Measurements of sea ice physical properties and ice strain and wave pattern generated by a load moving over sea ice near Tent Island, McMurdo Sound

An experiment designed to study, in detail, the wave pattern generated by a load moving over sea ice was conducted on a flat area of snow free, shore fast sea ice about 2km west of Tent Island in McMurdo Sound. Simultaneously, acoustic emission data was collected on a commercially available portable activity monitor to investigate acoustic emissions generated in the sea ice as a function of vehicle speed. A 6km long road was marked out and the position of the road and an accurate distance measurement between two flagged points along it were found by laser survey techniques. Strain meters were placed at various strategic positions on the ice sheet, measuring normal to the line of the road. Rosettes of strainmeters 0°, 45°, 90° and 135° were placed at 0, 30, 100, 200, 400 and 800m from the road and housed beneath wooden boxes covered in snow to minimise wind and temperature effects. The surface strain at each site was measured as a vehicle travelled along the road at a number of speeds. The strain signals were recorded as separate channels on a 4-channel chart recorder set in most cases to run at 30cm/min. Two moving loads were used, an extended cab Ford pick up (2100kg) and a US Navy C130 Hercules aircraft (50,000kg). The strain was recorded for the truck when it was moving at 10, 20, 30, 35, 40, 45, 50, 55, 60 mph (measured from the trucks speedometer). The strain was recorded when the aircraft flew at 50 feet altitude and at 100, 130 and 160 knot speeds. Actual speeds were recorded using the laser survey marked flag points and calculating speed by distance travelled in a given time. A strainmeter at the roadside and parallel to the vehicles path gave the amplitude and phase information to enable interpretation of data from the distant sites. The physical properties of sea ice were also measured from cores taken at four locations in the vicinity of the strainmeter sites including salinity, temperature and structure of the sea ice.