Arctic Sea Ice: Using Airborne Topographic Mapper Measurements (ATM) to Determine Sea Ice Thickness

As the earth warms, signs of climate change range from subtle to significant, with the most dramatic alterations occurring in the Arctic. Because the concept of a new, navigable ocean to the north signals complications, the United States Navy is particularly interested in studying the Arctic region so as to project those changes and become better prepared for future operations in this emerging maritime environment. However, a key step in understanding sea ice fluctuation within the Arctic is being able to determine sea ice thickness over a vast area. Thus, obtaining an accurate sea ice thickness measurement for the entire expanse makes tracking further variations and predicting possible changes much easier. As such, this paper aims to look at the steps necessary in determining sea ice thickness based on laser altimetry data gathered during NASAs Operation IceBridge. Using the Airborne Topographic Mapper ATM, sea ice elevation can be measured from an aircraft flying overhead. From this elevation data, an approximate freeboard is calculated in relation to the earths geoid model. By determining locations of leads in the ice, further calculations may be performed to get a sea ice freeboard measurement. Then, through the use of the hydrostatic equation, sea ice thickness may be inferred for the region between successive leads. Therefore, flying over a lead in the ice is very important for determining the exact sea ice elevation. This paper outlines the process, approximations, and adjustments necessary to determine sea ice thickness by using laser altimetry measurements of sea ice elevation.