determined in this way. Though the technique works, it is not practical for 

 daily observations over an extended period. 



30. An alternative is to use fewer gages, use what is known of wave 

 behavior, and construct estimation algorithms to compute directional spectra 

 from a (relatively) sparse number of sea surface measurement points. This 

 method uses a practical number of gages (usually around 10 wave staffs or 

 pressure sensors) deployed with intergage spacing tuned to resolve the range 

 of wavelengths expected at a given site. These are called spatial arrays 

 (since they are distributed in space) , phased arrays (since they determine 

 direction by phase differences in passing wave forms), or just arrays. 

 Criteria for optimum spacing, layout, and data analysis from gage arrays have 

 been described by Barber (1961); Davis and Regier (1977); Donelan, Hamilton, 

 and Hui (1985); and others. Such arrays can give higher directional resolu- 

 tion than the simpler gages described previously because they measure more 

 properties of the sea surface and their gage elements can be positioned for 

 optimum response to a wave field given the input requirements of the data 

 analysis algorithm used. 



31. Array gages cannot be used everywhere. One practical limitation is 

 that a number of gages must be operating simultaneously. The set of gages 

 therefore requires rather constant monitoring and attention. Another is that 

 the wave field must be uniform (i.e., have the same basic statistics) through- 

 out the area covered by the array. This condition is not expected in regions 

 of irregular bathymetry or in regions of high reflectivity (near structures) . 



32. There is a wealth of literature on the topic of spatial arrays. 

 The bulk of it deals with theoretical considerations of array design, analysis 

 algorithms, and field tests of particular configurations. One of these 

 schemes is described in more detail below. For the purpose of this introduc- 

 tion, the interest is in reports of long-term observations which provide 

 guidance in high-resolution characteristics of nearshore seas. 



33. Such observations are scant, especially in inshore waters. Long- 

 term oceanic observations are nonexistent. Donelan, Hamilton, and Hui (1985) 

 performed a 14-month experiment using an array of 14 wave staffs in 10-m water 

 depth at the southern end of Lake Ontario. Their primary interest was in the 

 evolution of wind- generated wave fields, so they collected wave data only when 

 local winds were changing significantly. The resulting set of eighty-four 1- 

 hr observations did not constitute a complete wave climate. Furthermore, the 



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