TERRAIN-FOLLOWING RADAR SYSTEM

In a terrain-following radar system, spatial filter means for improved indication of discrete terrain obstacles such as towers, Terrain-following samples ( DELTA gamma ) for a given radar range-time are time averaged over a preselected plurality (n) of successive pulse repetition intervals, the time-averaged samples being thresholded by a time-varied threshold value which varies from a preselected + DELTA gamma maximum through a null to a preselected - DELTA gamma maximum over each system pulse repetition period, as to be indicative of a probable terrain warning situation of interest at such sampled range. Non-averaged samples are dual-level thresholded by the time-varied threshold value and tested to determine the occurrence of at least a preselected number (M) of samples of substantially like magnitudes out of n successive pulse repetition intervals as to be indicative of a detected probable discrete obstacle or tower occurring within the general clutter at such sampled range. The occurrence of such "M out of n samples" condition having a common value larger than (worse than) the time-averaged clutter value DELTA gamma avg results in substitution of such "worst" case filtered value for the time-average clutter value, for terrain following purposes. In other words, the worst one of the commonly occurring M out of n tower signal and time-averaged clutter signal is applied as an input to a bipolar peak detector for determining the maximum maneuver or warning signal condition.