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Articles

Number 6 (2011)

Producing Chart Data from Interferometric Sonars on Small AUVs

Submitted
August 13, 2013
Published
2011-06-06

Abstract

High frequency (100kHz to 500kHz) ‗interferometric‘ or phase measuring sonars are a common tool for boat-mounted hydrographic surveys. Recent improvements in sonar and positioning technology have led to improved data quality: 2005 saw the first interferometric survey accepted for charting by the UK Hydrographic office. In parallel with this there have been significant advances in man-portable autonomous underwater vehicles (AUVs). These technologies can be combined: there are now growing numbers of small AUVs running interferometric bathymetry surveys worldwide. The ability to access hazardous areas, provide cost-effective force-multiplication, and acquire higher resolution data from deeper water has proven very attractive.This paper discusses the influences on data quality when acquiring swath bathymetric data using interferometric sonars on small AUVs, including how the data can be processed and qualified for hydrographic charting. Commercial AUV capabilities are illustrated using data collected by a 7-inch diameter Gavia AUV (Teledyne Gavia, Iceland) carrying a 500kHz GeoSwath sonar (GeoAcoustics, UK). Error budgets are discussed, showing that existing technology is capable of achieving IHO S-44 Ed.5 Special Order surveys, within certain operational limits and using appropriate survey planning and data processing.Possible future improvements in data analysis methods are mentioned, including the use of SLAM (Simultaneous Localisation and Mapping) methods to improve navigation. This is illustrated using sample data processed in CleanSweep software (OIC Inc., Hawaii).