抄録
The performance of Cross Correlation Method for identifying aircraft noise was im provedby adding a pre-whitening procedure in advance of the computation of the cross correlation function. The pre-whitening procedure was realized using one or both of pre-emphasis with first order differentiation of signals and inverse filtering based upon linear prediction. In the result of examination with about half of the conventional microphone spacing, the cross correlation function was successfully modified into im pulselike shape by the effect of pre-whitening. It was able to detect changes in time delay of correlation peak, even if the maximum elevation angle of sound arrival was only about 10°. From the result of automatic detection of correlation peak, the best rate of correct peak detection was attained when both pre-emphasis and inverse filtering were applied. The greater part of errors was mis-detection to peaks due to ground reflection, especially in the case of taking-off noise beneath the flight path. Then, a means using a shielding disk and inverted microphone technique was invented for de creasingdetection errors. Finally, a prototype device implementing pre-whitening was successfully developed, resulting in the confirmation of real time operation and improved ability of correlation peak detection.
