacon and the calibration station establish communication links with at least four identical medium-orbit satellites, and each medium-orbit satellite establishes a communication link with a ground central station.

7. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 5, It is characterized in that Orbital Satellite S i The error correction factor PRC i (T 0 ): Among them, TOA i is the i-th medium orbit satellite S i The observed value of the arrival time of the forwarded rescue calibration signal, i = 1, 2, ..., n, indicating that there are n medium-orbit satellites forwarding the rescue signal sent by the beacon; δ T L i It's TOA i The error of the observed quantity; c is the speed of light; (X i ,Y i ,Z i ) is a medium orbit satellite S i Coordinates in the Earth-fixed coordinate system; (X g ,Y g ,Z g ) is the coordinate of the site of the ground central station in the ground-fixed coordinate system; (X b ,Y b ,Z b ) is the coordinate of the calibration station in the earth-fixed coordinate system; T 0 is the transmission time of the search and rescue calibration signal, ΔT b is the advance of the calibration station clock relative to the ground station clock; ε i is the correction amount.

8. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 7, It is characterized in that The ground central station uses the error correction factor to perform error correction on the distress beacon joint positioning process, and the differential pseudorange of the distress beacon is calculated. for: in, For distress beacons at t 0 The search and rescue beacon signal transmitted at any time is transmitted from the distress beacon to the medium-orbit satellite S i , and then from the medium orbit satellite S i Pseudorange transmitted to the ground central station; PRC i (T 0 ) is a medium orbit satellite S i In T 0 Error correction factor PRC at time i (T 0 );T 0 The time is close to the time t 0 ; (X, Y, Z) are the position coordinates of the distress beacon, and ΔT is the advance of the distress beacon clock relative to the ground station clock.

9. The GNSS MEOSAR positioning enhancement method based on a calibration station according to claim 7, It is characterized in that In the arrival time positioning method, the end of the same bit position is used as the reference point of the arrival time for both the search and rescue calibration signal and the search and rescue beacon signal to calculate the arrival time at the ground center station.

10. A positioning enhancement system for implementing the GNSS MEOSAR positioning enhancement method based on a calibration station as described in any one of claims 1 to 9, It is characterized in that include: Ground central station, distress beacon and networked calibration stations; Each of the calibration stations establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and transmits a search and rescue calibration signal to the medium-orbit satellite; The distress beacon establishes a satellite communication link with the medium-orbit satellite of the MEOSAR system and sends a search and rescue beacon signal to the medium-orbit satellite; The ground central station receives and performs joint positioning processing based on the search and rescue beacon signals and search and rescue calibration signals received and forwarded by multiple medium-orbit satellites; in the joint positioning processing, the distress beacon is matched with the calibration station, and the error correction factor used for locating the distress beacon is calculated by matching the search and rescue calibration signal of the calibration station.

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