Snowfall rate and supercooled liquid water content retrieval using the dual-frequency radar technique

In winter weather situations, accretion of supercooled liquid water (SLW) droplets onto aircraft results in icing. Icing continues to be one of the primary causes of aviation accidents. The problem of icing detection is that of identification of SLW. Direct remote sensing of SLW is almost impossible using conventional S-, C-, X- and K-Band radars because of the negligible backscatter cross section of cloud droplets (diameters < = 50 microns). Microwave radiometers can remotely estimate the path-integrated SLW, but cannot themselves provide spatial distribution. The differential attenuation parameter, whose direct measurement is available via the dual-frequency radar technique (X- and K-Band) may be able to provide spatial distribution of SLW. The dual-frequency technique is susceptible to problems which are due to non-Rayleigh scattering at the shorter of the two wavelengths. Particularly in the presence of aggregates and gradients in snowfall rate along the radar beam, the dual-frequency technique might yield false SLW concentrations because of non-Rayleigh scattering effects. However, regions of considerable SLW concentrations may not co-exist with aggregates. Thus, by carefully avoiding the non-Rayleigh scattering regions, a better estimate of the differential attenuation can be obtained. Also, dual-frequency ratio and X-band reflectivity observations can be used to estimate the snowfall rate. Radar model computations at X- and K-band are presented in this paper. Precipitation media comprising of snow and SLW are considered. Primarily the Rayleigh-Gans scattering method is used to investigate scattering and attenuation characteristics. Modeling results are analyzed to improve radar retrieval of SLW and snowfall rate.