Inter-node Distance Estimation for Subsurface Drifting Hydrophones Using Ambient Acoustic Noise

As the number of units in underwater sensor arrays grow, low-cost localization becomes increasingly important to maintain network scalability. Methods using ambient ocean noise are promising solutions because they do not require external infrastructure, nor expensive on-board sensors. Here we extend past work in stationary array element localization from correlations of ambient noise to a mobile sensor array. After obtaining inter-node distance estimates using ambient noise correlations, these distances can be used to determine a relative localization of an array of mobile underwater sensor platforms without introducing any external infrastructure or on-board localization sensors.In this work we explore the effects of receiver mobility on inter-node distance estimation via correlations of ambient acoustic noise. Through analysis and simulation, we develop an exact solution along with a more tractable approximation to the peak amplitude of the time-domain Green's function between the two mobile receivers, which provides an estimate of their spatial separation. Here we demonstrate that the mobile noise correlation amplitude at the average time delay between the receivers can be modeled with the wideband ambiguity function of a single sound source. We then use this approximation to discuss selection of design parameters and their effects on the noise correlation function.This work acts as a piece in the larger problem of infrastructure-free localization for mobile underwater sensor networks. Combining a relative localization from this method with the absolute positions of several units could provide an absolute localization of an entire array, without the need for external infrastructure