Branch Seminar Series: John Heinrichs

Fort Hays State University
Early in the development of techniques for measuring sea ice freeboard from ICESat, wavelike elevation patterns near the sea ice edge were noted and the suggestion was made that these patterns were due to ocean swells penetrating into the ice pack. In this study, ICESat sea ice profiles with wavelike patterns were identified, compared with near-concurrent visible and infrared imagery, and analyzed using spectral techniques. The ocean swell hypothesis was confirmed, and attenuation coefficients were calculated as a function of ocean surface wavelength. The derived attenuation rates are lower than previously measured from ships and aircraft, most likely because the direction of the ICESat pass is at an angle to the propagation direction of the ocean swells. Consistent with previous observations, attenuation of the ocean surface waves passing into a sea ice cover tends to be greater at lower frequencies. The longest waves, with lengths of up to 100 km, can penetrate hundreds of km into the ice pack. The analysis of ocean swells visible in ICESat profiles has the potential to improve sea ice freeboard retrievals near the ice edge.