Absolute sea surface elevation measurement system based on offshore mobile platform

Abstract

The invention discloses an absolute sea surface elevation measurement system based on an offshore mobile platform, which relates to the field of marine surveying and mapping and satellite remote sensing calibration and comprises an offshore mobile platform part, a shore-based static GNSS (Global Navigation Satellite System) base station and a data processing module, the offshore mobile platform part is integrated with a GNSS antenna and receiver, an attitude sensor, a radar tide gauge and a data acquisition and storage module; the shore-based static GNSS base station provides static coordinates and GNSS observation data, and the data processing module comprises a shore-based base station resolving module for resolving to obtain three-dimensional coordinates; the offshore platform GNSS dynamic resolving module is used for resolving a dynamic position; and the absolute sea surface height calculation module is used for calculating the initial sea surface height and outputting a final result through low-pass or median filtering. The device does not need to distribute a buoy, can be directly carried on a ship, a floating platform and other mobile platforms, realizes high-precision, continuous and safe absolute sea surface elevation measurement, and is suitable for satellite altimeter calibration and other application scenes.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ocean mapping and satellite remote sensing calibration, in particular to an absolute sea surface height measurement system based on a marine mobile platform. BACKGROUND

[0002] The absolute sea surface height (SSH) is a key parameter in oceanography and geodesy, and is widely used in sea level change monitoring, ocean circulation inversion and satellite altimeter calibration. At present, high-precision absolute sea surface height measurement mainly relies on GNSS buoy systems. The GNSS antenna and tide gauge are integrated on the buoy, which is placed on the sea surface, and the centimeter-level precision sea surface height is obtained through post-processing.

[0003] However, the existing GNSS buoy has obvious defects: (1) it needs to be carried by a scientific research ship and manually placed on the sea surface, which is complex and risky to operate, and cannot be placed near the tide well in the nearshore area such as wharf and dike due to GNSS signal loss caused by shielding; (2) the buoy is only suitable for fixed-point observation and cannot be used for towing or underway measurement; (3) the equipment is immersed in seawater for a long time, which is prone to corrosion, biological attachment and wave impact, resulting in high maintenance cost and short service life.

[0004] In addition, although the conventional tide station can provide long-term water level sequence, its height reference depends on the land leveling point, and it is difficult to directly obtain the absolute sea surface height (i.e. the height relative to the Earth's center of mass), and the spatial resolution is low.

[0005] Therefore, there is an urgent need for an absolute sea surface height measurement system that does not need to enter the water, can be directly carried on a mobile platform, and has high precision and convenient operation, to solve the problems of difficult placement, large nearshore blind area, and inability to continuously underway measurement in the prior art. SUMMARY

[0006] The purpose of the present application is to provide an absolute sea surface height measurement system based on a marine mobile platform, to solve the problems of difficult placement, limited nearshore measurement, and inability to continuous observation of the existing GNSS buoy system, and to realize high-precision, safe and convenient absolute sea surface height measurement.

[0007] To achieve the above purpose, the present application provides the following solutions: The present application provides an absolute sea surface height measurement system based on a marine mobile platform, comprising: a marine mobile platform part, a shore-based static GNSS reference station and a data processing module; The marine mobile platform part comprises a first GNSS antenna, a first GNSS receiver, an attitude sensor, a radar tide gauge, a data acquisition module and a data storage module; The first GNSS antenna is configured to collect first GNSS satellite signals and transmit the first GNSS satellite signals to the first GNSS receiver. The first GNSS receiver is configured to convert the first GNSS satellite signals into first raw observation data and store the first raw observation data. The attitude sensor is configured to collect attitude data of the offshore mobile platform in real time. The radar tide gauge is configured to measure the distance from the zero point thereof to the sea surface in real time to obtain water level difference data. The data collection module is configured to synchronously collect the first raw observation data output by the first GNSS receiver, the attitude data output by the attitude sensor, and the water level difference data output by the radar tide gauge, and transmit the first raw observation data, the attitude data, and the water level difference data to the data storage module. The shore-based static GNSS reference station comprises a second GNSS antenna, a second GNSS receiver, and a data transmission module. The second GNSS antenna is configured to collect second GNSS signals and transmit the second GNSS signals to the second GNSS receiver. The second GNSS receiver is configured to convert the second GNSS signals into second raw observation data and store the second raw observation data. The data transmission module is configured to collect the second raw observation data output by the second GNSS receiver and transmit the second raw observation data to the data processing module. The data processing module comprises a shore-based static GNSS reference station solving unit, an offshore mobile platform GNSS dynamic solving unit, and an absolute sea surface height calculation unit. The shore-based static GNSS reference station solving unit is configured to output three-dimensional coordinates of the shore-based static GNSS reference station. The offshore mobile platform GNSS dynamic solving unit is configured to output dynamic three-dimensional coordinates of a phase center of the first GNSS antenna in the offshore mobile platform. The absolute sea surface height calculation unit is configured to calculate an absolute sea surface height.

[0008] Optionally, the offshore mobile platform further comprises: an instrument support; The instrument support is configured to rigidly fix the first GNSS antenna, the attitude sensor, and the radar tide gauge, so that the phase center of the first GNSS antenna, the measurement center of the attitude sensor, and the measurement zero point of the radar tide gauge are located in the same vertical plane.

[0009] Optionally, the shore-based static GNSS reference station further comprises: a power supply module configured to supply power to each device.

[0010] Optionally, the shore-based static GNSS reference station further comprises: The observation pier is used to house the second GNSS antenna and lightning rod.

[0011] Optionally, the shore-based static GNSS reference station further includes: Protective equipment; The protective device is a box structure used to house the power supply module and the data transmission module.

[0012] Optionally, the attitude data of the offshore mobile platform includes: roll angle, pitch angle, and tilt angle.

[0013] Optionally, the shore-based static GNSS reference station calculation unit is executed according to the following steps: Receive raw GNSS observation data collected by shore-based static GNSS reference stations; By combining data from at least 20 nearby GNSS reference stations, precise ephemeris, antenna phase center correction files, ionospheric files, broadcast ephemeris, ionospheric models, tropospheric models, tidal correction models, solid tide correction modules, polar tide correction modules, and light pressure models, static calculations and adjustments are performed using GAMIT / GLOBK, Bernese, or GIPSY software to output the three-dimensional coordinates of the shore-based static GNSS reference station.

[0014] Optionally, the GNSS dynamic calculation unit of the marine mobile platform specifically performs the following steps: The system receives the three-dimensional coordinates, second raw observation data, first raw observation data, precise ephemeris, and satellite clock error files from the shore-based static GNSS reference station. It then uses the TRACK module of RTKlib or GAMIT / GLOBK to perform dynamic precise single-point positioning or relative positioning. Finally, it outputs the dynamic three-dimensional coordinates of the phase center of the first GNSS antenna in the offshore mobile platform, including the X / Y / Z coordinates in the geocentric coordinate system or the latitude / longitude / altitude in the geodetic coordinate system, where the altitude is denoted as Height.

[0015] Optionally, the absolute sea level height calculation unit performs the following steps: According to the formula Calculate the elevation difference correction value caused by attitude; where, This is the elevation difference correction value caused by attitude. For water level difference data, The roll angle, The pitch angle; According to the formula Calculate the initial absolute sea level; where, The initial absolute sea level, The altitude is in the geodetic coordinate system. The vertical distance from the antenna phase center to the radar tide gauge; Finally, the initial absolute sea surface height is filtered to filter out high-frequency noise caused by waves, and the final absolute sea surface height SSH of the measured position is output.

[0016] Optionally, the data acquisition module synchronously acquires the first raw observation data, attitude data and water level difference data at a frequency of 1 Hz, and realizes multi-source data fusion and uploading through an embedded controller STM32H743IIT6. The RS232 interface is used for communication with the attitude sensor, and DMA double buffering and CRC-16 checking are adopted; The RS485 or 4-20mA interface is used for communication with the radar tide gauge, and protocol adaptive switching is supported; The first raw observation data, attitude data and water level difference data collected are uploaded to a data storage module or a remote server through an Ethernet interface.

[0017] According to the specific embodiments provided in the application, the application has the following technical effects: The application provides an absolute sea surface height measurement system based on a marine mobile platform, which has the following significant advantages: No need to deploy in water: The system is installed on the deck or fence of a mobile platform such as a ship or a floating platform, avoiding the risk of deploying GNSS buoys at sea, improving operation safety and efficiency; Suitable for nearshore areas: It can be directly installed near the pier fence or tide gauge, eliminating the spatial representative error caused by the too far distance between the measurement point and the tide gauge; Supports underway measurement: It can continuously collect data during platform movement, realizing absolute sea surface height profile measurement in a measurement line mode, and expanding the application range; High precision guarantee: The multi-sensor co-vertical line is ensured by a rigid support, dh is calibrated on site, attitude correction and precise dynamic solution are realized, and the overall precision can reach centimeter level, which is comparable to GNSS buoys; Strong anti-interference capability: The embedded system is used to realize multi-source synchronous acquisition, supporting RS485 / 4-20mA adaptive communication, CRC checking and DMA transmission, ensuring data reliability; Wave noise is effectively suppressed by filtering: 1Hz high-frequency SSH is low-passed or median filtered, effectively filtering out the influence of waves with a period of 5-20 seconds, and improving the stability of the results. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 A data processing flowchart of an absolute sea level elevation measurement system based on a part of a marine mobile platform according to an embodiment of the present application; Figure 2 An overhead view of an instrument support of a marine mobile platform according to an embodiment of the present application; Figure 3 A front view of an instrument support of a marine mobile platform according to an embodiment of the present application; Figure 4 A left view of an instrument support of a marine mobile platform according to an embodiment of the present application.

[0020] Reference signs: instrument support-1; horizontal bubble-2; cylinder-3; hollow round hole-4; threaded hole-5. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0022] The above-mentioned purposes, features and advantages of the present application can be more obvious and easy to understand. The present application will be described in further detail below with reference to the drawings and specific embodiments.

[0023] In an exemplary embodiment, an absolute sea level elevation measurement system based on a part of a marine mobile platform is provided, referring to Figures 2-4 , comprising: a part of a marine mobile platform, a shore-based static GNSS reference station and a data processing module; The part of the marine mobile platform comprises: a first GNSS antenna, a first GNSS receiver, an attitude sensor, a radar tide gauge, a data acquisition module and a data storage module. The first GNSS antenna is configured to collect a first GNSS satellite signal and transmit the first GNSS satellite signal to the first GNSS receiver. The first GNSS receiver is configured to convert the first GNSS satellite signal into first raw observation data and store the first raw observation data. The attitude sensor is configured to collect attitude data of the marine mobile platform in real time. The attitude data comprises: a roll angle, a pitch angle and a yaw angle. The radar tide gauge is used for measuring the distance from its own zero point to the sea surface in real time to obtain water level difference data; the radar tide gauge is arranged in the cylinder 3; the upper part of the cylinder 3 is used for mounting the first GNSS antenna, and the lower part is used for mounting the attitude sensor; The top of the instrument support is also provided with a plurality of hollow circular holes 4 and screw holes 5, wherein the hollow circular holes 4 are used for measuring the vertical distance from the phase center of the GNSS antenna to the radar tide gauge; and the screw holes 5 are used for fixing the cylinder 3 on the instrument support through screws; The data acquisition module is used for synchronously acquiring the first raw observation data output by the first GNSS receiver, the attitude data output by the attitude sensor and the water level difference data output by the radar tide gauge, and transmitting the data to the data storage module; The shore-based static GNSS reference station comprises a second GNSS antenna, a second GNSS receiver and a data transmission module; The second GNSS antenna is used for collecting a second GNSS signal and transmitting the second GNSS signal to the second GNSS receiver; The second GNSS receiver is used for converting the first GNSS satellite signal into first raw observation data and storing the first raw observation data; The data transmission module is used for collecting second raw observation data output by the second GNSS receiver and sending the second raw observation data to the data processing module; The data processing module comprises a shore-based static GNSS reference station solving unit, a marine mobile platform GNSS dynamic solving unit and an absolute sea surface height calculation unit; the shore-based static GNSS reference station solving unit is used for outputting the three-dimensional coordinates of the shore-based static GNSS reference station; the marine mobile platform GNSS dynamic solving unit is used for outputting the dynamic three-dimensional coordinates of the phase center of the first GNSS antenna in the marine mobile platform part; and the absolute sea surface height calculation unit is used for calculating the absolute sea surface height.

[0024] In an optional embodiment, in order to ensure that the phase center of the first GNSS antenna and the measurement centers of the radar tide gauge and the attitude sensor are located in the same vertical plane, the above marine mobile platform part further comprises: an instrument support 1; The instrument support 2 is used for rigidly fixing the first GNSS antenna, the attitude sensor and the radar tide gauge, so that the phase center of the first GNSS antenna, the measurement center of the attitude sensor and the measurement zero point of the radar tide gauge are located in the same vertical plane.

[0025] The instrument support 1 further comprises a horizontal bubble 2, which is used for ensuring the level of the instrument equipment during installation.

[0026] In an alternative embodiment, the shore-based static GNSS reference station further comprises: a power supply module, an observation tower, and a protection device; The power supply module is configured to supply power to each device in the shore-based static GNSS reference station. The observation tower is configured to place the second GNSS antenna and lightning rod. The protection device is a box structure configured to place the power supply module and the data transmission module to prevent lightning strikes, water damage, damage by wild animals, and adapt to the field environment, thereby enhancing the service life of the device.

[0027] In an alternative embodiment, the data processing module comprises three function modules executed in sequence, and the data processing process is described in Figure 1 : (1) Shore-based static GNSS reference station solution module: receiving GNSS raw observation data collected by the shore-based static GNSS reference station, combining with data of at least 20 GNSS reference stations nearby, precise ephemeris, antenna phase center correction file, ionosphere model, broadcast ephemeris, ionosphere model, troposphere model, sea tide correction model, solid tide correction module, polar tide correction module, and light pressure model, using GAMIT / GLOBK, Bernese or GIPSY software for static solution and adjustment, outputting high-precision three-dimensional coordinates of the shore-based static GNSS reference station; (2) Offshore mobile platform GNSS dynamic solution module: receiving high-precision three-dimensional coordinates of the shore-based static GNSS reference station, shore-based GNSS raw observation data, offshore mobile platform GNSS raw observation data, precise ephemeris and satellite clock error file, using RTKlib or TRACK module of GAMIT / GLOBK for dynamic precise point positioning or relative positioning, outputting dynamic three-dimensional coordinates of the GNSS antenna phase center of the offshore mobile platform, including X / Y / Z coordinates in the Earth-Centered Earth-Fixed coordinate system or latitude / longitude / height (Lat / Lon / Height) in the geodetic coordinate system, wherein the height is denoted as Height; (3) Absolute sea surface height calculation module: receiving dynamic height Height, water level difference dh measured by the radar tide gauge, roll angle and pitch angle measured by the attitude sensor, and vertical height difference dh of the GNSS antenna phase center to the zero point of the radar tide gauge obtained through on-site calibration; First, calculate the height difference correction value caused by the attitude according to formula (1): (1); Then, calculate the initial absolute sea surface height according to formula (2): (2); Because the initial absolute sea level has a high frequency (1Hz) during the measurement process, it is affected by factors such as waves in the ocean, and its period is generally 5~20s. Therefore, it needs to be filtered. In this application, low-pass filtering, median filtering or other filters are used to finally obtain the absolute sea level of the location to be measured.

[0028] On-site calibration The method for calculating the value is as follows: Before and after the measurement operation, use a steel tape measure to measure the vertical distance from the GNSS antenna reference point to the zero point of the radar tide gauge sensor at the two pre-set measurement holes on the top of the instrument bracket and the pre-set blue marked area on the side wall of the bracket. Take the average of the three measurements as the mean. The value has a calibration accuracy better than 1mm.

[0029] The data acquisition module synchronously acquires the first raw observation data, attitude data, and water level difference data at a frequency of 1Hz, and realizes multi-source data fusion and uploading through the embedded controller STM32H743IIT6, wherein: Communicating with the attitude sensor via RS232 interface, using DMA double buffering and CRC-16 checksum; Communicates with radar tide gauge via RS485 or 4-20mA interface, supporting adaptive protocol switching; The first raw observation data, attitude data, and water level difference data are uploaded to the data storage module or remote server via the Ethernet interface.

[0030] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0031] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An absolute sea level elevation measurement system based on a mobile offshore platform, characterized in that, The absolute sea level height measurement system based on the offshore mobile platform comprises: an offshore mobile platform part, a shore-based static GNSS reference station and a data processing module; the offshore mobile platform part comprises a first GNSS antenna, a first GNSS receiver, an attitude sensor, a radar tide gauge, a data acquisition module and a data storage module; the first GNSS antenna is used for collecting first GNSS satellite signals and transmitting the first GNSS satellite signals to the first GNSS receiver; the first GNSS receiver is used for converting the first GNSS satellite signals into first raw observation data and storing the first raw observation data; the attitude sensor is used for collecting attitude data of the offshore mobile platform in real time; the radar tide gauge is used for measuring the distance from the zero point thereof to the sea surface in real time to obtain water level difference data; the data acquisition module is used for synchronously collecting the first raw observation data output by the first GNSS receiver, the attitude data output by the attitude sensor and the water level difference data output by the radar tide gauge and transmitting the first raw observation data, the attitude data and the water level difference data to the data storage module and the data processing module; the shore-based static GNSS reference station comprises a second GNSS antenna, a second GNSS receiver and a data transmission module; the second GNSS antenna is used for collecting second GNSS signals and transmitting the second GNSS signals to the second GNSS receiver; the second GNSS receiver is used for converting the second GNSS signals into second raw observation data and storing the second raw observation data; the data transmission module is used for collecting the second raw observation data output by the second GNSS receiver and sending the second raw observation data to the data processing module; the data processing module comprises a shore-based static GNSS reference station solving unit, an offshore mobile platform GNSS dynamic solving unit and an absolute sea surface height calculation unit; the shore-based static GNSS reference station solving unit is used for outputting the three-dimensional coordinates of the shore-based static GNSS reference station; the offshore mobile platform GNSS dynamic solving unit is used for outputting the dynamic three-dimensional coordinates of the phase center of the first GNSS antenna in the offshore mobile platform part; and the absolute sea surface height calculation unit is used for calculating the absolute sea surface height.

2. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The offshore mobile platform part further comprises: an instrument support; the instrument support is used for rigidly fixing the first GNSS antenna, the attitude sensor and the radar tide gauge so that the phase center of the first GNSS antenna, the measurement center of the attitude sensor and the measurement zero point of the radar tide gauge are located in the same vertical plane.

3. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The shore-based static GNSS reference station further comprises: a power supply module used for supplying power to each device.

4. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The shore-based static GNSS reference station further comprises: an observation pier used for placing the second GNSS antenna and a lightning rod.

5. The offshore mobile platform based absolute sea level elevation measurement system of claim 3, wherein, The shore-based static GNSS reference station further comprises: a protection device; the protection device is in the form of a box and is used for placing the power supply module and the data transmission module.

6. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The attitude data of the offshore mobile platform comprises a roll angle, a pitch angle and a yaw angle.

7. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The shore-based static GNSS reference station solving unit specifically performs the following steps: receiving the GNSS raw observation data collected by the shore-based static GNSS reference station; The static solution and adjustment are performed by using GAMIT / GLOBK, Bernese or GIPSY software in combination with data of no less than 20 GNSS reference stations in the vicinity, precise ephemeris, antenna phase center correction files, ionosphere files, broadcast ephemeris, ionosphere model, troposphere model, ocean tide correction model, solid tide correction model, polar tide correction model and light pressure model, and three-dimensional coordinates of the shore-based static GNSS reference station are output.

8. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The GNSS dynamic solution unit of the offshore mobile platform specifically performs the following steps: The three-dimensional coordinates of the shore-based static GNSS reference station, the second raw observation data, the first raw observation data, the precise ephemeris and the satellite clock error file are received, dynamic precise point positioning or relative positioning is performed by using TRACK module in RTKlib or GAMIT / GLOBK, and dynamic three-dimensional coordinates of the first GNSS antenna phase center in the offshore mobile platform part are output, including X / Y / Z coordinates in the Earth-Centered Earth-Fixed coordinate system or latitude / longitude / height in the geodetic coordinate system, wherein the height is denoted as Height.

9. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The absolute sea surface height calculation unit specifically performs the following steps: The height difference correction value caused by the attitude is calculated according to the formula ; wherein, is the height difference correction value caused by the attitude, is the water level difference data, is the roll angle, is the pitch angle; The initial absolute sea surface height is calculated according to the formula wherein, is the initial absolute sea surface height, is the height in the geodetic coordinate system, is the vertical distance from the antenna phase center to the radar tide gauge. Finally, the initial absolute sea surface height is filtered to remove high-frequency noise caused by waves, and the final absolute sea surface height SSH of the to-be-measured position is output.

10. The offshore mobile platform based absolute sea level elevation measurement system of claim 1, wherein, The data acquisition module synchronously acquires the first raw observation data, attitude data and water level difference data at a frequency of 1 Hz, and realizes multi-source data fusion and uploading through an embedded controller STM32H743IIT6, wherein: The RS232 interface is used to communicate with the attitude sensor, DMA double buffering and CRC-16 check are adopted; The RS485 or 4-20mA interface is used to communicate with the radar tide gauge, and protocol adaptive switching is supported; The Ethernet interface is used to upload the acquired first raw observation data, attitude data and water level difference data to the data storage module or remote server.

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