A numerical model for electromagnetic scattering from sea ice

A numerical model for scattering from sea ice based on the finite differenc e time domain (FDTD) technique is presented, The sea ice medium is modeled as consisting of randomly located spherical brine scatterers with a specifi ed fractional volume, and the medium is modeled both with and without a ran domly rough boundary to study the relative effects of volume and surface sc attering. A Monte Carlo simulation is used to obtain numerical results for incoherent vv backscattered normalized radar cross sections (RCS's) in the frequency range from 3 to 9 GHz and for incidence angles from 10 degrees to 50 degrees from normal incidence. The computational intensity of the study necessitates an effective permittivity approach to modeling brine pocket e ffects and a nonuniform grid for small scale surface roughness. However, co mparisons with analytical models show that these approximations should intr oduce errors no larger than approximately 3 dB, Incoherent vv cross section s backscattered from sea ice models with a smooth surface show only a small dependence on incidence angle, while results for sea ice models with sligh tly rough surfaces are found to be dominated by surface scattering at incid ence angles less than 30 degrees and by scattering from brine pockets at an gles greater than 30 degrees, As the surface roughness increases, surface s cattering tends to dominate at all incidence angles, Initial comparisons wi th measurements taken with artificially grown sea ice are made, and even th e simplified sea ice model used in the FDTD simulation is found to provide reasonable agreement with measured data trends. The numerical model develop ed can be useful in interpreting measurements when parameters such as surfa ce roughness and scatterer distributions lie outside ranges where analytica l models are valid.