The estimation of Antarctic sea ice thickness from multi-source satellite radar altimeters
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摘要: 南极海冰是极地气候系统的重要组成部分，对全球气候有着深远影响。海冰厚度作为海冰的关键属性之一，了解其时空分布特征和变化趋势对理解和预估气候变化进程具有重要意义。然而，目前对于南极海冰厚度的监测局限在时空分布有限的实地观测和短时间序列的卫星观测阶段，长时间序列的冰厚数据仍然缺失。针对这一问题，基于时空连续的卫星雷达高度计Envisat和CryoSat-2，构建了一致性较高的雷达干舷高度数据，定量估算了高度计雷达信号在积雪中的穿透深度，发展了一种适用于南极海冰的厚度遥感估算方法。估算的冰厚与Australian Antarctic Data Centre实测数据的平均绝对偏差约为0.28 m；与ICESat激光雷达高度计冰厚的平均绝对偏差约为0.65 m，相关系数为0.71，一致性较高。2002–2023年南极海冰厚度时空变化分析结果表明，厚冰主要分布于西威德尔海和别林斯高晋海/阿蒙森海，其他海域海冰相对较薄。南极海冰厚度在2011年之前呈现轻微降低趋势，在2011年后加速降低（−0.03 m/a）。南极海冰厚度的分布和变化趋势存在明显的季节和区域特征。Abstract: Antarctic sea ice is a crucial component of the polar climate system, with profound implications for global climate. Sea ice thickness, as one of the key properties of sea ice, holds significant importance for understanding and predicting the influences of climate change by revealing its spatial and temporal distribution patterns and variation trends. However, current monitoring of Antarctic sea ice thickness is constrained by limited ground observations with restricted spatial and temporal coverage or short-term satellite observations, long-term sea ice thickness data remains elusive. To address this issue, this study utilized the continuous satellite radar altimetry data from Envisat and CryoSat-2 and constructed a consistent dataset of radar freeboard of Antarctic sea ice. Then, the penetration depth of radar signals through the snow covers over Antarctic sea ice was quantitatively estimated, and a method applicable to various sea ice-snow scenarios for estimating Antarctic sea ice thickness was developed. The estimated sea ice thickness shows an average absolute bias of approximately 0.28 m compared to in situ measurements from the Australian Antarctic Data Centre, and an average absolute bias of approximately 0.65 m compared to ICESat laser altimeter with a high correlation coefficient of 0.71. Analysis of the spatiotemporal variations of Antarctic sea ice thickness from 2002 to 2023 reveals that thick ice is predominantly concentrated in the western Weddell Sea and Bellingshuan/Amundsen Seas, while ice in other sea sectors is relatively thin. Antarctic sea ice thickness exhibited a slight decreasing trend before 2011, followed by an accelerated decline after 2011 (−0.03 m/a). The distribution and trends of Antarctic sea ice thickness exhibit distinct seasonal and regional characteristics.
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Key words:
- sea ice thickness /
- sea ice freeboard /
- radar signal penetration depth /
- radar altimeters /
- Antarctica
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图 1 OIB机载观测数据（a）、ASPeCt船载观测数据和AADC实测数据的空间分布（b）
图中经度线为南极6个子海域的分界线
Fig. 1 The spatial distributions of OIB airborne measurements (a), ASPeCt shipborne observations and AADC in situ measurements (b)
The longitude lines show the boundary of six sea sectors in Antarctica
图 2 2011年基于Envisat和CryoSat-2雷达高度计的雷达干舷高度对比
Fig. 2 The comparisons of radar freeboard estimates from Envisat and CryoSat-2 in 2011
图 3 雷达信号穿透深度与积雪深度的散点图
Fig. 3 The scatter diagram of the radar penetration depth and snow depth
图 4 南极海冰静力平衡示意图
a.正海冰干舷高度，b.负海冰干舷高度
Fig. 4 The schematic diagram of hydrostatic balanceof Antarctic sea ice
a. Positive ice freeboard, b. negative ice freeboard
图 5 Envisat与ICESat估算的积雪干舷高度对比
a.经过穿透深度校正，b.未经过穿透深度校正。20031011代指2003年10–11月，其他类似
Fig. 5 The comparisons between the snow freeboard estimates from Envisat and ICESat
a. Corrected for the penetration depth, b. no correction for the penetration depth. 20031011 indicates from October to November in 2003, others are similar
图 6 CryoSat-2与ICESat-2估算的积雪干舷高度对比
a.经过穿透深度校正，b.未经过穿透深度校正
Fig. 6 The comparisons between the snow freeboard estimates from CryoSat-2 and ICESat-2
a. Corrected for the penetration depth, b. no correction for the penetration depth
图 7 雷达高度计海冰厚度与两种ICESat海冰厚度的对比
20031011代指2003年10月–11月，其他类似
Fig. 7 The comparison between sea ice thickness estimates from radar altimeters and ICESat (based on two methods)
20031011 indicates from October to November in 2003, other are simlar
图 8 基于雷达高度计估算的海冰厚度与两种基于ICESat激光雷达高度计估算的海冰厚度的详细对比
a.与文献[52]的对比，b.与文献[34]的对比。20031011代指2003年10月–11月，其他类似
Fig. 8 The detailed comparisons between the sea ice thickness estimates from radar altimeters and sea ice thickness estimates from ICESat (based on two methods)
a. Comparison to reference [52], b. comparison to reference[34]. 20031011 indicates from October to November in 2003, other are simlar
图 9 2002–2010年Envisat时期不同季节平均海冰厚度（a）及其不确定度（b）的空间分布，2011–2023年CryoSat-2时期不同季节平均海冰厚度（c）及其不确定度（d）的空间分布（1～4依次为春季、夏季、秋季和冬季）
Fig. 9 The spatial distributions of averaged sea ice thickness (a) and its uncertainty (b) in different seasons during 2002–2010 (Envisat period); the spatial distributions of averaged sea ice thickness (c) and its uncertainty (d) in different seasons during 2011–2023 (CryoSat-2 period) (the figures 1–4 are in order: spring, summer, autumn and winter)
图 10 2002–2023年海冰厚度的月异常变化
a.南极，b.西威德尔海，c.东威德尔海，d.印度洋海域，e.太平洋海域，f.罗斯海，g.别林斯高晋海/阿蒙森海
Fig. 10 The monthly anomaly variations of Antarctic sea ice thickness estimates from 2002 to 2023
a. Antarctica, b. Western Weddell Sea, c. Eastern Weddell Sea, d. Indian Ocean, e. Pacific Ocean, f. Ross Sea, g. Bellingshausen/Amundsen Seas
图 11 2002–2023年不同季节南极海冰厚度的空间变化趋势
a.春季，b.夏季，c.秋季，d.冬季
Fig. 11 The spatial distributions of sea ice thickness trends in different seasons from 2002 to 2023
a. Spring, b. summer, c. autumn, d. winter
表 1 Envisat、CryoSat-2、ICESat和ICESat-2数据的基本介绍
Tab. 1 The brief introduction of Envisat, CryoSat-2, ICESat and ICESat-2 data
Envisat CryoSat-2 传感器 Radar Altimeter-2 Synthetic Aperture Interferometric
Radar Altimeter探测波段 Ku波段 Ku波段 空间分辨率 足迹为2～10 km，
足迹间隔约为7 km沿轨约0.3 km，
跨轨约1.5 km重访周期 35 d 30 d 空间范围 82°N～82°S 88°N～88°S ICESat ICESat-2 传感器 Geoscience Laser
Altimeter SystemAdvanced Terrain Laser
Altimeter System空间分辨率 足迹为70 m，
足迹间隔约为170 m足迹为17 m，
足迹间隔约为0.7 m重访周期 183 d 91 d 空间范围 88°N～88°S 88°N～88°S 
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表 2 基于不同年份OIB机载测量数据的穿透深度估算公式回归系数
Tab. 2 The regression coefficients of the penetration depth estimation equations based on OIB airborne measurements in different years
样本中被去除数据所在的年份 斜率 截距 格网数 2009 0.76 −0.05 208 2010 0.88 −0.10 196 2012 0.75 −0.09 218 2013 0.51 0.00 98 2014 0.65 −0.04 216 2016 0.68 −0.05 199 2017 1.07 −0.18 79 2018 0.52 0.01 36 应用所有数据 0.73 −0.06 1250
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