Synectic Aperture Radar(SAR)backscatter coefficient is sensitive to glacier surface physical characteristic changes,including the states of melting and refreezing,but it is also sensitive to incidence angle variation....Synectic Aperture Radar(SAR)backscatter coefficient is sensitive to glacier surface physical characteristic changes,including the states of melting and refreezing,but it is also sensitive to incidence angle variation.This study explores the capability of monitoring Greenland Ice Sheet(GrIS)melting status with Sentinel-1 dual-polarized images by referring to Automatic Weather Station(AWS)records.Sentinel-1 SAR images at five coastal regions of the GrIS are obtained from 2017 to 2021.The backscatter coefficients are normalized to an incidence angle of 30°with an empirical model.Time series of five backscatter coefficients profiles covering AWS illustrates different patterns of the ice surface dielectric constant dynamics in different elevations.The wet snow radar zone shows clear backscatter coefficients decreasing during the melting seasons,but the bare ice radar zone behaves more complexly during the melting seasons.The numbers of melting days at different elevations are also derived for each profile based on−3 dB backscatter coefficient decrease of HH and/or HV polarization,showing the heterogeneous ablation processes over the GrIS.The daily maximum 2 m air temperature on two consecutive days(before and on the SAR acquisition day)exceeds 0℃,and the daily average 2 m air temperature exceeds−0.5℃on the SAR acquisition day that was recorded by the AWS finds good agreements with the−3 dB decrease of the backscatter coefficients,suggesting the GrIS surface melting can be well captured by dual-polarized Sentinel-1 C-band SAR images.The overall agreement and Kappa coefficients are mostly better than 0.85 and 0.70,respectively,for HH images and 0.80 and 0.60,respectively,for HV images,suggesting a better performance of the co-polarized image.High temporal resolution and wide-swath SAR sequence imagery provide suitable data sources for monitoring glacier surface melting-refreezing stats;further analysis is requested to quantitatively link the volume of melting with backscatter coefficient and other SAR data sources.展开更多
Satellite geodesy is capable of observing glacier height changes and most recent studies focus on the decadal scale due to limitations of data acquisition and precision.Glaciers at the Mt.Everest(Qomolangma),locating ...Satellite geodesy is capable of observing glacier height changes and most recent studies focus on the decadal scale due to limitations of data acquisition and precision.Glaciers at the Mt.Everest(Qomolangma),locating at the central Himalaya,have been studied from the 1970s to 2015.Here we obtained TerraSAR-X/TanDEM-X images observed in two epochs,a group around 2013 and another in 2017.Together with SRTM observed in 2000,we derived geodetic glacier mass balance between 2000 and 2013 and 2013 and 2017.We proposed two InSAR procedures for deriving the second period,which yields with basically identical results of geodetic glacier mass balance.The differencing between DEMs derived by TerraSAR-X/TanDEM-X shows better precision than that between TerraSAR-X/TanDEM-X formed DEM and SRTM,and it can capable of providing geodetic glacier mass balance at a sub-decadal scale.Glaciers at the Mt.Everest(Qomolangma)and its surroundings present obvious speeding up in mass loss rates before and after 2013 for both the Chinese and the Nepalese sides.The previous obtained spatial heterogeneous pattern for glacier downwasting between 2000 and 2013 generally kept the same after 2013.Glaciers with lacustrine terminus present the most rapid lost rates.展开更多
基金supported by the National Key Research and Development Program of China[grant number 2021YFC2801300]the Guangdong Basic and Applied Basic Research Foundation[grant number 2021B1515020032]+1 种基金Science and Technology Projects in Guangzhou[grant number 202102020337]the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)[grant number 311022003].
文摘Synectic Aperture Radar(SAR)backscatter coefficient is sensitive to glacier surface physical characteristic changes,including the states of melting and refreezing,but it is also sensitive to incidence angle variation.This study explores the capability of monitoring Greenland Ice Sheet(GrIS)melting status with Sentinel-1 dual-polarized images by referring to Automatic Weather Station(AWS)records.Sentinel-1 SAR images at five coastal regions of the GrIS are obtained from 2017 to 2021.The backscatter coefficients are normalized to an incidence angle of 30°with an empirical model.Time series of five backscatter coefficients profiles covering AWS illustrates different patterns of the ice surface dielectric constant dynamics in different elevations.The wet snow radar zone shows clear backscatter coefficients decreasing during the melting seasons,but the bare ice radar zone behaves more complexly during the melting seasons.The numbers of melting days at different elevations are also derived for each profile based on−3 dB backscatter coefficient decrease of HH and/or HV polarization,showing the heterogeneous ablation processes over the GrIS.The daily maximum 2 m air temperature on two consecutive days(before and on the SAR acquisition day)exceeds 0℃,and the daily average 2 m air temperature exceeds−0.5℃on the SAR acquisition day that was recorded by the AWS finds good agreements with the−3 dB decrease of the backscatter coefficients,suggesting the GrIS surface melting can be well captured by dual-polarized Sentinel-1 C-band SAR images.The overall agreement and Kappa coefficients are mostly better than 0.85 and 0.70,respectively,for HH images and 0.80 and 0.60,respectively,for HV images,suggesting a better performance of the co-polarized image.High temporal resolution and wide-swath SAR sequence imagery provide suitable data sources for monitoring glacier surface melting-refreezing stats;further analysis is requested to quantitatively link the volume of melting with backscatter coefficient and other SAR data sources.
基金National Natural Science Foundation of China(No.41901384)National Basic Research Program of China(No.2015CB954103)+1 种基金General Research Fund of HKSAR(Nos.CUHK 14233016,CUHK 14206818)Open Foundation of State Key Laboratory of Geodesy and Earth’s Dynamics(No.SKLGED2018-2-3-EZ)。
文摘Satellite geodesy is capable of observing glacier height changes and most recent studies focus on the decadal scale due to limitations of data acquisition and precision.Glaciers at the Mt.Everest(Qomolangma),locating at the central Himalaya,have been studied from the 1970s to 2015.Here we obtained TerraSAR-X/TanDEM-X images observed in two epochs,a group around 2013 and another in 2017.Together with SRTM observed in 2000,we derived geodetic glacier mass balance between 2000 and 2013 and 2013 and 2017.We proposed two InSAR procedures for deriving the second period,which yields with basically identical results of geodetic glacier mass balance.The differencing between DEMs derived by TerraSAR-X/TanDEM-X shows better precision than that between TerraSAR-X/TanDEM-X formed DEM and SRTM,and it can capable of providing geodetic glacier mass balance at a sub-decadal scale.Glaciers at the Mt.Everest(Qomolangma)and its surroundings present obvious speeding up in mass loss rates before and after 2013 for both the Chinese and the Nepalese sides.The previous obtained spatial heterogeneous pattern for glacier downwasting between 2000 and 2013 generally kept the same after 2013.Glaciers with lacustrine terminus present the most rapid lost rates.
