How does off-nadir geometry affect the calculations of water vapor and aerosols

In using FLAASH (based on MODTRAN 4+), if a user designates an off-nadir geometry, how does this affect calculations of water vapor and aerosols?  What calculations in MODTRAN are affected through designating an off-nadir geometry in FLAASH?

The MODTRAN spectral radiance simulations used by FLAASH are all performed using the off-nadir view specified in the Advanced Parameters of the FLAASH dialog. That means that a given amount of atmospheric water vapor or aerosol produces more absorption, scattering, etc.

Ideally, the result should be equivalent retrieved water vapor and visibility parameters from different off-nadir views through the same atmosphere, as these parameters are always referenced to one type of path. That is, water vapor is measured in the vertical column, and visibility is measured horizontally at the ground.

Review on 12/31/2013 MM