1.1 Project Summary
A concept of geomagnetic field measurement using a three-component magnetic sensor mounted on a ship is proposed, which solves the problem of eliminating the magnetic field interference of the ship under measurement in any ship attitude. The tester uses a geomagnetic module to measure the three-component value of the magnetic field, and uses a 3-axis gyroscope to perform three kinds of state information of roll, pitch and heading included in any ship attitude, and calculates the collected data, thereby The three component values ​​of the earth's magnetic field are obtained. At the same time, the module also includes a pressure sensor and a temperature sensor to detect the air pressure and temperature on the sea surface in real time.
1.2 Project Background / Motivation
"Magnetic geomagnetic ship destroyer magnetic" is the degaussing method adopted by the shipboard degaussing system. If the geomagnetic field value of the ship's navigational sea area can be measured in advance and a database is established, the ship can be based on the local geomagnetic field during the navigation process. The value is used to adjust the current of the degaussing system to improve the control method of the shipboard degaussing system.
At present, the acquisition of geomagnetic data is mainly through the method of establishing a geomagnetic mode group. A special group of the International Geomagnetic and Upper Air Atmospheric Physics Association publishes an international geomagnetic reference field every five years, and China publishes a geomagnetic map of China every 10 years. The establishment of these two geomagnetic field models mostly comes from geomagnetic stations on land, and the earth's magnetic field at specific locations on the ocean is also affected by many factors such as local geography and structure. This has led to the failure of the global geomagnetic field model and the local geomagnetic model to describe the ocean geomagnetic field in a timely and accurate manner. Therefore, the error caused by the current adjustment for the shipboard degaussing system is relatively large. In order to obtain more accurate geomagnetic field values ​​at specific locations on the ocean, field measurements can be made on the ocean.
At present, the measurement of the magnetic field on the ocean is mainly to obtain the total amount of the magnetic field, but in the application of the traverse adjustment of the shipboard degaussing system, a three-component geomagnetic field is required. The three-component value of the magnetic field can be measured using a 6-axis geomagnetic module mounted on the mast of the ship, but the measured magnetic field value is not the value of the earth's magnetic field, but a complex one that contains the ship's own magnetic field and the sensor's own interference. The value of the magnetic field is affected by the attitude of the ship, and its value is also changed. Therefore, the 3-axis gyroscope can be used to measure the three attitude angles of the ship, and then mathematically modeling the method from a complex three-component magnetic field value. The earth's magnetic field is separated.
Second, the demand analysis2.1 Functional requirements
1, LPR430AL axis gyroscope (rolling, pitching) can detect ship roll, pitch information and output, LY330ALH gyroscope (yaw) can detect the ship's heading angle and output.
2, LSM303DLH geomagnetic module can detect the magnetic field information output of the ship where it is located.
3. The final output information also includes geomagnetic field information after removal of the fixed interference.
4, pressure sensor and temperature sensor can detect the temperature and pressure on the sea surface in real time and output.
2.2 Performance standards
Finally, after software calculation, the error of the horizontal and vertical components of the geomagnetic field does not exceed 50nT, and the magnetic declination error does not exceed 0.3°.
Third, the program design3.1 System function realization principle (except for pictures, there is a text introduction)
Magnetic sensor mathematical model analysis
For a magnetic sensor mounted on a survey vessel, the magnetic field value it receives is:
(1)
Where: E is a unit matrix; K is a matrix of induced magnetization coefficients; 
They are the horizontal and vertical components of the geomagnetic field; A is the transformation matrix of the ship coordinate system and the geomagnetic coordinate system under arbitrary attitude; the vector is the synthesis of various fixed interference quantities. The expressions of the elements of matrix A are:
To measure the ship's pitch angle, roll angle and magnetic deflection angle. The matrix K can be specifically expressed as:
Analysis (1) can know the amount to be measured 
` 
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(In fact, the magnetic declination is measured, but the magnetic heading angle is measured. After that, it is possible to find the magnetic declination from the heading angle provided by the navigation device, and the vector h can be directly read from the magnetic sensor. 
, First, the inductive susceptibility matrix K and the fixed interference vector should be measured. 
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