Antenna Beam Patterns and Dual-Wavelength Processing

Abstract

The detection of hail with a dual-wavelength radar system can succeed only when the two essentially independent radars used are correctly calibrated, when attenuation is correctly handled, and when the radars sample the same volume in space. The primary point of this paper is to examine the effects of mismatched antenna beam patterns on dual-wavelength processing. We examine and develop techniques to handle calibration problems, range differences, scan-rate-dependent pointing errors, and attenuation. We also develop a technique (using a ground target) to determine the antenna beam patterns of the two antennas and use these to simulate numerically the effects of mismatched antenna beam patterns on dual-wavelength hail signals. With the National Center for Atmospheric Research CP-2 (10.7 cm wavelength) and M33 (3.2 cm wavelength) dual-wavelength radar system, mismatched beam patterns produce numerous erroneous hail signals of large amplitude. Beam patterns must be well matched to avoid producing erroneous hail signals. Mismatched beam patterns may have contributed to erroneous interpretations in several studies using dual-wavelength data.