Airborne source multistatics

HLS Research has participated in several research initiatives for various sponsors pursuing innovative concepts that strive to exploit"ambient"noise sources to illuminate targets and environment features in the underwater acoustic waveguide. This theme has engaged researchers in many fields, such as correlating random seismic noise to image the Earth, correlating surface generated ocean noise to image the seabed, and similar efforts in the EM spectrum where the term"passive radar"has been coined. In this effort, HLS Research will adapt the integrated modeling and signal processing technology developed for these related applications to exploit the advantages provided by using an aircraft already on station to prosecute an ASW mission as an acoustic source. The challenges presented by this concept include: a direct blast that is conceptually always on (requiring capable interference cancellation), a source waveform that may have both narrowband and broadband components but for which no exact replica may be available (and thus has to be recovered from the multiple and interfering arrivals along paths from the aircraft through the rough and moving ocean surface), and relatively extreme source motion as aircraft speeds far exceed typical platform speeds underwater (suggesting wideband Doppler compensation will be an important component).