GPS-Based Bistatic Radar for Terrain Awareness - Methods and Preliminary Results

The application of GPS bistatic radar to terrain awareness is presented. By measuring the path delay between direct and reflected GPS signals, a measure of distance to terrain can be inferred. This direct land measurement can provide an integrity check to an aircraft's location relative to surrounding terrain given by the standard GPS position solutions coupled with a terrain model. Specifically, the methods of construction for measured and expected path delays between direct and land reflected GPS signals are described. Preliminary results are presented and factors affecting performance are identified. Land reflection data obtained with a delay mapping receiver over Las Cruces, New Mexico show promising results. Agreement between expected and measured path delays for a 2-minute section of data has reached rootmean- square residual levels of less than 13m with standard deviations less than 10.5m. The main factor affecting performance at this point is the modeling of reflected signal correlation waveforms, to be the focus of improvement in future study. We are hopeful that this approach will provide a low-cost augmentation to, or implementation of, terrain awareness and warning systems using GPS bistatic radar.