Water vapor content in the atmosphere is very significant for atmospheric correction of optical remote sensing data. Nowadays, the common atmospheric correction models use a single value of the average water vapor con...Water vapor content in the atmosphere is very significant for atmospheric correction of optical remote sensing data. Nowadays, the common atmospheric correction models use a single value of the average water vapor content of the study area to perform atmospheric correction. As the distribution of water vapor content varies greatly with time and space, it is obviously inaccurate to represent the total water vapor conditions of the whole area by just reading the average water vapor content. In this study, we altered the 6S sources so that it could read the water vapor content image which was retrieved from MODIS 1 km data. Atmospheric correction was implemented for the band 1 of MODIS 500 m data pixel-by-pixel using the improved 6S model. In comparison with the traditional 6S model, this improved 6S model is more reasonable in atmospheric correction, for it considers the spatial distribution of the water vapor content retrieved from MODIS data in the near infrared to define the atmospheric conditions for simulating the atmospheric radiative transfer. The results corrected by the improved 6S model showed more reasonable in pixel spatial distribution and closer histogram with the original image than those by traditional 6S model.展开更多
Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The res...Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The results show that the extreme precipitation frequency was regional dependent.Southern Gansu,northern Qinghai,and southern Shaanxi provinces exhibited a high extreme precipitation frequency and were prone to abrupt changes in the frequency.Northwest China was further divided into three sub-regions（northern,central,and southern） based on cluster analysis of the 50-yr extreme precipitation frequency series for each meteorological station.The extreme precipitation frequency changes were manifested in the northern region during the late 1970 s and in the central region from the end of the 1980 s to the 1990 s.The southern region fluctuated on a timescale of quasi-10 yr.This study also explored the mechanism of changes in extreme precipitation frequency.The results demonstrate that stratification stability,atmospheric water vapor content,and upward motion all affected the changes in extreme precipitation frequency.展开更多
文摘Water vapor content in the atmosphere is very significant for atmospheric correction of optical remote sensing data. Nowadays, the common atmospheric correction models use a single value of the average water vapor content of the study area to perform atmospheric correction. As the distribution of water vapor content varies greatly with time and space, it is obviously inaccurate to represent the total water vapor conditions of the whole area by just reading the average water vapor content. In this study, we altered the 6S sources so that it could read the water vapor content image which was retrieved from MODIS 1 km data. Atmospheric correction was implemented for the band 1 of MODIS 500 m data pixel-by-pixel using the improved 6S model. In comparison with the traditional 6S model, this improved 6S model is more reasonable in atmospheric correction, for it considers the spatial distribution of the water vapor content retrieved from MODIS data in the near infrared to define the atmospheric conditions for simulating the atmospheric radiative transfer. The results corrected by the improved 6S model showed more reasonable in pixel spatial distribution and closer histogram with the original image than those by traditional 6S model.
基金Supported by the China Meteorological Administration Special Public Welfare Research Fund(GYHY201006017)National Natural Science Foundation of China(41375121 and 41305079)Scientific Research and Innovation Plan for College Graduates of Jiangsu Province of China(CXZZ13_0500 and CXZZ13_0521)
文摘Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The results show that the extreme precipitation frequency was regional dependent.Southern Gansu,northern Qinghai,and southern Shaanxi provinces exhibited a high extreme precipitation frequency and were prone to abrupt changes in the frequency.Northwest China was further divided into three sub-regions（northern,central,and southern） based on cluster analysis of the 50-yr extreme precipitation frequency series for each meteorological station.The extreme precipitation frequency changes were manifested in the northern region during the late 1970 s and in the central region from the end of the 1980 s to the 1990 s.The southern region fluctuated on a timescale of quasi-10 yr.This study also explored the mechanism of changes in extreme precipitation frequency.The results demonstrate that stratification stability,atmospheric water vapor content,and upward motion all affected the changes in extreme precipitation frequency.
