作 者 ：Zhang Ren-hua, Rao N X and Liao K N
Keywords:Vegetation index, Resistant, Atmosphere,
Abstract:Estimation of vegetation information at the regional scales using remote sensing data has been a subject of considerable research and development in view of the importance of land-atmosphere interactions in global climate change. The normalized difference vegetation index (NDVI) approach has been a popular method. Many experiments on the‘ ground had indicated that NDVI was closely correlated to the leaf area index (LAI) and photosynthetically active radiation (PAR). In order to determine LAI and PAR accurately in a region by means of NDVI from available satellite inages, atmospheric effects must be largely elucidated. Although substantial progress has been made to improve the NDVI method, removal of the atmospheric effects has not been completely satisfactory. The atmospheric effect on NDVI has been contemplated in the experiments conducted at Yucheng Experimental Comprehensive Station, China. Kaufman and his colleagues also had verified the atmospheric effect on NDVI even the effect still existed after using 5s algorithm to remove rayleigh scattering and ozone absorption. For this reason they presented an atmosphere resistant vegetation index (ARVI) which was based on correlation between blue and red wave bands of the atmo. The authors also proposed the values for calculating IAVI in absence of the gound-based spectrum-radiometer measurements to approximately correct the atmosphere effect. For summer condition: γ↑=0. 656–0.006 sinθ+0.124 Sin2θ for rural area, visibility〉22 km γ↑=0. 656–0. 018 sinθ+0. 106 Sin2θ for urban area, Visibility〉22 km γ↑ =0. 722–0. 011 sinθ+0.165 sin2θ for rural area, 7 km〈visibility〈20 km γ↑=0. 646–0.002 sinθ+0, 140 sin2θ for urban area, 7 km〈visibility〈20 km γ↑ =0. 788+0. 015 sinθ+0. 206 sin2θ for rural area, visibility<5 km γ↑ =0. 643+0. 007 sinθ+0. 174 sin2θ for urban area, visibility〈5 km For winter condition γ↑ =0. 677+0. 019 sinθ+0. 200 sin2θ for rural area, visibility>22 km γ↑ =0. 642-0. 009 sinθ+0. 196 sin2θ for urban area, visibility>22 km γ↑ =0. 785+0, 040 sinθ+0. 237 sin2θ for rural area, 7 km〈visibility〈20 km γ↑ =0. 664+0. 021 sinθ+0.223 sin2θ for urban area, 7 km〈visibility〈20 km γ↑ =0. 893+0.060 sinθ+0. 273 sin2θ for rural area, visibility〈5 km γ↑ =0. 686+0. 051 sinθ+0. 249 sin2θ for urban area, visibility〈5 km The correction factor γ↑ was a crucial parameter for upward path radiance. It varied with atmosphere aerosol co ndition and viewing angles and was deviated from 1. Based on the above analysis: the range of γ↑ was from 0.65 to 1.21. For hazy atmosphere conditions it varied more significantly with aerosol type and viewing angles than clear condition. The percentage of error of vegetation index for the two cases studied were less than 4 % as compared with 16% and 31% using NDVI, and 19% using ARVI.
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