Fast Subsurface Sar Simulator Based on Geometrical Optics

In previous work [1], we investigated the design of a two frequency synthetic aperture radar interferometer for estimating the sand layer thickness and the bedrock topography in deserts and arid areas. This was shown to be very useful in many applications such as oil field explorations, environmental studies and archaeological surveys. In order to test the inversion algorithm for different complex top surface scenarios, a fast subsurface SAR simulator is required. Such a simulator can also be used to perform subsurface focusing to further improve the accuracy of the height estimation. Based on scaled model measurements [2], it was found that geometrical optics-based ray launching provides a suitable approximation for the wave propagation through the sand on condition that the top sand surface undulations are much larger than the operating wavelength. Compared to conventional SAR simulators [3] where the path between the radar and the scattering centers is a straight line, subsurface SAR simulations are much more computationally intensive since the path is a straight line from the radar to the top surface incidence point then another straight line with a different slope from the incidence point to the subsurface scattering center requiring the solution of a set of nonlinear equations to determine the incidence point for each scattering center as well as the transmission coefficient for the used polarization(s). In this work, we exploit the fact that the top sand surface is relatively smooth to significantly enhance the speed of the subsurface SAR simulations. We also present a sample test scenario of a common sand dune and the use of the inversion algorithm developed in [1] to determine the subsurface height.