Radar reflection from clouds: gigahertz backscatter cross sections and Doppler spectra

This work deals with reflection of GHz radar signals from typical clouds over The Netherlands. Four principal mechanisms of reflection are identified. While the backscatter cross sections for these are mostly well known, there is a need to identify which, if any, are dominant in each frequency range. Numerical studies of superpositions of the main backscatter mechanisms are presented for a range of parameter values thought to occur commonly. These studies confirm previous results, but are generalized to incorporate gamma-function particle drop-size distributions. The results are relatively insensitive to the power of the diameter in the distribution function. The Doppler spectra of the reflected signals sometimes exhibit a bimodal form. One possible mechanism investigated here is the observation of reflections that occur simultaneously from turbulently moving globules of particles and from incoherent reflections from particles with diameter-dependent spreads in velocities.