The second usable pass (238-Direct) occurred 9 days later, on 5 July 1963. 

 The data here had considerably more noise, but the basic SST patterns are still 

 visible. (See Fig. 5-12). 



Temperatures for this pass were 2. 5 to 5 K lower than in Pass 107-D. Upper 

 air data, again from the Washington station, indicated a slightly drier atmosphere 

 for this day, although the calculated correction was still approximately 5 K. As in 

 the previous case, there was no significant correction for sensor degradation in- 

 dicated by the usual degradation graphs. It should be noted, however, that the 

 periodic orbit- sun phase fluctuation does suggest a rapid degradation during this 

 period. This may account for part of the over-all temperature drop. The minimum 

 nadir angle was 10 higher than in the previous case, but was still a relatively low 

 20 . Thus, there seemed to be no adequate explanations for the general 2. 5 to 5 K 

 temperature drop across the field of view. As this is the time of year when one 

 would expect a gradual warming of the sea surface, it is unlikely that this temperature 

 drop is real. 



Conventional surface ship data were extracted from NMC charts for five day 

 periods centered on the dates of each of the selected 'ireal-time" cases. These 

 data indicated no significant change between the two cases, and agreed reasonably 

 well with mean monthly charts. They were converted to K and uniformly reduced by 

 12 K for easier comparison with the IR data. The "reduced'i data are plotted in both 

 Figure 5-11 and 5-12, In Figure 5-11 it is seen that there is good correlation between 

 the adjusted ship data and the recorded IR data. Good correlation can also be seen in 

 Figure 5-12, if the ship data are reduced another 2. 5 to 5 K to compensate for the 

 over-all drop in the IR data. 



The first of these two cases is a particularly good demonstration of how a 

 dependable surface temperature measurement may be used as a benchmark to 

 calibrate the recorded IR temperatures. Using this procedure false shifts in the 

 absolute values of a temperature field can be avoided. It may be that only an 

 occasional benchmark (occasional in both space and time) will be required to properly 

 calibrate recurring IR coverage. 



39 



