The astronomical theory and data compared - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 305

Figure 10.17. Spectra of sine wave and sawtooth wave with 100,000-year periods.

Figure 10.18. Three simple functions for spectral analysis. The solid curve is cos ð 2t Þ and the
dashed curves add noise to this curve. The period of the solid curve is .

Another simple example is given in Figure 10.20 , which displays 17 points
from the curve:

F ð t Þ¼ cos ð 2 : 5t Þþ cos ð 1 : 5t Þ

When the same spectral procedure is carried out on these 17 points, the resultant
frequency distribution is as shown in Figure 10.20 . There are now two primary
frequencies at 0.23 and 0.42 cycles per unit time, corresponding to periods of
4.5 2

/1.5 and 2.4 2 /2.5 time units (see Figure 10.21 ).