Analysis of a Dual-Wavelength Surface Reference Radar Technique

Among the methods that have been proposed for estimating precipitation parameters from a down-looking radar are those that use the scattered power from the surface to infer path attenuation. In this paper, an analysis of a dual-wavelength surface reference technique (DSRT) is presented. The principal of the method is that the ratio of the backscattered power from the surface at one wavelength to that at a second wavelength is proportional to the differential attenuation of the signals through the intervening rain. To account for differences in the backscattering cross section of the surface a σ
⁰
, and in the radar calibration constant at the two wavelengths, measurements are made of the surface return power during clear air conditions. The characteristics of the method are best understood by comparing it to two closely related methods: the single-wavelength surface reference technique (SRT) and the standard dual-wavelength technique (DWT). A comparison between the DWT and the DSRT shows that the rain rate estimates are identical in form and that the surface reference can be obtained from the standard estimate by replacing the statistics of the rain reflectivity with those of σ
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Advantages of the DSRT relative to its single wavelength counterpart occur when the wavelength correlation in σ
⁰
is high or when the mean values of σ
⁰
at the two wavelengths are nearly equal. To treat the methods under less restrictive assumptions a simulation is used. Error statistics of the rain rate estimates are presented for a space-borne radar operating at an attenuating wavelength.