Analysis on the influence of the multiple scattering effect on millimeter-wave cirrus measurements

To study the role of the multiple scattering effect of ice particles when retrieving the microphysical parameters of cirrus using millimeter-wave radar, spherical and non-spherical ice particle models with gamma size distributions were first established. Then, the XFDTD (X Finite Difference Time Domain) software, GMM (Generalized Multi-particle Mie) and simple addition method were used to calculate the radar cross section (RCS) values for the ice particle models at 94 GHz. For spherical raindrop models, the RCS values computed using the simple addition method are smaller than those computed using the XFDTD software and GMM algorithm. The maximum absolute difference reached 10.94 dB for ice particles in a volume of 0.1 m3 and 10.493 dB in a volume of 0.2 m3. For non-spherical raindrop models, the absolute difference between the XFDTD and the simple addition method was 1.632 dB for ice particles in a volume of 0.1 m3 and 3.971 dB in a volume of 0.2 m3. When the ice water content was constant, the radar reflectivity factor of the ice particles computed using the XFDTD was larger than that computed with the simple addition method, with an absolute difference of 1.351 dB in a volume of 0.1 m3 and 1.118 dB in a volume of 0.2 m3.