NOAA/ETL's Polarization-Upgraded X-band "Hydro" Radar

For three decades NOAA/ETL has operated and continually refined its transportable X-band Doppler radars for atmospheric and ocean surface research. Recent major upgrades to one of these scanning radars have greatly improved its usefulness, especially for hydrometeorology research. The recent improvements include the addition of a sophisticated new data system, new polarization diversity capabilities, and automation to allow longer periods of unattended and remotely controlled operations. The polarization capabilities include measurements of differential phase (Kdp), differential reflectivity (ZDR), and H-V correlation coefficient at zero lag. To our knowledge, this is the first X-band radar to employ differential phase methods. In preliminary studies, the polarization measurements have been used to overcome attenuation problems that have traditionally prevented X-band reflectivity data from yielding usefully accurate quantitative estimates of rainfall. Together, these new features make this an attractive system for high-resolution measurements of snowfall and light to moderate rainfall over ranges of approximately 50 km. The radar is especially well suited for hydrometeorology studies in small to moderate size watersheds, including mountainous and urban areas. High-resolution rain measurements obtained with this radar in Colorado and Virginia are currently being used to assess sub-pixel-size rain variability for NASA's space-borne Advanced Microwave Scanning Radiometer. An overview will be presented of the radar hardware configuration and data system architecture. Algorithms and procedures developed for estimating rain intensity at X-band from Kdp and ZDR measurements will be reviewed along with examples comparing these estimates to rain gage measurements.