Reverberation Consistency: DUSS-97 Data

Low frequency active sonar has been highlighted by a number of NATO nations as an important component of the next generation of undersea defense systems. However, the use of low frequencies in a shallow water environment is known to result in a high false alarm rate due to the large number of reverberation returns that can overload automatic tracking and classification algorithms. The SACLANT Undersea Research Centre is currently investigating techniques to aid in the reduction of these false alarms without a reduction in detection probability. To remove reverberation returns a single detection opportunity is usually not enough. Observations over time or from more than one receiving station must be combined to discriminate reverberation from true target returns. This study examined the stability of reverberation features from the Deployable Underwater Surveillance System (DUSS) as a function of time, frequency, and receiving station. DUSS is a multi-static system of small buoys that can cover an area. The experiment was executed in 1997 south of the Island of Elba in Italy. The first station was the NATO research vessel Alliance, which deployed a source and a receiver buoy. The two other elements were receiver buoys forming multi-static stations. Each buoy contained a receiving array formed of 25 calibrated hydrophones on five bars in a star shaped form. A digital compass was used to determine the orientation allowing beamforming relative to the North. Data were analyzed at three frequencies: 1900 Hz, 2700 Hz, and 3500 Hz. The main conclusion is that to associate detections over station and time accurate geographical mapping of the data is essential. Therefore, fixed buoys should have accurate calibrated compasses. Future work will concentrate on data from advanced towed array experiments. (1 table, 20 figures, 3 refs.) The original document contains color images. All DTIC reproductions will be in black and white.