A time-frequency method for classifying objects at low frequencies

Once they have been detected, objects buried in sediments need to be classified (i.e. given a category name : man-made or natural target). Because sound absorption in sediments increases exponentially with frequency, the sonars designed for the detection of buried objects usually operate in the low to medium frequency range 2 kHz - 50 kHz. At these frequencies, only poor resolutions can be obtained with conventional sonars. This increases the need for new classification criteria. This article gives new methods of analysis and decision criteria based on the time-frequency characteristics of the impulse response of the target.