Abstract
The snow depth on Antarctic sea ice is critical to estimating the sea ice thickness distribution from laser altimetry data, such as from Operation IceBridge or ICESat-2. Snow redistributed by wind collects around areas of deformed ice and forms a wide variety of features on sea ice; the morphology of these features may provide some indication of the mean snow depth. Here, we apply a textural segmentation algorithm to classify and group similar textures to infer the distribution of snow using snow surface freeboard measurements from Operation IceBridge campaigns over the Weddell Sea. We find that texturally-similar regions have similar snow/ice ratios, even when they have different absolute snow depth measurements. This allows for the extrapolation of nadir-looking snow radar data using two-dimensional surface altimetry scans, providing a two-dimensional estimate of the snow depth with ∼22% error. We show that at the floe scale (∼180 m), snow depth can be directly estimated from the snow surface with ∼20% error using deep learning techniques, and that the learned filters are comparable to standard textural analysis techniques. This error drops to ∼14% when averaged over 1.5 km scales. These results suggest that surface morphological information can improve remotely-sensed estimates of snow depth, and hence sea ice thickness, as compared to current methods. Such methods may be useful for reducing uncertainty in Antarctic sea ice thickness estimates from ICESat-2.
Highlights
Estimating sea ice thickness from remotely-sensed data requires either simultaneous snow depth measurements or some assumption about the snow distribution on the sea ice
The snow depth samples are likely biased by the deep snow around the ridge, which may only be a minority of the surface, and so the raw mean snow depth is higher than the extrapolated snow depth
We have demonstrated the viability of extrapolating snow depth measurements from nadir-looking (1-dimensional) radar datasets from Operation IceBridge, by texturally segmenting the high-resolution lidar scan of the snow freeboard and matching texturally-similar areas
Summary
Estimating sea ice thickness from remotely-sensed data (here, snow freeboard, which is the amount of snow and ice above water) requires either simultaneous snow depth measurements or some assumption about the snow distribution on the sea ice. Common approaches include using an empirical fit to in-situ data [4] or assuming that there is negligible ice freeboard (i.e., all the ice has been depressed by snow cover, and so F = D in Equation (1)). This is reasonable on a large scale (averaged over many kilometers), over which the majority of the sea ice surface may consist of relatively thin, undeformed ice. Mei et al [5] showed that this assumption is not valid at local scales (
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