Sea can cause individual (unexpected) rogue waves much higher than normal. Most waves are less than high and it is not unusual for strong storms to double or triple that height; offshore construction such as wind farms and oil platforms use metocean statistics from measurements in computing the wave forces (due to for instance the hundred-year wave) they are designed against. Rogue waves, however, have been documented at heights above . The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is
Sound pressure Since formula_18, the amplitude of the specific acoustic impedance is given by Consequently, the amplitude of the particle displacement is related to that of the acoustic velocity and the sound pressure by When measuring the sound pressure created by a sound source, it is important to measure the distance from the object as well, since the sound pressure of a "spherical" sound wave decreases as 1/"r" from the centre of the sphere (and not as 1/"r", like the sound intensity): This relationship is an "inverse-proportional law". If the sound pressure "p" is measured at a distance "r" from the centre