Adaptive filtering for air-to-ground surveillance

This paper introduces a new concept for air-to-ground noise radar based on adaptive filtering. A transmitting antenna illuminates a region of interest with a continuous, noise waveform. The processor within the receiver treats the illuminated scene as a linear system with unknown coefficients which filters the transmitted signal. Given access to the transmitted waveform and the digitized backscattered signal, the receiver adaptively estimates the unknown filter coefficients, using the same processing architecture as a wireless channel equalizer, and continues to update their values as the transmitter and receiver traverse their flight paths. The adapted filters correspond to range profiles of the illuminated scene which may be Doppler processed to yield synthetic aperture imagery.