Reduced rank models for travel time estimation of low order mode pulses

Abstract

Mode travel time estimation in the presence of internal waves (IWs) is a challenging problem. IWs perturb the sound speed, which results in travel time wander and mode scattering. A standard approach to travel time estimation is to pulse compress the broadband signal, pick the peak of the compressed time series, and average the peak time over multiple receptions to reduce variance. The peak-picking approach implicitly assumes there is a single strong arrival and does not perform well when there are multiple arrivals due to scattering. This article presents a statistical model for the scattered mode arrivals and uses the model to design improved travel time estimators. The model is based on an Empirical Orthogonal Function (EOF) analysis of the mode time series. Range-dependent simulations and data from the Long-range Ocean Acoustic Propagation Experiment (LOAPEX) indicate that the modes are represented by a small number of EOFs. The reduced-rank EOF model is used to construct a travel time estimator based on the Matched Subspace Detector (MSD). Analysis of simulation and experimental data show that the MSDs are more robust to IW scattering than peak picking. The simulation analysis also highlights how IWs affect the mode excitation by the source.

Vertical line array measurements of ambient noise in the North Pacific

“…Prior work on these experiments has been reported by Van Uffelen et al (2009), Van Uffelen et al (2010, Udovydchenkov and Brown (2008), Udovydchenkov et al (2012), Stephen et al (2009), Grigorieva et al (2009), Chandrayadula et al (2013a, and Chandrayadula et al (2013b). Figure 2 shows the annual sound speed profile calculated using the Del Grosso (1974) sound-speed equation and annual objectively analyzed temperature and salinity profiles for the SPICEX location from the World Ocean Atlas 2005 Locarnini et al, 2006), along with a diagram of the hydrophone arrays used in the experiment.…”

Deep Water Ambient Noise and Mode Processing

“…The two journal articles were published in the October 2013 special issue on deep water ocean acoustics in the Journal of the Acoustical Society of America (JASA). The first of these articles, by Chandrayadula, Worcester, Dzieciuch, Mercer, Andrew, and Howe, describes a statistical model for low mode signals propagating through internal waves and uses that model to design improved travel time estimators [3]. It analyzes data from the Long Range Ocean Acoustic Propagation Experiment (LOAPEX).…”

Deep Water Ambient Noise and Mode Processing

“…The article by Chandrayadula, Wage, Worcester, Dzieciuch, Mercer, Andrew, and Howe [3] describes a statistical model for low mode signals propagating through internal waves and uses that model to design improved travel time estimators. It analyzes data from the Long Range Ocean Acoustic Propagation Experiment (LOAPEX).…”