Figure 12. NOAA deep-sea tide gauge after return 

 to surface. 



square) would be transited more frequently than in the 

 study but the spacecraft would never pass over many 

 other areas and hence no data would be obtained for 

 these areas. 



A more likely (hence more serious) exception is the 

 sun-synchronous orbit. The transit time over a particu- 

 lar area will always be close to a particular solar time 

 or that time plus 12 hours. S2, the second largest semi- 

 daily tide, has a period of exactly 12 hours. Since the 



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