Comparison of Attenuation Correction Algorithms for Single-Polarized X-Band Radars

Attenuation due to liquid water is one of the largest uncertainties in radar observations. The magnitude of attenuation is generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C- and S-band systems. On the other hand, X-band radars can provide precipitation fields in higher temporal and spatial resolution and are more mobile and easier to install due to smaller antennas. Dual-polarization can be used to estimate attenuation but those systems are much more expensive than single-polarized radars.

Hitschfeld and Bordan (1954) proposed an algorithm for attenuation correction in single-polarized system but it gets unstable in case of strong attenuation. Therefore, methods have been developed that restrict attenuation correction to keep the algorithm stable, using e.g. surface echo (for space borne radars) and mountain returns (for ground radars) or adjustment of the radar constant. All these methods are based on the statistical relation between reflectivity and specific attenuation. Another way to correct for attenuation in X-band radar observations, is to use additional information from less attenuated radar systems, e.g. the ratio between X-band and C- or S-band radar measurements.

We will present a comparison of the original HB algorithm and three algorithms based on the statistical relation between reflectivity and specific attenuation as well as two methods implementing C-band radar measurements. Their performance in a convective and in a stratiform precipitation event will be investigated. Furthermore, a study of five month of radar observations examines the long-term performance of each algorithm.

Hitschfeld, W. and Bordan, J.: Errors Inherent in the Radar Measurement of Rainfall at Attenuating Wavelengths, J. Meteorol., 11, 58--67, 1954