| 摘要 |
<p>An apparatus for determining the time of the closest point of approach of an object such as a taxiing aircraft includes a microphone (12) producing a signal in response to the sound energy of the engines of the aircraft. Low and high pass filters (16,18) are also provided to receive the signal and pass low frequency signals having a frequency less than or equal to 1 KHZ and high frequency signals having a frequency greater than or equal to 1.5 KHZ respectively. A demodulator (24,26) receives the signals from both the high and low pass filters and is operable to produce a low frequency envelope from the low signal and a high frequency envelope from the high signal. Finally, a comparator (28,30,32) receives the low frequency envelope and the high frequency envelope and compares the amplitudes so as to provide a signal at the point in time when the amplitude of the low frequency envelope exceeds the amplitude of the high frequency envelope, this signal indicating in real time the point of closest appraoch of the aircraft.</p> |
