SINS / LDV-based continuous elevation measurement method and system

Abstract

The present application relates to a kind of continuous elevation measurement method and system based on SINS / LDV combination, belong to geodetic survey field.The system includes strapdown inertial navigation system, laser doppler velocimeter, UPS power supply and navigation computer, wherein, the angular motion and linear motion of sensitive carrier are used to strapdown inertial navigation system;Strapdown inertial navigation system is connected with laser doppler velocimeter and navigation computer respectively;Laser doppler velocimeter is connected with navigation computer, and UPS power supply is connected with strapdown inertial navigation system and laser doppler velocimeter respectively;In order to improve the precision of elevation measurement, the output of laser doppler velocimeter is triggered with the pulse output of strapdown inertial navigation system as benchmark, to prevent the data loss phenomenon caused by the inconsistency of internal crystal oscillator of strapdown inertial navigation system and laser doppler velocimeter.

Description

Technical Field

[0001] This invention relates to a continuous elevation measurement method and system based on a combination of a strapdown inertial navigation system (SINS) and a laser Doppler velocimeter (LDV, commonly referred to as a velocimeter), belonging to the field of geodesy. Background Technology

[0002] Elevation measurement plays a crucial role in geological exploration, topographic mapping, and gravity measurement. Continuous elevation measurements are typically required during fieldwork. However, current elevation measurement methods, such as geometric leveling and trigonometric leveling, cannot achieve continuous elevation measurements. While the Global Navigation Satellite System (GNSS) can perform continuous elevation measurements, poor GNSS signal strength in environments such as jungles, valleys, and densely populated areas leads to a sharp decline in measurement accuracy.

[0003] To achieve fully autonomous continuous elevation measurement, an inertial navigation system (INS) can be combined with a laser Doppler velocimeter. The INS can be either a rotating INS or a strapdown INS. Both systems combined with the laser Doppler velocimeter can avoid environmental influences in elevation measurements. However, the rotating INS / laser Doppler velocimeter combination for continuous elevation measurement places lower demands on the accuracy of the gyroscopes and accelerometers in the INS, and also presents the following problems:

[0004] First: The rotating inertial navigation system contains a rotation mechanism, which increases the complexity of the design and installation of the inertial navigation system, and also increases the instability of the measurement system;

[0005] Second: The indexing mechanism has a horizontal tilt angle during installation, and its compensation process increases the complexity of the measurement method.

[0006] Therefore, a combination of a strapdown inertial navigation system with higher precision gyroscopes and accelerometers / laser Doppler velocimeters can be used for continuous elevation measurement. This reduces the complexity of system design and measurement methods while improving the accuracy of the measurement methods. Summary of the Invention

[0007] To address the shortcomings of current continuous elevation measurement methods, the purpose of this invention is to propose a continuous elevation measurement method and system based on the SINS / LDV combination.

[0008] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows:

[0009] A continuous elevation measurement method based on SINS / LDV combination, using a continuous elevation measurement system composed of a strapdown inertial navigation system, a laser Doppler velocimeter, a UPS power supply, and a navigation computer, comprises the following steps:

[0010] S1: Connect the strapdown inertial navigation system to the laser Doppler velocimeter and the navigation computer respectively;

[0011] Connect the laser Doppler velocimeter to the navigation computer, and connect the UPS power supply to both the strapdown inertial navigation system and the laser Doppler velocimeter.

[0012] S2: When installing the assembled system onto a carrier (e.g., an experimental vehicle), due to installation errors, the velocimeter coordinate system (m-frame) and the carrier coordinate system (b-frame) cannot be completely aligned, requiring calibration. The installation errors affecting the velocity projection of the laser Doppler velocimeter include the pitch angle error θ, the heading angle error ψ, and the scaling factor K between the velocimeter coordinate system (m-frame) and the carrier coordinate system (b-frame). The calibration method is as follows:

[0013] S2.1: Turn on the laser Doppler velocimeter and strapdown inertial navigation system to sample data;

[0014] S2.2: First, let θ = 0, ψ = 0, and K = 1. The coordinates of the starting point landmark A are (X... A Y A Z A );

[0015] S2.3: After 1-2 minutes of linear motion, the carrier travels to landmark B, whose coordinates are (X... B Y B Z B The displacement from point A to point B is L1;

[0016] The laser Doppler velocimeter's calculated position after tracking is point C, and its coordinates are (X... C Y C Z C The displacement from point A to point C is L2. For the specific trajectory calculation method, please refer to the reference "One-dimensional reference-beam LDV for accurate altitude estimation in a land vehicle" (Rong Huang, Qi Wang, Xiaoming Nie, et al., Applied Optics, 2020.11).

[0017] The calibration result is:

[0018]

[0019] S2.4: The installation error matrix between the velocimeter coordinate system m and the carrier coordinate system b is calculated using the calibrated pitch installation angle error θ and heading installation angle error ψ.

[0020]

[0021] The installation error matrix between the speedometer coordinate system (m-frame) and the carrier coordinate system (b-frame) was calculated. And the scaling factor K, to obtain the projection of the laser Doppler velocimeter velocity in the b-frame at a certain navigation moment:

[0022]

[0023] In the formula, l represents the update iteration time of the navigation information. The velocity measured by the laser Doppler velocimeter at a certain navigation moment is projected onto the velocimeter's coordinate system m and is provided by the laser Doppler velocimeter.

[0024] S3: After completing the system installation and laser Doppler velocimeter installation error calibration, proceed to elevation measurement;

[0025] After entering the elevation measurement phase, the navigation computer performs attitude calculations on the output of the strapdown inertial navigation system during the measurement process, obtaining the real-time 3×3 attitude matrix between the vehicle coordinate system (b-frame) and the navigation coordinate system (n-frame).

[0026] Through real-time attitude matrix Further, the projection of the speedometer velocity at a certain navigation moment into the navigation coordinate system n is obtained.

[0027]

[0028] Inertial navigation systems, due to the lack of damping in the upward direction, will experience rapid divergence of system errors, affecting the real-time attitude matrix. The error will also increase rapidly, therefore the speed of the speedometer will... The error will also increase;

[0029] To obtain a stable, high-precision real-time attitude matrix The upward direction of the inertial navigation system must be damped by a laser Doppler velocimeter. Kalman filters are usually selected to fuse information between different sensors and estimate and feed back system errors, thereby suppressing the divergence of inertial navigation system errors. For the construction steps of the Kalman filter, please refer to the reference "Vehicle Integrated Navigation System Based on Two-Dimensional Laser Doppler Velocimeter" (Chen Hongjiang, Nie Xiaoming, Wang Mengcheng, Infrared and Laser Engineering, 2018.12).

[0030] This allows for the stable output of high-precision real-time attitude matrices.

[0031] S4: Expanding equation (4), the projection of the laser Doppler velocimeter velocity in each direction in the navigation coordinate system n at a certain navigation moment is:

[0032]

[0033] In the above formula, v E_LDV(l) v N_LDV(l) v U_LDV(l) Let the velocity projection of the laser Doppler velocimeter in the east, north, and sky directions of the navigation coordinate system n at a certain navigation moment be denoted as . The velocity projection of the laser Doppler velocimeter onto the x, y, and z axes of the carrier coordinate system b at a certain navigation moment;

[0034] The speed of the laser Doppler velocimeter The following calculations are performed to obtain the position information of the carrier at any navigation time:

[0035]

[0036] In the above formula, T is the velocity update period of the laser Doppler velocimeter, and L... (l) , λ (l) h (l) These are the latitude, longitude, and elevation information of the vehicle calculated from its trajectory at a specific navigation time, L. (l-1) , λ (l-1) h (l-1) These are the latitude, longitude, and elevation information of the vehicle calculated from the trajectory at the previous navigation time, where the starting point positions L0, λ0, and h0 are given by landmarks, and R... E R N These are the radii of the east-west circle and the meridian circle, respectively, representing the location of the carrier.

[0037] Finally, by using the third equation in (6), the elevation information of the vehicle during its travel can be continuously measured.

[0038] This invention also provides a continuous elevation measurement system based on the above method, including a strapdown inertial navigation system (SINS), a laser Doppler velocimeter, a UPS power supply, and a navigation computer. The SINS is used to sense the angular and linear motion of the carrier. The SINS is connected to both the laser Doppler velocimeter and the navigation computer. The laser Doppler velocimeter is connected to the navigation computer. The UPS power supply is connected to both the SINS and the laser Doppler velocimeter. To improve elevation measurement accuracy, the pulse output of the SINS is used as a reference to trigger the output of the laser Doppler velocimeter, preventing data loss caused by inconsistencies in the internal crystal oscillators of the SINS and the laser Doppler velocimeter.

[0039] To reduce the complexity of the system design, a laser Doppler velocimeter based on a solid-state detector is used, which does not require artificial doping with tracer particles, but instead utilizes the natural particles on the surface of the detector.

[0040] Compared with the prior art, the advantages of the present invention are as follows:

[0041] 1. This invention simplifies the elevation measurement method and system, thereby improving the efficiency of elevation measurement;

[0042] 2. The elevation measurement method of the present invention does not rely on GNSS signals at all and belongs to fully autonomous continuous elevation measurement. It can maintain high continuous elevation measurement accuracy in environments such as dense forests, valleys and extreme weather, which greatly improves the environmental adaptability of continuous elevation measurement.

[0043] 3. To prevent inconsistencies in crystal oscillators from causing mismatches in the data acquisition frequencies of the strapdown inertial navigation system and the laser Doppler velocimeter, the pulse output of the strapdown inertial navigation system is used to trigger the output of the laser Doppler velocimeter, further improving the accuracy of continuous elevation measurement. Attached Figure Description

[0044] To more clearly describe the technical solution of the present invention, it will be further elaborated below with reference to the accompanying drawings.

[0045] Figure 1 Schematic diagram of the composition principle of the system of the present invention

[0046] Figure 2 Installation diagram of the system of the present invention

[0047] The numbers in the diagram are explained as follows: 1-Laser Doppler velocimeter; 2-Strapdown inertial navigation system; 3-Global Positioning System; 4-Navigation computer; 5-UPS power supply.

[0048] Figure 3 Schematic diagram of the experimental path for vehicle-mounted continuous elevation measurement

[0049] Figure 4 Schematic diagram of elevation changes in vehicle-mounted continuous elevation measurement experiment

[0050] Figure 5 Schematic diagram of elevation measurement error variation in vehicle-mounted continuous elevation measurement experiment Detailed Implementation

[0051] To make the technical solutions and advantages of the present invention clearer, the present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0052] The feasibility of this invention can be verified through vehicle-mounted experiments:

[0053] The strapdown inertial navigation system used in the experiment achieved a gyroscope zero-bias stability better than 0.0015° / h, an accelerometer zero-bias stability better than 20μg, and a positioning accuracy better than 0.5nm / 1h. The laser Doppler velocimeter had a velocity measurement accuracy better than 0.05%, an output frequency of 100Hz, a UPS power supply with a rated power of 5400W and an output voltage of 110–220V, and a standard laptop computer for navigation. The system's composition and operating principle are as follows: Figure 1 As shown; for ease of comparison, the Global Positioning System (GPS) is used to provide a position reference benchmark (output frequency 1Hz, elevation positioning accuracy 3m in single-point state, elevation positioning accuracy 4cm in differential state).

[0054] The strapdown inertial navigation system is installed inside the test vehicle, the laser Doppler velocimeter is mounted on the underside of the vehicle, and the GPS antenna is located on the roof. Figure 2 The diagram shows the installation of the system.

[0055] The experiment was conducted on the Wanjiali Elevated Road in Changsha City, Hunan Province. A schematic diagram of the experimental route is shown below. Figure 3 As shown, the Wanjiali Elevated Road is approximately 15km one way, and the experiment consisted of one round trip, totaling 30km. The actual elevation changes during the experiment are as follows. Figure 4 As shown.

[0056] Before proceeding with the measurement, step S2 of the continuous elevation measurement method of this invention is used to calibrate the installation error of the velocimeter, wherein the pitch installation angle error θ = -6.2824°, the heading installation angle error ψ = 0.2613°, and the scaling factor K = 1.1783.

[0057] Finally, steps S3 and S4 in the continuous elevation measurement method according to the present invention complete the continuous elevation measurement, and the error change curve during the measurement process is shown in the figure. Figure 5As shown, the largest elevation measurement error is 0.54m, and the smallest elevation measurement error is -0.58m.

[0058] The experimental results of vehicle-mounted continuous elevation measurement show that the measurement results can meet the basic elevation measurement requirements.

[0059] In summary, this invention proposes a continuous elevation measurement system and method based on SINS / LDV, and makes claims regarding the key technologies therein. This invention belongs to the category of fully autonomous vehicle-mounted continuous elevation measurement, and features high accuracy, simple structure, and strong environmental adaptability.

[0060] The above describes the continuous elevation measurement system and method of the present invention. The scope of protection of the present invention is not limited to the above embodiments; all technical solutions falling within the scope of the present invention should be considered within the scope of protection. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A continuous elevation measurement method based on SINS / LDV combination, characterized in that, This method consists of the following steps: S1: Connect the strapdown inertial navigation system to the laser Doppler velocimeter and the navigation computer respectively; Connect the laser Doppler velocimeter to the navigation computer, and connect the UPS power supply to both the strapdown inertial navigation system and the laser Doppler velocimeter. S2: When installing the assembled system onto the carrier, due to installation errors, the velocimeter coordinate system (m-frame) and the carrier coordinate system (b-frame) cannot be completely aligned, requiring calibration. The installation errors affecting the velocity projection of the laser Doppler velocimeter include the pitch angle error θ, the heading angle error ψ, and the scale factor K between the velocimeter coordinate system (m-frame) and the carrier coordinate system (b-frame). The calibration method is as follows: S2.1: Turn on the laser Doppler velocimeter and strapdown inertial navigation system to sample data; S2.2: First, let θ=0, ψ=0, and K=1. The coordinates of the starting point landmark A are (X... A Y A Z A ); S2.3: After 1-2 minutes of linear motion, the carrier reaches landmark B, whose coordinates are (X... B Y B Z B The displacement from point A to point B is L1. The laser Doppler velocimeter's calculated position after tracking is point C, and its coordinates are (X...). C Y C Z C The displacement from point A to point C is L2; The calibration result is: (1)， S2.4: The installation error matrix between the velocimeter coordinate system m and the carrier coordinate system b is calculated using the calibrated pitch installation angle error θ and heading installation angle error ψ. : (2)， The installation error matrix between the speedometer coordinate system (m-frame) and the carrier coordinate system (b-frame) was calculated. And the scaling factor K, to obtain the projection of the laser Doppler velocimeter velocity in the b-frame at a certain navigation moment: (3)， In the formula, l represents the update iteration time of the navigation information. The velocity measured by the laser Doppler velocimeter at a certain navigation moment is projected onto the velocimeter's coordinate system m, and is provided by the laser Doppler velocimeter. S3: After completing the system installation and laser Doppler velocimeter installation error calibration, proceed to elevation measurement; After entering the elevation measurement phase, the navigation computer performs attitude calculations on the output of the strapdown inertial navigation system during the measurement process, obtaining the real-time 3×3 attitude matrix between the vehicle coordinate system (b-frame) and the navigation coordinate system (n-frame). ; Through real-time attitude matrix Furthermore, the projection of the speedometer velocity at a certain navigation moment onto the navigation coordinate system n is obtained. : (4)， This allows for the stable output of high-precision real-time attitude matrices. ; S4: Expanding equation (4), the projection of the laser Doppler velocimeter velocity in each direction in the navigation coordinate system n at a certain navigation moment is: (5)， In the above formula, , , Let the velocity projection of the laser Doppler velocimeter in the east, north, and sky directions of the navigation coordinate system n at a certain navigation moment be denoted as . , , The velocity projection of the laser Doppler velocimeter onto the x, y, and z axes of the carrier coordinate system b at a certain navigation moment; The speed of the laser Doppler velocimeter The following calculations are performed to obtain the position information of the carrier at any navigation time: (6)， In the above formula, T is the velocity update period of the laser Doppler velocimeter. , , These are the latitude, longitude, and elevation information of the vehicle calculated from its trajectory at a specific navigation time. , , These are the latitude, longitude, and elevation information of the vehicle calculated from the trajectory at the previous navigation time, where the starting point position is... , , Given by landmarks, , These are the radii of the east-west circle and the meridian circle, respectively, representing the location of the carrier. Finally, through the third equation in (6), the elevation information of the carrier during its travel can be continuously measured. Inertial navigation systems, due to the lack of damping in the upward direction, will experience rapid divergence of system errors, affecting the real-time attitude matrix. The error will also increase rapidly, therefore the speed of the speedometer will... The error will also increase.

2. A continuous elevation measurement method based on SINS / LDV combination according to claim 1, characterized in that: To obtain a stable, high-precision real-time attitude matrix It is necessary to use a laser Doppler velocimeter to dampen the inertial navigation system's upward direction, select a Kalman filter to fuse information between different sensors, and estimate and provide feedback on system errors, thereby suppressing the divergence of inertial navigation system errors.

3. A continuous elevation measurement system based on the method of claim 1 or 2, characterized in that: The system includes a strapdown inertial navigation system (INS), a laser Doppler velocimeter, a UPS power supply, and a navigation computer. The INS is used to sense the angular and linear motion of the carrier. The INS is connected to both the laser Doppler velocimeter and the navigation computer. The laser Doppler velocimeter is connected to the navigation computer. The UPS power supply is connected to both the INS and the laser Doppler velocimeter. The pulse output of the INS is used as a reference to trigger the output of the laser Doppler velocimeter, preventing data loss caused by inconsistencies in the internal crystal oscillators of the INS and the laser Doppler velocimeter.

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