Fast maximum likelihood estimation with multiple signal initialization

We are concerned with signal processing of acoustic signals resulting from active transmissions by high frequency sonar systems. These signals consist of structured interference related to propagation effects in the media, reflections from targets, and measurement noise. The methods herein model these signals as replicas of the transmitted signal, scaled in amplitude and time, and delayed. Furthermore, we are interested in signals with `simple´ time frequency profiles, such as linear frequency modulated (LFM) or hyperbolic frequency modulated (HFM) signals. These signals have the underlying property that the principle ridge of the autoambiguity function crosses the mid-point of the time-frequency plane in a smooth manner, with a simple relationship between time delay and time scaling (frequency shifting). This paper describes a method for estimating the delay and time scale of the signal components using fast maximum likelihood, while preserving the high resolution property of related time delay estimation techniques