A new towedlvertical array system has been built to support the ONR ocean acoustic program's 6.1 experimental research efforts. The array consists of both a linear section for standard beamforming and a cardioid section giving it portistarboard discrimination capabilities. The linear section is comprised of 4 modules with halfwavelength hydrophone spacing corresponding to cutoff frequencies of 250, 500, 1000. and 2000 Hz. Each linear aperture is made up of 64 hydrophone channels with a total linear aperture length of 189 meters. The cardioid module consists of 78 hydrophone triplets arranged in an equilateral triangle with 38.5 mm spacing between the individual phones. The linear spacing between each triplet set is 0.2 meters for a cutoff frequency of 3750 Hz. In addition to the acoustic sensors, the array contains 3 non-acoustic sensor suites and and additional pressure sensor to provide realtime array heading, pitch, roil, and depth along with temperature at various positions along the array. Array control for setting of sampling rates, array gain, and monitoring of both acoustic and non-acoustic data is provided by a standard PC. The array supports sampling rates from 6.25-25 kHz for the acoustic data with 24 bit AID conversion. Array telemetry is ATMISONET with a data rate of 155 Mbls. The acquisition system acquires directly to SCSl ultra 320 disk and is based on a COTS Linux workstation. Since taking delivery in May 2002, the FORA has been deployed during three separate sea trials, including the recent Geoclutter experiment held April-May 2003 on the NJ shelf in the Atlantic Ocean. Some preliminary results and data are presented from the different trials illustrating array Capabilities along with an assessment of the array data quality for meeting current and future scientific objectives.
This paper presents results of a range-independent perturbative inverse approach applied to data from the Shallow Water Experiment 2006. The inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues. Horizontal wave numbers were estimated from data collected from two distinct source/receiver tracks oriented along and across the shelf. The specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution. Locations of the R reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment.
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