Abstract
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.
Highlights
Electromagnetic waves in the radar bands propagating through the atmosphere are affected by clouds via scattering, absorption, and attenuation, which greatly affects the remote sensing performance of millimeter-wave radar, and affects the retrieval accuracy of microphysical parameters of cirrus
There are various algorithms to calculate the scattering of ice particles, including FDTD,[1] DDA discrete dipole approximation (DDA),[2] T-matrix,[3] finite element method (FEM),[4] method of moments (MOM),[5] geometric optical method (GOM),[6] and anomalous diffraction theory (ADT).[7]
The radar cross section (RCS) values computed using the simple addition method are smaller than those computed with the XFDTD software and the generalized multiple-particle Mie theory (GMM) algorithm, and the maximum absolute differences reach 10.94 dB (0.1 m3) and 10.493 (0.2 m3); this means that the multiple scattering effect of the ensemble of particles is an important factor affecting the retrieval accuracy of the microphysical parameters of particles
Summary
Electromagnetic waves in the radar bands propagating through the atmosphere are affected by clouds via scattering, absorption, and attenuation, which greatly affects the remote sensing performance of millimeter-wave radar, and affects the retrieval accuracy of microphysical parameters of cirrus. The above literature has studied the effect of non-spherical ice particles; ice particles have a certain size distribution in actual detection and multiple scattering effects should be considered. The objective of this paper is to study the multiple scattering effect of non-spherical ice particles with a certain size distribution with a conventional millimeter-wave radar band using the FDTD algorithm and to compare the results with those from a simple addition method. The results can provide a theoretical basis to accurately retrieve the microphysical characteristics of cirrus
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