The LSNR file contains a copy of the data in the LSAN file, but without the absolute responsivity correction and responsivity drift corrections applied. In some cases the drift correction does not work sucessfully. In these cases you may want to apply the absolute responsivity correction to the LSNR data.
In order to do the correction you need to look at the contents of the LGIF file produced by Auto-Analysis. Each record in the LGIF file identifies a time ordered group of data in the LSNR file which will have different correction factors. For each record in the LGIF file, extract the ITK start and end times of the group (fields LGIFITKS and LGIFITKE respectively). Locate all of the data in the LSNR file which have ITK values within this range using the ITK time key in field LSNRITK. For each detector within this time rage, divide the flux in the LSNR file by the appropriate absolute responsivity correction factor from the LGIF file. The correction factors are stored as an array of ten numbers in field LGIFABS in the LGIF file. Now divide the flux values in LSNRFLX by the relative responsivity correction factor for the appropriate detector. If the LGIF file contains a single record then the absolute responsivity correction factors can be applied to the whole LSNR file.