Discrete dipole method verification of physical optics approximation when calculating light backscattering
K.S. Salnikov1, A.V. Konoshonkin1,2, I.V. Tkachev1, N.V. Kustova1,2, V.A. Shishko1,2, D.N. Timofeev1, N. Kan1
1V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
2National Research Tomsk State University, Tomsk, Russia
Keywords: light scattering, physical optics approximation, method of discrete dipole, atmospheric ice crystals, cirrus clouds
Abstract
In atmospheric remote sensing, particularly in the interpretation of lidar signals from cirrus clouds, the accuracy of light scattering modeling on non-spherical randomly oriented ice particles plays a crucial role. Although the physical optics approximation is commonly used due to its computational efficiency, it does not always provide sufficient accuracy, especially when particle sizes are comparable to the wavelength of incident radiation. This introduces systematic errors into scattering matrix databases used for solving inverse problems. This study employs the discrete dipole approximation to verify the validity of the physical optics approximation. The primary focus is on comparing results obtained at wavelengths of 0.532 and 1.064 mm for particles of various shapes and sizes from 2 to 8 wavelengths. It is shown that in this size range, the physical optics approximation leads to relative errors of up to 20% in the linear depolarization ratio and reduces the backscattering intensity by half. The findings enable a more precise estimation of the applicability limits of the physical optics approximation and provide corrections for existing scattering matrix databases. This, in turn, will improve the accuracy of lidar data interpretation and enhance the quality of microphysical retrievals for cirrus clouds.
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