Abstract
In order to improve the performance of Terrain Referenced Navigation (TRN), an Interferometric Radar Altimeter (IRA) has been developed as a more accurate altimeter. The IRA outputs not only the relative distance (slant range, R) but also the cross-track angle (look angle, θ) of the closest point on the zero Doppler line by using the principle of interferometry and two or more antennas. To perform TRN using the IRA, the 3D relative position of the closest point should be calculated. There is a formula to calculate the relative position of the closest point using the Euler angles. However, in an actual flight environment in which the influence of wind exists, the angle of attack, the side slip angle and “the effective look angle” should be used rather than the Euler angles. In this paper, a new formula for calculating the relative position of the closest point is proposed and mathematically derived. The proposed formula was verified with real data from actual flight. The flight test results show that the positions of the closest points calculated using the conventional method and the proposed method are different because of the wind effect. The TRN simulation results indicate that the proposed formula calculates the closest points more accurately than the conventional formula.
Highlights
Terrain Referenced Navigation (TRN) is a technique for estimating the position of an aircraft by comparing the Digital Elevation Model (DEM) with the altitude of the terrain measured by an altimeter.This technique is used to correct the position error of the inertial navigation system, which increases as the navigation time becomes longer
We proposed a new formula using Interferometric Radar Altimeter (IRA) output to calculate the relative position of the closest point
We derived the “effective look angle” equation using IRA’s look angle calculation principle and proposed a formula to calculate the relative position of the closest terrain point by using the velocity vector of the aircraft and the effective look angle
Summary
Terrain Referenced Navigation (TRN) is a technique for estimating the position of an aircraft by comparing the Digital Elevation Model (DEM) with the altitude of the terrain measured by an altimeter. This technique is used to correct the position error of the inertial navigation system, which increases as the navigation time becomes longer. TRN has the advantage of being able to operate normally regardless of hostile jamming signals. Because of this advantage, TRN is applied to various weapon systems such as Tomahawk and TAURUS missiles [1,2]
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