Passive Target Velocity Measurement System

This project characterizes and designs a sensor able to measure passive airglow reflections in a wide-field to detect anomalous velocity enhancements - the aused by reflections of airglow emission features from fast moving objects. To achieve the required fast spectral integration, durability, and background rejection, the system features solid-state Fabry-Perot etalons using electronically tunable liquid crystals to achieve spectral line profile scanning. The feasibility of the proposed three-etalon system is evaluated by testing the transmission and spectral resolution capabilities of existing liquid crystal etalons, and by measurements of candidate airglow features using a conventional air-gap Fabry-Perot interferometer. The Phase I project delivers an optical and mechanical design balancing the field-of-view, spectral resolution, and sensitivity parameters into a device best suited for covert velocity detection in a cluttered atmospheric or littoral environment. The mechanical design permits selection of 2 - 4 spectral features depending on the field conditions, and permits two or three etalon operation optimizing throughput to daytime or nighttime background conditions. Laboratory and field-testing of extant, high spectral resolution liquid crystal etalons is a central feature of the Phase I initiative, permitting expeditious fabrication of a PAR-WAVE prototype in Phase II.