11. 4 OBSERVATIONAL COVERAGE 



Coverage is defined as the frequency at which a chlorophyll data set for a 

 given extended experimental region is available, assuming ideal, cloud- 

 free conditions. The data set may be composited from several OCI images 

 taken at various resolutions over an extended time period. By their 

 nature, satellites provide a high density of observations within their 

 swath coverage; however, one or more passes must be composited to generate 

 the field of data which the scientists require. The satellite coverage is, 

 then, a function of swath size, orbit configuration, and cloudiness. The 

 time it takes for some part of the satellite swath to revisit every spot 

 within an experimental area defines the length of time it takes to generate 

 a data field. Repeat coverage is the time it takes to generate another 

 such field in the same area. For example, a small experimental area, less 

 than one swath width in size, might be entirely covered in one pass, while 

 repeated coverage may not be available for several days or weeks. Phyto- 

 plankton variability in the ocean has a time scale of less than a week 

 depending on seasonal changes of wind events and algal growth. It would be 

 desirable, then, to have worldwide chlorophyll observations at least every 

 3 or 4 days. This is impossible due to natural cloudiness, reasonable 

 orbit, and swath configurations, so there must be an accompanying program 

 of in situ moored observations in the experiments to allow interpolation of 

 satellite observations. 



To make even this possible, it is required that a satellite system's swath 

 pass over any given spot at least weekly. 



11. 5 NAVIGATIONAL ACCURACY 



Location of pixels in latitude-longitude coordinates is important for 

 quantative scientific use of color scanner data. In order to make these 

 data useful for other than individual scene analyses, the scientists must 

 be able to use observations from many passes to generate time series and do 

 statistical analysis. This implies that location accuracy of data from 

 different passes must be sufficiently precise to allow compositing. For 

 these purposes, we require an absolute navigational accuracy of 5 km for 

 high-resolution local data and 25 km for low-resolution global data. 



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