Radar Detection and Tracking of Small Maritime Targets at High Grazing Angles

The proposed work further develops and supports transition of a long integration mode for radar detection and tracking of small maritime targets at high grazing angles in the presence of highly variable Doppler spectra characteristics that occur in the littoral sea clutter environment. Radar detection of small maritime targets can be very challenging at high grazing angles because the radar reflectivity is masked by the much stronger reflectivity of the surrounding sea especially. Maritime wide area surface search radars have traditionally operated at low altitudes (=1000 ft ) and short coherent integration times (some non-coherently) which provide for low grazing angles where the mean clutter levels are low but where sea spikes returns may be larger than target returns. Short integration times with Scan-to-Scan integration were a necessity to maintain fast search revisit rates to provide detection of limited exposure targets. For persistently exposed targets like small boats and semi-submersibles, an alternative approach is to use longer coherent processing. Coherent processing adds the dimension of the Doppler spectrum as a radar observable. If the Doppler spectra of the small boat's return can be adequately separated from that of the sea then improved detection performance is possible. The Doppler spectra of the littoral seas varies from being rather homogeneous to being highly inhomogeneous with large discrete Doppler packets associated with free and trapped capillaries riding on surface gravity waves and swell. Likewise the target Doppler spectra of the small boat target set of interest can be highly variable containing relatively narrow Doppler spectra from the vessel itself and a much wider response from the speed dependent boat wake and spray.