Quantitative Improvement in the Estimates of NDVI Values from Remotely Sensed Data by Correcting Thin Cirrus Scattering Effects

The Normalized Difference Vegetation Index (NDVI) has been used extensively for remote sensing of vegetation for many years. This index uses radiances or reflectances from a red channel at 0.66 μm and near-infrared channel at 0.86 μm. Thin cirrus clouds frequently contaminate remotely sensed data acquired from aircraft and satellite platforms. They introduce additional scattered radiances to the 0.66-μm and 0.86-μm channels. To obtain unbiased estimates of NDVI values from remotely sensed data, the cirrus scattering effects must be removed. We recently have developed an empirical technique for removing thin cirrus scattering effects using the sensitive 1.375-μm cirrus-detecting channel. In this article, we demonstrate that the estimates of NDVI values can be improved quantitatively after the removal of thin cirrus effects. Pairs of spectral imaging data, with and nearly without thin cirrus contamination, acquired with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) are used in this study. Because a special channel centered at 1.375 μm has been implemented on the Moderate Resolution Imaging Spectrometer (MODIS) for detecting thin cirrus clouds from space, it is possible to remove thin cirrus scattering effects from MODIS channels below 1 μm and to yield improved global estimates of NDVI values from MODIS data.