Statistical Measures of Ambient Noise: Algorithms, Program, and Predictions.
BOLT BERANEK AND NEWMAN INC ARLINGTON VA
Pagination or Media Count:
In a band of rather low frequencies, almost all of the ambient noise in the ocean is generated by ship traffic. If the averaged squared noise pressure in this band is monitored at a point in the ocean, it would be found to fluctuate in a random manner. For a given time, this quantity can be regarded as a random variable X characterized by a probability density function. Although this function contains information about the variability of X, it gives no information about its time variation. If X sub tau represents observations taking place tau time units after observations X, the joint probability density of X and X sub tau contains information about the average time variations of X. From this density, lower-order statistical measures can be derived. In order to predict surveillance system performance, the directional characteristics of shipping noise must also be considered. For a first level of approximation, this can be done by predicting the noise arriving from ships within narrow azimuth sectors. The algorithm derived for the calculation of the joint density of X and X sub tau is organized according to shipping routes in an acoustic basin, and the types of ships on those routes. The algorithm first calculates the joint characteristic function and then transforms it to obtain the joint density function.
- Acoustic Detection and Detectors