title: Travel-time tomography in shallow water: experimental demonstration at an ultrasonic scale.
abstract: Acoustic tomography in a shallow ultrasonic waveguide is demonstrated at the laboratory scale between two source-receiver arrays. At a 1/1,000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. Two coplanar arrays record the transfer matrix in the time domain of the waveguide between each pair of source-receiver transducers. A time-domain, double-beamforming algorithm is simultaneously performed on the source and receiver arrays that projects the multi-reflected acoustic echoes into an equivalent set of eigenrays, which are characterized by their travel times and their launch and arrival angles. Travel-time differences are measured for each eigenray every 0.1 s when a thermal plume is generated at a given location in the waveguide. Travel-time tomography inversion is then performed using two forward models based either on ray theory or on the diffraction-based sensitivity kernel. The spatially resolved range and depth inversion data confirm the feasibility of acoustic tomography in shallow water. Comparisons are made between inversion results at 1 and 3 MHz with the inversion procedure using ray theory or the finite-frequency approach. The influence of surface fluctuations at the air-water interface is shown and discussed in the framework of shallow-water ocean tomography.
authors: Institut des Sciences de la Terre, Université Joseph Fourier, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5275, 1381 Rue de la Piscine, Saint-Martin d'Hères, France. philippe.roux@obs.ujf-grenoble.fr
authors: Philippe
authors: P
authors: Roux
authors: Ion
authors: I
authors: Iturbe
authors: Barbara
authors: B
authors: Nicolas
authors: Jean
authors: J
authors: Virieux
authors: Jérôme I
authors: JI
authors: Mars
mesh_terms: D000465:Algorithms; D009038:Motion; D009792:Oceans and Seas; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013696:Temperature; D013997:Time Factors; D014054:Tomography / Q000295:instrumentation; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation; D014867:Water
chemical_list: D014867:Water