GRAWAC: DUAL-FREQUENCY FMCW RADAR WITH DIFFERENTIAL ABSORPTION MEASUREMENT IN G-BAND FOR WATER VAPOR AND ARCTIC CLOUDS

J. Goliasch¹, S. Schnitt², M. Mech², L. Bühler², T. Rose¹, S. Crewell²

¹RPG Radiometer physics GmbH, ²Institute for Geophysics and Meteorology, University of Cologne

Quantifying the vertical distribution of water vapor throughout the lower troposphere is central to understanding cloud and precipitation formation and evolution processes. Current observational systems perform well in clear-sky conditions, but lack vertical resolution and accuracy in cloudy or precipitating conditions.

We demonstrate the development of a novel and unique Doppler capable FMCW-RADAR. The Instrument allows for differential absorption measurements in G-Band on the water vapor absorption line to derive water vapor profiles in Clouds and precipitation.

In this presentation, insights on the technical details of the GRaWAC Instrument are given. This FMCW Radar allows for simultaneous dual frequency operation at 167.3 and 174.7 GHz. The Radar consists of a bistatic antenna design with a beam width of 0.36°. Chirp generation is realized by Direct Digital Synthesis and the chirps for transmitter and receiver are fully synchronized for both frequencies. By applying the Differential Absorption Radar (DAR) technique retrieval of water vapor profiles in cloudy and precipitating conditions is achieved. The Instrument has been operated for observation periods at ground-based sites in the Arctic and the mid-latitudes. With GRaWAC mounted in a bellypod in dual-frequency configuration with the W-band radar Mirac, first airborne measurements were performed from Kiruna, Sweden aboard the Alfred-Wegener-Institute’s Polar-6 aircraft. We here illustrate first results of measured radar moments, spectra and retrieved water vapor profiles. Radar measurements and retrieval of water vapor profiles are evaluated using radiosonde and dropsonde measurements. We further discuss the potential for synergy with passive microwave radiometer measurements and conventional cloud radar measurements for water vapor profiling and cloud microphysics.