is again indicated. The process of latent heat transfer plays a dominant role in determining 

 the temperature of the surface film. 



Precipitation 



A change of temperature of the surface film may be brought about by the addition of 

 colder or warmer precipitation. The magnitude of this change depends on the phase of the 

 precipitation, the initial temperatures of surface and precipitation and the equivalent depth 

 of both constituents involved in the final mixture. The depth of sea water involved is in- 

 fluenced by the degree of mixing. Hence, factors which cause mixing, i.e., wind action, 

 mechanical effects of the falling substance, and unstable stratification, are critical. The 

 latter factor depends on fluid viscosity and on vertical density differences which in turn de- 

 pend on differences in temperature and salinity. The largest deviations observed between 

 skin and "bucket" temperatures occur in areas of active precipitation. These deviations may 

 amount to several degrees Celsius. (See appended data). The conversion of kinetic energy 

 of falling rain into thermal energy is assumed to have little influence on the resulting surface 

 temperature. 



Wind Mixing 



As mentioned in the preceding paragraphs, wind is directly involved in several of the 

 processes considered. Since it creates a stirring of the water (momentum transfer) it also 

 leads to the generation of heat due to internal friction, i.e., viscosity. It is anticipated that 

 this effect may be minor when compared with effects of other processes. 



From the above it is apparent that all meteorological factors normally observed in- 

 fluence the temperature of the surface. The degree of influence must be determined for a 

 better understanding of the problem. 



METEOROLOGICAL FACTORS INFLUENCING IRT READINGS 



A brief review of factors influencing IRT readings is beyond the scope of this note. 

 However, since the device senses ir-radiation, a comment in this regard may be in order. 



Since we are dealing with an IRT which remotely senses radiation over the limited 

 waveband of 8-13 microns, and since optical paths to the target surface are relatively short 

 (usually less than 1,000 ft), the influence of atmospheric water vapor and carbon dioxide will 

 be assumed negligible. Also, since penetration distance of ir-radiation within water is small, 

 i.e., tenths of millimeters, concern will be with the surface film from which upward directed 

 radiation emanates. Consequently, the effective temperature of this film will be referred to 

 as the surface temperature. 



Consider the upward directed stream of long-wave radiation above the ocean surface 

 under an overcast sky. In particular, consider the radiation between 8-13 microns. If we 



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