Preliminary Results of an Analysis of Beam Noise in the Mediterranean
NAVAL RESEARCH LAB WASHINGTON DC
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The beam noise measured on the LAMBDA II array system in the Mediterranean Sea is currently being analyzed in two 30 Hz frequency bands A 275-305 Hz band and a 30-60 Hz band. The preliminary results of that analysis, indicate that the beam noise in the HF band, as well as the MF band, is primarily due to shipping. The variation with azimuth in both frequency bands is in qualitative agreement with ship location data. There are, however, many instances where different noise sources contribute in each band, indicating the presence of more than one Acoustic ship class. The beam noise in the HF band exhibits fewer spectral lines than in the MF band and the power in those lines is distributed over a smaller range. As a consequence, the extent of the line clutter due to false targets is a more sensitive function of the detection threshold. This result, together with the results of an earlier analysis, suggests that the 300 Hz line of a Type II target can be detected in a low clutter environment, but that the 50 Hz line should rarely be visible and then only in a high clutter environment. Finally, an algorithm is described which significantly reduces the error in the beam noise that results from three missing hydrophones in the otherwise, equally spaced, HF array segment.
- Acoustic Detection and Detectors