GNSS wave measurement missing compensation method based on imu

Abstract

The present invention relates to the field of marine environment monitoring. Disclosed is a GNSS wave measurement missing compensation method based on an IMU, comprising the following steps: using a carrier carrying a GNSS to form a sea surface wave measurement apparatus, mounting an IMU in a carrier apparatus compartment, and acquiring an acceleration and an angular acceleration in real time; decoding acquired IMU data and converting same into a three-axis velocity increment and a three-axis angular velocity increment; when GNSS measurement missing is detected, solving a carrier attitude using the carrier velocity and acceleration of a GNSS epoch before the measurement missing; performing recursion on the carrier velocity at the measurement missing moment to obtain a carrier velocity sequence during the GNSS measurement missing; and after a sampling interval of the IMU, if GNSS data is still missing, performing recursion on the attitude at the measurement missing moment to obtain latest attitude information. The method disclosed in the present invention can supplement a GNSS velocity sequence, thereby enhancing the consecution of the GNSS velocity sequence, and improving the integrity of wave measurement.

Description

A GNSS wave measurement missing compensation method based on IMU Technical Field

[0001] The present invention belongs to the field of marine environment monitoring, and in particular relates to a GNSS wave measurement missing compensation method based on IMU. Background Art

[0002] Waves, as a key dynamic phenomenon in the ocean, play a vital role in monitoring their changes and studying their patterns. A deeper understanding of this phenomenon is crucial for maritime activities and disaster reduction and prevention efforts. In recent decades, humanity's continued exploration of the ocean and the rapid development of satellite navigation technology have not only advanced research in ocean observation methods but also facilitated the development of advanced instruments and equipment.

[0003] GNSS wave buoys utilize the Global Navigation Satellite System (GNSS) to obtain the buoy's three-dimensional position, velocity, and time information, effectively inverting wave elements. However, GNSS wave buoys may occasionally experience GNSS measurement failures in certain scenarios (e.g., when seawater covers the antenna), compromising the integrity of the 3D velocity data obtained by GNSS.

[0004] An inertial measurement unit (IMU) is a device that integrates multiple inertial sensors to measure and record an object's acceleration and angular velocity. IMUs are autonomous and independent of external signal sources, making them more reliable in some GNSS-denied environments. They can also provide highly accurate position and velocity information in a short period of time, effectively assisting GNSS in completing three-dimensional position and velocity information during periods of measurement loss. MEMS (micro-electromechanical system) IMUs offer low power consumption and cost, making them suitable for combining MEMS with GNSS for wave measurement.

[0005] Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a GNSS wave measurement missing compensation method based on IMU. When GNSS measurement missing occurs, the IMU can compensate the buoy's speed, position and other information into the GNSS speed and position sequence. It is suitable for scenarios such as oceans, rivers, and lakes, and can still work normally under GNSS denial conditions, and can obtain short-term high-precision buoy speed compensation results.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A GNSS wave measurement missing compensation method based on IMU includes the following steps:

[0009] Step 1: Use a carrier equipped with GNSS to construct a sea surface wave measurement device, install the IMU in the carrier device cabin, and collect the acceleration and angular acceleration of the current carrier compared to the inertial system in real time;

[0010] Step 2: Decode the collected IMU data into three-axis velocity increments and three-axis angular velocity increments and save them;

[0011] Step 3: Check whether the GNSS velocity time series is coherent. If a missing GNSS observation is detected, use the velocity and acceleration measured by the GNSS in the previous GNSS epoch to determine the carrier attitude in the previous GNSS epoch.

[0012] Step 4: Using the obtained carrier attitude and the three-axis velocity increments and three-axis angular velocity increments collected by the IMU, recursively extrapolate the carrier velocity starting from the GNSS epoch before the missing GNSS measurement to obtain the velocity sequence during the GNSS missing period. The obtained velocity sequence is then added to the velocity sequence measured by the GNSS to complete the supplementation of the missing GNSS velocity sequence. If GNSS data can be detected at the next IMU sampling time, return to step 1. If GNSS data is still not detected after one IMU sampling interval, proceed to step 5.

[0013] Step 5: Use the three-axis velocity increments and three-axis angular velocity increments collected by the IMU to recursively infer the carrier attitude starting from the previous GNSS epoch before the missing measurement to obtain the latest carrier attitude information, and then return to step 4.

[0014] In the above scheme, in step 3, the attitude matrix from the b system to the n system before the missing GNSS epoch is expressed as The b system is the carrier coordinate system, and the n system is the station center horizontal coordinate system;

[0015] The equations for solving the carrier posture are shown in equations (1), (2), and (3):

[0016] in, is the heading angle, θ is the pitch angle, γ is the roll angle, v n 、v e 、v u They are the north, east, and vertical velocity components respectively, l is the lifting acceleration, and the specific expression is l = a n -g n , where α n is the component of acceleration along the velocity normal vector, g n is the component of gravitational acceleration along the velocity normal direction; the composition of P is shown in formula (4): P = g n×v (4)

[0017] After obtaining the heading angle, roll angle and pitch angle through GNSS, the attitude matrix of the previous GNSS epoch is constructed. It is expressed as shown in formula (5):

[0018] In the above scheme, in step 4, the velocity sequence recursively solved during the GNSS absence period is shown in equation (6):

[0019] Among them, v n(k-1) is the projection of the velocity at the previous IMU moment in the n system, The three-dimensional acceleration obtained by the IMU at the current IMU moment is compensated by formula (7) and then passed through the attitude matrix at the current IMU moment. The velocity increment obtained by projecting to the n system is, represents the projection of the velocity increment caused by the Coriolis acceleration in the n-frame, The calculation formula is shown in formula (8):

[0020] Where Δv k Represents the velocity increment calculated based on the three-dimensional acceleration collected by the IMU at the current IMU moment, Δθ k Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the current IMU moment. Represents the projection of the angular velocity caused by the carrier motion at the current IMU moment in the n-frame; Represents the projection of the Earth's rotation angular velocity in the n-frame at the current IMU moment; represents the projection of local gravity in the n-frame; Δt represents the sampling interval of the IMU.

[0021] In the above scheme, in step 5, the recursive calculation equation of the carrier posture matrix is ​​shown in formula (9):

[0022] in, Represents the attitude matrix of the previous IMU moment, Represents the attitude transformation matrix from the n-frame at the previous IMU moment to the n-frame at the current IMU moment. Its solution equation is shown in formula (10):

[0023] Where E represents the third-order identity matrix; ζ k The equivalent rotation vector representing the angular velocity, (ζ k ×) represents the vector ζ kThe antisymmetric matrix, ζ k The calculation formula is as follows:

[0024] Represents the projection of the angular velocity of the current IMU moment in the n-frame, Represents the projection of the Earth's rotation angular velocity in the n-frame at the current IMU moment, and Δt represents the sampling interval of the IMU;

[0025] represents the attitude transformation matrix from the b-frame at the current IMU moment to the b-frame at the previous IMU moment. Its solution equation is shown in formula (12):

[0026] in, It is the equivalent vector obtained by compensating and correcting the three-dimensional angular acceleration obtained by the IMU at the current IMU moment, Δθ k Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the current IMU moment, Δθ k-1 Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the previous IMU moment, (Φ k ×) represents the vector Φ k The antisymmetric matrix of .

[0027] In the above solution, the carrier includes a drifting buoy, an anchored buoy, a ship, a wave glider or an unmanned ship.

[0028] Through the above technical solution, the IMU-based GNSS wave measurement missing compensation method provided by the present invention has the following beneficial effects:

[0029] The present invention only requires an additional low-cost, low-power MEMSIMU on the GNSS wave measurement carrier, which can solve the GNSS wave measurement occasional GNSS measurement omission phenomenon and increase the information consistency and system stability of the GNSS wave measurement.

[0030] The IMU used in the present invention is a low-cost MEMS IMU, which has the advantages of low cost and low power consumption; the present invention does not require an additional storage card to store IMU information, and reduces power consumption and storage space compared to the combined navigation algorithm.

[0031] The method of the present invention is suitable for application on a GNSS wave measurement carrier in scenarios where GNSS measurement loss may occur, and is particularly suitable for scenarios where the GNSS antenna is covered by seawater or GNSS signal denial is severe. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0033] FIG1 is a flow chart of a method for compensating for GNSS wave measurement omissions based on an IMU disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0035] The present invention provides a GNSS wave measurement missing compensation method based on IMU, as shown in FIG1 , comprising the following steps:

[0036] Step 1: Use a carrier equipped with GNSS to construct a sea surface wave measurement device, install the IMU in the carrier device cabin, and collect the acceleration and angular acceleration of the current carrier compared to the inertial system in real time.

[0037] The carriers of the present invention include drifting buoys, anchored buoys, ships, wave gliders, unmanned boats and other carriers that can operate on the water surface. Carriers equipped with GNSS have the functions of positioning and speed measurement.

[0038] The GNSS of this invention covers global navigation satellite systems such as BeiDou, GPS, GLONASS, Galileo, etc., as well as regional navigation satellite systems such as QZSS and NAVIC. Through the IMU carried by the buoy, the acceleration and angular acceleration of the current buoy and other carriers compared to the inertial system are collected, and then the carrier's attitude information is calculated by the carrier speed and acceleration calculated by the GNSS before the measurement is missing. Finally, the mechanical arrangement algorithm of inertial navigation is used to complete the calculation of the buoy's speed and position during the GNSS measurement absence. The sampling frequency of the IMU carried by sea surface carriers such as wave buoys equipped with IMU is 50Hz or above.

[0039] The IMU is connected to the processor through a serial port or other means; the processor runs embedded data processing software, obtains IMU data in real time and stores it in temporary memory. At the same time, the embedded system detects whether the GNSS data is missing. When the embedded system detects that the GNSS data is missing, it reads the information obtained by the IMU from the temporary memory and stores the solved results in the memory.

[0040] Step 2: Decode the collected IMU data into three-axis velocity increments and three-axis angular velocity increments, and save them.

[0041] Step 3: Check whether the GNSS velocity time series is coherent. If a missing GNSS observation is detected, use the velocity and acceleration measured by the GNSS in the previous GNSS epoch to determine the carrier attitude in the previous GNSS epoch.

[0042] The attitude matrix from the b system to the n system before the missing GNSS epoch is expressed as The b system is the carrier coordinate system, and the n system is the station center horizontal coordinate system;

[0043] The equations for solving the carrier posture are shown in equations (1), (2), and (3):

[0044] in, is the heading angle, θ is the pitch angle, γ is the roll angle, v n 、v e 、v u They are the north, east, and vertical velocity components respectively, l is the lifting acceleration, and the specific expression is l = a n -g n , where a n is the component of acceleration along the velocity normal vector, g n is the component of gravitational acceleration along the velocity normal direction; the composition of P is shown in formula (4): P = g n ×v (4)

[0045] After obtaining the heading angle, roll angle and pitch angle through GNSS, the attitude matrix is ​​constructed, and the carrier attitude matrix of the previous GNSS epoch is missing. It is expressed as shown in formula (5):

[0046] In step 4, the carrier velocity is recursively extrapolated from the previous GNSS epoch using the obtained carrier attitude and the three-axis velocity increments and three-axis angular velocity increments collected by the IMU to obtain the velocity sequence during the GNSS omission period. The obtained three-dimensional velocity sequence is then added to the velocity sequence measured by the GNSS to complete the supplementation of the GNSS omission velocity sequence. If GNSS data can be detected at the next IMU sampling time, the process returns to step 1. If no GNSS data is detected after an IMU sampling interval, the process proceeds to step 5.

[0047] The recursive solution equation for the velocity sequence during the GNSS absence period is shown in equation (6):

[0048] Among them, v n(k-1) is the projection of the velocity of the IMU moment before the missing measurement in the n system, The three-dimensional acceleration obtained by the IMU at the current IMU moment is compensated by formula (7) and then passed through the attitude matrix at the current IMU moment. The velocity increment obtained by projecting to the n system is, represents the projection of the velocity increment caused by the Coriolis acceleration in the n-frame, The calculation formula is shown in formula (8):

[0049] Where Δv k Represents the velocity increment calculated based on the three-dimensional acceleration collected by the IMU at the current IMU moment, Δθ k Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the current IMU moment. Represents the projection of the angular velocity caused by the carrier motion at the current IMU moment in the n-frame; Represents the projection of the Earth's rotation angular velocity in the n-frame at the current IMU moment; represents the projection of local gravity in the n-frame; Δt represents the sampling interval of the IMU.

[0050] Step 5: Use the three-axis velocity increments and three-axis angular velocity increments collected by the IMU to recursively infer the carrier attitude starting from the previous GNSS epoch before the missing measurement to obtain the latest carrier attitude information, and then return to step 4.

[0051] The recursive calculation equation of the carrier posture matrix is ​​shown in formula (9):

[0052] in, Represents the attitude matrix of the previous IMU moment, Represents the attitude transformation matrix from the n-frame at the previous IMU moment to the n-frame at the current IMU moment. Its solution equation is shown in formula (10):

[0053] Where E represents the third-order identity matrix; ζ k The equivalent rotation vector representing the angular velocity, (ζ k ×) represents the vector ζ k The antisymmetric matrix, ζ k The calculation formula is as follows:

[0054] Represents the projection of the angular velocity of the current IMU moment in the n-frame, Represents the projection of the Earth's rotation angular velocity in the n-frame at the current IMU moment, and Δt represents the sampling interval of the IMU;

[0055] represents the attitude transformation matrix from the b-frame at the current IMU moment to the b-frame at the previous IMU moment. Its solution equation is shown in formula (12):

[0056] in, It is the equivalent vector obtained by compensating and correcting the three-dimensional angular acceleration obtained by the IMU at the current IMU moment, Δθ k Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the current IMU moment, Δθ k-1 Represents the angular velocity increment calculated based on the three-dimensional angular acceleration collected by the IMU at the previous IMU moment, (Φ k ×) represents the vector Φ k The antisymmetric matrix of .

[0057] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compensation method for missing measurements of GNSS wave measurement based on IMU, characterized in that, The method includes the following steps: Step 1: Use a carrier equipped with GNSS to form a sea wave measurement device. Install the IMU in the carrier device cabin to collect the acceleration and angular acceleration of the current carrier relative to the inertial system in real time; Step 2: Decode the collected IMU data and convert it into triaxial velocity increments and triaxial angular velocity increments, and save them; Step 3: Detect whether the velocity time series of GNSS is continuous. When it is detected that there is a missing measurement in the GNSS observation data, use the velocity and acceleration measured by GNSS at the previous GNSS epoch before the missing measurement to solve the carrier attitude at the previous GNSS epoch before the missing measurement; Step 4: Use the obtained carrier attitude and the triaxial velocity increments and triaxial angular velocity increments collected by the IMU to recursively calculate the carrier velocity starting from the previous GNSS epoch before the missing measurement, obtain the velocity sequence during the GNSS missing measurement period, and supplement the obtained velocity sequence to the velocity sequence measured by GNSS to complete the supplementation of the GNSS missing velocity sequence; if GNSS data can be detected at the next IMU sampling moment, return to Step 1; if GNSS data still cannot be detected after an IMU sampling interval, continue to execute Step 5; Step 5: Use the triaxial velocity increments and triaxial angular velocity increments collected by the IMU to recursively calculate the carrier attitude starting from the previous GNSS epoch before the missing measurement, obtain the latest carrier attitude information, and then return to Step 4.

2. The GNSS wave measurement missing measurement compensation method based on IMU according to claim 1, wherein In step 3, the attitude matrix representation from the b-frame to the n-frame for the missing previous GNSS epoch is The b-frame is the vehicle coordinate system, and the n-frame is the local-level coordinate system centered at the station; The equations for solving the carrier attitude are shown in Equations (1), (2), and (3): Among them, is the heading angle, θ is the pitch angle, γ is the roll angle, v n , v e , v u are the velocity components in the north, east, and vertical directions respectively, l is the lifting acceleration, and the specific expression is l = a n -g n , where a n is the component of the acceleration along the normal vector of the velocity, and g n is the component of the gravitational acceleration along the normal of the velocity; The composition of P is shown in Equation (4): P = g n × v (4) After obtaining the heading angle, roll angle, and pitch angle through GNSS, construct the attitude matrix at the previous GNSS epoch before the missing measurement. Attitude matrix of the previous GNSS epoch before measurement It is represented as shown in Formula (5):

3. A GNSS wave measurement missing measurement compensation method based on IMU according to claim 1, characterized in that, In step 4, the recurrence solution equation for the velocity sequence during the GNSS outage is shown in Equation (6) as follows: where v n(k-1) is the projection of the velocity at the previous IMU moment in the n coordinate system, is the three-dimensional acceleration obtained by the IMU at the current IMU time, compensated by Equation (7), and then passed through the attitude matrix at the current IMU time The velocity increment obtained by projecting onto the n - system, Represents the projection of the velocity increment caused by the Coriolis acceleration in the n-system. The calculation formula is as shown in Equation (8): where, Δv k represents the velocity increment calculated from the three-dimensional acceleration collected by the IMU at the current IMU time, and Δθ k represents the angular velocity increment calculated from the three-dimensional angular acceleration collected by the IMU at the current IMU time, Represents the projection of the angular velocity caused by the carrier motion at the current IMU moment in the n system; Represents the projection of the Earth's angular velocity at the current IMU moment in the n-frame; represents the projection of the local gravity in the n - system; Δt represents the sampling interval of the IMU.

4. A method for compensating missing measurements of GNSS wave measurement based on IMU according to claim 1, characterized in that, In step 5, the recurrence calculation equation of the carrier attitude matrix is shown in Equation (9): Among them, Represents the attitude matrix at the previous IMU moment, Represents the attitude transformation matrix from the n-frame at the previous IMU moment to the n-frame at the current IMU moment, and its solution equation is shown in Equation (10): where, E represents the third-order identity matrix; ζ k represents the equivalent rotation vector of the angular velocity, (ζ k ×) represents the skew-symmetric matrix of the vector ζ k , and the calculation formula of ζ k is as follows: Represents the projection of the transport angular velocity at the current IMU moment in the n - frame, represents the projection of the earth's angular velocity at the current IMU moment in the n - system, and Δt represents the sampling interval of the IMU; Represents the attitude transformation matrix from the b-frame at the current IMU moment to the b-frame at the previous IMU moment, and its solution equation is shown in Equation (12): Among them, is the equivalent vector obtained after compensation and correction of the three-dimensional angular acceleration acquired by the IMU at the current IMU time, Δθ k represents the angular velocity increment calculated from the three-dimensional angular acceleration collected by the IMU at the current IMU time, Δθ k-1 represents the angular velocity increment calculated from the three-dimensional angular acceleration collected by the IMU at the previous IMU time, (Φ k ×) represents the skew-symmetric matrix of the vector Φ k of.

5. A method for compensating for missing measurements of GNSS wave measurement based on IMU according to claim 1, characterized in that, The carrier includes a drifting buoy, a moored buoy, a ship, a wave glider, or an unmanned ship.

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