6. DISCUSSION OF THE PROPOSED EXTENSIVE 

 DATA PROCESSING APPROACH 



The problems encountered in attempting to find suitable cases which simul- 

 taneously satisfied the three criteria of clear skies, large SST gradients, and 

 adequate conventional data included the following: (1) frequent absence of usable 

 IR data due to high nadir angle or closed mode conditions; (2) frequent lack of 

 TIROS TV picture data for use in determining whether the area of interest was 

 adequately clear; (3) inadequacy or lack of conventional surface meteorological data 

 over the oceans for determining clear areas; (4) the impossibility of determining 

 the clear areas from the IR data themselves, (using the threshold albedo techniques) 

 until the expenses required for FMRT processing have already been incurred; and 

 (5) the tendency for areas of greatest synoptic interest and change, such as the Gulf 

 Stream, to have frequent and persistent fronts and cloud cover. 



Using the currently available (TIROS) IR data, little can be done with regard 

 to Point (1) above; it will be totally alleviated as regards closed mode, and con- 

 siderably as regards nadir angle, when Nimbus MRIR data becomes available. 

 Points (Z) and (3), however, can presently be avoided by facing up to Point (4) and 

 accepting the costs and inefficiencies inherent in FMRT runs without specific prior 

 knowledge as to the presence or absence of adequate clear areas. (Of course, a 

 general examination of any available data, prior to an FMRT run, is desirable to 

 rule out obviously hopeless cases, or to select the more promising of alternative 

 cases. ) Rejection of cloud contaminated data on the basis of a Channel 5 albedo 

 threshold value seems feasible, as demonstrated above, and resonable modifications 

 of the existing data reduction programs should permit automatic rejection of these 

 data. Point (5) is really the only condition inherently imposed by nature, and like 

 Point (1) must be lived with. The long and tedious chore of trying to find areas of 

 clear sky over such difficult regions of the oceans, however, can be relegated to a 

 computer when repeated passes over a given area for some specific time period 

 are to be automatically processed. In all probability, the savings in human search, 

 comparison, and decision time vi/ill more than compensate for the increased computer 

 costs. 



For the initial pilot investigation using these procedures, areas with a reasonable 

 probability of synoptic change should be chosen, and cases would then be run for 

 those periods which, by reference to other readily available meteorological sources 

 (seasonal tendencies, conventional weather charts, TIROS TV data, etc), present 



41 



