Title: A 183 GHz Humidity Sounding Radar Transceiver
Presenting Author: Ken B. Cooper
Organization: Jet Propulsion Laboratory

Abstract:
Conventional microwave methods for humidity sounding in the upper troposphere are based on passive radiometric sounding of the 183 GHz water absorption band, but the accuracy of these measurements is limited by the presence of clouds. The resulting measurement uncertainty of relative humidity in ice-phase clouds leads to uncertainty in ice crystal growth rates, crystal fall velocities, and ultimately to the water cycle and global climate models. To overcome the cloud-cover limitation of passive radiometric sounding, an active differential absorption radar near 183 GHz can be used. In this method, radar signals scatter off of ice crystals inside clouds, and by measuring how the received signal power depends on the transmitted frequency over the water absorption line, the range-resolved relative humidity inside the cloud can be inferred. In this talk, we will describe progress toward building a compact, highly tunable, continuous-wave 183 GHz radar transceiver for making such measurements. Our work builds on state-of-the-art GaN millimeter-wave power amplifiers available from Industry, as well as JPL-developed GaAs Schottky diode frequency multipliers capable of generating 1 Watt power levels using novel on-chip power-combining methods. The transceiver also relies on a JPL-developed 183 GHz low-noise InP amplifier, which will be protected from transmit noise using an ultra-high isolation quasioptical circular polarization duplexer. Our models indicate that, from an airborne platform, this new radar transceiver will enable relative humidity measurements inside ice clouds with few-percent measurement error and 250 m range resolution. This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with National Aeronautics and Space Administration (NASA).