Figure 11.16 compares the observed and the predicted second order moment spectra 
and also U;, U2, and U3 correspond to the first, second, and third terms of Eq. 11.75. It is 
rather surprising that the observed value can be almost fully explained theoretically by 
Eq. 11.75. It is also interesting to find in the upper second figure of Fig. 11.16, that the 
linear estimated spectrum (shown by solid line) is pretty largely distorted by the existence 
of cubic frequency response H3 as are shown by Eq. 11.73 and by the first term of Eq. 
11.75, and is modified into U; (w) shown by the dotted line in the same figure. 
\\ 
Ne 
S i 
HM IM 
NS 
Fig. 11.14. Truncated quadratic discrete kernel g;,. 
(From Dalzell.17) 
322 
