1. A method for detecting channel-induced and target-induced chirps in a signal or for classifying a target from a signal using spectral feature extraction, the method comprising: in a spectral feature extracting engine: given a signal having impairments including multiplicative and additive noise, removing direct current bias from the signal producing a bias-free signal; transforming the bias-free signal into a time-frequency spectrum; slicing the time-frequency spectrum across time into time-frequency slices, each of the time-frequency slices having spectral content representing a measure of power spectral density of the bias-free signal at a given point in time; computing an initial detection threshold associated with the given signal from the time-frequency slices; comparing, for at least some of the time-frequency slices. the spectral content of a subject time-frequency slice with the computed initial detection threshold to identify an initial detection; determining a spectral detection density as a function of a number of initial detections being identified and number of time-frequency slices being compared; and detecting in a chirp detecting engine channel-induced and target-induced chirp(s) present in the given signal based on the determined spectral detection density or, classifying in a target classifying engine a target from the given signal based on the determined spectral detection density.