Weekly Mapping of Sea Ice Freeboard in the Ross Sea from ICESat-2

Younghyun Koo,Alberto M Mestas-Nuñez,Stephen F Ackley,Hongjie Xie,Nathan T Kurtz

doi:10.3390/rs13163277

Younghyun Koo, Alberto M Mestas-Nuñez + Show 3 more

Open Access

https://doi.org/10.3390/rs13163277

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Journal: Remote sensing	Publication Date: Aug 19, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: The University of Texas at San Antonio

Abstract

NASA’s ICESat-2 has been providing sea ice freeboard measurements across the polar regions since October 2018. In spite of the outstanding spatial resolution and precision of ICESat-2, the spatial sparsity of the data can be a critical issue for sea ice monitoring. This study employs a geostatistical approach (i.e., ordinary kriging) to characterize the spatial autocorrelation of the ICESat-2 freeboard measurements (ATL10) to estimate weekly freeboard variations in 2019 for the entire Ross Sea area, including where ICESat-2 tracks are not directly available. Three variogram models (exponential, Gaussian, and spherical) are compared in this study. According to the cross-validation results, the kriging-estimated freeboards show correlation coefficients of 0.56–0.57, root mean square error (RMSE) of ~0.12 m, and mean absolute error (MAE) of ~0.07 m with the actual ATL10 freeboard measurements. In addition, the estimated errors of the kriging interpolation are low in autumn and high in winter to spring, and low in southern regions and high in northern regions of the Ross Sea. The effective ranges of the variograms are 5–10 km and the results from the three variogram models do not show significant differences with each other. The southwest (SW) sector of the Ross Sea shows low and consistent freeboard over the entire year because of the frequent opening of wide polynya areas generating new ice in this sector. However, the southeast (SE) sector shows large variations in freeboard, which demonstrates the advection of thick multiyear ice from the Amundsen Sea into the Ross Sea. Thus, this kriging-based interpolation of ICESat-2 freeboard can be used in the future to estimate accurate sea ice production over the Ross Sea by incorporating other remote sensing data.

Highlights

Sea ice in the polar regions plays an important role in global climate by interacting with the ocean and atmosphere [1]
In contrast with the Arctic, several Antarctic studies have reported that sea ice extent increased for last 40 years, but started to decrease dramatically after a record high in 2014 [17,18]
Before applying kriging interpolation for mapping, we conduct a cross validation to check the reliability of this kriging method for freeboard mapping

Summary

Introduction

Sea ice in the polar regions plays an important role in global climate by interacting with the ocean and atmosphere [1]. Snow-covered sea ice reflects a significant amount of incoming solar radiation back to space [2,3,4,5], working as an insulator between the ocean and atmosphere [6]. The annual variations of sea ice cover can influence ocean and atmospheric circulation [7,8], surface temperature [9], and ecology [10,11]. Sea ice extent and thickness in the Arctic has decreased since the. In contrast with the Arctic, several Antarctic studies have reported that sea ice extent increased for last 40 years, but started to decrease dramatically after a record high in 2014 [17,18].

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Conclusion