The Use of APT Satellite Imagery in a Subarctic Airborne Oceanographic Survey

Abstract

During an airborne oceanographic survey of ice conditions in the east Greenland drift-stream in April 1972, earth-oriented satellite photographs were received aboard the research aircraft Arctic Fox of the U.S. Naval Oceanographic Office. These photographs, broadcast directly from the satellites Nimbus 4 and ESSA 8 (Environmental Survey Satellite) were received by means of an APT (automatic picture transmission) satellite receiver station equipped with a specially-modified airborne satellite communication antenna. The satellite photographs showed the ice and cloud conditions for the Greenland Sea as they existed during each flight. This information was used both as a planning and operational aid during the survey and as a post-survey data source of ice and cloud conditions. ... The satellites used during the experiment were in polar orbits. ... In the latitudes of the study area, the overlap in the paths of each consecutive orbit was approximately 50 per cent. Thus, it was possible during the experiment to use the early morning satellite photographs in the pre-flight planning sessions to examine the general conditions of ice distribution and weather over the entire Greenland Sea, and to locate regions within the study area having the specific ice and cloud conditions required for that day's survey. Photographs obtained late in the morning and early in the afternoon were used to delineate the exact extent of the ice and cloud conditions in the chosen survey region. As mentioned earlier, these later photographs were retained as a data source of the survey region's ice and cloud conditions. ... The region examined during the survey by the Arctic Fox was the ice-entrained area in the east Greenland drift-stream bounded by the latitudes 68° and 73°N, and the longitudes 5° and 20° W. Altogether, six flights were made over the ice during the period 16-26 April. ... A necessary environmental condition for the successful utilization of the aircraft's remote sensing equipment under these conditions is good visibility. By using the satellite photographs provided by the APT station, essentially no flight time was lost searching for cloud free regions suitable for operations. In addition to cloud-free regions, each day's survey required specific ice conditions. ... Again, the photographs obtained by the Arctic Fox APT station showed the ice conditions in the cloud-free areas, so that a selection could be made of a region with the desired ice conditions. ... The satellite APT photographs received during this survey were the first operationally received aboard an aircraft. Their successful utilization during the survey demonstrated that satellite photographs provided by an airborne APT station can be useful in the planning and operation of a subarctic airborne oceanographic survey. In addition, the experiment showed that the photographs collected during the survey can provide valuable data on the regional and local ice and weather conditions for use in the post-survey analysis.