ARM’s scanning cloud radars are fully coherent dual-frequency, dual-polarization Doppler radars mounted on a common scanning pedestal. Each pedestal includes a Ka-band radar (2kW peak power) and the deployment location determines whether the second radar is a W-band (WSACR; 1.7 kW peak power) or X-band (XSACR; 20 kW peak power). At ARM’s tropical sites, X-band radars are paired with the Ka-band because they are better suited for the atmospheric attenuation in this region.
Beamwidth for the X-band is approximately 1 degree, and the Ka-band beamwidth is roughly 0.3 degrees. Due to the narrow antenna beamwidth, ARM’s scanning cloud radars use scanning strategies unlike typical weather radars. Rather than focusing on plan position indicator, or PPI, scans, the X-SACR uses range height indicator, or RHI, scans at numerous azimuths to obtain cloud volume data.
For the second ARM Mobile Facility (AMF2), the X-SACR can be dismounted from the pedestal it shares with the Ka-SACR and mounted on a separate pedestal. This allows the X-SACR to operate more like a weather (precipitation) radar in deployments where such local coverage is lacking.
Measurements collected with the X-SACR are copolar and cross-polar radar reflectivity, Doppler velocity, spectra width and spectra when not scanning, differential Reflectivity (Zdr), correlation coefficient (rho-hv), and specific differential phase (phi-dp).