| 摘要 |
In a radar system it is necessary to distinguish signals reflected from wanted targets such as aircraft from those reflected from fixed terrain features, known as clutter. The clutter 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 occupies, and a detection is only reported if the signal exceeds the background by a pre-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 ship-borne radar near land, a conventional clutter map will not work well. This is because as the ship moves, the positions of land scatterers relative to the ship will not be fixed. Individual terrain features will therefore be moved from one clutter map cell to another. In the cell into which a strong scatterer moves, the land clutter reflections 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 time to adapt to the new lower clutter level. |
