Worst earth curvature over water

Does anyone know how worst earth curvature is calculated?

I've run into a situation where the worst earth curvature over the ocean is a rather excessive 15m above the ocean.

Just wondering if I can safely ignore this recommendation.

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The worst earth curvature is calculated using Figure 2 in ITU-R P.530 and is dependent on the path length. It is calculated for a continental temperate climate and so may be a little different in other regions, however the concept of earth curvature and its impact on radio signals is not dependent on whether the path is over ocean or land.

If you are designing for availabilities above 99.9% then it should be taken into consideration. You can see the impact by looking at the "Excess Path Loss at ke" parameter which is available as a selectable column in the PTP links view (see Managing Lists for more information on managing the list views) or from the blue information icon against Lowest Mode Availability on PTP 820 links. If you have sufficient fade margin on your link to be able to tolerate this additional loss then it can be ignored.

In the image you have provided there is only a small incursion into the Fresnel zone and therefore unless your link is already very marginal it may well be able to tolerate the additional loss.