Estimating true altitude of a track from local 3-D Cartesian coordinates of a radar

Estimating the true altitude of a track from 3-dimensional Cartesian coordinates of a radar has always been a challenge. In the early days of radar a 4/3 earth-radius refraction model algorithm was sufficient to describe the altitude of a track, since planes didn´t fly too high and radars had less power and range. Many present radars track objects outside the limits of this simple model and better estimates are needed. This article outlines a series of simple algorithm approximations that are used to compute the altitude of a track. Altitude estimation errors are more than a factor of 10 smaller than the 4/3 earth model. The algorithm approximations for computing the altitude are relatively simple and very efficient to code