Wet-Radome Attenuation in ARM Cloud Radars and Its Utilization in Radar Calibration Using Disdrometer Measurements

Abstract. A relative calibration technique is developed for the U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) user facility Ka-Band ARM Zenith Radars (KAZRs). The technique utilizes the signal attenuation due to water collected on the radome for estimates of the reflectivity factor (Ze) offset. The wet-radome attenuation (WRA) is assumed to follow a logarithmic relationship with rainfall rate in light and moderate rain conditions, measured by a collocated surface disdrometer. A practical advantage of this WRA approach to shorter-wavelength radar monitoring is that while it requires a reference disdrometer, it is shown viable for a wider range of collocated disdrometer measurements than traditional disdrometer direct comparisons in light rain. Adding such techniques may provide an additional, cost-effective monitoring tool for remote/longer-term deployments.

This technique has been applied during the ARM TRacking Aerosol Convection interactions ExpeRiment (TRACER) from October 2021 through September 2022. The estimated offsets in Ze are evaluated against traditional radar calibration and monitoring methods based on datasets available during this campaign. This WRA technique reports offsets that compare favorably with the mean offsets found between the cloud radars and a nearby disdrometer near the time of rain onset, while also demonstrates similar offset and campaign-long trends with respect to collocated and independently-calibrated reference radars. Overall, the KAZR Ze offsets estimated during TRACER remains stable and at a level 2 dBZ lower than the Ze estimated by disdrometer from the campaign start until the end of June 2022. Thereafter, the radar offsets increase to near 7 dBZ at the end of the campaign.