Beam forming on bottom-interacting tow-ship noise

The MAPEX2000 experiments were conducted in the Mediterranean Sea in March, 2000 to determine seabed properties using a towed acoustic source and receiver array. Towed systems are advantageous because they are easy to deploy from a ship and the moving platform offers the possibility for estimating spatially variable (range-dependent) seabed properties. In this paper, seabed parameters are determined using a matched-field geoacoustic inversion approach with measured, towed array data. Previous research has successfully applied matched-field geoacoustic inversion techniques to measured acoustic data. However, in nearly all cases the inverted data were collected on moored, vertical receiver arrays. Results here show that seabed parameters can also be extracted by inverting acoustic measurements from a towed array of receivers, and these agree with those inverted using data received simultaneously on a vertical array. These findings imply that a practical technique could be developed to map range-dependent seabed parameters over large areas using a towed acoustic system. An example of such a range-dependent inversion is given using measurements from the MAPEX2000 experiments.

Section: Fig 2 Measured Time Seriesmentioning

confidence: 99%

Range-dependent seabed characterization by inversion of acoustic data from a towed receiver array

Siderius

Nielsen

Gerstoft

2002

“…For reasons related to localization and operational advantages, there exists a high level of interest in using towed horizontal line arrays ͑HLAs͒ for geoacoustic inversions. [6][7][8][9][10][11][12][13] With a towed array, there is the possibility of using ship self-noise as the source. These inversions yield bottom properties of the local area, rather than an average over the traditionally longer source-receiver range.…”

Section: Introductionmentioning

confidence: 99%

Consistency and reliability of geoacoustic inversions with a horizontal line array

Fialkowski

Yang

Yoo

et al. 2006

Geoacoustic inversions with a towed horizontal array are of interest for rapidly characterizing sediment properties over changing regions. To be of practical value, inversions must yield consistent and reliable results for consecutive or neighboring data. A method of determining inversion reliability a priori is delineated using an empirical approach and confirmed with inversion results in terms of consistency. Geoacoustic parameter hierarchy and resolvability are empirically analyzed using two different methods: one requires knowledge of the source function and the other does not. Inversion results using the two methods are compared using both synthetic data and experimental data from MAPEX2000. The inversions employ a global optimization technique which navigates the parameter space in directions aligned with valleys of the cost function, increasing inversion algorithm efficiency and disclosing parameter correlations and hierarchy.

“…1,2 In order to avoid this degradation of resolution, towed horizontal line array ͑HLA͒ inversion schemes have been proposed and implemented. [3][4][5][6] The short distance between a sound source and HLA enables us to simplify the range dependence into local segments of range-independent sectors. 6 The towed HLA system possesses additional advantages of mobility and manageability, which are inherently suitable for a towed sonar system compared to a VLA.…”

Section: Introductionmentioning

confidence: 99%

Geoacoustic inversion in time domain using ship of opportunity noise recorded on a horizontal towed array

Park

Seong

Gerstoft

2005

A time domain geoacoustic inversion method using ship noise received on a towed horizontal array is presented. The received signal, containing ship noise as a source of opportunity, is time-reversed and then back-propagated to the vicinity of the ship. The back-propagated signal is correlated with the modeled signal which is expected to peak at the ship's location in case of a good match for the environment. This match is utilized for the geoacoustic parameter inversion. The objective function for this optimization problem is thus defined as the normalized power focused in an area around the source position, using a matched impulse response filter. A hybrid use of global and local search algorithms, i.e., GA and Powell's method is applied to the optimization problem. Applications of the proposed inversion method to MAPEX 2000 noise experiment conducted north of the island of Elba show promising results, and it is shown that the time domain inversion takes advantage of dominant frequencies of the source signature automatically.