Brief Communication: Retrieval-Driven Spread in Antarctic Winter Freeboards (CryoSat-2, 2013&ndash;2018)

Liu, Xinlong; Corney, Stuart Paul; Tilling, Rachel Louise; Heil, Petra

doi:10.5194/egusphere-2026-662

Preprints

https://doi.org/10.5194/egusphere-2026-662

Preprints

12 Feb 2026

| 12 Feb 2026

Status: this preprint is open for discussion and under review for The Cryosphere (TC).

Brief Communication: Retrieval-Driven Spread in Antarctic Winter Freeboards (CryoSat-2, 2013–2018)

Xinlong Liu, Stuart Paul Corney, Rachel Louise Tilling, and Petra Heil

Abstract. The accuracy of remotely-sensed Antarctic sea-ice thickness is limited by assumptions of snow properties and processing choices that are often informed from the Arctic. To quantify retrieval-driven spread, we compare winter radar freeboard and snow-corrected sea-ice freeboard from four CryoSat-2–era products for 2013–2018. All products reproduce the large-scale spatial structure, yet each shows systematic offsets relative to CCI that persist across multiple spatial scales. Both the Western Weddell and Ross Sea sectors display interannual variability, while correlation, bias and RMSE exhibit sector- and variable dependent performance relevant to thickness.

Received: 04 Feb 2026 – Discussion started: 12 Feb 2026

Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Xinlong Liu, Stuart Paul Corney, Rachel Louise Tilling, and Petra Heil

Status: open (until 16 May 2026)

Post a comment Subscribe to comment alert

RC1:
'Comment on egusphere-2026-662', Anonymous Referee #1, 01 Apr 2026 reply
A well-written manuscript with clear purpose and description as a ‘compact comparison benchmark’ captures the scope well. However, a lack of specifics on the retrieval methods limits the accessibility of key points in the manuscript.

Additionally, is there a reason why all sectors are not included in the main paper making a longer paper? More clarification should be given as to why these two sectors (Western Weddell and Ross) are chosen. This may result in a stronger regular length paper than the current brief communication which is too short on detail, to fully explore the difference between the products.
We have provided details comments below.
Abstract
Line 5 CCI should be defined

Numerical quantification could be included

Introduction
Line 11 change word 'space' to satellites or remote sensing more precisely

Line 11 specify deep as relative to the Arctic or provide a number e.g. X in the Antarctic vs Y in the Arctic.

Additionally Willatt 2025 (already referenced later) could be referenced here regarding the heterogeneity and second year snow in the Weddell Sea.

Consider phrasing of altimeter retrieval sensitivity relative to Arctic - whilst it has often been assumed that the radar will penetrate through cold, dry snow on Arctic sea ice and scatter from the snow-ice interface, providing basis for original parameterisations as pointed out, not all recent studies support this (e.g. Nab et al., 2023; 2024, King et al., 2018, Willatt et al., 2023; 2011).

Line 13 should be Willatt et al., 2010 (not 2009), and Giles 2008 should be included.

Line 21 explain what the retrievals are based on (to later aid interpretation at line 77 of results).

Data and Methods
Why does it begin in 2013 rather than 2010 for the Cryosat common era?

Line 31-32 define LEGOS/CTOH as all other abbreviated products are defined in full here.

Line 36 'To maintain a concise and reproducible intercomparison, we analyse the freeboard fields as distributed by each provider' please explain why this is more precise and reproducible exactly, with further detail.

Lines 38-40 what else differs between the products e.g. atmospheric corrections, retracking, that would not be snow related? Could it just be called a correction rather than snow-related correction? E.g. you mention 'associated processing choices', what are those choices and are they all related to the snow?

Was there a reason the CCI grid is chosen as the practical reference / the one to compare relative to? And why bilinear interpolation? Please expand more.

Line 59 opening parenthesis missing to parenthesis used after Supplement.

Line 58-59, was there a reason these two sectors were chosen? Noted as contrasting but in what sense? Please explain how you decided on these two regions, whether it was based on the study data or assumptions made prior to conducting the study.

Results
Figure 1 should have the sectors labelled as referred to throughout the text.

Figure 1 (or another figure) should show the original products themselves before differences to CCI.

Figure 1 small l on LEGOS.

Figure 2 explain panels a-d in the caption.

Figures 2 and 3 text too small and text cut off on LHS of Figure 3.

Figure 3, over what time period? Is it monthly data over full 2013-2018 period? How many data points are there? Include in caption or text.

Line 74 and 75, move (Figure 1) to end of sentence and replace : with ;

Line 77 see comment re line 21 to make this result clear.

Line 88 please define freeboards as used in rest of paper, i.e. is the high-freeboard regime, radar or ice freeboard?

Line 94 'The' missing before Western Weddell.

Discussion
Extra full stop after the word Figures is not needed (only needed if abbreviating to Fig.) e.g. line 120.

Line 123 please clarify why this can only be attributed to the snow propagation-speed correction.

Conclusion
Point 1 - referring back to our recommendation to show the actual products before comparison to CCI in Figure 1, this would show the large-scale structure that you highlight here.

Point 3 is nicely made.

In final sentence please describe other sources of uncertainty e.g. retracking. Please also mention the importance and status of in-situ comparisons (given the scope you outline in the final sentence of the discussion).

Reply
Citation: https://doi.org/10.5194/egusphere-2026-662-RC1

Xinlong Liu, Stuart Paul Corney, Rachel Louise Tilling, and Petra Heil

Viewed

Total article views: 271 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
159	88	24	271	50	56

HTML: 159
PDF: 88
XML: 24
Total: 271
BibTeX: 50
EndNote: 56

Views and downloads (calculated since 12 Feb 2026)

Month	HTML	PDF	XML	Total
Feb 2026	94	46	9	149
Mar 2026	55	33	8	96
Apr 2026	10	9	7	26

Cumulative views and downloads (calculated since 12 Feb 2026)

Month	HTML	PDF	XML	Total
Feb 2026	94	46	9	149
Mar 2026	55	33	8	96
Apr 2026	10	9	7	26

Viewed (geographical distribution)

Total article views: 251 (including HTML, PDF, and XML) Thereof 251 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 13 Apr 2026

Short summary

Antarctic sea-ice thickness from satellites depends on how snow is treated. We compared four widely used CryoSat-2 radar products for winters 2013–2018 on the same map grid. All show similar large-scale patterns, but each gives systematically higher or lower values, with the biggest differences in the snowier western Weddell Sea. Year-to-year changes are similar across products, yet these offsets can shift thickness estimates, so users should account for product choice and snow assumptions.


Total:	0
HTML:	0
PDF:	0
XML:	0