Comparative Analysis of Multiposition Strapdown Azimuth Determining Schemes

Abstract

Navigation is a method of determining or planning a vehicle’s position and path/trajectory; employing sensors, geometry, astronomy and radio signals etc. Navigation is a combination of science, engineering and art. The determination of the position, velocity and attitude of a moving body with respect to a known reference-frame is the science or engineering of navigation. The planning and maintaining the intended path from one point to another, evading hindrances and crashes, is the art of navigation and has the forms as guidance, pilotage, or routing depending on the type of applications. Inertial Navigation System (INS) is a completely self-contained form of navigation and regarded as the most robust and complete navigation-system, as it renders navigation information including position, velocity, acceleration, attitude and attitude rates of the host body. INS does not require any external communication for its functioning. But INS always require information of initial position, velocity and attitude-angles. Afterwards, it keeps on updating position, velocity and attitude of the moving body using the outputs of inertial sensors. The azimuth (angle of forward axis of vehicle with respect to the True North) is the most important and critical initial information required for the INS. Initial azimuth angle can be provided to INS by optical means or gyro-compassing. Conventional Gyrocompasses (using suspended gyroscopes) have been in use for high precision azimuth determination for last several decades. Conventional gyrocompass gives azimuth information by sensing the combined effect of Earth spin-rate and local-gravity. But gyrocompasses are highly delicate and expensive equipment requiring careful handling/transportation, periodic calibration and challenging storage conditions. To overcome these issues, extensive research has been going-on for development of rugged north finding systems based on Strapdown inertial sensors for last few decades. Herein one or more strapdown gyroscopes are used to measure the component of Earth Spin Vector in the local horizontal plane. Azimuth is mathematically computed from the output of gyroscopes. This research paper is focused on the comparative analysis of different schemes used in strapdown Azimuth Determining Systems (ADS), including, single-position, 2-position, 4-position and multi-position azimuth finding schemes. We have analyzed the pros and cons of all schemes viz-a-viz accuracy/precision, sampling-time and total process time. Besides usage in INS, other applications of ADS include Satellite- Tracking, Tunneling, Telescope/Antenna/Solar-Panels Alignment, Mining/Drilling operations, Precision Farming, Buildings/Bridges Construction and submarines etc.