Prospects for precision active tracking using a quadrant detector

A general model is developed for an active quadrant tracking system constrained to track the nose or leading edge of incoming missiles and aircraft. The basic system consists of a shortpulse Nd:YAG 1.06-micrometer laser transmitter and a laser receiver with a quadrant avalanche photodiode detector in a direct detection mode. Using the model with carefully selected target, atmospheric, system, and detector parameters, estimates are made of the random tracking errors to be expected under various conditions. The conditions are noted under which tracking errors of 10 micro rad. (maximum) can be expected.