3. 2 Case Selection Criteria 



As has been mentioned previously, much time and effort was spent in 

 attempting to locate cases which simultaneously satisfied the combined criteria of 

 (1) generally clear skies, (2) significant SST gradients, and (3) adequate conventional 

 ship coverage to provide data for comparison. Another significant restriction is 

 that, for all practical purposes, periods of closed naode IR operation must be 

 avoided due to the frequent errors in geographical location of the data. This, of 

 course, is simply a limitation of the measurement device itself. 



3. 2. 1 Clear Skies Criterion 



In our initial case selections, IR passes were chosen on the basis of generally 

 clear skies as determined from nearly simultaneous TV coverage by TIROS VII or 

 other meteorological satellites. Cases were selected by first examining the 



Q 



nephanalyses contained in the Catalogs of Cloud Photography , and then from an 

 examination of the actual satellite pictures for areas that the nephanalyses suggested 

 as promising. This approach, combined with efforts to concentrate on areas with 

 significant SST patterns, led to an obviously insufficient number of usable cases. In 

 particular, it excluded IR passes with no essentially concurrent TV data. Later in 

 the study, attempts were made to use conventional weather maps over the ocean as 

 a naeans of determiining the cloudiness of an area. Since the conventional maps were 

 rarely drawn for the precise time in question, this meant interpolating cloud cover 

 between maps which were already based on sparse information. After reviewing 

 the amount of tinae required to arrive at sonne conclusion regarding the cloudiness 

 of an area from conventional data alone, and the undependable nature of the 

 conclusion, this approach was rejected. 



The remaining alternative was to determine cloudiness from the IR data 

 themselves. This means, unfortunately, incurring the expense of FMR tape 

 processing before it can be decided whether or not the area scanned includes adequately 

 cloud free portions. The methods of deternnining cloudiness from the IR data will be 

 discussed in a later section. 



This method was used as the sole method for determining cloud cover in 

 only one set of cases, that discussed in Section 6. 



