The main purpose of this study is to develop a more accurate forest area assessment using satellite data. It is well known that the radiation effects from the atmosphere can degrade the satellite image quality, rendering inaccurate interpretation of the data. An accurate assessment is unable to be obtained, unless the atmospheric effect is properly factored in. As the MODIS sensor scans in several different wavelengths in the infrared region, it is possible to make use of its shortwave IR segments, which are capable of penetrating through the atmosphere with less attenuation than the red or blue bands. Various modified vegetation indexes have been investigated in this study by replacing the red and blue wavelengths with the shortwave infrared band. Furthermore, these vegetation indices have also been chosen to compare their atmospheric and soil resistant capabilities in finding the most suitable index for forestry monitoring in Taiwan.