Direct Detection Polarimetric Radiometer

Problem or opportunity: The presence of supercooled liquid in clouds creates hazard conditions for aircraft as it may cause icing, possibly leading to fatal accidents. Early detection of such conditions is an important safety problem yet to be solved.The most advanced detection techniques are based on polarimetric microwave measurements. Both polarimetric radiometry and polarimetric radar have proven to be promising for detecting the hazardous condition in flight. However, current equipment is veryexpensive and cumbersome, and is therefore inappropriate for both military flying platforms and civilian aircraft. A polarimetric enhancement of the radar imaging is needed to improve target detection and obstacle avoidance for the Army's rotary wingplatforms.Project Objectives: Using a revolutionary new design developed during Phase I, WaveBand Corporation will develop a novel microwave polarimetric front-end sensor. The instrument will detect Supercooled Cloud Drops (5-50 microns diameter), SupercooledLiquid Droplets, SLD, (50-500 microns diameter), and raindrops (>500 microns diameter). The instrument will be compact (fit in 1 ft3), lightweight, and cost effective. Also, with WaveBand's previously developed beam-steering antennas, the new instrumentwill be capable of imaging runways, and remotely detect wires and other targets. In nonpolarized operation mode it also will deliver brightness temperature.The new instrument will measure four Stokes parameters at two millimeter-wave frequencies (94 GHz and 35 GHz). The key element of the instrument, its front-end variable phase retarder, will be also compatible with most of the existing or futureradiometers and radars. It can be readily integrated with WaveBand's MMW imaging system providing polarization information that will greatly enhance target discrimination and clutter rejection capability. The development will benefit the US Armyhelicopter upgrade programs such as: BLACKHAWK, COMMANCHE and APACHE as well as potential applications in civilian aviation and atmospheric science.