Space-Based Bistatic GPS Radar Orbit Analysis

There has been significant research into the use of reflected GPS signals for remote sensing. The reflected GPS signals may contain information on soil moisture, ocean waves, and altitude [1]-[4]. Space radar systems have also been a topic of intense interest for several decades, as a means of providing global coverage for both military and geoscience applications [5]-[7]. These systems implement Synthetic Aperture Radar (SAR), Ground Moving Target Indicator (GMTI), and Space Time Adaptive Processing (STAP) algorithms to detect targets and form images. Orbit selection is important for these systems to provide optimum coverage and performance. By using reflected GPS signals to implement space-based bistatic radar, a more robust and cost-effective system could be fielded. However, the performance analysis of such a system would be complex, since the orbits of the receiving spacecraft and the GPS constellation will be significantly different, and their interactions dynamic. This relationship between the receiving satellite's orbit and the GPS constellation was the subject of the research. A prototype antenna array was used to estimate the resolution and signal levels of the system for various transmitter/receiver relationships. Based on an understanding of the desired signal characteristics for bistatic GPS, a family of orbits was simulated to determine the dependency on inclinations and altitudes.