| 摘要 |
In a radar system it is necessary to dis-tinguish signals reflected from wanted targets such as aircraft from those reflected from fixed terrain features, known as clutter. The clut-ter signals can in some cases be significantly stronger than the wanted signals. One method for dealing with land clutter is the use of a high resolution clutter map. The area around the radar is considered to be divided into cells, and an array of background signal estimates is maintained for these cells. Whenever a signal is received by the radar, it is compared with the stored background level for the cell it oc-cupies, and a detection is only reported if the signal exceeds the background by a pro-set threshold. Received signals are also used to modify the stored background levels so that the clutter map adapts to the reflections from clutter which are present over long periods. Clutter maps have so far only been used successfully for radars at fixed locations. In the case of a shipborne radar near land, a conventional clutter map will not work wel l. This is because as the ship moves, the positions of land scatterers relative to the ship will not be fixed. Individual terrain featur es will therefore be moved from one clutter map cell to another. In the cell into which a strong scatterer moves, the land clutter reflection s will be reported as targets until the stored background has had time to adapt to the new higher level. Similarly, in the cell which the scatterer has left, the stored background level will be higher than necessary, and may cause actual targets to be suppressed until it has had ti me to adapt to the new lower clutter level. The method of operating a radar system in accordance with the present invention provides compensation of ship movement so that fixed terrain features always stay within the same clutter map cell, periodically re-centering the clutter map so that its origin of co-ordinates does not depart too far from the actual ship position. Two separate clutter maps are used so that one can be re-centered and initialised (filled with suitable background estimates) whilst the other is in use for determining radar detections. A method for accelerating the initialisation time so that re-centering can be achieved sufficiently often during rapid movement is provided, and the updating of cell background levels is combined with the detection process in order to streamline the process and reduce computational load.
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