Sea-ice freeboard and thickness in the Ross Sea from airborne (IceBridge 2013) and satellite (ICESat 2003–2008) observations

Abstract

NASA's Operation IceBridge mission flew over the Ross Sea, Antarctica (20 and 27 November 2013) and collected data with Airborne Topographic Mapper (ATM) and Digital Mapping System (DMS). Using the DMS and reflectivity of ATM L1B, leads are detected to define local sea level height. The total freeboard is then obtained and converted to ice thickness. The estimated mean sea-ice thickness values are found to be in the 0.48–0.99 m range. Along the N-S track, sea ice was thinner southward rather than northward of the fluxgate, resulting in two peaks of modal thickness: 0.35 m (south) and 0.7 m (north). This supports that new ice produced in coastal polynyas is transported northward by katabatic winds off the ice-shelf. The lowest (2%) elevation method used for freeboard retrieval for ICESat is also tested for ATM data. It is found that the lowest elevation method tends to overestimate freeboard, but mean values are less affected than mode values. Using mean thickness values of ICESat and ATM along the ‘fluxgate’, separating the shelf from the deep ocean, the exported ice volume at this ‘fluxgate’ is found to be higher during the ICESat years (2003–2008) than during the IceBridge year (2013).

Morphological approaches to understanding Antarctic Sea ice thickness

“…In addition, the 2013 OIB flight over the Ross Sea operated without a snow radar onboard, and this technique may be used to obtain snow depth estimates for the Ross Sea. The Ross Sea shows similar SIE trends to the Weddell Sea, and the 2013 data show a multimodal mixture of due to the significant new (thin) ice formation and ridging, but without multi-year ice (Tian et al, 2019). It is thus plausible that the Ross Sea surface features are also a subset of the Weddell Sea ones.…”

Sea Ice Freeboard in the Ross Sea from Airborne Altimetry IcePod 2016–2017 and a Comparison with IceBridge 2013 and ICESat 2003–2008

“…The datasets with acquisition time and corresponding tracks used in this study. (ICESat track here is a pseudo track, i.e., ICESat data within 30 km each side of the central IcePod track; refer to Figure 12 of Reference [22]). The OIB laser scanner (ATM) is a conically scanning laser altimeter of using 532 nm wavelength, with a pulse repetition frequency of 5 kHz and an off-nadir scan angle of~15 • (T2 scanner) or 23 • (T3 scanner) [25].…”

“…We call this "the lowest elevation method" in this study. The other methods include local sea identification from apparent reflectivity, waveform characteristics, or optical images [22]. As ICESat freeboard products (2003)(2004)(2005)(2006)(2007)(2008) were derived by using a local sea level reference obtained by the lowest (2%) elevation values within a 50 km section [28], we used the lowest elevation method for OIB and IcePod, so the results were comparable among all three datasets.…”

“…In a recent study [22], the OIB 2013 data were used to analyze the distribution of sea ice over the Ross Sea. The goal of this study was to investigate the patterns of interannual variations of total freeboard (sea ice thickness) in the Ross Sea by comparing the IcePod 2016-2017 data with both the OIB 2013 and the ICESat 2003-2008 data.…”

Decadal Variations of Sea Ice Thickness in the Amundsen‐Bellingshausen and Weddell Seas Retrieved From ICESat and IceBridge Laser Altimetry, 2003–2017

“…There were no valid ATM sea ice data in these regions in 2015. No surveys were conducted in the ABS or Weddell Sea in 2013; instead, a single campaign was flown in the Ross Sea that year (Tian et al, 2019). These OIB campaigns provide unique opportunities to study the Antarctic sea ice total freeboard and thickness variations along ground tracks at very high precision.…”