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TECHNICAL ARTICLES
| Published in issue No 118, October
2005 of The Hydrographic Journal |
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EFFICACY OF AN INTERFEROMETRIC SONAR FOR HYDROGRAPHIC
SURVEYING: DO INTERFEROMETERS WARRANT AN IN-DEPTH EXAMINATION?
Caleb Gostnell, National Oceanic and Atmospheric
Administration (NOAA), USA
Abstract
This paper describes a preliminary evaluation of an interferometric sonar system
for possible use in nautical charting hydrographic survey work. The goal of the
study was to determine whether phase differencing sonar technology currently
shows enough promise to warrant a full scale examination. The GeoAcoustics
GeoSwath system was selected as being representative of the current state of
interferometric technology. GeoSwath data were acquired in Portsmouth Harbour,
New Hampshire, in June 2004 for statistical and visual comparison to previously
acquired Reson 8125 and Simrad EM3002 shallow water multibeam data coverage of
the same region. The standard deviation of the GeoSwath data sampled in several
5m x 5m areas was shown to be approximately 3-5 times that of the Reson and
Simrad data. This agrees with a previous industry report which argued that due
to higher data density and Gaussian distribution about the true surface a grid
generated from interferometric data would be similar to a grid generated from
multibeam sonar data. A point-to-surface comparison showed this to be true. In
all comparisons with Reson and Simrad grids, the GeoSwath point data met IHO
Order 1 requirements or better. A visual comparison between the GeoSwath and
Simrad datasets showed that the GeoSwath faithfully reproduced sandwaves as
small as 0.1m in amplitude. Visual comparison between the GeoSwath, Reson and
Simrad showed less ephemeral features, such as boulders and rock outcrops, as
small as 2m across and several decimetres high were present in all datasets.
Based on these findings an official study is recommended to determine if recent
advances in algorithms, electronics, and manufacturing have improved
interferometers to the point where they may be used for nautical charting
hydrographic survey work.
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