The definition of north finding is to find true north, not magnetic north, and the north seeking methods mentioned in this article are all described closely around true north.
True north refers to the Earth’s north pole, which is the intersection of 90° north latitude or the meridian. It is also known as true north. It is the direction that passes through a point on the Earth and points toward the Earth’s geographical north pole. The tangent direction of the true meridian passing through a certain point on the earth’s surface becomes the true meridian direction of that point.
The theory of finding north
Magnetic north is the north indicated by a compass, primarily because the poles of the Earth’s magnetic field do not coincide with the geographic north and south poles. Therefore, the north indicated by a compass is magnetic north, not true north, and magnetic north changes over time.
North finding uses a gyroscope to measure the component of the earth’s rotation angular velocity combined with the acceleration value, and then calculates the angle with true north to obtain the azimuth angle value.
The methods of north finding
North seeking mainly includes two north seeking methods: static north seeking and dynamic north seeking. The application principles of these two north seeking methods are introduced below.
Principle of static north finding
Static north seeker includes MEMS gyro north seeker and fiber optic gyro north finder.
Principle: The rotation axis of the gyroscope maintains a constant direction relative to the inertial space, while the Earth rotates around the polar axis relative to the inertial space at its rotational angular velocity. If you use the Earth as a reference, you will see that the gyroscope’s axis of rotation rotates relative to the Earth, so the gyroscope can track and measure the angular velocity of the Earth’s rotation.
MEMS gyro north seeker, which has an input axis and a rotation axis. The sensor includes a motor drive structure, a motor signal output from the motor drive structure, a gyroscope, and a sensor rate for the sensor rate signal output from the gyroscope.
Fiber optic gyro north seekers are mainly used to quickly and autonomously determine the true north direction. The Earth’s rotation angular velocity is obtained through high-precision fiber optic gyroscope tracking, and the Earth’s rotation angular velocity signal is decomposed and solved to calculate the angle between the gyroscope’s main axis and the Earth’s true north to provide the carrier with orientation information.
Principles of dynamic north finding
Dynamic north seeking includes fiber optic gyro compass and fiber optic gyro compass (vehicle, ship, airborne)
Principle: Use the strapdown compass effect to find the direction of true north.
The fiber optic gyro compass consists of: three-axis dynamically adjustable gyroscope, three-axis acceleration sensor, data acquisition and processing module, secondary power supply, optocoupler isolated input and output serial port circuit and other related structural parts.
With so many methods available, they are suitable for different circumstances and are not one-size-fits-all. For north seekers used in most fields, inertial measurement device FOG north seekers and MEMS north seekers are relatively advanced in technology.
Comparison of various gyro north seeking systems
By comparing two gyro north-seeking systems, we discovered the similarities and differences between the static north-seeking method and the dynamic north-seeking method.
Common points:
1.They all use the precession and axis fixation of the gyroscope to be sensitive to the earth’s rotation angular speed.
2.The working principle uses the characteristics of the edge of the gyro chamber, that is, the effect of gravity.
Differences:
The more details have shown in the reference
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