In order to apply alternate atmospheric correction algorithms (Polymer and Neural Network) to SeaWiFS, MODIS and VIIRS in the frame of OC-CCI, we are using l2gen to produce so-called "L1C" files, which are obtained by applying l2gen to L1A files with the following options, in order to produce only the TOA signal and polarization correction, and bypassing application of gains and actual atmospheric correction :
l2gen ifile="..." geofile="..." ofile="..." l2prod="rhot_nnn polcor_nnn sena senz sola solz latitude longitude" gain="1.0 1.0 ... 1.0" atmocor=0 aer_opt=-99 brdf_opt=0
For VIIRS, we have recently noticed a strange behaviour when switching from SeaDAS v7.4 to v7.5, which seems to be due to a change in the following look-up table :
The impact of this change is a very large offset in rho_t, which varies from band to band, and is worst at 443nm, where there is an increase of about 5% (the file is V2012004140000). Do you have an explanation for this change ?