Melting layer model evaluation in Singapore

Propagation characteristics in the melting layer are not only relevant to slant path attenuation predictions for satellite links but also for spaceborne radar remote sensing of rainfall. In the latter case, the radar retrieval algorithms rely heavily on accurate estimates of the melting layer attenuation, since the radar signal traverses this region twice, both in the forward direction and in the return direction. Several models have been proposed for predicting the attenuation in the melting layer. One such method is the non-coalescence-non-break up (N-N) model based on spherical melting particles made of dielectric composites, Nishitsuji and Hirayama (1971). The model assumes the melting particles to be composed of a homogenous mixture of water, ice and air, and calculates the complex permittivity from Wiener\´s theory. The calculation includes the parameter "form factor", U, as well as the volume content of water, ice and air. The height variation of these parameters has been inferred fairly accurately in the past from satellite propagation data, Awaka et al. (1985). This paper compares the N-N model predictions with Doppler radar measurements taken in Singapore. Comparisons are presented in terms of the radar reflectivity (dBZ) as well as the mean fall speed (View) and the Doppler width (w).