Measurements of high-frequency shallow-water acoustic phase fluctuations

Stanic, Steve; Goodman, Ralph R.; Meredith, Roger W.; Kennedy, E.

doi:10.1109/48.895358

Cited by 5 publications

(3 citation statements)

References 12 publications

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“…Salinity was assumed to be unchanged from 33.6 ppt, measured previously with a hydrometer. (1) where ff[m, n] = ff(mAr, nAy) is a portion of the reconstructed image of size M by N pixels, r is the range coordinate, and y is the along-track coordinate. The image portion is carefully chosen to include only the BSU and an uncluttered area of seabed so that the non-stationary objects, which do not properly reconstruct, do not skew the result.…”

Section: B Estimating the Speed Of Soundmentioning

confidence: 99%

“…After motion compensation (MOCOMP) has been performed, SAS image quality is ultimately limited by the ability of autofocus algorithms to correct for blur caused by medium fluctuations [1]. Conventional approaches to this two-stage problem use navigation systems, typically based around an inertial navigation system (INS) and Doppler velocity log (DVL) [2] [3], to remove the bulk motion error.…”

Section: Introductionmentioning

confidence: 99%

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An active beacon for measuring the tow-path of a synthetic aperture sonar: Purau Bay sea trial results

Pilbrow

Gough

Hayes

2007

OCEANS 2007 - Europe

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In this paper we present experimental results of a method for determining the path of a synthetic aperture sonar (SAS), with sub-centimeter accuracy, by autofocussing images of an active beacon. The beacon sits on the seabed, listens for sonar pings using a matched filter, and retransmits in a different frequency band after a fixed time delay. The sonar forms a separate image containing just this point-target, blurred by sonar motion, with a high signal to noise ratio (SNR) and no contamination from close range objects. A simple narrowbeam autofocus algorithm is applied to estimate the sonar path, providing motion compensation (MOCOMP) data to correct the SAS images of the other objects in the scene. Independent one-way and twoway approaches to measuring the time of flight (TOF) were investigated, with the two-way approach producing better results. Significant improvement was achieved for two runs at 30kHz with a small improvement achieved in one run at 100kHz. Fitting a hyperbola, to the separate beacon raw data produced a velocity estimate for the sonar that was within ±0.025 m/s of the tow boat velocity, for both runs, when compared with the global positioning system (GPS) velocity measurements averaged over the run length.

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Section: B Estimating the Speed Of Soundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An active beacon for measuring the tow-path of a synthetic aperture sonar: Purau Bay sea trial results

Pilbrow

Gough

Hayes

2007

OCEANS 2007 - Europe

View full text Add to dashboard Cite

show abstract

“…After motion compensation (MOCOMP) has been performed, SAS image quality is ultimately limited by the ability of autofocus algorithms to correct for blur caused by medium fluctuations [1]. Conventional approaches to this two-stage problem involve using navigation systems, typically based around an inertial measurement unit (IMU) and Doppler velocity log (DVL) [2][3], to remove the bulk error.…”

Section: Introductionmentioning

confidence: 99%

Autofocus of Active Beacons for Measuring the Tow-path of a Synthetic Aperture Sonar: Preliminary Sea Test Results

Pilbrow

Hayes

Gough

Proceedings of OCEANS 2005 MTS/IEEE

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We present operational details and preliminary experimental results of a portable freely-deployed "active beacon" used to perform motion compensation on images from the KiwiSAS-IV synthetic aperture sonar. The beacon sits on the seabed, listens for sonar pings using a matched filter, and retransmits in a different frequency band after a fixed time delay. The sonar forms a separate image containing just this point-target, blurred by towfish motion, with a high SNR and no contamination from close range objects. Autofocus algorithms tailored for point targets are then applied to estimate the sonar path. The experimental results are from the first sea test in a shallow marina environment and reveal several areas where improvement needs to be made before good results can be achieved. The main problems encountered were multipath and nulls in the sonar beampattern.

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Panama City 2003 Broadband Shallow-water Acoustic Coherence Experiments

Stanic¹,

Kennedy²,

Malley³

et al. 2004

AIP Conference Proceedings

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In June 2003 a series of acoustic propagation experiments were conducted off the coast of Panama City, Florida. The experiments were designed to measure and provide an understand of signal phase and amplitude fluctuations, and signal spatial and temporal coherence over several large horizontal and vertical arrays. The propagation measurements were conducted in a water depth of 8.8m and at ranges of 70 m and 150 m. The acoustic measurements cover frequencies from 1 to 140 kHz. The propagation measurements were supported by data obtained by wave rider buoys, CTD's, thermister chains and current meters. Bottom penetration data was also obtained using a buried hydrophone array. The experiments will be outlined and the data sets described.

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Measurements of high-frequency shallow-water acoustic phase fluctuations

Cited by 5 publications

References 12 publications

An active beacon for measuring the tow-path of a synthetic aperture sonar: Purau Bay sea trial results

An active beacon for measuring the tow-path of a synthetic aperture sonar: Purau Bay sea trial results

Autofocus of Active Beacons for Measuring the Tow-path of a Synthetic Aperture Sonar: Preliminary Sea Test Results

Panama City 2003 Broadband Shallow-water Acoustic Coherence Experiments

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