Conditioning lofargrams using empirical mode decomposition

Recorded sonar data is processed in many different ways to extract target information from the source signals. Trying to separate different sources of sound, or identifying vessels by examining the emitted tonals, is often done in the time-frequency domain, e.g. using the lofargram. Narrowband components appear as long-time duration lines and transients as broadband short-time duration pulses. The transients may be generated by the same source as the tonal lines or by other sources in the vicinity, or they can be a part of the additional ambient noise. If transients and narrowband components are mixed in the estimation window, distortion and masking of the lines may occur especially in low SNR regimes. A method for improving the visibility of relevant spectral lines in a lofargram is applied. Instead of using filtering or outlier rejection methods to condition the data, the signal is decomposed by using the method of empirical decomposition.