Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ...Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ecological index(RSEI)model for this region by combining dryness,moisture,greenness,and desertification indicators.Using the Moderate-resolution Imaging Spectroradiometer(MODIS)data in Google Earth Engine(GEE)platform,this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020.We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI,and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI.Further,the correlation analysis was used to analyze the correlation between RSEI and precipitation,and Hurst index was applied to evaluate the change trend of RSEI in the future.The results show that RSEI of the Sahel region exhibited spatial heterogeneity.Specifically,it exhibited a decrease in gradient from south to north of the Sahel region.Moreover,RSEI in parts of the Sahel region presented non-zonal features.Different land-cover types demonstrated different RSEI values and changing trends.We found that RSEI and precipitation were positively correlated,suggesting that precipitation is the controlling factor of RSEI.The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend.In the Sahel region,the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02%and 28.29%of the total study area,respectively,and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42%and 15.26%of the whole area,respectively.In the face of the current ecological environment and future change trends of RSEI in the Sahel region,the research results provide a reference for the construction of the"Green Great Wall"(GGW)ecological environment project in Africa.展开更多
The Qinghai Lake is the largest inland lake in China.The significant difference of dielectric properties between water and ice suggests that a simple method of monitoring the Qinghai lake freeze-up and break-up dates ...The Qinghai Lake is the largest inland lake in China.The significant difference of dielectric properties between water and ice suggests that a simple method of monitoring the Qinghai lake freeze-up and break-up dates using satellite passive microwave remote sensing data could be used.The freeze-up and break-up dates from the Qinghai Lake hydrological station and the MODIS L1B reflectance data were used to validate the passive microwave remote sensing results.The validation shows that passive microwave remote sensing data can accurately monitor the lake ice.Some uncertainty comes mainly from the revisit frequency of satellite overpass.The data from 1978 to 2006 show that lake ice duration is reduced by about 14―15 days.The freeze-up dates are about 4 days later and break-up dates about 10 days earlier.The regression analyses show that,at the 0.05 significance level,the correlations are 0.83,0.66 and 0.89 between monthly mean air temperature(MMAT) and lake ice duration days,freeze-up dates,break-up dates,respectively.Therefore,inter-annual variations of the Qinghai Lake ice duration days can significantly reflect the regional climate variation.展开更多
MPI （microwave polarization index） method can use different frequencies at vertical polarization to retrieve soil moisture from TMI （tropical microwave imager） data, which is mainly suitable for bare soil. This pa...MPI （microwave polarization index） method can use different frequencies at vertical polarization to retrieve soil moisture from TMI （tropical microwave imager） data, which is mainly suitable for bare soil. This paper makes an improvement for MPI method which makes it suitable for surface covered by vegetation. The MPI by using single frequency at different polarizations is used to discriminate the bare soil and vegetation which overcomes the difficulty in previous algorithms by using optical remote sensing data, and then the revision is made according to the different land surface types. The validation by using ground measurement data indicates that revision for different land surface types can improve the retrieval accuracy. The average error is about 24.5% by using the ground truth data obtained from ground observation stations, and the retrieval error is about 13.7% after making a revision by using ground measurement data from local observation stations for different surface types. The improved MPI method and precipitation are used to analyze the drought in Southwest China, and the analysis indicates the soil moisture retrieved by improved MPI method can be used to monitor the drought.展开更多
Sea ice cover plays an important role in modulating local temperature through heat and moisture fuxes.The infuence of thin ice lead and polynya has been wellinvestigated,however,the effect of perennial ice(also called...Sea ice cover plays an important role in modulating local temperature through heat and moisture fuxes.The infuence of thin ice lead and polynya has been wellinvestigated,however,the effect of perennial ice(also called muliyear ice,MYI)has not.This study is motivated by it and investigated a hypothesis that changes in MYI concentration in winter triggers changes in short-term local 2-m air temperature.The hypothesis was tested using time series analysis of the two parameters and correlation between them.Data from the winters of 2004-2009 were used for the examination at three spatial scales.The hypothesis is found to be potentially accepted when MYI exists in a consolidated ice regime with negligible thin ice or open water in the surroundings,and the air temperature is low enough.Conditions for the acceptance of the hypothesis were quantitatively identified.The qualifications entail that the ice cell must experience daily change of MYI concentration meanwhile satisfy the criteria of total ice concentration(TIC),young ice concentration(YIC)and air temperature(Tar)in the surrounding area,which are TIC>88.3%,YIC<9.5%and T_(air)<-19.0℃.Inverse relationships between changes in MYI concentration and the corresponding changes in air temperature were developed retroactively using data that satisfied the acceptance conditions.The relationships varied with years,depending on ice conditions such as ice type distributions and snow cover.This study offers a first attempt to assess the effect of MYI on the same-day local surface air temperature using satelite observations,and provides evidence of this effect under quantitatively quanlifying conditions.展开更多
基金This research was financially supported by the West Light Foundation of the Chinese Academy of Science(2017-XBQNXZ-B-018)the National Natural Science Foundation of China(41861144020)the National Key Research and Development Program of China-Joint Research on Technology to Combat Desertification for African Countries of the“Great Green Wall”(2018YFE0106000).
文摘Long-term monitoring of the ecological environment changes is helpful for the protection of the ecological environment.Based on the ecological environment of the Sahel region in Africa,we established a remote sensing ecological index(RSEI)model for this region by combining dryness,moisture,greenness,and desertification indicators.Using the Moderate-resolution Imaging Spectroradiometer(MODIS)data in Google Earth Engine(GEE)platform,this study analyzed the ecological environment quality of the Sahel region during the period of 2001-2020.We used liner regression and fluctuation analysis methods to study the trend and fluctuation of RSEI,and utilized the stepwise regression approach to analyze the contribution of each indicator to the RSEI.Further,the correlation analysis was used to analyze the correlation between RSEI and precipitation,and Hurst index was applied to evaluate the change trend of RSEI in the future.The results show that RSEI of the Sahel region exhibited spatial heterogeneity.Specifically,it exhibited a decrease in gradient from south to north of the Sahel region.Moreover,RSEI in parts of the Sahel region presented non-zonal features.Different land-cover types demonstrated different RSEI values and changing trends.We found that RSEI and precipitation were positively correlated,suggesting that precipitation is the controlling factor of RSEI.The areas where RSEI values presented an increasing trend were slightly less than the areas where RSEI values presented a decreasing trend.In the Sahel region,the areas with the ecological environment characterized by continuous deterioration and continuous improvement accounted for 44.02%and 28.29%of the total study area,respectively,and the areas in which the ecological environment was changing from improvement to deterioration and from deterioration to improvement accounted for 12.42%and 15.26%of the whole area,respectively.In the face of the current ecological environment and future change trends of RSEI in the Sahel region,the research results provide a reference for the construction of the"Green Great Wall"(GGW)ecological environment project in Africa.
基金Supported by the National Basic Research Program of China (Grand No.2007CB411506)National Natural Science Foundation of China (Grand Nos.40601065 and 40701030)
文摘The Qinghai Lake is the largest inland lake in China.The significant difference of dielectric properties between water and ice suggests that a simple method of monitoring the Qinghai lake freeze-up and break-up dates using satellite passive microwave remote sensing data could be used.The freeze-up and break-up dates from the Qinghai Lake hydrological station and the MODIS L1B reflectance data were used to validate the passive microwave remote sensing results.The validation shows that passive microwave remote sensing data can accurately monitor the lake ice.Some uncertainty comes mainly from the revisit frequency of satellite overpass.The data from 1978 to 2006 show that lake ice duration is reduced by about 14―15 days.The freeze-up dates are about 4 days later and break-up dates about 10 days earlier.The regression analyses show that,at the 0.05 significance level,the correlations are 0.83,0.66 and 0.89 between monthly mean air temperature(MMAT) and lake ice duration days,freeze-up dates,break-up dates,respectively.Therefore,inter-annual variations of the Qinghai Lake ice duration days can significantly reflect the regional climate variation.
基金supported by the National Basic Research Program of China (2010CB951503)the National Natural Science Foundation of China(40930101)+2 种基金the Open Fund of the State Key Laboratory of Remote Sensing Sciencejointly sponsored by the Institute of Remote Sensing Applications of the Chinese Academy of Sciences and Beijing Normal University, Chinathe Open Fund of Key Laboratory of Agrometeorological Safeguard and Applied, China Meteorological Administration
文摘MPI （microwave polarization index） method can use different frequencies at vertical polarization to retrieve soil moisture from TMI （tropical microwave imager） data, which is mainly suitable for bare soil. This paper makes an improvement for MPI method which makes it suitable for surface covered by vegetation. The MPI by using single frequency at different polarizations is used to discriminate the bare soil and vegetation which overcomes the difficulty in previous algorithms by using optical remote sensing data, and then the revision is made according to the different land surface types. The validation by using ground measurement data indicates that revision for different land surface types can improve the retrieval accuracy. The average error is about 24.5% by using the ground truth data obtained from ground observation stations, and the retrieval error is about 13.7% after making a revision by using ground measurement data from local observation stations for different surface types. The improved MPI method and precipitation are used to analyze the drought in Southwest China, and the analysis indicates the soil moisture retrieved by improved MPI method can be used to monitor the drought.
基金supported by the National Key Research and Development Program of China(2019YFC1509104)National Natural Science Foundation of China(42106225,41976214).
文摘Sea ice cover plays an important role in modulating local temperature through heat and moisture fuxes.The infuence of thin ice lead and polynya has been wellinvestigated,however,the effect of perennial ice(also called muliyear ice,MYI)has not.This study is motivated by it and investigated a hypothesis that changes in MYI concentration in winter triggers changes in short-term local 2-m air temperature.The hypothesis was tested using time series analysis of the two parameters and correlation between them.Data from the winters of 2004-2009 were used for the examination at three spatial scales.The hypothesis is found to be potentially accepted when MYI exists in a consolidated ice regime with negligible thin ice or open water in the surroundings,and the air temperature is low enough.Conditions for the acceptance of the hypothesis were quantitatively identified.The qualifications entail that the ice cell must experience daily change of MYI concentration meanwhile satisfy the criteria of total ice concentration(TIC),young ice concentration(YIC)and air temperature(Tar)in the surrounding area,which are TIC>88.3%,YIC<9.5%and T_(air)<-19.0℃.Inverse relationships between changes in MYI concentration and the corresponding changes in air temperature were developed retroactively using data that satisfied the acceptance conditions.The relationships varied with years,depending on ice conditions such as ice type distributions and snow cover.This study offers a first attempt to assess the effect of MYI on the same-day local surface air temperature using satelite observations,and provides evidence of this effect under quantitatively quanlifying conditions.
