Hydroradar.

Hydro-Radar

The recent addition of differential phase (Kdp) capability now allows ETL's X-band radar to circumvent the attenuation problem by using signal phase rather than amplitude to measure rainfall. The method is also superior to traditional reflectivity-based estimates of rain intensity in that it avoids problems associated with calibration, partial beam filling, partial blockage by terrain, the presence of hail, and because it is less affected by variations in drop size distribution. Light to moderate rain rates are more readily measured at shorter wavelengths, such as X-band, with the differential phase method than can be done at longer wavelengths. The radar also measures differential reflectivity, ZDR, which further increases the rain rate accuracies and allows inferences of particle type. Moreover, ETL is implementing automated, remote, unattended operating capabilities for this radar. These new features combine to make the ETL X-band research radar a very attractive tool for hydrometeorology applications, especially for small to moderate size watersheds and in complex terrain.

The radar's differential phase capability has been tested in Colorado and Texas. It was also employed at Wallops Island, Virginia, in 2001 for rain statistics studies to support of NASA's space-borne Advanced Microwave Scanning Radiometer. These experiments have shown that the X-band differential phase estimates of rain rate and rainfall accumulation are applicable for even heavier intensities than originally anticipated. For more details see the short conference article. On-going tests on the northern California coast also demonstrated the usefullness of this kind of radar for filling gaps in the National Weather Service's area coverage of WSR-88D storm surveillance radars.