During Sandy’s aftermath 21.7 foot waves were observed in Lake Michigan. How are wave heights measured?
—Bill Gunther, Downers Grove
The National Oceanic and Atmospheric Administration deployed a buoy in the middle of Lake Michigan east of Kenosha, Wis., in 1981 that takes a variety of measurements, including barometric pressure; wind direction, speed and gust; air and sea temperature; dew point; and wave energy spectra. From these, significant wave height, wave period and wave direction are measured or derived.
The wave height is not obtained by direct measurement but derived in a complicated process based on accelerometers or inclinometers on board that measure the buoy’s vertical displacement during a specified time period.