Airborne Temperature Survey of Harrison Bay

Abstract

During 10 August 1973 while conducting an oceanographic program in deep waters off the North Slope of Alaska, an opportunity arose to make an airborne radiation thermometer (ART) flight to map the surface water temperature of Harrison Bay .... Little is known about the oceanography of the Bay. Yet this zone may well come under considerable, if not great, environmental stresses stemming from present localization of resource development and exploitation. This paper presents a summary of the results of the low-altitude ART flight. ... A Barnes Engineering Company PRT-5, 9.5-11.5 µ Infrared Radiometer with a field of view of 2 degrees was used .... The temperature survey was carried out using 2 helicopters ... flying a grid pattern and measuring the surface temperature along the flight track. The flight was conducted at a nominal altitude of 46 metres, with a flight speed of 150 km/hr. Navigation was done by visual contact with the coast and by radar tracking from the Glacier. Clear, cloud-free conditions existed in the entire study area during the survey. Continuous winds (>3.0 m/sec) mixed the surface waters so that the radiometer measurements are representative of bulk temperature rather than the skin temperature of the water. The ART equipment was calibrated before, during, and after the flight. ... Contours of the surface-water temperature distribution of Harrison Bay are presented .... Two major features are exhibited: the lack of large river effluent plumes; and the penetration of relatively cold water from the west into Harrison Bay. The weak packing of isotherms (4° to 8°C) near the Colville River delta indicates that river runoff was very low in early August and freshwater influence was restricted to near the shore. This was expected. ... the Colville River has a total annual discharge of 16 × 10**9 m³ of which 80 per cent occurs the first twenty days of June. During the rest of the summer, river flow is very low. In the second feature ... the 3°C isotherm represented the boundary of the cold water and was accompanied by a sharp colour separation: offshore of the isotherm the water was green whereas inshore the water was brown. It is also interesting to note that the 3°C isotherm paralleled the 5.5 metre isobath in Harrison Bay. Along the North Slope coast, surface currents depend largely on local winds, are highly variable (0 to 60 cm/sec), and may even reverse direction .... The wind is generally from the east during the summer and rarely exceeds 10 m/sec. However, from 6 to 11 August 1973, the wind direction was from the west-southwest at an average of 4 m/sec. This was sufficient to cause the nearshore waters to flow easterly, pushing the colder coastal waters into Harrison Bay. Assuming steady state conditions the magnitude of the wind-driven cold-water current was 12 cm/sec. The pocket of <4°C water near Cape Halkett ... may represent an eddy. The surface water temperature distribution of Harrison Bay observed 10 August 1973 is probably unique in that the winds were blowing from the west causing the presence of a tongue of cold water to occur which covered a great part of the bay. However, the data should add to our sparse understanding of the area and point out the need for continued study.