Polar and Climate Center, Postgraduate Program in Remote Sensing, Federal University of Rio Grande do Sul-UFRGS, Avenida Bento Gonçalves, 9500, Building 43136, rooms 208 and 210, Porto Alegre, Rio Grande do Sul, 91501-970, Brazil.
Department of Geosciences, Federal University of Santa Maria, Av. Roraima, 1000, Santa Maria, Rio Grande do Sul., 97105-900, Brazil.
Environ Monit Assess. 2020 Aug 3;192(9):559. doi: 10.1007/s10661-020-08526-5.
This article aims to analyze the dynamics of freezing and thawing of Antarctic lakes located in ice-free areas on Nelson Island and Fildes Peninsula, where response to changes in air temperature and precipitation rates occur rapidly, during the period from July 2016 to December 2018. In these places, which are difficult to access, remote sensing is an important alternative, especially considering the use of active remote sensors such as the Synthetic Aperture Radar (SAR), which has less restriction regarding the presence of clouds over the study area. Three backscatter thresholds were defined (σ) for the identification of the physical state of the water of the lakes of the study region, applied in Sentinel 1A SAR (S1A) images under Horizontal Horizontal (HH) polarization and Interferometric Wide (IW) imaging mode. These images, along with the air temperature data obtained by the Interim Re-Analysis (ERA-Interim) atmospheric reanalysis model, provided the evidence for the interpretation of the freezing and thawing periods of the lakes. The thresholds applied for the definition of the physical state of the lake water were greater than - 14 dB for frozen water, between - 14 and - 17 dB for the surface, with up to 60% of their frozen area, and less than - 17 dB for open water. The temporal analysis revealed that the lakes start to thaw in October, become completely thawed in February, and freeze again in March. Nevertheless, it can be said that the S1A satellite allows a satisfactory identification of the liquid and solid phases of the water in the lakes of the study region.
本文旨在分析 2016 年 7 月至 2018 年 12 月期间位于纳尔逊岛和菲尔德斯半岛无冰区的南极湖泊的冻结和解冻动态，这些地区的气温和降水率变化迅速，对其进行研究时，遥感是一种重要的替代方法，特别是考虑到使用主动传感器，如合成孔径雷达（SAR），它对研究区域云层的存在限制较少。本研究定义了三个后向散射阈值（σ），用于识别研究区域湖泊的水体物理状态，这些阈值应用于 Sentinel-1A SAR（S1A）图像的水平极化和干涉宽（IW）成像模式。这些图像以及通过中期再分析（ERA-Interim）大气再分析模型获得的空气温度数据，为解释湖泊的冻结和解冻期提供了证据。应用于定义湖水物理状态的阈值为，冻结水的后向散射值大于-14dB，表面的后向散射值在-14 到-17dB 之间，其冻结面积可达 60%，而开阔水面的后向散射值小于-17dB。时间分析表明，湖泊于 10 月开始解冻，2 月完全解冻，3 月再次冻结。然而，可以说 S1A 卫星能够令人满意地识别研究区域湖泊的水体的液态和固态。
