A static target calibration method for airborne radar system based on POS

Abstract

The invention discloses a static target calibration method for an airborne radar system based on POS, and belongs to the technical field of SARMTI reconnaissance and surveillance radars carried by unmanned aerial vehicles. The static target calibration method for an unmanned aerial vehicle radar system based on POS efficiently and conveniently solves the problem that each set of traditional unmanned aerial vehicle SARMTI reconnaissance and surveillance radar equipment must be calibrated for installation errors when installed, resulting in high system maintenance time and cost, and even reducing the combat effectiveness of the equipment, thereby greatly saving equipment maintenance time and cost, and improving the maintainability and combat effectiveness of the equipment.

Description

Technical Field

[0001] The invention relates to the technical field of unmanned aerial vehicle-borne SARMTI reconnaissance and surveillance radar technology, and in particular to a static target calibration method for an airborne radar system based on POS. Background Art

[0002] With the rapid development of electronic communication technology, SARMTI reconnaissance and surveillance radar technology suitable for UAV platforms has developed rapidly, and its functions and performance have been continuously enhanced, greatly improving its combat effectiveness and survivability in the future unmanned battlefield. The UAV-mounted SARMTI reconnaissance and surveillance radar system has the characteristics of all-day, all-weather, long-distance, large-range, and high-resolution. It is developing in the direction of multi-function, lightweight, and high reliability. It is one of the indispensable intelligence acquisition equipment in the future unmanned combat scene.

[0003] However, due to the strict installation position and space restrictions of the carrier platform, there will inevitably be installation errors between the radar equipment and the carrier platform, which will affect the radar system's high-precision positioning and tracking of targets. It is necessary to calibrate and correct the errors when each set of equipment is installed, which will greatly increase the maintenance time and cost of the airborne radar system and reduce the combat effectiveness of the equipment. It is urgent to propose an efficient and convenient base-level static calibration method. To this end, a static calibration method for airborne radar systems based on POS is proposed. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to solve the problems of long maintenance time, high cost and low combat effectiveness of installation error calibration between unmanned aerial vehicle (UAV) radar system and carrier platform, and provide a static target calibration method for airborne radar system based on POS.

[0005] The present invention solves the above technical problems through the following technical solutions, and the present invention comprises the following steps:

[0006] S1: Install a prism on the inertial measurement unit of the POS system and calibrate the installation error of the prism's X, Y, and Z directions and the inertial measurement unit's X, Y, and Z directions;

[0007] S2: Control the normal direction of the radar system antenna array through the servo turntable to achieve 360° rotation of the radar azimuth and perform initial zero position control correction of the antenna;

[0008] S3: By measuring and calculating the error angle between the normal direction of the radar system antenna array and the X-axis direction when the prism on the inertial measurement unit is installed, the initial zero-position pointing angle of the antenna is adjusted until the calibration accuracy requirements are met, thereby realizing the indoor static target calibration of the radar system.

[0009] Furthermore, the radar system includes an antenna unit, a servo turntable, and a processing unit; the antenna unit is used to generate and radiate electromagnetic waves and receive reflected electromagnetic wave signals; the servo turntable is used to control the direction and azimuth of the antenna unit to rotate 360°; the processing unit is used to perform signal and data processing, remote control and telemetry command distribution, and equipment status monitoring.

[0010] Furthermore, in the step S1, the POS system is installed inside the servo turntable, and includes an inertial measurement unit, a navigation solution module, and a satellite navigation antenna; the inertial measurement unit is used to measure the angular velocity and acceleration information of the radar, collect real-time motion information of the carrier platform and provide it to the navigation solution module; the navigation solution module is used to use the measurement value of the satellite navigation antenna and the measurement information of the inertial measurement unit for real-time combined solution, obtain the position, heading, speed and attitude information of the carrier platform, and transmit it to the radar system in real time for storage and processing.

[0011] Furthermore, in step S1, the prism is a hexahedral prism, each face of which is a plane, and two connected faces are perpendicular to each other.

[0012] Furthermore, the specific process of step S1 is as follows:

[0013] S11: The inertial measurement unit with the prism installed is fixed on the servo turntable, and the angle between the normal line of a certain surface of the prism and the north direction of the geographic coordinate system is measured using an autocollimation theodolite, where the normal line of the surface is perpendicular to the X-axis direction of the inertial measurement unit;

[0014] S12: Use an autocollimation theodolite to measure the vertical angle between the normals of two adjacent vertical surfaces of the prism (in the same direction as the X-axis of the IMU) and the horizontal plane of the geographic coordinate system, and calculate the attitude angles of the prism in the X, Y, and Z directions;

[0015] S13: Using the four-position method to collect the inertial measurement unit to obtain the initial position X, Y, and Z direction attitude angles;

[0016] S14: using the prism attitude angle and the inertial measurement unit attitude angle obtained by measurement and calculation, subtracting each other to calibrate and correct the installation errors of the prism and the inertial measurement unit in the X, Y, and Z directions.

[0017] Furthermore, in step S12, according to the relative rotation relationship between the geographic coordinate system and the prism carrier coordinate system, the attitude angle between the prism carrier coordinate system and the geographic coordinate system is recorded as θ0, γ0, but:

[0018]

[0019] in:

[0020]

[0021] Then we have:

[0022]

[0023] According to the above formula, x b0 and b0 The projection relationship of the axis in the geographic coordinate system, calculate the x b0 and b0 The angles between the axes and the geographic horizontal plane are as follows:

[0024]

[0025]

[0026]

[0027] Among them, ∠α1 and ∠α2 are the elevation angles measured by the autocollimation theodolite;

[0028] The autocollimation theodolite measures the vertical angle and horizontal angle between the vertical plane of the prism and the geographic horizontal plane by receiving the collimated light reflected by the prism.

[0029] Fix the inertial measurement unit equipped with prism on the X, Y, Z three-axis turntable so that the ABCD surface of the prism points to the 0 degree direction of the three-axis turntable, that is, when the outer frame axis of the three-axis turntable points to its own scale ring 0 degree, the mirror normal of the outer frame reflector of the three-axis turntable coincides with the true north direction, and the horizontal angle of the autocollimation theodolite passing through the collimation outer frame reflector is ∠Φ1, and the horizontal angle of the autocollimation theodolite when the prism mirror is collimated is ∠Φ2. At this time, the angle between the horizontal component of the prism mirror normal and the north direction of the geographic coordinate system is:

[0030]

[0031] Assume that the normal is aligned with the hexahedral prism y b0 The axes are parallel, then the angle between the horizontal component of the normal and the north direction of the geographic coordinate system is:

[0032]

[0033] Get the attitude angles of the prism in a certain measurement θ0,γ0, The installation deviation angle between the prism and the inertial measurement unit can be obtained by combining the attitude angle of the inertial measurement unit obtained at the same time.

[0034] Furthermore, in step S13, the specific process of the four-position method is as follows:

[0035] The fiber optic gyroscope of the IMU is used to measure the angular velocity components of the heading axis at positions 90° apart, which are ω1, ω2, ω3, and ω4 respectively. The following formula is used:

[0036]

[0037] From the above formulas, we can conclude that: Arranged:

[0038]

[0039] Among them, θ is the heading angle of the inertial measurement unit, and the horizontal attitude angle of the inertial measurement unit is calculated by the measurement value of the accelerometer, and the formula is as follows:

[0040]

[0041]

[0042] Among them, φ is the roll angle, γ is the pitch angle, A xg , A yg are the measurements of the x-axis and y-axis accelerometers respectively, and g is the acceleration due to gravity.

[0043] Furthermore, in the step S3, four points are marked as object points with a cross target on the antenna array surface of the antenna unit, and the cursor position of the autocollimation theodolite is reflected by the prism to the wall and marked as an image point. The autocollimation theodolite is used to measure the X, Y, and Z direction attitude values ​​of the object point and the image point respectively, and the deviation angle between the normal of a certain surface of the prism and the normal of the antenna array surface is obtained through processing and calculation, and the normal of the surface is perpendicular to the X-axis direction of the inertial measurement unit.

[0044] Compared with the prior art, the present invention has the following advantages: each set of SARMTI reconnaissance and surveillance radar carried by traditional unmanned aerial vehicles must be calibrated for installation errors when installed, resulting in high system maintenance time and cost, and even reducing the combat effectiveness of the equipment; the static target calibration method of the unmanned aerial vehicle radar system based on POS efficiently and conveniently solves this problem, greatly saves equipment maintenance time and cost, improves the maintainability and combat effectiveness of the equipment, and is worthy of promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the structure of the SARMTI reconnaissance and surveillance radar system carried by an unmanned aerial vehicle in an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the POS system structure in an embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of the interconnection between the radar system and the POS device in an embodiment of the present invention;

[0048] Figure 4 a is a schematic diagram of the structure of a hexahedral prism in an embodiment of the present invention;

[0049] Figure 4 b is a schematic diagram of the installation of the hexahedral prism structure on the IMU in an embodiment of the present invention;

[0050] Figure 5 a is a schematic diagram of the projection of ∠α1 in the X, Y, Z geographic coordinate system in an embodiment of the present invention;

[0051] Figure 5 b is a schematic diagram of the projection of ∠α2 in the X, Y, Z geographic coordinate system in an embodiment of the present invention;

[0052] Figure 6 a is a schematic diagram of the projection of the right normal component of the prism in an embodiment of the present invention;

[0053] Figure 6 b is a plan view of the X, Y, and Z three-axis turntable in an embodiment of the present invention;

[0054] Figure 7 is a schematic diagram of the axial direction of the IMU gyroscope in an embodiment of the present invention;

[0055] Figure 8 Schematic diagram of mutual aiming and transmission between antenna array prisms in an embodiment of the present invention;

[0056] Fig. 9 It is a schematic diagram of the "cross" target layout of the radar antenna array in an embodiment of the present invention;

[0057] Fig.10 It is a schematic diagram of the target calibration process in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0059] like Figure 1 As shown, it is a structural schematic diagram of the unmanned aerial vehicle SARMTI reconnaissance and surveillance radar system of the present invention. The unmanned aerial vehicle SARMTI reconnaissance and surveillance radar system is installed on an unmanned aerial vehicle (carrier platform). The system includes an antenna unit, a servo turntable (including a POS system), and a processing unit. The main function of the antenna unit is to generate and radiate electromagnetic waves and receive reflected electromagnetic wave signals; the servo turntable is used to control the direction and azimuth of the antenna unit to rotate 360°; the processing unit is mainly used for signal and data processing, remote control and telemetry command distribution, equipment status monitoring and other functions.

[0060] like Figure 2 As shown in FIG. 1 , it is a schematic diagram of the structure of the combined navigation positioning and orientation system (POS system) of the present invention. Figure 3 As shown, Figure 1 Schematic diagram of the interconnection between the radar system and POS equipment.

[0061] The integrated navigation positioning and orientation system (POS system) is installed inside the servo turntable, including an inertial measurement unit (IMU), a navigation solution module (PCS), and a satellite navigation antenna. The power module of the radar system outputs +5V to power the POS system. The satellite navigation antenna is used to receive Beidou / GPS / GNSS satellite information in real time. The inertial measurement unit is used to measure the angular velocity and acceleration information of the radar, collect the real-time motion information of the carrier platform and provide it to the navigation solution module. The navigation solution module uses the measurement values ​​of the antenna receiver (satellite navigation antenna) and the measurement information of the inertial measurement unit for real-time combined solution to obtain the high-precision position, heading, speed and attitude information of the carrier platform, and transmits it to the radar system in real time for storage and processing.

[0062] like Figure 4 As shown in a, it is a schematic diagram of the hexahedral prism structure. Figure 4 As shown in b, Figure 2 Schematic diagram of the installation of IMU and hexahedral prism in the POS system.

[0063] Each face of the hexahedral prism ABCD-A1B1C1D1 is a plane. Different from the total reflection prism used in surveying and mapping, no matter where the light comes from, the reflected light will be reflected back in parallel:

[0064] 1) The surface ABCD is approximately perpendicular to the x of the IMU b Axis, denoted as surface 1;

[0065] 2) The surface BB1C1C is approximately perpendicular to the y axis of the IMU. b Axis, denoted as surface 2;

[0066] 3) It is known that the perpendicularity between adjacent faces of a hexahedral prism is within 2” (strictly orthogonal);

[0067] 4) The attitude angle of the hexahedral prism is the three deflection angles of the body coordinate system composed of the three axes A1A, A1B1, and A1D1 relative to the geographic coordinate system.

[0068] The hexahedral prism and IMU are fixed by the designed mounting bracket (see the specific installation form for details). Figure 4 b), the ABCD plane is perpendicular to the x direction of the IMU. b Axis, installation error calibration is required, for specific implementation methods see Figure 5-7 illustrate.

[0069] like Figure 5 5a and 5b are schematic diagrams of projection of angles ∠α1 and ∠α2 in the X, Y, and Z geographic coordinate systems of the present invention, respectively. The X axis represents the east direction, the Y axis represents the sky direction, and the Z axis represents the north direction. ∠α1 and ∠α2 are the angles between the BB1C1C and ABCD surfaces of the prism and the horizontal plane of the geographic coordinate system.

[0070] When the autocollimation theodolite emits a light beam S0S1 perpendicular to the hexahedral prism mirror surface and is reflected back into the autocollimation theodolite by the hexahedral prism plane perpendicular to S0S1, a yellow cross can be seen in the autocollimation theodolite overlapping with the black cross in the mirror. At this time, the optical axis is perpendicular to both the hexahedral prism surface and the autocollimation theodolite mirror surface. The vertical angle ∠α1 rotated by the autocollimation theodolite is the angle between the surface BB1C1C and the geographic horizontal plane, which is also the angle between the normal AB of the surface BB1C1C and the geographic horizontal plane, that is, the angle between a horizontal axis of the hexahedral prism carrier system and the horizontal plane of the geographic coordinate system; the same applies to the collimation of the other surface.

[0071] According to the process of aligning the prism mirror surface by the autocollimation theodolite, the angle between the two mutually perpendicular mirror surfaces of the prism and the horizontal plane of the geographic coordinate system can be obtained, which is recorded as ∠α1 and ∠α2. At the same time, ∠α1 and ∠α2 are also the angles between the two horizontal axes of the carrier system formed by the hexahedral prism and the horizontal plane of the geographic coordinate system.

[0072] According to the relative rotation relationship between the geographic coordinate system and the hexahedral prism carrier system, the hexahedral prism carrier system (ox b0 y b0 z b0 , right front upper) and the geographic coordinate system have an attitude angle of θ0,γ0, but:

[0073]

[0074] in:

[0075]

[0076] Then we have:

[0077]

[0078] According to formula (2), x b0 and b0 The projection relationship of the axis in the geographic coordinate system can be calculated b0 and b0 The angles between the axes and the geographic horizontal plane are as follows:

[0079]

[0080]

[0081]

[0082] In formula (3), ∠α1 and ∠α2 are the elevation angles measured by the autocollimation theodolite.

[0083] The autocollimation theodolite can measure the vertical angle and horizontal angle between the vertical plane of the prism and the geographic horizontal plane by receiving the collimated light reflected by the prism.

[0084] like Figure 6 As shown in a, it is a schematic diagram of the projection of the right normal component of the prism in the present invention; Figure 6 b is a plan view of the X, Y, and Z three-axis turntable in the present invention.

[0085] The inertial measurement unit equipped with a hexahedral prism is fixed on the X, Y, Z three-axis turntable (three-axis turntable, a customized measurement device), so that the ABCD surface of the prism points to the 0 degree direction of the three-axis turntable, that is, when the outer frame axis of the three-axis turntable points to its own scale ring 0 degree, the mirror normal of the outer frame reflector of the three-axis turntable coincides with the true north direction, and the horizontal angle of the autocollimation theodolite passing through the collimation outer frame reflector is ∠Φ1, and the horizontal angle of the autocollimation theodolite when the prism mirror is collimated is ∠Φ2. At this time, the normal of the prism mirror (hexahedral prism carrier system x b0 or b0 The angle between the horizontal component of the axis and the north direction of the geographic coordinate system is:

[0086]

[0087] Assume that the normal is aligned with the hexahedral prism y b0 The axes are parallel, then the angle between the horizontal component of the normal and the north direction of the geographic coordinate system is:

[0088]

[0089] According to equations (3) to (5), the attitude angles of the prism in a certain measurement are θ0, γ0, The installation deviation angle between the prism and the IMU can be obtained by combining the attitude angle of the IMU obtained at the same time.

[0090] like Figure 7 FIG. 2 is a schematic diagram of the axial direction of the IMU gyroscope of the present invention.

[0091] The attitude angle of the IMU is calculated using the four-position north-seeking method. The specific principle of the four-position method is as follows:

[0092] The fiber optic gyroscope of the IMU is used to measure the angular velocity components of the heading axis at positions 90° apart, which are ω1, ω2, ω3, and ω4 respectively. The following formula is used:

[0093]

[0094] From the above formulas, we can conclude that: Arranged:

[0095]

[0096] Among them, θ is the heading angle of the IMU, and the horizontal attitude angle of the IMU can be calculated from the measurement value of the accelerometer. The formula is as follows:

[0097]

[0098]

[0099] Among them, φ is the roll angle, γ is the pitch angle, A xg , A yg are the measurements of the x-axis and y-axis accelerometers respectively, and g is the acceleration due to gravity.

[0100] According to the attitude value of the IMU obtained by the four-position method and the attitude value of the prism obtained by calibration calculation, the installation error angle of the IMU and the prism is directly obtained by difference, and the error calibration is performed.

[0101] Figure 8 Schematic diagram of the mutual aiming between the antenna array and the prism of the present invention. Fig. 9 This is a schematic diagram of the "cross" target layout of the radar antenna array of the present invention:

[0102] The IMU with prism is installed on the servo turntable, and four points on the radar antenna array are marked with a "cross" target as object points. The cursor position on the wall is reflected by the collimator theodolite through the prism and marked as image points. The X, Y, and Z attitude values ​​of the object point and image point are measured respectively using the collimator theodolite according to the four-position method. The deviation angle between the normal line of one side of the prism (in the same direction as the X-axis of the IMU) and the normal line of the antenna array is obtained through processing and calculation.

[0103] Fig.10 The present invention is a flow chart of the static zero-position calibration of the antenna installation based on POS.

[0104] Using this method, according to the above steps, first calibrate the installation error between the IMU and the prism, then calibrate the error between the prism and the antenna array zero position, and realize the installation error calibration between the IMU and the antenna array through prism error transfer, and measure multiple times until the system installation accuracy is met.

[0105] The present invention adopts a two-dimensional active phased array + azimuth mechanical scanning system. The unmanned aerial vehicle reconnaissance and surveillance radar system includes an antenna unit, a servo turntable, and a processing unit. The hardware is highly integrated, the unit composition is simple, and the system volume and weight are reduced.

[0106] The radar system of the present invention is equipped with a MEMS-based integrated navigation positioning and orientation system (POS system), including an inertial measurement unit (IMU), a navigation solution module (PCS), a satellite navigation antenna and other equipment, which can output the high-speed and high-precision position, heading, speed and attitude information of the UAV platform in real time;

[0107] The present invention uses a servo turntable to control the normal direction of the antenna array, realizes 360° rotation of the radar azimuth and controls and corrects the initial zero position of the antenna (the direction of the nose of the carrier aircraft);

[0108] The present invention adopts a four-position method, fixes the prism on the IMU through a mounting bracket, fixes the IMU on the servo turntable through a mounting hole, and uses a collimating theodolite to measure and obtain the accurate initial position X, Y, and Z attitude values ​​of the IMU; measures and calculates the prism attitude angle and the IMU attitude angle, and makes a difference between them to calibrate and correct the installation errors of the prism and the IMU in the X, Y, and Z directions;

[0109] In the present invention, the X-axis direction of the IMU installation is parallel to the normal direction of the antenna array surface, and the X, Y, and Z attitude values ​​of the object point and the image point of the antenna array surface are measured respectively using a collimating theodolite. The deviation angle between the normal line of a certain surface of the prism (in the same direction as the X-axis of the IMU) and the normal line of the antenna array surface is obtained through processing and calculation;

[0110] The calculation and control of the present invention are all designed by software. The deviation angle value obtained by measurement is input by software, and the servo turntable adjusts the normal pointing direction of the antenna array surface and corrects the initial zero position of the antenna array surface (the direction of the nose of the carrier aircraft) until the system calibration accuracy requirement is met.

[0111] In summary, each set of SARMTI reconnaissance and surveillance radar on traditional drones must be calibrated for installation errors when installed, which results in high system maintenance time and cost, and even reduces the combat effectiveness of the equipment. The static target calibration method for the drone-mounted radar system based on POS in the above embodiment solves this problem efficiently and conveniently, greatly saves equipment maintenance time and cost, improves the maintainability and combat effectiveness of the equipment, and is worthy of promotion and use.

[0112] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A static target calibration method for an airborne radar system based on POS, characterized in that: The following steps are involved: S1: Install a prism on the inertial measurement unit of the POS system and calibrate the installation error of the prism's X, Y, and Z directions and the inertial measurement unit's X, Y, and Z directions; In the step S1, the POS system is installed inside the servo turntable, and includes an inertial measurement unit, a navigation solution module, and a satellite navigation antenna; the inertial measurement unit is used to measure the angular velocity and acceleration information of the radar, collect the real-time motion information of the carrier platform and provide it to the navigation solution module; The navigation solution module is used to perform real-time combined solution using the measurement values ​​of the satellite navigation antenna and the measurement information of the inertial measurement unit to obtain the position, heading, speed and attitude information of the carrier platform, and transmit it to the radar system in real time for storage and processing; S2: Control the normal direction of the radar system antenna array through the servo turntable to achieve 360° rotation of the radar azimuth and perform initial zero position control correction of the antenna; The radar system includes an antenna unit, a servo turntable, and a processing unit; the antenna unit is used to generate and radiate electromagnetic waves and receive reflected electromagnetic wave signals; the servo turntable is used to control the direction and azimuth of the antenna unit to rotate 360 ​​degrees; the processing unit is used to perform signal and data processing, remote control and telemetry command distribution, and equipment status monitoring; S3: By measuring and calculating the error angle between the normal direction of the radar system antenna array and the X-axis direction when the prism on the inertial measurement unit is installed, the initial zero-position pointing angle of the antenna is adjusted until the calibration accuracy requirements are met, thereby realizing the indoor static target calibration of the radar system.

2. The static target calibration method of an airborne radar system based on POS according to claim 1, characterized in that: In the step S1, the prism is a hexahedral prism, each face of which is a plane, and two connected faces are perpendicular to each other.

3. The static target calibration method of an airborne radar system based on POS according to claim 2, characterized in that: The specific process of step S1 is as follows: S11: The inertial measurement unit with the prism installed is fixed on the servo turntable, and the angle between the normal line of a certain surface of the prism and the north direction of the geographic coordinate system is measured using an autocollimation theodolite, where the normal line of the surface is perpendicular to the X-axis direction of the inertial measurement unit; S12: Use an autocollimation theodolite to measure the vertical angles between the normals of two adjacent vertical surfaces of the prism and the horizontal plane of the geographic coordinate system, and calculate the attitude angles of the prism in the X, Y, and Z directions; S13: Using the four-position method to collect the inertial measurement unit to obtain the initial position X, Y, and Z direction attitude angles; S14: using the prism attitude angle and the inertial measurement unit attitude angle obtained by measurement and calculation, subtracting each other to calibrate and correct the installation errors of the prism and the inertial measurement unit in the X, Y, and Z directions.

4. The static target calibration method of an airborne radar system based on POS according to claim 3 is characterized in that: In step S12, according to the relative rotation relationship between the geographic coordinate system and the prism carrier coordinate system, the attitude angle between the prism carrier coordinate system and the geographic coordinate system is recorded as θ0, γ0, but: in: Then we have: According to the above formula, x b0 and b0 The projection relationship of the axis in the geographic coordinate system, calculate the x b0 and b0 The angles between the axes and the geographic horizontal plane are as follows: Among them, ∠α1 and ∠α2 are the elevation angles measured by the autocollimation theodolite; The autocollimation theodolite measures the vertical angle and horizontal angle between the vertical plane of the prism and the geographic horizontal plane by receiving the collimated light reflected by the prism. Fix the inertial measurement unit equipped with prism on the X, Y, Z three-axis turntable so that the ABCD surface of the prism points to the 0 degree direction of the three-axis turntable, that is, when the outer frame axis of the three-axis turntable points to its own scale ring 0 degree, the mirror normal of the outer frame reflector of the three-axis turntable coincides with the true north direction, and the horizontal angle of the autocollimation theodolite passing through the collimation outer frame reflector is ∠Φ1, and the horizontal angle of the autocollimation theodolite when the prism mirror is collimated is ∠Φ2. At this time, the angle between the horizontal component of the prism mirror normal and the north direction of the geographic coordinate system is: Assume that the normal is aligned with the hexahedral prism y b0 The axes are parallel, then the angle between the horizontal component of the normal and the north direction of the geographic coordinate system is: Get the attitude angles of the prism in a certain measurement θ0,γ0, The installation deviation angle between the prism and the inertial measurement unit can be obtained by combining the attitude angle of the inertial measurement unit obtained at the same time.

5. The static target calibration method of an airborne radar system based on POS according to claim 4, characterized in that: In step S13, the specific process of the four-position method is as follows: The fiber optic gyroscope of the inertial measurement unit is used to measure the angular velocity components of the heading axis at positions 90° apart, which are ω1, ω2, ω3, and ω4 respectively. The following formula is used: From the above formulas, we can conclude that: Arranged: Among them, θ is the heading angle of the inertial measurement unit, and the horizontal attitude angle of the inertial measurement unit is calculated by the measurement value of the accelerometer, and the formula is as follows: Among them, φ is the roll angle, γ is the pitch angle, A xg , A yg are the measurements of the x-axis and y-axis accelerometers respectively, and g is the acceleration due to gravity.

6. The static target calibration method of an airborne radar system based on POS according to claim 5, characterized in that: In the step S3, four points are marked as object points by a cross target on the antenna array surface of the antenna unit, and the cursor position on the wall is reflected by the autocollimation theodolite through the prism and marked as an image point. The autocollimation theodolite is used to measure the X, Y, and Z direction attitude angles of the object point and the image point respectively, and the deviation angle between the normal of a certain surface of the prism and the normal of the antenna array surface is obtained through processing and calculation, and the normal of the surface is perpendicular to the X-axis direction of the inertial measurement unit.

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