closer to the shore, allowing resolution of local outwelling and upwellinq 

 zones, which tend to be nearshore phenomena in many cases. Such a high 

 data rate may be relaxed somewhat for wide area studies of open ocean 

 phytoplankton where statistical rather than process experiments are more 

 likely. In this case, a degradation to about 4-kilometer resolution can be 

 accepted. Therefore, a satellite system is required that can operate in 

 two modes, analogous to the present infrared system: (1) local area 

 coverage of high-resolution to about one km and (2) global area coverage of 

 lower resolution to about four km (Table 4-2). 



5.4 OBSERVATIONAL COVERAGE 



Coverage here is defined as the frequency at which a field of chlorophyll 

 data is available (barring cloud cover interference) which completely 

 covers an experiment area at some density and composited over some lenqth 

 of time. Typically in meteorology, this means the entire earth, at varyinq 

 density of some hundreds of kilometers every 3 or 6 hours. 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 scientist requires. The satellite coverage is, 

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

 time it takes from 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, but 

 wait for several days or weeks for repeat coverage. Phytoplankton vari- 

 ability 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 and reasonable orbit 

 and swath conf iguations, so there must be an accompanying program of in - 

 situ moored observations in the experiments to provide temporal sampling 

 below the Nyquist period and thereby to allow interpolation of satellite 

 observations (Table 4-2). To make even this possible, it is required that 

 a satellite system's swath pass over any given spot at least weekly. 



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