10' 



10° 



10- 



SPECTRAL ANALYSIS OF ANCHORAGE RESIDUALS 



•-\ 37 CONSTITUENTS 



I \^ 



I \ 



I 1 



/ 1 



_L 



± 



5 6 7 



Frequency in cpd 



10 



n 



Figure 4 



Spectral distribution of residual energy 

 (Anchorage tides — predicted minus 

 observed hourly heights). 



12 



spectral distribution of residual energy (observed minus 

 predicted hourly heights) with the standard 37 constituents 

 and when the set was expanded to 111+ constituents. The 

 principal improvement is found at six cycles per day, but 

 some improvement is found in other bands, for example five 

 cycles per day, where no constituents has been considered 

 in the past. 



Identifying unknown frequencies of important consti- 

 tuents is quite difficult to the accuracy required for tide 

 predictions. It was a considerable help that it could be 

 assumed that the frequency of any constituent must consist 



26-10 



