Improved torpedo range estimation using modified fast orthogonal search techniques

This work introduces a modified torpedo detection algorithm (MTDA) that improves upon the range estimates of an earlier torpedo detection algorithm (TDA). The original TDA detects the presence of a direct path and a surface reflected path for a torpedo acoustic tonal using the fast orthogonal search (FOS) algorithm. In the original TDA the candidate functions used by FOS were sinusoidal functions at a constant frequency. Using the frequencies of the direct and reflected path signal, the TDA estimated the torpedo range. It is known that the frequency of the direct path and reflect path signal will vary in time. It is also well known that correlating a received signal with the expected signal results in the lowest probability of error in detection (matched filter). Thus in this work the candidate functions used by FOS are functions whose frequencies vary in time (chirp signals) as theoretically expected for the direct and reflected path signals. Also, the FOS algorithm is modified to fit the direct and reflected paths in pairs. The pair of frequencies that fit the highest energy is determined to be the direct and reflected path signal and the range used to generate that candidate pair is used as the range estimate. The MTDA algorithm is simulated for a torpedo approaching an receiver at several angles and the range estimations are shown. These results are compared with the earlier TDA and shown to be significantly improved.