A 183 GHz Humidity Sounding Radar Transceiver

We will develop a compact and tunable radar transceiver operating in the underutilized short-millimeter-wave frequency regime to enable high-precision global mapping of humidity inside upper tropospheric (UT) clouds for the first time. This work addresses the Focus Area of Climate Variability and Change because clouds are a leading source of uncertainty in estimating the climate sensitivity from global models, and UT humidity affects radiative feedback and cloud formation. Over three years we will build and validate a radar transceiver to enable humidity sounding inside UT clouds using the technique of Differential Absorption Radar (DAR) operating around the 183 GHz water absorption line. By capitalizing on recently-developed III-V semiconductor Schottky diode and amplifier millimeter-wave devices with state-of-the-art efficiency and power handling capabilities, our approach offers the fastest, lowest cost, and lowest risk route to realizing an active instrument capable of range-resolved water vapor absorption measurements in cirrus clouds. The transceiver will integrate all-solid-state source and detector devices inside a compact (~10x6x2 cm) module with 5% tuning bandwidth. Continuous, 1 W transmit power will be reached in two steps. First, commercially available GaN power amplifiers at 90 GHz will drive a JPL-fabricated GaAs diode frequency doubler with 20% conversion efficiency and 0.5 W output power capacity. Then 1 W will be achieved either through a chip-stack waveguide power-combining geometry or, pending commercial availability in 2016, by 183 GHz power amplifiers. For receiving, an InP low-noise amplifier and a 100 dB isolation quasioptical duplexer will achieve a noise temperature of 500 K even while transmitting. The DAR technique will be validated in ground-based measurements using a custom-built millimeter-wave radar test bench. We anticipate demonstrating DAR sensitivities with few-percent precision, thus enabling a new class of future airborne and orbital measurements for cloud and climate science.

Accelerate mission development and reduce risk by developing critical components and subsystems for advanced instruments and observing systems

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