It's so surprising that we don't use a precise method of gauging wave height for these records. AFAIK they still estimate the surfers height while riding, and then count those heights up the side of the wave in a photograph.

I'd imagine we would have a method closer to surveying techniques by now.

there is a new, exotic method for measuring gigantic waves, that uses atmospheric disturbances to gps signals and gravity waves that ocean waves generate. SWOT

https://www.nasa.gov/missions/swot/us-french-swot-satellite-...