Loss of multiyear ice(MYI)is of great importance for Arctic climate and marine systems and can be monitored using active and passive microwave satellite data.In this paper,we describe an upgraded classification algori...Loss of multiyear ice(MYI)is of great importance for Arctic climate and marine systems and can be monitored using active and passive microwave satellite data.In this paper,we describe an upgraded classification algorithm using the data from the scatterometer and radiometer sensors onboard the Chinese Haiyang-2B(HY-2B)satellite to identify MYI and first-year ice(FYI).The proposed method was established based on K-means and fuzzy clustering(K-means+FC)and was used to focus on the transition zone where the ice condition is complex due to the highly commixing of MYI and FYI,leading to the high challenge for accurate classification of sea ice.The K-means algorithm was applied to preliminarily classify MYI using the combination of scatterometer and radiometer data,followed by applying fuzzy clustering to reclassify MYI in the transition zone.The HY-2B K-means+FC results were compared with the ice type products[including the Ocean and Sea Ice Satellite Application Facility(OSI SAF)sea ice type product and the Equal-Area Scalable Earth-Grid sea ice age dataset],and showed agreement in the time series of MYI extent.Intercomparisons in the transition zone indicated that the HY-2B K-means+FC results can identify more old ice than the OSI SAF product,but with an underestimation in identifying second-year ice.Comparisons between K-means and Kmeans+FC results were performed using regional ice charts and Sentinel-1 synthetic aperture radar(SAR)data.By adding fuzzy clustering,the MYI is more consistent with the ice charts,with the overall accuracy(OA)increasing by 0.9%–6.5%.Comparing against SAR images,it is suggested that more scattered MYI floes can be identified by fuzzy clustering,and the OA is increased by about 3%in middle freezing season and 7%–20%in early and late freezing season.展开更多
Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic de...Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic devices. Herein, we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In2Se3/MoSe2 heterostructures. Transmission electron microscopy characterization reveals clearly that the In2Se3 has well-aligned lattice orientation with the substrate of monolayer MoSe2. Due to the interaction between the In2Se3 and MoSe2 layers, the heterostructure shows the quench- ing and red-shift of photoluminescence. Moreover, the current rectification behavior and photovoltaic effect can be observed from the heterostructure, which is attributed to the unique band structure alignment of the heterostructure, and is further confirmed by Kevin probe force microscopy measurement. The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.展开更多
ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含...ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含了设备噪声、大气颗粒散射噪声、背景干扰噪声等大量噪声光子。本研究提出了一种新的海面信号光子提取和海浪要素反演方法,首先将原始ICESat-2数据沿垂直方向均匀分段,统计各段内光子数,对其进行高斯拟合和迭代中值滤波,确定精确的海面光子上下界,从而提取出海面信号光子。进一步采用支持向量回归拟合,提取瞬时海面轮廓。在此基础上,利用频谱分析方法计算出有效波高和初步海浪峰值波长,通过对同步的强弱激光束相位相干分析,估算海浪波向,并修正海浪峰值波长和计算海浪峰值周期。对来自好望角和萨摩亚海域的24条轨道ICESat-2数据进行海面光子提取和海浪要素反演,并将结果与ERA5再分析数据进行对比验证。结果表明,海浪有效波高、波向和峰值周期的均方根误差(RMSE)分别为0.12 m、28.58°和0.48 s,表明该方法具有较高的海浪要素反演精度,具备进一步探索更大范围激光雷达数据海浪要素提取和分析的潜力。展开更多
GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration. This study introduces the results of the Qinglan calibration campaign for the HY-2A and Jason-2 altimeter...GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration. This study introduces the results of the Qinglan calibration campaign for the HY-2A and Jason-2 altimeters. It took place in two time slices;one was from August to September 2014, and the other was in July 2015. One GPS buoy and two GPS reference stations were used in this campaign. The GPS data were processed using the real-time kinematic (RTK) technique. The fi nal error budget estimate when measuring the sea surface height (SSH) with a GPS buoy was better than 3.5 cm. Using the GPS buoy, the altimeter bias estimate was about -2.3 cm for the Jason-2 Geophysical Data Record (GDR) Version ‘D' and from -53.5 cm to -75.6 cm for the HY-2A Interim Geophysical Data Record (IGDR). The bias estimates for Jason-2 GDR-D are similar to the estimates from dedicated calibration sites such as the Harvest Platform, the Crete Site and the Bass Strait site. The bias estimates for HY-2A IGDR agree well with the results from the Crete calibration site. The results for the HY-2A altimeter bias estimated by the GPS buoy were verifi ed by cross-calibration, and they agreed well with the results from the global analysis method.展开更多
A retrieval algorithm of arctic sea ice concentration （SIC） based on the brightness temperature data of “HY-2” scanning microwave radiometer has been constructed. The tie points of the brightness temperature were ...A retrieval algorithm of arctic sea ice concentration （SIC） based on the brightness temperature data of “HY-2” scanning microwave radiometer has been constructed. The tie points of the brightness temperature were selected based on the statistical analysis of a polarization gradient ratio and a spectral gradient ratio over open water （OW）, first-year ice （FYI）, and multiyear ice （MYI） in arctic. The thresholds from two weather filters were used to reduce atmospheric effects over the open ocean. SIC retrievals from the “HY-2” radiom-eter data for idealized OW, FYI, and MYI agreed well with theoretical values. The 2012 annual SIC was calcu-lated and compared with two reference operational products from the National Snow and Ice Data Center （NSIDC） and the University of Bremen. The total ice-covered area yielded by the “HY-2” SIC was consistent with the results from the reference products. The assessment of SIC with the aerial photography from the fifth Chinese national arctic research expedition （CHINARE） and six synthetic aperture radar （SAR） images from the National Ice Service was carried out. The “HY-2” SIC product was 16% higher than the values de-rived from the aerial photography in the central arctic. The root-mean-square （RMS） values of SIC between “HY-2” and SAR were comparable with those between the reference products and SAR, varying from 8.57% to 12.34%. The “HY-2” SIC is a promising product that can be used for operational services.展开更多
基金the National Key Research and Development Program of China under contract No.2021YFC2803301the Fundamental Research Funds for the Central Universities,China under contract Nos 2042024kf0037 and 2042022dx0001the Natural Science Foundation of Wuhan under cocntract No.2024040701010030.
文摘Loss of multiyear ice(MYI)is of great importance for Arctic climate and marine systems and can be monitored using active and passive microwave satellite data.In this paper,we describe an upgraded classification algorithm using the data from the scatterometer and radiometer sensors onboard the Chinese Haiyang-2B(HY-2B)satellite to identify MYI and first-year ice(FYI).The proposed method was established based on K-means and fuzzy clustering(K-means+FC)and was used to focus on the transition zone where the ice condition is complex due to the highly commixing of MYI and FYI,leading to the high challenge for accurate classification of sea ice.The K-means algorithm was applied to preliminarily classify MYI using the combination of scatterometer and radiometer data,followed by applying fuzzy clustering to reclassify MYI in the transition zone.The HY-2B K-means+FC results were compared with the ice type products[including the Ocean and Sea Ice Satellite Application Facility(OSI SAF)sea ice type product and the Equal-Area Scalable Earth-Grid sea ice age dataset],and showed agreement in the time series of MYI extent.Intercomparisons in the transition zone indicated that the HY-2B K-means+FC results can identify more old ice than the OSI SAF product,but with an underestimation in identifying second-year ice.Comparisons between K-means and Kmeans+FC results were performed using regional ice charts and Sentinel-1 synthetic aperture radar(SAR)data.By adding fuzzy clustering,the MYI is more consistent with the ice charts,with the overall accuracy(OA)increasing by 0.9%–6.5%.Comparing against SAR images,it is suggested that more scattered MYI floes can be identified by fuzzy clustering,and the OA is increased by about 3%in middle freezing season and 7%–20%in early and late freezing season.
文摘Two-dimensional transition metal dichalcogenides heterostructures have stimulated wide in- terest not only for the fundamental research, but also for the application of next generation electronic and optoelectronic devices. Herein, we report a successful two-step chemical vapor deposition strategy to construct vertically stacked van der Waals epitaxial In2Se3/MoSe2 heterostructures. Transmission electron microscopy characterization reveals clearly that the In2Se3 has well-aligned lattice orientation with the substrate of monolayer MoSe2. Due to the interaction between the In2Se3 and MoSe2 layers, the heterostructure shows the quench- ing and red-shift of photoluminescence. Moreover, the current rectification behavior and photovoltaic effect can be observed from the heterostructure, which is attributed to the unique band structure alignment of the heterostructure, and is further confirmed by Kevin probe force microscopy measurement. The synthesis approach via van der Waals epitaxy in this work can expand the way to fabricate a variety of two-dimensional heterostructures for potential applications in electronic and optoelectronic devices.
文摘ICESat-2(Ice,Cloud and Land Elevation Satellite 2)卫星激光雷达数据被广泛应用于地形地貌测绘、森林监测、水域监测等多个领域。当ICESat-2飞越海面时,可以检测到被海面反射回的微弱光子信号,其反映了海面的起伏状态,但同时也包含了设备噪声、大气颗粒散射噪声、背景干扰噪声等大量噪声光子。本研究提出了一种新的海面信号光子提取和海浪要素反演方法,首先将原始ICESat-2数据沿垂直方向均匀分段,统计各段内光子数,对其进行高斯拟合和迭代中值滤波,确定精确的海面光子上下界,从而提取出海面信号光子。进一步采用支持向量回归拟合,提取瞬时海面轮廓。在此基础上,利用频谱分析方法计算出有效波高和初步海浪峰值波长,通过对同步的强弱激光束相位相干分析,估算海浪波向,并修正海浪峰值波长和计算海浪峰值周期。对来自好望角和萨摩亚海域的24条轨道ICESat-2数据进行海面光子提取和海浪要素反演,并将结果与ERA5再分析数据进行对比验证。结果表明,海浪有效波高、波向和峰值周期的均方根误差(RMSE)分别为0.12 m、28.58°和0.48 s,表明该方法具有较高的海浪要素反演精度,具备进一步探索更大范围激光雷达数据海浪要素提取和分析的潜力。
基金Supported by the National Key R&D Program of China(No.2016YFC1401003)the National Natural Science Foundation of China(Nos.41406204,41501417)the Marine Public Welfare Project of China(No.201305032-3)
文摘GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration. This study introduces the results of the Qinglan calibration campaign for the HY-2A and Jason-2 altimeters. It took place in two time slices;one was from August to September 2014, and the other was in July 2015. One GPS buoy and two GPS reference stations were used in this campaign. The GPS data were processed using the real-time kinematic (RTK) technique. The fi nal error budget estimate when measuring the sea surface height (SSH) with a GPS buoy was better than 3.5 cm. Using the GPS buoy, the altimeter bias estimate was about -2.3 cm for the Jason-2 Geophysical Data Record (GDR) Version ‘D' and from -53.5 cm to -75.6 cm for the HY-2A Interim Geophysical Data Record (IGDR). The bias estimates for Jason-2 GDR-D are similar to the estimates from dedicated calibration sites such as the Harvest Platform, the Crete Site and the Bass Strait site. The bias estimates for HY-2A IGDR agree well with the results from the Crete calibration site. The results for the HY-2A altimeter bias estimated by the GPS buoy were verifi ed by cross-calibration, and they agreed well with the results from the global analysis method.
基金The International Science and Technology Cooperation Project of China under contract No.2011DFA22260the National Natural Science Foundation of China under contract No.41276191+1 种基金the Public Science and Technology Research Funds Projects of Ocean by the State Oceanic Administration under contract No.201205007-05the Chinese Polar Environment Comprehensive Investigation & Assessment Program by the State Oceanic Administration under contract Nos 2013-02-04 and 2012-04-03-02
文摘A retrieval algorithm of arctic sea ice concentration （SIC） based on the brightness temperature data of “HY-2” scanning microwave radiometer has been constructed. The tie points of the brightness temperature were selected based on the statistical analysis of a polarization gradient ratio and a spectral gradient ratio over open water （OW）, first-year ice （FYI）, and multiyear ice （MYI） in arctic. The thresholds from two weather filters were used to reduce atmospheric effects over the open ocean. SIC retrievals from the “HY-2” radiom-eter data for idealized OW, FYI, and MYI agreed well with theoretical values. The 2012 annual SIC was calcu-lated and compared with two reference operational products from the National Snow and Ice Data Center （NSIDC） and the University of Bremen. The total ice-covered area yielded by the “HY-2” SIC was consistent with the results from the reference products. The assessment of SIC with the aerial photography from the fifth Chinese national arctic research expedition （CHINARE） and six synthetic aperture radar （SAR） images from the National Ice Service was carried out. The “HY-2” SIC product was 16% higher than the values de-rived from the aerial photography in the central arctic. The root-mean-square （RMS） values of SIC between “HY-2” and SAR were comparable with those between the reference products and SAR, varying from 8.57% to 12.34%. The “HY-2” SIC is a promising product that can be used for operational services.
