Mean water vapor amount 
Figure 4. Variation of the Split-Window coefficients versus total water vapor content. 
This result has been compared to the SST retrieved when using the water vapor classes. The 
water vapor amount for the ATSR image is 1.267 g/cm^ (radiosonde measurement). The closest water 
vapor class have been chosen to determine the SW sea surface temperatures (with e=0.99 too) : the third 
one, W mean value : 1.26 g/cm^. Fig. 5 displays the comparison between these retrieved SSTs with the 
reference SSTs. The results shows a better agreement than the one obtained with the climatic coefficients 
(Mid-Latitude or Tropical) : the mean difference is 0.16 K (the rms being 0.09 K). It may be noted that if 
a wrong class is used the mean difference becomes larger : -0.26 K with the 0.72 g/cm^ class (and 0.48 
K.with the 1.71 g/cm^ class). 
Différences Tsw - Tradsond (K) 
Figure 5. Application of the Split-Window technique on an ATSR image 
(12000 sea pixels over the English Channel) 
2.3.2. Application on the Coral Sea. A set of 15 ATSR sea pixels on the Coral Sea for different days 
(October, November and December 1992) with coincident SST measurements and some water vapor 
measurements has been used for this study (Barton, personnal communication). As very few water vapor 
amounts were available, we first used the Mid-Latitude coefficients to calculate the SW sea surface 
temperatures. Results are plotted on Fig. 6. The mean difference is -0.18 K (with a 0.40 K rms). This 
negative mean difference shows that the Mid-latitude mean water vapor amount is lower than the real 
water vapor amount. When using the water vapor data, results are a little better (mean difference is -0.13 
K, although no significative statistic may be given for 5 points). 
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