Figure 2,-Relationship between the logarithm of /? and the water vapor content, W. The line represents the least 
squares fitting lnf=-0.621W+5.648. 
Then, the operational split-window algorithm proposed for LST is 
T = T 4 + [ 1.0+0.58(T4-T 5 )](T4-T 5 ) + 0.51 + 40(1 -e) - pAe (5) 
where the coefficient p can be choosen according to the different procedures outlined above. The modified split- 
window equation includes an A coefficient depending on the interchanncl temperature difference, T 4 -T 5 , which 
takes into account the atmospheric variability at global scale. For the emissivity correction, the larger source of 
error is the knowledge of the effective surface emissivity. Table 1 shows the error in the emissivity correction, 
5T e , for various values of the emissivity errors 8 e and 8 Ae. Assuming an error of 0.01 in both e and Ae, the 
error associated to B(e) ranges from 0.7 K for moist atmospheres, to 1.4 K for dry atmospheres. The total error 
in LST retrieval, 8 T, is the combination of 8 T e and the error due to the atmospheric correction, 8 T a . Table 2 
shows the total error of equation (5), considering 6T=[(5T a ) 2 +(5T e ) 2 ] ,/2 . Thus, the current accuracy in LST 
retrieval using the split-window technique ranges from 0.7 to 1 .8 °C depending on the errors in the atmospheric 
and emissivity corrections, which also depends on the atmospheric water vapor content and on the error in 
determining and mapping emissivities. Wc can observe that the error in the emissivity correction is two limes 
larger than the error in the atmospheric correction. 
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