EM 1110-2-1100 (Part II)
30 Apr 02
Figure II-1-34. A directional spectrum and its frequency and direction spectrum
(Briggs et al 1993)
η (t) ' j An ∆f
4
2
2
0
1 2 2
2
An '
an %bn
(II-1-143)
2
bn
εn ' tan&1
an
(e) By induction, an estimate of the continued energy spectrum of η(t) may be obtained by
2
j η(n∆t) e
N
1
2 π i f (n ∆t)
E(f) '
(II-1-144)
∆t
Tr n'0
where Tr is the record length and ∆t is the sampling interval.
II-1-82
Water Wave Mechanics
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