Inertial navigation systems rely on two natural Earth reference quantities for positioning and attitude calculation: the Earth's angular velocity of rotation and gravitational acceleration. These two core natural parameters are the foundation of inertial navigation technology, and are also important bases for aerospace, geographic positioning and Earth research. Leveraging the core technical advantage of accurately calculating the two reference quantities, high-quality inertial navigation products work completely independently without relying on external signals such as satellites or base stations. Featuring anti-interference capability, all-weather operation and high stability, they can adapt to various harsh and complex working scenarios, and provide accurate and continuous positioning, velocity measurement and attitude measurement services for all types of moving carriers.
1. Earth's Angular Velocity of Rotation
The Earth's angular velocity of rotation refers to the speed at which the Earth spins on its axis. The Earth rotates steadily from west to east. For daily application, its rotation speed is approximately 15 degrees per hour, with a standard physical value of 7.292×10⁻⁵ rad/s. The most intuitive phenomenon brought by Earth’s rotation is the alternation of day and night. The stable rotation also provides a regular time rhythm for life on Earth.
Unlike the unified angular velocity, the linear rotation speed varies in different regions on Earth. It reaches the maximum of about 465 meters per second at the equator, and gradually decreases as the latitude increases, dropping to zero at the North and South Poles. In addition, at the same latitude, the higher the altitude, the slightly higher the linear speed. This is why most space launch bases are built in low-latitude areas and rockets launch eastward, which can save fuel by taking advantage of the Earth’s rotation speed.
The Earth’s rotation speed is not absolutely fixed, with tiny changes that can only be detected by high-precision equipment and are imperceptible to humans. In the long run, tidal friction gradually slows down the Earth’s rotation. Annually, affected by atmospheric and ocean movements, the rotation speed has slight seasonal fluctuations, generally slower in winter and faster in summer. Besides, internal Earth activities and celestial gravitational forces also cause irregular tiny fluctuations in rotation speed. Earth’s rotation also produces the Coriolis effect, subtly affecting global atmospheric circulation, ocean currents and surface landforms. In response to these dynamic tiny changes in rotation parameters, our inertial navigation products are equipped with high-precision dynamic compensation algorithms. They can adapt to subtle fluctuations of the Earth’s rotation angular velocity in real time, automatically correct measurement errors, and greatly improve the long-term positioning accuracy and stability of equipment, suitable for multiple scenarios such as drones, vehicle navigation, ship navigation and industrial surveying and mapping.
2. Gravitational Acceleration
Gravitational acceleration refers to the falling acceleration of objects near the Earth’s surface under gravity. It is the combined acceleration of Earth’s gravitational force and centrifugal force caused by Earth’s rotation, serving as a core basic parameter for inertial navigation, engineering surveying and geological exploration. In the operation of inertial navigation systems, accurate local gravitational acceleration data is required to calibrate equipment errors and eliminate gravity interference, so as to accurately calculate the real motion state of carriers.
Gravitational acceleration is not uniform across the Earth and has slight differences affected by multiple factors, among which latitude is the dominant one. The Earth is an oblate sphere slightly flattened at the poles and bulging at the equator. Combined with the offset effect of rotational centrifugal force, gravitational acceleration increases with latitude, with the minimum value at the equator sea level and the maximum at the polar sea level. At the same latitude, the higher the altitude, the smaller the gravitational acceleration. Moreover, uneven density of underground rocks, minerals, water bodies and other geological structures causes local deviations of gravity values. High-density mining areas and compact rock layers have higher gravity values, while loose strata, lake and oil-gas areas have lower values. This principle is widely applied in gravity prospecting.
Gravitational acceleration also has subtle dynamic changes. In the long term, geological activities such as plate movement, glacier melting and sea level rise cause extremely slow tiny changes in local gravity values. In the short term, gravitational forces of the sun and moon as well as atmospheric load changes trigger periodic small fluctuations of gravitational acceleration. Many common natural phenomena including free fall and periodic swing of pendulums are derived from gravitational acceleration, which is also a key reference for architectural engineering, ship design, and other fields. Aiming at gravity differences and dynamic fluctuations caused by latitude, altitude and regional environments, our inertial navigation products are built with a full-range high-precision gravity database. They support adaptive accurate calibration, effectively eliminate gravity interference and compensate environmental errors, and solve the accuracy drift problem of traditional navigation equipment in complex areas and long-term operation. With strong adaptability, high measurement accuracy and stable operation, the products meet the high-precision navigation and measurement needs of multiple industries including civil surveying and mapping, intelligent driving, special equipment and geological exploration.
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