Comparison of reflectance between MODIS image and simulation using radiation transfer model

Abstract

In this paper, we focus on the area covered by vegetation and compare the canopy reflectance derived from MODIS images with reflectance simulated by radiation transfer model. Instead of statistic models, physical models are chosen because of the explicit physical foundation that they possess. Two sampling areas are collected in Jiangxi province in China. Detailed information of vegetation in these two sampling areas has been measured and recorded, including leaf biochemical component content, canopy structure information and some environment parameters. And the MODIS images in this period are also collected. By combining leaf model and canopy model, canopy reflectance is calculated using biochemical component content as the input parameters. Comparison between simulative canopy reflectance and reflectance derived from MODIS images shows that, considering the whole wave length region, these two kinds of reflectance match well. At 250 m spatial resolution, reflectance from MODIS band 1 (650 nm) is higher than simulative value; while reflectance from MODIS band 2 (860 nm) is lower than simulative value. These two bands focus on the vegetation status. So the experiment indicates that satellite image weakens the vegetation impact. At 500 m spatial resolution, the band 4 (560 nm) and band 3 (465 nm) both have higher value, while the ratio between them are lower. Similar problem appears in other bands. These results are useful in physical models inversion of vegetation biochemical parameters.