Abstract
Sea ice surface roughness affects ice-atmosphere interactions, serves as an indicator of ice age, shows patterns of ice convergence and divergence, affects the spatial extent of summer meltponds, and affects ice albedo. We have developed a method for mapping sea ice surface roughness using angular reflectance data from the Multi-angle Imaging SpectroRadiometer (MISR) and lidar-derived roughness measurements from the Airborne Topographic Mapper (ATM). Using an empirical data modeling approach, we derived estimates of Arctic sea ice roughness ranging from centimeters to decimeters within the MISR 275-m pixel size. Using independent ATM data for validation, we find that histograms of lidar and multi-angular roughness values were nearly identical for areas with a roughness < 20 cm, but for rougher regions, the MISR-estimated roughness had a narrower range of values than the ATM data. The algorithm was able to accurately identify areas that transition between smooth and rough ice. Because of its coarser spatial scale, MISR-estimated roughness data have a variance about half that of ATM roughness data.
Highlights
Sea ice roughness is created by surface-atmosphere interactions, ice motion, and ice surface melt.Roughness caused by ice motion depends on wind speed and direction, ocean currents, and coastline interactions [1]
We note that the values shown here are separate from the Airborne Topographic Mapper (ATM) and Multi-angle Imaging SpectroRadiometer (MISR)
Visual identification of clouds remains the best approach but is overly time consuming. This multi-angular remote sensing approach to mapping sea ice surface roughness appears to show promise. These results demonstrate the ability to map changes in surface roughness at centimeter to decimeter scales in a 275 m MISR pixel
Summary
Roughness caused by ice motion depends on wind speed and direction, ocean currents, and coastline interactions [1]. Surface roughness is a characteristic of different sea ice types [2,3,4] and can serve as indicator of ice thickness, divergence, and convergence, all of which affect ship navigation in the polar regions [3]. Sea ice thickness is related to sea ice age where first-year ice is typically thinner (and smoother) than multi-year ice [5] New ice types such as so-called grease ice, nilas, and pancake ice are relatively smooth, while pack ice, multi-year ice, and sea ice in the marginal ice zone tend to be rougher as they are affected by compression, shear, and wave action [5,6]. Convergence causes ice ridges, which are very challenging for ship navigation
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