Detection of Lofar Lines

. The problem of extracting spectral lines from sonar images is treated using a complete scheme that combines an edge detector with a line tracking process. That is, the edge detection process allows øltering the sonar image and ønding a region (zero-crossings of the second derivative of the sonar image) that includes a spectral line. The founded region is then used to initialize and to limit the extent of the line tracking process. Comparative performance results conørm the eOEciency and the reliability of the proposed approach. 1 Introduction The fundamental objective of a passive sonar system is to detect the presence of target-like signals in underwater acoustic øelds. Signals emitted from the acoustic source are recorded by an array of hydrophones, beamformed and spectrum analysed. Narrow-band components of the signals' result provide an image of frequency power versus time, more commonly referred to as a ilofargramj. Lofar is an acronym for LOw Frequency Analysis and Recording. ..