Browsing by Author "Bernstein, E. Rachel"
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Item Antarctic sea-ice thickness and volume estimates from ice charts between 1995 and 1998(International Glaciological Society, 2015-10-01) Bernstein, E. Rachel; Geiger, Cathleen A.; DeLiberty, Tracy L.; Lemcke-Stampone, Mary D.; E. Rachel BERNSTEIN, Cathleen A. GEIGER, Tracy L. DeLIBERTY, Mary D. LEMCKE-STAMPONE; Bernstein, E. Rachel; Geiger, Cathleen A.; DeLiberty, Tracy L.This work evaluates two distinct calculations of central tendency for sea-ice thickness and quantifies the impact such calculations have on ice volume for the Southern Ocean. The first calculation, area-weighted average thickness, is computed from polygonal ice features and then upscaled to regions. The second calculation, integrated thickness, is a measure of the central value of thickness categories tracked across different scales and subsequently summed to chosen regions. Both methods yield the same result from one scale to the next, but subsequent scales develop diverging solutions when distributions are strongly non-Gaussian. Data for this evaluation are sea-ice stage-ofdevelopment records from US National Ice Center ice charts from 1995 to 1998, as proxy records of ice thickness. Results show regionally integrated thickness exceeds area-weighted average thickness by as much as 60% in summer with as few as five bins in thickness distribution. Year-round, the difference between the two calculations yields volume differences consistently >10%. The largest discrepancies arise due to bimodal distributions which are common in ice charts based on current subjective-analysis protocols. We recommend that integrated distribution be used for regional-scale sea-ice thickness and volume estimates from ice charts and encourage similar testing of other large-scale thickness data archives.Item Impact of spatial aliasing on sea-ice thickness measurements(International Glaciological Society, 2015-10-01) Geiger, Cathleen A.; Müller, Hans-Reinhard; Samluk, Jesse P.; Bernstein, E. Rachel; Richter-Menge, Jacqueline A.; Cathleen GEIGER, Hans-Reinhard MÜLLER, Jesse P. SAMLUK, E. Rachel BERNSTEIN, Jacqueline RICHTER-MENGE; Geiger, Cathleen A.; Samluk, Jesse P.; Bernstein, E. RachelWe explore spatial aliasing of non-Gaussian distributions of sea-ice thickness. Using a heuristic model and >1000 measurements, we show how different instrument footprint sizes and shapes can cluster thickness distributions into artificial modes, thereby distorting frequency distribution, making it difficult to compare and communicate information across spatial scales. This problem has not been dealt with systematically in sea ice until now, largely because it appears to incur no significant change in integrated thickness which often serves as a volume proxy. Concomitantly, demands are increasing for thickness distribution as a resource for modeling, monitoring and forecasting air–sea fluxes and growing human infrastructure needs in a changing polar environment. New demands include the characterization of uncertainties both regionally and seasonally for spaceborne, airborne, in situ and underwater measurements. To serve these growing needs, we quantify the impact of spatial aliasing by computing resolution error (Er) over a range of horizontal scales (x) from 5 to 500 m. Results are summarized through a power law (Er = bxm) with distinct exponents (m) from 0.3 to 0.5 using example mathematical functions including Gaussian, inverse linear and running mean filters. Recommendations and visualizations are provided to encourage discussion, new data acquisitions, analysis methods and metadata formats.