30 

 28 

 26 



I 



;24 



i 22 



i 20 



: 18 

 ! 16 

 JK 

 [ 12 

 10. 



VALIDITY OF AIRBORNE 

 IR TEMPERATURE 

 MEASUREMENTS 



.V 



u WAVES 

 A RIPPLES 

 • CALM 



I 



10 12 14 16 18 20 22 24 26 28 30 32 34 

 MEASURED WATER SURFACE TEMPERATURE "C 



Figure 1 . Validity of Airborne Infrared Temperature Measurements 



measurements must be interpreted with caution if the actual temperature of the upper meter 

 or two of water is desired. However from the point of view of the meteorologist who is con- ' 

 cerned with problems of heat and moisture flux through the true surface of the water, infrared 

 measurements are probably superior to in situ surface layer measurements. Air-water in- 

 terface processes depend on temperature and vapor pressure gradients between the true 

 water surface and the overlying air, and the infrared thermometer very likely comes closer 

 to indicating the effective surface temperature than any other means. 



Much more field checking needs to be done. It is especially important when com- 

 parisons between the two methods are made, that detailed observations be made of the con- 

 ditions of the sea surface, the wind, the thermal stratification of the upper layer of water 

 and the temperature and humidity of the air above the surface. Sky conditions and sun angle 

 may also be important in establishing the radiation input. Only with complete supporting 

 data will it be possible to separate the surface heating and cooling cases and assign some 

 level of importance to the various meteorological factors. With the present state of our 

 knowledge it is not yet possible by flying over a body of water to determine with any degree 

 of reliability whether the IT will yield a higher or lower temperature than an ■" situ meas- 

 urement of the surface layer, nor will a single check on a particular day be applicable to 

 other parts of a large body of water or to other lakes in the same region on that day. Hope- 

 fully this situation can be improved by continued and more careful field observations. 



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