Initial selection of the atmospheric file for processing reflectance data

[rese_support]

How critical is the initial selection of the atmospheric file for processing reflectance data?  At the moment, I have no way (other than by experiment or guessing) to know the water vapour column.  Does it matter if I guess and get it wrong?  Does the water vapour retrieval routine correct for errors?
I have surface temperature and relative humidity information for our data; do you have a reference to a means of estimating the water vapour column from surface conditions?

The water vapor is quite critical. If your sensor is sensitive enough, the initial selection of the water vapor amount by the atmospheric file is not critical - this value is only of relevance if the water vapor retrieval has to be switched off for whatever reason. The water vapor retrieval will correct for these errors as long as it works; preconditions are a good spectral calibration of your system (better than approx. 0.5 nm absolute) and a correct selection of the retrieval bands; for VNIR sensors we recommend using the 820 nm band because the 940 is often not sensitive enough at the edge of the silicon response.