3. SELECTION OF DATA 

 3. 1 Choice of TIROS VII 



All of the cases selected for investigation used the TIROS VII data. This 



satellite was chosen because the degradation of the Channel 2 sensor (8-12 micron) 



7 

 is well known. Moreover, because IR sensor degradation generally increases 



with time, an attempt was made to the degree feasible to choose cases early in 



the lifetime of TIROS VU (TIROS VU was laiinched 19 June 1963). 



It was deternnined that the use of the Nimbus HRIR data during the current 



study wculd not be feasible for the following reasons: 



1. The availability of these data is extremely limited at the present time, 

 and until the digitization is completed, full documentation of the magnetic tape 

 format (to appear as Nimbus I High Resolution Radiation Catalog and Users' Manual, 

 Volume 2, "Nimbus Meteorological Radiation Tapes - HRIR") is not available. 



2. There appears to be no reliable way to discern the presence or absence 

 of cloudiness, other than by abrupt changes in the recorded temperature, which 

 may not detect scattered to broken or low cloudiness. The daylight HRIR cannot be 

 expected to be applicable because of the reflected component. The problems of 

 detecting partial cloud cover at night from infrared data have no apparent solution, 

 as will be discussed in some detail in Section 4. 2. 2. 



3. Those areas which appear clear in the Nimbus I HRIR photofacsinaile film 

 strips are of mininnunn interest insofar as the detection of sea surface temperature 

 patterns are concerned. The probability of finding an area with distinctive patterns 

 which was known to be clear and has presently available digitized Nimbus I HRIR 

 data seemed too small to justify an exhaustive search. 



It should be emphasized that the increased resolution capabilities of the 

 Nimbus HRIR data represent a potentially significant advantage over those of the 

 TIROS IR, and any future investigation of sea surface tennperature determination 

 should reconsider the Nimbus data when they become available in digitized form. 

 However, the success of such a study will depend on solving the problem of detection 

 of small or low clouds. Because of the HRIR resolution, even very small isolated 

 clouds may be a greater source of error than they would when using the lower 

 resolution TIROS data. One possibility may be a joint use of the digitized data 

 and the analog visicorder record, as discussed in our proposal for this study, 

 but not attempted for the reasons discussed above. 



