title: 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.
authors.affiliation: Department of Oceanography, Naval Postgraduate School, 833 Dyer Road, Monterey, California 93943.
authors.forename: Tarun K
authors.initials: TK
authors.lastname: Chandrayadula
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: Wage
authors.forename: Peter F
authors.initials: PF
authors.lastname: Worcester
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Dzieciuch
authors.forename: James A
authors.initials: JA
authors.lastname: Mercer
authors.forename: Rex K
authors.initials: RK
authors.lastname: Andrew
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Howe
mesh_terms: D000162:Acoustics; D003198:Computer Simulation; D008962:Models, Theoretical; D009038:Motion; D009716:Numerical Analysis, Computer-Assisted; D009791:Oceanography / Q000379:methods*; D009792:Oceans and Seas; D012542:Scattering, Radiation; D012623:Seawater; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013997:Time Factors; D014872:Water Movements