Simulation of bistatic scattering for assessing the application of existing communication satellites to remote sensing of rough surfaces

Communications and navigation satellites may be used as the transmitter sources for bistatic scattering measurements of the Earth's surface. In specific, the GPS satellite constellation is of great interest as these satellites provide multiple incidence angles and operate at L-band frequencies appropriate for remote sensing of soil moisture and ocean surfaces. Inherent in GPS signal is a pseudo noise phase modulation used for ranging and source identification. The ranging capability of GPS signal allows for the implementation of multistatic radar system in a rather straightforward manner. Using a sensitive receiver with a narrow beam that is directed at the ground on an airborne platform, the bistatic signals reflected from the surface can be range gates and measured from which the bistatic scattering coefficients can be retrieved. To examine the feasibility of such multistatic radar measurement of surfaces a sensitivity analysis on system parameters such as receiver, bandwidth, noise figures, antenna beamwidth, orientation, and altitude, as well as bistatic scattering properties of rough surfaces, is carried out in this paper. Rough surface bistatic calculations are performed using a Monte Carlo simulation of rough surfaces of known surface statistics in conjunction with an iterative physical optics approach. It is shown that the signal strength at the receiver is independent of antenna beamwidth (for narrow-beam antennas) and height above the ground and is proportional to the bistatic scattering coefficient of the surface and square of the wavelength.