PNNL

Abstract

A relative calibration technique is developed for the U.S. Department of Energy’s (DOE) 37 Atmospheric Radiation Measurement (ARM) user facility Ka-Band ARM Zenith Radars 38 (KAZRs). The technique utilizes the signal attenuation due to water collected on the radome for 39 estimates of the reflectivity factor (Ze) offset. The wet-radome attenuation (WRA) is assumed to 40 follow a logarithmic relationship with rainfall rate in light and moderate rain conditions, measured 41 by a collocated surface disdrometer. A practical advantage of this WRA approach to shorter 42 wavelength radar monitoring is that while it requires a reference disdrometer, it is shown viable 43 for a wider range of collocated disdrometer measurements than traditional disdrometer direct 44 comparisons in light rain. Adding such techniques may provide an additional, cost-effective 45 monitoring tool for remote/longer-term deployments. 46 This technique has been applied during the ARM TRacking Aerosol Convection 47 interactions ExpeRiment (TRACER) from October 2021 through September 2022. The estimated 48 offsets in Ze are evaluated against traditional radar calibration and monitoring methods based on 49 datasets available during this campaign. This WRA technique reports offsets that compare 50 favorably with the mean offsets found between the cloud radars and a nearby disdrometer near the 51 time of rain onset, while also demonstrates similar offset and campaign-long trends with respect 52 to collocated and independently-calibrated reference radars. Overall, the KAZR Ze offsets 53 estimated during TRACER remains stable and at a level 2 dBZ lower than the Ze estimated by 54 disdrometer from the campaign start until the end of June 2022. Thereafter, the radar offsets 55 increase to near 7 dBZ at the end of the campaign.