Accurate estimation of the duration of tonal signals emitted by marine mammals

Passive acoustic marine mammals detection and classification is of great importance nowadays. The goal of this article is to present a tool that can be used to accurately measure the duration of tonal emissions from marine mammals, helping to classify them. Marine mammals emissions can be split into two different kinds and one of them is tonal emission. It can be defined by its narrow band frequency pattern. Narrow band signals can be detected in the time/frequency space thanks to the use of the spectrogram and thanks to a quadratic contrast criterion. The expression of this criterion for signal-only and noise-only is straightforward. This article will introduce the expression of a lower bound of the expectation of the criterion when signal and noise are mixed. As this lower bound is a function of signal to noise ratio, it can be used to threshold the criterion with the desired signal to noise ratio value. When the criterion is computed along time on a sliding window, narrow band signals with a higher snr than the thresholding one are detected as soon as they appear and until they vanish, giving an accurate estimation of the duration of such signals.