545 
Transmitance ratio R 
11,12 
Figure 3: Scatter plot of the calculated transmittance ratio Rj 112 from ATSR/IR versus the columnar water 
vapour content retrieved from ATSR/MW 
The correlation is equal to 0.81, the regression intercept is 8.229 and the slope is 7.705. 
On Figure 4 , this relationship is compared to the one given by Harris and Mason (1992) and 
Kleespies and McMillin (1990) algorithms and the one simulated by Lowtran7 radiative transfer model for a 
summer temperate atmosphere. 
Figure 4 : Comparison of different IR algorithms for columnar water vapour retrieval 
The plot shows that the other algorithms have greater slopes and that the algorithm of Hams and Mason(1992) 
is quite different from the 3 others. No conclusion can be drawn for the reasons of these discrepancies since 
different models and different set of atmospheres have been used for each of these studies.