A radar surveillance system is described in which the radar beam re-visits each area of interest after a short period of time, by electronically reconfiguring a scanned beam to an offset position for an interleaved sub-dwell, within a scan period. This ‘look-back’ capability, where the area under test is re-visited after approximately 1 second, allows the natural de-correlation of sea clutter to take place between the initial and look-back samples of the surveillance area. The re-visit time can be adjusted to best exploit the de-correlation characteristics of the sea clutter return.