1. The far infra gravity (FIG) wave signal is derived from the tide gauge signal
by an involved process described
here.
2. Once the FIG signal is extracted from the tide gauge signal, it can be
processed just like a wave record except that it is continuous, not in 20 min bursts.
3. For the plots here, we have used a 6 hour window with 4 hour overlap to calculate
the average of the highest third of the waves. This gives a continuous record of wave height
and period at 2 hour intervals.
4. Because we are using a 6 hour window, the last estimate of wave height
was 3 hours before the present (i.e., half the length of the window).
5. The dashed line is a quadratic of best fit through the data and can be used an
indication of whether the FIG waves are rising or falling.
6. The setdown of a vessel as a result of FIG waves can be estimated using the following equation:
Setdown = Factor * Hs / 2
For most places, including Port Taranaki, Factor has been found to be 1.5.
Use the figure beside the red dashed line for Hs.
7. FIG waves under 200 mm are usually insignificant.