7
2
|E (ω)| z
2
|E (ω)|
−10
y 2
2
B |h(ω)| Theory
−12
10
2
∝ 1/ω
2
2
2
Ei(ω) [sV /m ]
10
−14
10
−16
10
−18
10
−1
0
10
ω[1/s]
10
Figure 6: Deeper sea measurements and theoretical predictions of the sea bottom electric fields at depth d=313 m. The black, thick curve shows the power spectrum of the vertical E-field component, and the magenta curve the associated theory given above. The noisy stapled curve shows the power spectrum of a horizontal field component, and the stapled blue curve has a slope of -2. The red curve shows the ships heave power spectrum multiplied by a squared B-field of 15 µT.
1/ω 2 noise is quite sharp since the wave signal has such a pronounced decay. Also, in Figs. 5 a and 5 b there is significant discrepancies between the low frequency measurements and predictions. This is most likely due to noise in the heave spectrum. Any kind of random drift in the GPS altitude measurements would contribute an 1/ω 2 noise (if the steps in the drift are uncorrelated) We also see some low frequency oscillations in the Ex spectrum of Fig. 5 b which are not presently understood.
log10(Ey(ω)/Ez(ω))
-1.5 -2 -2.5 -3 -3.5 -4 -3
-2
-1 log10(ω/Hz)
0
Figure 7: The ratio of the horizontal- to the vertical field components that are generated by ocean waves at the sea bottom, calculated from Eq. (A-19). The sea depths are d=122 meters (full curve) and 300 meters (stapled curve). The ratio Ey /Ez , which is calculated exactly, for finite β in Appendix , is shown in Fig. 7, and it seen that the horizontal component of the wave induced field is more than