Historical hypsometry analysis of the Dotson and Crosson Ice Shelves using trimetrogon aerial imagery with structure-from-motion processing techniques

Abstract:

Elevation and elevation change data for the Dotson and Crosson Ice Shelves has a limited temporal scale. Hypsometric measurements from altimetry data only began at the start of the 1990s. This early research, and further work since then, has shown that these ice shelves have experienced dramatic thinning, rapid and complex ice dynamic changes and grounding line retreat of tens of kilometers. Prior to 1990, the pace and extent of ice shelf thinning is largely unknown due to a lack of elevation data. Basal melting from increased circulation of Circumpolar Deep Water beneath the shelves is thought to be the cause of the thinning and glacier dynamic changes. However, it is unclear how long ago the Dotson and Crosson Ice Shelves began experiencing these changes. We will report on recent work that has the goal of extending the ice shelf change record back by 25 years, using historical trimetrogon aerial imagery collected in the late 1960s to produce digital elevation models for the region. The trimetrogon camera captures one 0° nadir image and two oblique images that include the horizon in opposite directions. We use both image types with structure-from-motion software to generate ice shelf surface elevations from ~55 years ago. We calculate change rates by differencing the historical elevations with present-day measurements. This allows us to assess whether the behavior of the ice shelves from the last ~25 years has been a discrete event or a continuation of a long-term pattern, and what the long-term pace of change has been. The hypsometry analysis also extends to the ice shelves’ surrounding outlet glaciers (e.g. Smith and Kohler Glaciers) so as to better understand the role dynamic thinning is playing in ice shelf thinning versus that of basal melt. In creating an extended timeline of ice shelf elevation changes, our objective is to improve parameters necessary for accurate predictive modeling of ice sheets and ice shelves.