Earth’s rotation: observations and theory - Earth Dynamics: Deformations and Oscillations of the Rotating Earth - page 289

10 4

10 3

95% C.I.

10 2

10

1

-1.5 -1.0 -0.5 0.0

Frequency in cycles per year (cpy)

0.5 1.0 1.5

Figure 4.6 Spectral density of the VLBI polar motion, based on the pole path
interpolated onto equally spaced time points using natural splines.

PI=3.141592653589793D0
OMEGA=2.D0*PI
C Set segment length.
T=26.25D0
C Set midpoint.
T0=17.125D0
C Set number of interpolates, N.
N=3513
AN=DFLOAT(N)
C Find time domain sample interval.
DT=T/AN
C Find number of positive harmonics.
NP=(N-1)/2
ANP=DFLOAT(NP)
C Set mean of pole path to zero.
GTM=(0.D0,0.D0)
C Read in interpolated pole path.
DO 10 I=1,N
READ(1,11)J,IYYY,MM,ID,DAY(I),GT(I)
11 FORMAT(1X,4I5,F12.7,2F12.6)
C Accumulate sum of co-ordinates.
GTM=GTM+GT(I)
10 CONTINUE
C Find mean of pole positions.
GTM=GTM/AN
C Reduce co-ordinates to zero mean and window sequence.
DO 12 I=1,N
GT(I)=GT(I)-GTM
CALL WINDOW(DAY(I),T0,T,W)
GT(I)=GT(I)*W
12 CONTINUE
C Prepare to calculate spectral density.
IS=-1
C Calculate FFT.
CALL FFTN(N,GT,IS,L,WK1,WK2)
C Convert to DFT.