This paper extends the NURC distributed multihypothesis tracking technology to include Doppler sensitive (CW) processing. The assessment of the value-added of CW processing in automated undersea detection and tracking is ongoing.
Abstract-Cardioid or triplet towed arrays are utilized in sonar applications to resolve left/right ambiguity by placing a null on the ambiguous direction. This leaves an uncalibrated residual signal on the opposite direction from which the desired signal is arriving. Here the mechanism of cardioid beamforming is presented and analytical expressions for the calibration of continuous wave (CW) and linear frequency-modulated (LFM) signals are derived. The validity of these expressions is verified using simulated and real data. The same data sets are also used for comparing the performance between the standard beamformer and a modified version designed to suppress endfire singularities. The effect of correlated vs. uncorrelated intratriplet noise is assessed using a simulation scenario with a point target.
Seafloor features that cause low-frequency, active sonar clutter are discussed and illustrated with data gathered in the Mediterranean Sea for signals with a 1 kHz bandwidth, centered on 1.3 kHz. A method is proposed to reduce the number of sonar contacts formed due to random returns in the data, i.e. "clutter points". The method uses band-pass filters to split the signal into a number of sub-bands and processes the sub-band data after contact-forming, using knowledge of the physical causes of clutter to reject clutter while retaining real contacts. Comparisons are made between sub-band and full-band processing and the improvements obtainable via the method are illustrated using the measured data with a shipwreck target. It is shown that the proportion of contacts associated with man-made features is increased when sub-band processing is used, relative to the full-band case.
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