Surface irradiance measurements with high temporal resolution can be used to detect clear skies,which is a critical step for further study,such as aerosol and cloud radiative effects.Twenty-one clear-sky detection(CSD...Surface irradiance measurements with high temporal resolution can be used to detect clear skies,which is a critical step for further study,such as aerosol and cloud radiative effects.Twenty-one clear-sky detection(CSD)methods are assessed based on five years of 1-min surface irradiance data at Xianghe—a heavily polluted station on the North China Plain.Total-sky imager(TSI)discrimination results corrected by manual checks are used as the benchmark for the evaluation.The performance heavily relies on the criteria adopted by the CSD methods.Those with higher cloudy-sky detection accuracy rates produce lower clear-sky accuracy rates,and vice versa.A general tendency in common among all CSD methods is the detection accuracy deteriorates when aerosol loading increases.Nearly all criteria adopted in CSD methods are too strict to detect clear skies under polluted conditions,which is more severe if clear-sky irradiance is not properly estimated.The mean true positive rate(CSD method correctly detects clear sky)decreases from 45%for aerosol optical depth(AOD)≤0.2%to 6%for AOD>0.5.The results clearly indicate that CSD methods in a highly polluted region still need further improvements.展开更多
One of the biggest factors to deteriorate the satellite product quality is cloud coverage. Therefore, cloud masking process is important to improve the quality of various satellite products. However, satellite-based c...One of the biggest factors to deteriorate the satellite product quality is cloud coverage. Therefore, cloud masking process is important to improve the quality of various satellite products. However, satellite-based cloud discrimination algorithm has been developing and efficient ground-based cloud observations are necessary to validate satellite-based cloud discrimination. The purpose of this study is to develop the efficient ground-based cloud observation methodology using whole sky camera. This paper deals with methods how to discriminate cloud portions on whole sky image, how to apply the ground-based cloud observation to the validations for satellite products. For the cloud discrimination on whole sky image, we propose SI （sky index） and BI （brightness index） calculated from RGB （red, green and blue） channels. SI shows the extent of the blueness and gray scale and BI indicates the extent of the brightness. Sun, cloud and blue sky portions are divided by SI and BI threshold. As an application of ground-based cloud observation for the validation of satellite products, clouds portions discriminated from whole sky image are projected onto ground surface with map coordinate. We also examine to compare with cloud portions on whole sky images and MODIS （MODerate resolution Imaging Spectroradiometer） image as one of experiments. The proposed ground-based cloud observation method and its extension to satellite-based cloud discrimination should be connected to improve the quality of satellite products.展开更多
The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ec...The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ecological patterns between regions and over time.Based on the interpretation of remote sensing image data for Tianjin in 1980,2000,2010 and 2019,supported by software such as ArcGIS and GeoDa,the changes of land use in the study area are calculated by using the land use dynamic degree.Then,the land ecological security index and spatial autocorrelation analysis methods are used to study the spatial correlations and internal heterogeneity of land ecological security in each district in Tianjin.The results show that:(1)The land use of Tianjin has changed dramatically in the past 40 years:the building land has been expanding,while the farmland and barren have been shrinking continuously.(2)The overall level of land ecological security is in the high security area,and Jizhou District is the highest,while the Central areas and Binhai are low.(3)The spatial heterogeneity of land ecological security is not obvious,but the spatial agglomeration is strong.展开更多
基金supported by the National Key R&D Program of China grant number 2017YFA0603504the Strategic Priority Research Program of the Chinese Academy of Sciences grant number XDA17010101the National Natural Science Foundation of Chinagrant number 41875183。
文摘Surface irradiance measurements with high temporal resolution can be used to detect clear skies,which is a critical step for further study,such as aerosol and cloud radiative effects.Twenty-one clear-sky detection(CSD)methods are assessed based on five years of 1-min surface irradiance data at Xianghe—a heavily polluted station on the North China Plain.Total-sky imager(TSI)discrimination results corrected by manual checks are used as the benchmark for the evaluation.The performance heavily relies on the criteria adopted by the CSD methods.Those with higher cloudy-sky detection accuracy rates produce lower clear-sky accuracy rates,and vice versa.A general tendency in common among all CSD methods is the detection accuracy deteriorates when aerosol loading increases.Nearly all criteria adopted in CSD methods are too strict to detect clear skies under polluted conditions,which is more severe if clear-sky irradiance is not properly estimated.The mean true positive rate(CSD method correctly detects clear sky)decreases from 45%for aerosol optical depth(AOD)≤0.2%to 6%for AOD>0.5.The results clearly indicate that CSD methods in a highly polluted region still need further improvements.
文摘One of the biggest factors to deteriorate the satellite product quality is cloud coverage. Therefore, cloud masking process is important to improve the quality of various satellite products. However, satellite-based cloud discrimination algorithm has been developing and efficient ground-based cloud observations are necessary to validate satellite-based cloud discrimination. The purpose of this study is to develop the efficient ground-based cloud observation methodology using whole sky camera. This paper deals with methods how to discriminate cloud portions on whole sky image, how to apply the ground-based cloud observation to the validations for satellite products. For the cloud discrimination on whole sky image, we propose SI （sky index） and BI （brightness index） calculated from RGB （red, green and blue） channels. SI shows the extent of the blueness and gray scale and BI indicates the extent of the brightness. Sun, cloud and blue sky portions are divided by SI and BI threshold. As an application of ground-based cloud observation for the validation of satellite products, clouds portions discriminated from whole sky image are projected onto ground surface with map coordinate. We also examine to compare with cloud portions on whole sky images and MODIS （MODerate resolution Imaging Spectroradiometer） image as one of experiments. The proposed ground-based cloud observation method and its extension to satellite-based cloud discrimination should be connected to improve the quality of satellite products.
基金Tianjin Art and Science Planning Project(D16007)。
文摘The problem of land ecological security directly threatens the sustainable development of many regions,and exploring the spatio-temporal characteristics of land ecological security is helpful for analyzing the land ecological patterns between regions and over time.Based on the interpretation of remote sensing image data for Tianjin in 1980,2000,2010 and 2019,supported by software such as ArcGIS and GeoDa,the changes of land use in the study area are calculated by using the land use dynamic degree.Then,the land ecological security index and spatial autocorrelation analysis methods are used to study the spatial correlations and internal heterogeneity of land ecological security in each district in Tianjin.The results show that:(1)The land use of Tianjin has changed dramatically in the past 40 years:the building land has been expanding,while the farmland and barren have been shrinking continuously.(2)The overall level of land ecological security is in the high security area,and Jizhou District is the highest,while the Central areas and Binhai are low.(3)The spatial heterogeneity of land ecological security is not obvious,but the spatial agglomeration is strong.
