The Gavia man-portable autonomous underwater vehicle (AUV) from Hafmynd, Iceland, has returned from its latest trip to the Arctic circle, where it carried a GeoSwath wide swath sonar (GeoAcoustics, UK), collecting bathymetry and side scan data from the underside of the Arctic ice sheet.
The Gavia was deployed from the Applied Physics Laboratory Ice Station 2007 (APLIS07), which has been built in the Beaufort Sea approximately 300 miles North of Alaska. The 2.6m long by 20cm diameter Gavia AUV was launched through a 3m by 1m hole melted through the ice, and sent on a series of short out-and-back survey missions from the ice hole. For this survey it was ballasted to fly upside-down so that the camera, GeoSwath mapping sonar and Doppler velocity log (DVL) were looking upwards. The survey team were fascinated by the haunting photographs returned by the Gavia showing the spring sun shining through the 3m thick ice sheet.
First indications are that the bathymetry and side-scan data collection was fully successful, with only small changes required in the GeoSwath post-processing routines in order to cope with the Gavia AUV's inverted flying. The Kearfott Inertial Navigation System (INS), which provided positioning fixes for the survey operations, also coped remarkably well with this fairly unusual deployment.
The mission to APLIS is part of an ongoing research programme led by Professor Peter Wadhams, Head of the Polar Ocean Physics Group, Department of Applied Mathematics and Theoretical Physics (DAMTP), Centre for Mathematical Sciences, University of Cambridge (UK). This research is aimed at investigating the ability of airborne ice thickness measurements to truly reflect the volume of the ice contained in areas with complex cracking and ridging, and also at understanding the structure of ridges and why they are melting so fast. This could have a significant impact on the accuracy of parameters used in climate change modeling. The ability of the GeoSwath sonar to generate a 3-D digital terrain map of the ice underside allows significant new advances to be made in understanding the nature of the ice. The survey results are currently being analysed at the Polar Ocean Physics Group, with a view to publication in scientific journals in the near future.