| 摘要 |
<p>PURPOSE: To discriminate a bird group definitely from a target (vessel, rain cloud, land, etc.). CONSTITUTION: A Doppler frequency component DF having a predetermined bandwidth or above is extracted from Doppler frequency components DF extracted from a reflected signal VD through a Doppler filter 51 and it is regarded as a bird group. Since each bird flaps the wings, the Doppler frequency component DF has a predetermined bandwidth. On the other hand, the Dappler frequency component DF of a vessel is normally constant, and even if the vessel moves the Doppler frequency component DF is very low. Furthermore, the Doppler frequency component DF of wind cloud present in a relatively low sky and frequently mistaken for a bird group is constant or increases constantly. Since the Doppler frequency component DF related to a land depends upon the speed of a host vessel, it can be removed easily. Consequently, a target including a Doppler frequency component DF having a predetermined bandwidth or above can be regarded as a bird group.</p> |
