DISCUSSION 



It was very surprising and rather annoying to us that the differences between the IRT 

 and mercury thermometer readings AT were so large both in indoor and outdoor calibrations, 

 as indicated in Figures 2 and 3. These differences are much larger than those reported by 

 other studies (Pirart, 1961; Richardson and Wilkins, 1957) although the calibrations in these 

 studies were made in the situation of much smaller air-water temperature differences than 

 the extreme cases of the present calibrations. The results of Figure 2 clearly indicate that 

 the IRT at the constant distance from the water surface gives higher readings than mercury 

 thermometers when the air is warmer than the water and vice versa. Those of Figure 3 in- 

 dicate that these differences between IRT and mercury thermometers increase with the air 

 path between the sensor and the water if the air-water temperature differences are constant. 



The relation between the absolute temperatures of the ocean, and atmosphere T^ and 

 T and those obtained by the IRT readings T. is expressed approximately by 



a 1 



a 



4 4 4 



T. =EtT +(l-Et)T^ 

 1 w a 



where E is emissivity of the ocean; t is the trans mis sivity of the atmosphere (Frank, 1964). 

 E is almost constant and equals to 0.98 but t is dependent on the radiative characteristics of 

 the air column between the sensor and the sea surface. In ordinary meteorological situations 

 without actual precipitations, the most important factor affecting t is the amount of water 

 vapor in the air path. The values of t in percentage as a function of the precipitable water 

 in cm were determined by Yates and Taylor (1960). However, the calculation based on these 

 results gives much smaller values of AT than those in Figures 2 and 3. Instead, t. is de- 

 termined from equation (1) by using the observed values of T. (with the IRT), T^^ (with the 

 mercury thermometer) and T . For the averaged values of T^ of the curves C and D of Fig- 

 ure 3, the computed values of t are as follows: 



t (%) 95, 93, 94, 92, 92 for T^ = 30°F 

 T (°F) 60, 70, 80, 90, 100 



w 



For the change of T from 33°F to 38°F, as observed in this calibration experiment, the 



3, 



variation of t is 1% at the most. The value of t estimated from the results of Yates and 

 Taylor (1960) equals to 99.8% for the saturated air of 8.5 m deep with temperature 36^ F. 

 This estimation is based on the assumption that the water vapor is in a gaseous form. How- 

 ever, evidently there was a layer of steam close to the water surface in the outdoor experi- 

 ment of Figure 3, particularly when the water temperature was higher than 80° F. WTien 

 water-droplet radius is near the wave length of radiation, Mie -scattering becomes effective 

 and the absorption is much larger than in the gaseous form of water vapor (McDonald, 1960). 

 Therefore, the large values of t obtained from the experiments seem to be due to this effect. 



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