DVL-based ocean current flow velocity and flow direction measurement method and device suitable for AUV

Abstract

The invention discloses a DVL-based ocean current flow velocity and flow direction measurement method and device suitable for an AUV, and the method comprises the steps: obtaining the speed of a seabed and the speed of a to-be-measured water layer at the same time through a Doppler velocimeter DVL, and carrying out the subtraction of the speed of the seabed and the speed of the to-be-measured water layer, and obtaining the ocean current three-dimensional speed under a DVL carrier coordinate system; converting the ocean current speed to a geographic coordinate system based on attitude information of the AUV; performing track plotting on the converted ocean current speed, and accumulating the displacement of the ocean current in the east direction and the north direction in a preset duration in real time; and calculating and outputting the flow velocity and the flow direction of the ocean current in the geographic coordinate system according to the accumulated displacement and the calculated time length. According to the method, time integration is carried out on ocean current movement through track plotting, DVL instantaneous velocity measurement noise is effectively smoothed, the measurement precision and stability in a small-flow-velocity environment are remarkably improved, hardware does not need to be newly added, an existing combined navigation system of the AUV can be directly reused, and the method has the advantages of being low in cost, easy to integrate, high in engineering practicability and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of underwater current measurement, specifically relating to a method and apparatus for measuring ocean current velocity and direction based on DVL, suitable for AUVs. Background Technology

[0002] Autonomous underwater vehicles (AUVs) are playing an increasingly important role in marine development and national defense due to their numerous advantages, including small size, low operating costs, intelligent autonomous operation, convenient maintenance, and good stealth capabilities. As the application areas of AUVs gradually expand, the requirements for control systems are also increasing, especially the autonomous control capabilities for attitude, trajectory, and hovering in complex ocean current environments, to adapt to operational conditions in such environments. This necessitates that AUVs be able to accurately measure the speed and direction of ocean currents in real time, providing current information to the control system and enhancing their adaptability to complex ocean current environments.

[0003] Currently, most AUVs measure ocean currents by simultaneously measuring bottom velocity and water column velocity using a dynamic velocity range (DVL). However, the three axial velocity outputs of the DVL contain some measurement noise, resulting in large fluctuations in current direction measurements in environments with weak currents, making it difficult to effectively obtain ocean current information. Summary of the Invention

[0004] To address the aforementioned shortcomings and enable effective measurement of ocean currents with low velocities, this invention provides a DVL-based ocean current velocity and direction measurement method and apparatus suitable for AUVs. This method can solve the need for effective measurement of ocean current velocity and direction by AUVs in environments with low velocities. The method is simple, efficient, and has high engineering application value.

[0005] The technical solution for implementing the present invention is as follows: A DVL-based method for measuring ocean current velocity and direction suitable for AUVs includes the following steps: S1. Use the Doppler velocity meter (DVL) to simultaneously acquire the velocity of the seabed and the velocity of the water layer to be measured, and then subtract the two to obtain the three-dimensional velocity of the ocean current in the DVL carrier coordinate system. S2. Based on the attitude information of the AUV, the three-dimensional velocity of the ocean current is transformed from the DVL carrier coordinate system to the geographic coordinate system; S3. Based on the converted ocean current velocity, perform trajectory estimation to accumulate the displacement of the ocean current in the geographic coordinate system within a preset time period in real time. S4. Based on the accumulated displacement and the preset duration, calculate and output the velocity and direction of the ocean current in the geographic coordinate system.

[0006] Further, in step S1, the difference between the two specifically means: subtracting the velocity at the seabed from the velocity of the water layer to be tested.

[0007] Further, in step S2, the conversion includes: First, based on the installation error parameters and scaling coefficients between the DVL and the inertial navigation system, the three-dimensional velocity of the ocean current in the DVL carrier coordinate system is transformed to the inertial navigation system carrier coordinate system. Then, using the real-time attitude matrix of the AUV, the ocean current velocity in the carrier coordinate system of the inertial navigation system is converted to the geographic coordinate system.

[0008] Furthermore, in step S3, the starting point position of the trajectory calculation is the real-time position of the AUV at the beginning moment, and the displacement includes at least an eastward displacement component and a northward displacement component.

[0009] Further, in step S4, the calculation of flow velocity and flow direction specifically includes: The combined horizontal displacement of the ocean current within the preset time period is calculated based on the eastward displacement component and the northward displacement component. The average velocity of the ocean current is calculated based on the composite planar displacement and the preset duration. The direction angle of the ocean current is calculated based on the ratio of the eastward displacement component to the northward displacement component.

[0010] Furthermore, the method is executed by the integrated navigation system mounted on the AUV, which integrates satellite navigation equipment, inertial navigation equipment, and the Doppler velocimeter (DVL).

[0011] A DVL-based ocean current velocity and direction measurement device suitable for AUVs, comprising: At least one processor; and A memory that is communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which, when executed by the at least one processor, enables the at least one processor to perform the above-described method.

[0012] Beneficial effects: 1. This invention effectively smooths out instantaneous measurement noise in DVL by integrating ocean current velocity over time and accumulating displacement, significantly improving the stability and accuracy of ocean current direction and velocity measurements in low-velocity environments.

[0013] 2. This invention utilizes displacement inversion to determine flow velocity, thereby reducing the stringent requirements on the accuracy of single-point velocity measurement in DVL and improving the robustness and practicality of the system under actual ship conditions.

[0014] 3. This invention directly reuses the data and architecture of existing AUV integrated navigation systems (satellite navigation / INS / DVL), and realizes ocean current measurement through algorithms, saving costs, space and power consumption, and facilitating equipment upgrades.

[0015] 4. The method of the present invention can provide more reliable real-time ocean current information, supporting AUVs to perform accurate trajectory tracking, positioning hovering and path planning in complex ocean currents, thereby improving their operational capabilities in dynamic marine environments. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0017] This invention proposes a method and apparatus for measuring ocean current velocity and direction based on DVL (Direct Current Measurement) for AUVs. The method of this invention solves the technical problem in the prior art that when AUVs use their own configured DVL to measure ocean currents, the measurement noise in the three axial velocity outputs of the DVL leads to a large fluctuation range in the direction measurement in environments with small ocean currents, making it impossible to effectively obtain ocean current information.

[0018] First, combine Figure 1 This invention describes a method for measuring ocean current velocity and direction based on DVL and track estimation, applicable to AUVs, according to one embodiment of the present invention. Figure 1 As shown, the method includes the following steps: Step S101: Use DVL to simultaneously measure the velocity at the bottom and the velocity in the water column below the vehicle. Subtract the velocity at the bottom and the velocity in the water column from the DVL velocity to obtain the three-dimensional velocity of the ocean current in the DVL carrier coordinate system; Step S102: Use inertial navigation attitude to convert the ocean current velocity from the DVL carrier coordinate system to the geographic coordinate system; Step S103: Calculate the trajectory of the ocean current and accumulate the eastward and northward displacement of the ocean current over a certain period of time in real time; Step S104: Calculate the cumulative displacement and calculation time from the trajectory of the ocean current, and calculate and output the geographic velocity and direction of the ocean current.

[0019] Step S101: Use DVL to simultaneously measure the bottom velocity and the velocity of the water layer below the vehicle; calculate the difference between the bottom velocity and the water layer velocity using DVL to obtain the three-dimensional velocity of the ocean current in the DVL carrier coordinate system. The AUV is equipped with a high-precision satellite navigation / INS (Inertial Navigation System) / DVL (Doppler Velocimetry) combined navigation system. The Doppler velocimetry system simultaneously measures bottom velocity and convective velocity relative to the water layer below the transducer. The real-time output of the DVL is recorded. The velocity relative to the seabed in the system is The speed of the vehicle in the water below it is .

[0020] Then the ocean currents are Speed ​​of the system for: .

[0021] Step S102: First, the ocean current is... Speed ​​of the system Transform to the inertial navigation carrier coordinate system b. Let the installation error angle between the inertial navigation system and the DVL be . The DVL scaling factor is k ,but: (1) Secondly, the ocean currents are placed in the inertial navigation carrier coordinate system b. Real-time attitude via inertial navigation , converted Speed ​​of the system ,Right now: (2) (3) (4) (5) in: For real-time heading angle, For real-time pitch angle, The roll angle is given in real time by the inertial navigation system.

[0022] Step S103: Calculate the trajectory of the ocean current, and accumulate the eastward and northward displacements of the ocean current over a certain period of time in real time, including: Since inertial navigation attitude updates typically occur at frequencies above 200 Hz, while the DVL velocity output frequency is generally 1 Hz, the trajectory estimation update frequency is limited by the DVL update frequency. Let the trajectory estimation update period be denoted as... t， The estimated duration of the flight path is t DVL measures the converted ocean current velocity in real time. The position of the ocean current at the starting moment of the trajectory calculation is taken as the real-time latitude and longitude of the inertial navigation system at that moment, and denoted as . Record the estimated endpoint time of the flight path ( t The latitude and longitude of the ocean current can be calculated from the trajectory of the ship at a given time. .

[0023] The update equation for the position (latitude, longitude, and altitude) estimated by ocean currents is: (6) (7) (8) in: The latitude calculated from the previous moment's trajectory. The longitude calculated from the previous flight path. The altitude calculated from the previous flight path; The current latitude calculated from the flight path, The current longitude calculated from the flight path. The current altitude calculated from the flight path.

[0024] Step S104: Calculate the cumulative displacement and calculation time from the ocean current's trajectory, and calculate and output the ocean current's velocity and direction in the geographic system, including: Duration estimated from flight track t The ocean current position at the start of the trajectory calculation is used, and the real-time latitude and longitude of the inertial navigation system at that moment is taken. ; Estimated endpoint time of flight path ( t The latitude and longitude of the ocean current can be calculated from the trajectory of the ship at a given time. Assuming the ocean current flows approximately at a uniform velocity within the time t estimated by the trajectory, then: (9) (10) in: (11) (12) in, The radius is the Earth's radius. , These are the longitude and latitude of the starting point for calculating the ocean current track, respectively. , These are the longitude and latitude of the endpoint of the ocean current track, respectively. , These represent the northward and eastward distances between the start and end times of the track estimation, respectively. The calculated distances... and That is, the ocean currents in terms of duration t The internal flow velocity and outflow direction.

[0025] This invention further provides a method for measuring ocean current velocity and direction based on DVL and track estimation, applicable to AUVs, including: A processor is used to execute multiple instructions; Memory, used to store multiple instructions; The aforementioned instructions are stored in the memory and loaded and executed by the processor, as described above, for measuring ocean current velocity and direction based on DVL and track estimation, applicable to AUVs.

[0026] The present invention further provides a computer-readable storage medium storing a plurality of instructions; the plurality of instructions are used by a processor to load and execute the aforementioned method for measuring ocean current velocity and direction based on DVL and track estimation, applicable to AUVs.

[0027] According to the above-described scheme of the present invention, the AUV is equipped with a high-precision satellite navigation / INS (Inertial Navigation System) / DVL (Doppler Velocimetry) combined navigation system. The Doppler velocimetry system has the function of simultaneously measuring bottom velocity and convective velocity relative to the water layer below the transducer. When the AUV needs to measure the velocity and direction of the surrounding ocean current, it first uses DVL to simultaneously measure the bottom velocity and the velocity of the water layer below the vehicle; the difference between the bottom velocity and the water layer velocity is obtained to obtain the three-dimensional velocity of the ocean current in the DVL carrier coordinate system; the inertial navigation attitude is used to convert the ocean current velocity from the DVL carrier coordinate system to the geographic coordinate system; the trajectory of the ocean current is calculated, and the eastward and northward displacements of the ocean current over a certain period of time are accumulated in real time; based on the accumulated eastward and northward displacements and time, the geographic velocity and direction of the ocean current are calculated and output. This method, based on the existing combined navigation system of satellite navigation / inertial navigation / Doppler velocimeters for AUVs, utilizes DVL (Direct Velocity Measurement) to simultaneously measure bottom velocity and water column velocity, enabling the measurement of ocean current velocity and direction. In particular, by extrapolating the trajectory from the real-time measured three-dimensional ocean current velocity and using the accumulated ocean current displacement to obtain the velocity and direction, it solves the problem of inaccurately obtaining ocean current velocity and direction when the current is low. This significantly improves the motion control capability of AUVs in ocean current environments and has high engineering application value.

[0028] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring ocean current velocity and direction based on DVL suitable for AUVs, characterized in that, Includes the following steps: S1. Use the Doppler velocity meter (DVL) to simultaneously acquire the velocity of the seabed and the velocity of the water layer to be measured, and then subtract the two to obtain the three-dimensional velocity of the ocean current in the DVL carrier coordinate system. S2. Based on the attitude information of the AUV, the three-dimensional velocity of the ocean current is transformed from the DVL carrier coordinate system to the geographic coordinate system; S3. Based on the converted ocean current velocity, perform trajectory estimation to accumulate the displacement of the ocean current in the geographic coordinate system within a preset time period in real time. S4. Based on the accumulated displacement and the preset duration, calculate and output the velocity and direction of the ocean current in the geographic coordinate system.

2. The method according to claim 1, characterized in that, In step S1, the difference between the two specifically means: subtracting the velocity at the seabed from the velocity of the water layer to be tested.

3. The method according to claim 1, characterized in that, In step S2, the conversion includes: First, based on the installation error parameters and scaling coefficients between the DVL and the inertial navigation system, the three-dimensional velocity of the ocean current in the DVL carrier coordinate system is transformed to the inertial navigation system carrier coordinate system. Then, using the real-time attitude matrix of the AUV, the ocean current velocity in the carrier coordinate system of the inertial navigation system is converted to the geographic coordinate system.

4. The method according to claim 1, characterized in that, In step S3, the starting point position of the trajectory calculation is the real-time position of the AUV at the beginning moment, and the displacement includes at least an eastward displacement component and a northward displacement component.

5. The method according to claim 4, characterized in that, In step S4, the calculation of flow velocity and flow direction specifically includes: The combined horizontal displacement of the ocean current within the preset time period is calculated based on the eastward displacement component and the northward displacement component. The average velocity of the ocean current is calculated based on the composite planar displacement and the preset duration. The direction angle of the ocean current is calculated based on the ratio of the eastward displacement component to the northward displacement component.

6. The method according to any one of claims 1 to 5, characterized in that, The method is executed by the integrated navigation system mounted on the AUV, which integrates satellite navigation equipment, inertial navigation equipment and the Doppler velocimeter (DVL).

7. A DVL-based ocean current velocity and direction measurement device suitable for AUVs, characterized in that, include: At least one processor; as well as A memory that is communicatively connected to the at least one processor; The memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enable the at least one processor to perform the method as described in any one of claims 1 to 6.

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