This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Ae...This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) aerosol data, assuming that there exists "nonturbid" water in the study area where MODIS aerosol optical properties can be retrieved accurately. Aerosol properties from CALIOP measurements were obtained and related to those from MODIS. This relationship, combined with CALIOP aerosol data, was extended to turbid water to derive MODIS aerosol properties, where atmospheric correction using MODIS data alone often fails. By combining MODIS and CALIOP data, aerosol signals were separated from the total signals at the satellite level, and water-leaving radiances in turbid waters were subsequently derived. This method was tested on several MODIS/Aqua ocean color images over South China turbid waters. Comparison with field data shows that this method was effective in reducing the errors in the retrieved water-leaving radiance values to some extent. In the Zhujiang (Pearl) River Estuary, this method did not overestimate the aerosol effects as severely, and provided far fewer negative water-leaving radiance values than the NASA (National Aeronautics and Space Administration) default methods that used MODIS data alone.展开更多
The authors derived the normalized difference vegetation index （NDVI） from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during t...The authors derived the normalized difference vegetation index （NDVI） from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index （NDVI） in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China＇s vegetation cover had tended to increase, compared to the early 1980s; mean annual NDVl increased 3.8%. The agricultural regions （Henan, Hebei, Anhui and Shandong） and the west of China are marked by an increase, while the eastern coastal regions are marked by a decrease. The correlation between monthly NDVl and monthly precipitation/temperature in the period 1982 to 2001 is significantly positive （R^2 =0.80, R^2 =0.84）; indicating the close coupling between climate conditions （precipitation and temperature） and land surface response patterns over China. Examination of NDVl time series reveals two periods： （1） 1982-1989, marked by low values below average NDVI and persistence of drought with a signature large-scale drought during the 1982 and 1989; and （2） 1990-2001, marked by a wetter trend with region-wide high values above average NDVl and a maximum level occurring in 1994 and 1998.展开更多
基金Supported by the National Basic Research Program of China (973 Program, Nos. 2009CB723905, 2006CB701300)the National High Technology Research and Development Program of China (863 Program, No. 2007AA12Z161)+3 种基金the NSFC (Nos. 40676094, 40721001, 40706060)MOST, China (No. 2007BAC23B05)Open Fund of Nanchang University (No. Z03975)the Open Fund of Ocean University of China for visiting Ph. D students.
文摘This paper demonstrates an atmospheric correction method to process MODIS/Aqua (Moderate-resolution Imaging Spectroradiometer) ocean color imagery over turbid coastal waters with the aid of concurrent CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) aerosol data, assuming that there exists "nonturbid" water in the study area where MODIS aerosol optical properties can be retrieved accurately. Aerosol properties from CALIOP measurements were obtained and related to those from MODIS. This relationship, combined with CALIOP aerosol data, was extended to turbid water to derive MODIS aerosol properties, where atmospheric correction using MODIS data alone often fails. By combining MODIS and CALIOP data, aerosol signals were separated from the total signals at the satellite level, and water-leaving radiances in turbid waters were subsequently derived. This method was tested on several MODIS/Aqua ocean color images over South China turbid waters. Comparison with field data shows that this method was effective in reducing the errors in the retrieved water-leaving radiance values to some extent. In the Zhujiang (Pearl) River Estuary, this method did not overestimate the aerosol effects as severely, and provided far fewer negative water-leaving radiance values than the NASA (National Aeronautics and Space Administration) default methods that used MODIS data alone.
基金Supported by the National 973 Program of China (No2006CB701300)the National Natural Science Foundation of China (No40721001)the Sino-Germany Joint Project (No 2006DFB91920)
文摘The authors derived the normalized difference vegetation index （NDVI） from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index （NDVI） in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China＇s vegetation cover had tended to increase, compared to the early 1980s; mean annual NDVl increased 3.8%. The agricultural regions （Henan, Hebei, Anhui and Shandong） and the west of China are marked by an increase, while the eastern coastal regions are marked by a decrease. The correlation between monthly NDVl and monthly precipitation/temperature in the period 1982 to 2001 is significantly positive （R^2 =0.80, R^2 =0.84）; indicating the close coupling between climate conditions （precipitation and temperature） and land surface response patterns over China. Examination of NDVl time series reveals two periods： （1） 1982-1989, marked by low values below average NDVI and persistence of drought with a signature large-scale drought during the 1982 and 1989; and （2） 1990-2001, marked by a wetter trend with region-wide high values above average NDVl and a maximum level occurring in 1994 and 1998.
