The 0.86 µm band will be used in part to monitor vegetation trends, specifically the Normalized Difference Vegetation Index (NDVI). Determining the bandwidth for the 0.86 µm is critical due to an atmospheric water vapor absorption feature near 0.86 µm. The 0.86 µm bandwidth (0.84 µm – 0.88 µm) have been chosen such that it will not encounter the atmospheric absorption feature. By avoiding the water vapor absorption feature, the NDVI will reflect actual vegetation trends and will not reflect changes in atmospheric water vapor content. The bandwidth was determined by using NASA AVIRIS (Airborne Visible InfraRed Imaging Spectrometer) aircraft data. This data has a very high spectral resolution offering over 200 bands between 0.4 µm and 2.5 µm. A tool from Massachusetts Institute of Technology-Lincoln Labs (MIT/LL) was used to create radiance files of proposed ABI bands. There were various modifications to the tool, including the addition of ASCII input spectral response function. These files were used to compare the proposed ABI bandwidths with bands on operational and other proposed satellites (e.g.- current GOES, MODIS (MODerate resolution Imaging Spectroradiometer), METEOSAT (METEOrological SATellite) Second Generation (MSG), etc).
The 1.38 µm band will be used during daylight hours to detect very thin cirrus clouds that are not currently detected by the current GOES satellites. The bandwidth of the 1.38 µm band was developed using the same techniques as the 0.86 µm band. The proposed bandwidth (1.365 µm – 1.395 µm) has been placed in an atmospheric water vapor absorption feature. By selecting a bandwidth within the water vapor absorption feature, the atmosphere will absorb the scattered solar radiation from the surface and lower troposphere, hence preventing surface and low cloud features from hindering thin cirrus detection.
Three scenes have been used in the ABI research, ranging from a highly vegetated scene to a cirrus/water cloud scene to a forest fire scene. Future work will entail the use of more AVIRIS data scenes as well as comparisons with other future satellites (e.g.- Visible Infrared Imager/Radiometer Suite (VIIRS)).