Towards navigation of underwater gliders in seasonal sea ice

Abstract

The suitability of the available navigational aids for underwater gliders for year round use in waters which experience seasonal sea ice is evaluated and a path towards an operational system on the Labrador Shelf is presented. The extent of ice coverage is generally found to be limited to the shelf areas and with a duration of up to 20 weeks. For a desired navigational accuracy of 100 meters over a potential trackline in from the shelf break and back out again, around 400 kilometers, a series of low frequency sound sources or geophysical navigational methods are proposed. Acoustic methods require more maintenance and are more prone to loss, while geophysical methods require additional evaluation in the operational region and potential digital elevation model refinement. A three phase strategy is proposed to enable under ice observations. The first phase involves operating the gliders in the ice free season over the proposed track-lines. This data collection phase would allow the evaluation of the available methods and build confidence for later under ice operations. The second phase involves the refinement of the available DEMs both bathymetric and magnetic to the degree that successful navigation by geophysical methods is achieved during the ice free season. Upon the success of the vehicles navigation without surface access during the ice free season, the third phase would commence, that of under ice observations.