4.4 FREQUENCY OF SAMPLING 



U.S. fishery needs for future ocean color measurements are primarily in 

 the productive coastal waters within the 200 mile economic zone 

 surrounding the continental U.S., islands, and territories (Table 4-1). 

 Mid-ocean regions, where U.S distant water fisheries are located, and 

 through which highly migratory fish and mammals move during migration to 

 coastal waters are also important. The frequency of required satellite 

 coverage and information will vary depending on location and perhaps to 

 some extent on season. Generally 2-day coverage will be required in 

 coastal/local waters and 3- to 5-day coverage for most mid-ocean appli- 

 cations. Global coverage may be needed on the order of every 15 to 30 

 days. In addition to measurements made from satellites, fishery 

 research studies will generally require oceanographic data measured from 

 ships, buoys, and aircraft. 



Unfortunately, it has not been possible to obtain CZCS-type measurements 

 of the global oceans on anything close to a daily basis. On any given 

 day, the major fraction of our watery planet is obscured by clouds. A 

 qualitative idea of realizable sampling characteristics has been gleaned 

 by the MAREX working group members from screening a few time sequences 

 of CZCS data for which regular sampling was attempted. This experience 

 suggests that in a month of data collection, useful data will be 

 obtained on several days within randomly distributed clear-sky domains 

 which are a few hundred km in extent, and less frequently > 1000 km in 

 extent. Of the nominal 2 hours of Nimbus-7 CZCS coverage taken and 

 recorded per day, an average of approximately 30 to 40 percent is 

 rejected and not processed due to total cloud cover (no significant open 

 water areas) . 



In sum, our experience to date suggests that global CZCS coverage would 

 yield, on average, between 10 (at the equator) and 20 (at 40 degrees N) 

 usable images per month. This figure represents the required sampling 

 interval of every 1.5 days, for a given 1000 km x 1000 km ocean domain, 

 with the majority of usable data in patchy subscenes of typically a few 

 hundred km in extent , and with an occasional clear view of most of the 

 domain in one image. Coverage frequencies will assuredly fluctuate 

 seasonally (and regionally) around these nominal estimates; coverage 



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