Circumpolar Thin Arctic Sea Ice Thickness and Small-Scale Roughness Retrieval Using Soil Moisture and Ocean Salinity and Soil Moisture Active Passive Observations

Young-Joo Kwon,Sungwook Hong,Suna Jo,Hyun-Cheol Kim

doi:10.3390/rs11232835

Young-Joo Kwon, Sungwook Hong + Show 2 more

Open Access

https://doi.org/10.3390/rs11232835

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Abstract

The variations in the Arctic sea ice thickness (SIT) due to climate change have both positive and negative effects on commercial human activities, the ecosystem, and the Earth’s environment. Satellite microwave remote sensing based on microwave reflection signals reflected by the sea ice surface has been playing an essential role in monitoring and analyzing the Arctic SIT and sea ice concentration (SIC) during the past decades. Recently, passive microwave satellites incorporating an L-band radiometer, such as soil moisture and ocean salinity (SMOS) and soil moisture active passive (SMAP), have been used for analyzing sea ice characteristics, in addition to land and ocean research. In this study, we present a novel method to estimate thin SIT and sea ice roughness (SIR) using a conversion relationship between them, from the SMAP and SMOS data. Methodologically, the SMAP SIR is retrieved. The SMAP thin SIT and SMOS SIR are estimated using a conversion relationship between thin SIT data from SMOS data and SMAP-derived SIR, which is obtained from the spatial and temporal collocation of the SMOS thin SIT and the SIR retrieved from SMAP. Our results for the Arctic sea ice during December for four consecutive years from 2015 to 2018, show high accuracy (bias = −2.268 cm, root mean square error (RMSE) = 15.919 cm, and correlation coefficient (CC) = 0.414) between the SMOS-provided thin SIT and SMAP-derived SIT, and good agreement (bias = 0.03 cm, RMSE = 0.228 cm, and CC = 0.496) between the SMOS-estimated SIR and SMAP-retrieved SIR. Consequently, our study could be effectively used for monitoring and analyzing the variation in the Arctic sea ice.

Highlights

Sea ice is an essential climate variable that is very sensitive to climate change
In the Arctic region, sea ice extent has been decreasing and Sea ice thickness (SIT) has reduced in the past few decades [1,2,3,4,5,6], affecting climate [7,8], Earth’s surface energy budget [9], atmospheric CO2 [10], atmospheric circulation [11], water budget [12], clouds [13], fresh-water [14], and global temperature [15]
The interannual changes of Arctic sea ice were found to be closely linked to the Arctic cyclone numbers [16], abnormal summer storm activity [17], atmospheric internal variability (AIV) [18], and changes in polar tropospheric and stratospheric circulation [19]

Summary

Introduction

Sea ice is an essential climate variable that is very sensitive to climate change. Sea ice thickness (SIT) (Dice) and sea ice concentration (SIC) are important sea ice parameters because of their high sensitivity to heat flux and radiative balance. Data from satellites with radar altimeters (ICESat and CryoSat-2) or microwave radiometer (SMOS) have been used for SIT estimation. A small-scale sea ice roughness (SIR) (σ) retrieval and its time-series using a satellite-based passive microwave radiometer were presented [1,45]. We used the polarized brightness temperatures (TB,V and TB,H) and sea ice surface temperatures (TS) of SMAP Level-3 (L3) data, which have 9 km × 9 km spatial resolution and one-day temporal resolution, for estimating the SMAP SIR. The study area of the Arctic sea ice was determined using SMAP surface flag information with 9 km spatial resolution, CryoSat-2 L2 data with 5 km spatial resolution from SAR, and interferometric radar altimeter from the European Space Agency (ESA)

Method

Conversion Relationship between SIR and SIT

Retrievals of SMAP SIT and SMOS SIR

Results