I am trying to conduct atmospheric correction of landsat 8 image using i.atcorr of Grass GIS. In thıs regard, I need to know Aerosol Optical Depth (AOD) as stated in Grass wiki page. I've found some valuable leads ın this site and explored Aeronet (http://aeronet.gsfc.nasa.gov/new_web/aerosols.html). I prefer it (relative to MODIS MOD08) since it offers a lot more detail and timeseries of data (I think I just need the data for the time when image was taken). However, the data file for my specific site contains no data at AOT_550 (I presume that is the exact wavelength sought). there is AOT_555 and AOT_551 but without any data. The closest data I found is AOT_500 and AOT_675. Another thing I noticed, the data value gradually decreases from AOT_340 to AOT_1640. My question, Is it possible to use a linearly interpolated value for AOT_550 by using AOT_500 and AOT_675 data?