qBandwidth (Df)= width of the frequency band è resolution of spectrum
q Df = 1/N (cycle per time
interval)
qFor example, if a time series has 900 monthly-mean data:
q bandwidth = 1/900 (cycle per month).
q Nyquist frequency = ½ (cycle per month)
q Total number of frequency bands = (0-Nyquist
frequency)/bandwidth
q =
(0.5)/(1/900) = 450 = N/2
q Each frequency band has about 2 degree of freedom.
qIf we average several bands together, we increase the degrees of
freedom but reduce the
resolution (larger bandwidth).