The comparisons show a rather good agreement over a 35°F temperature range. The 

 gradients detected by the trailing probe and the ART were nearly identical; however, the ART 

 values were about 7°F lower than those of the probe. This difference was also recorded dur- 

 ing individual flights over the ship. After correction for water vapor, the ART measurements 

 were found to be about 6°F lower than measurements made at the surface. This inexplicable 

 difference is the largest observed during comparison tests and suggests that evnironmental 

 influence showed a pronounced effect on infrared measurements during winter. 



The correction for water vapor in the air column was approximated with the equation: 

 tE = (t^-y (1-0.8W) 



t = temperature error of the instrument 

 E 



t = mean temperature of the air column 

 t = surface water temperature 



w = optical thickness (measurement of water vapor in the air column) 



0.8 = mean value of transmission coefficients for wavelengths between 8 and 13 

 microns 



Another example of comparative measurements is shown in figure 5. The area be- 

 tween Bermuda and the Gulf Stream contains relatively weak horizontal surface temperature 

 gradients. The USNS DAVIS recorded sea surface temperatures with bucket thermometers 

 between Norfolk and Bermuda. A flight over a portion of the route was made on 10 March 

 1963. The DAVIS transited the area between 11 and 14 March. The temperature-distance pro- 

 files show good agreement, considering the time and space separation between the two sam- 

 plings. The features were reproduced well, and the trend was indicated in most cases. In areas 

 where comparison was possible, the temperature range was only about 3°F. Meteorological 

 and oceanographic conditions over the flight track on 10 March are listed below: 



Wind speed 12-30 knots 



Wave height 4-8 feet 



Air temperature (flight level) 60°-68°F 



Rel. humidity (flight level) 70-80% 



On 28 March 1963, flights were made over ARGUS ISLAND to compare ART readings 

 to bucket thermometer temperatures taken as the aircraft passed overhead. The aircraft 

 flew at various altitudes over the tower during a 3 -hour period. The results are shown in 

 figure 6. Differences between thermometer and ART readings generally increased as altitude 



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