AUV measurements of under-ice thermal structure

Abstract

Underwater technologies have advanced to the point where the development of autonomous underwater vehicles, or AUVs, is driven by the scientific end user rather than the AUV developer. This results from AUV platforms becoming increasingly commercially available and finding application in a wide range of fields including physical, chemical, biological and geological sciences. Scientific payloads carried by these vehicles in ice-covered waters dramatically increase the quality of data being collected while concurrently increasing the range of observation (e.g. the Beaufort Sea, the Weddell Sea). They also present a unique opportunity to access under-ice regions where it is operationally difficult or logistically impossible to operate with surface vehicles. This reduces deployment infrastructure, associated expenses and facilitates the collection of water property measurements beneath ice-cover, a difficult and potentially dangerous endeavour using conventional techniques, especially when ice-cover is thin, frazil, candled or partially open. This latter capability is extremely important for making observations and conducting scientific research in ocean, coastal, and inland waters in the Canadian Arctic. Since initial deployments in 2006, dasiaUBC-Gaviapsila, an AUV operated by the University of British Columbia Environmental Fluid Mechanics (UBC-EFM) group, has been deployed in several under ice experiments. In February 2008, measurements were made under ice cover by UBC-Gavia in Pavilion Lake, BC. These were a follow up to the successful AUV deployments conducted at the same site in 2007 as well as deployments in the Beaufort Sea. In addition to resolving horizontal variability in the previously measured thermal structure, the primary scientific objective was to examine the thermal structure correlation with the physical properties of the overlying ice cover. In May 2008, the same vehicle was deployed through sea-ice off the north coast of Ellesmere Island, NU, in the Canadian High Arctic, with the objective of measuring the draft of deformed ice using multibeam swath bathymetry. Initial measurements of near shore horizontal temperature variability was quantified by a CTD onboard the AUV while concurrent measurements were being made from a thermistor chain moored on the ice surface. This paper will review the initial scientific results of these two experiments examining the thermal structure in the context of scientific questions driving AUV under-ice experimentation. In addition, novel techniques of AUV deployment, navigation and recovery, developed for this project, are described in the context of operational problems forecasted for Polar Regions.