Design of a dither mirror control system

Abstract

Staring focal plane optical systems are subject to two main sources of optical noise: scene variations and non-uniformity of the focal plane detector. It is well known that adding dither to such an optical system will serve to reduce the magnitude of these noise sources, while, at the same time, reducing electrical and mechanical disturbances in the optical measurement. A typical dither pattern consists of two phases during which measurements are made—stare and scan—and two transition periods which smoothly connect the measurement phases. Once the transition time, dither amplitude, and dither frequency are chosen, a simple analysis yields the necessary closed-loop system bandwidth and mechanical properties of the system. Furthermore, a simple computer model can be generated based on the measured performance of the system components and this model can be used to predict the behavior of the dither system. This work describes the analysis performed and hardware designed to simply and inexpensively implement a dither mirror control system. The performance of the hardware is compared with predicted performance and it is shown that after making modest changes in the electronics, the hardware behavior can be reasonably well described with the simple modeling techniques and acceptable dynamic performance can be achieved.