Wave Measurements and Surf Height
By Jennifer McWhorter, CDIP
What are wave buoys and what can they tell us about the surf?
The Coastal Data Information Program (CDIP), based at the Scripps Institution of Oceanography, provides near real-time wave and sea information through a network of 70+ buoys in 15 states and island territories. As waves approach the nearshore coastal environment, they become more complex due to physical features such as deep water canyons or the curvature of the coastline. The CDIP network specifically accounts for the nearshore wave environment of wind generated waves. Averaging 17,000 unique visitors per day, these data serve the surf community as well as military, policy, industry and academic sectors benefiting maritime and coastal communities at large.
How it Works
CDIP uses a wave buoy technology produced by Datawell, called the Directional Waverider. This wave motion sensor measures wave height, wave period, direction, and sea surface temperature. This information can then be used by surfers and beach goers to assess wave conditions. But first, users will need to understand each component:
Wave height is the vertical distance between a crest, the highest part of a wave, and a preceding trough, the lowest part of a wave. In the field of ocean wave measurements, we measure wave height as ‘significant wave height’ referring to the one-third highest waves of a give wave group defined by the average heights and periods.
The wave period is a measurement of time. The time for a wave crest to traverse a distance equal to one wavelength. Wavelength can be defined as the horizontal distance between similar points on two successive waves measured perpendicular to the crest.
Wave direction simply refers to the direction from which a wave approaches. The directional measurements are in degrees, similar to a compass.
Types of Waves
In order to make these measurements relevant to the surf community, it is important to understand the difference between ‘seas’ and ‘swell’. Seas refer to waves caused by wind at the place and time of observation. We can recognize a wind wave event by looking at the wave period, classifying seas or wind wave events with periods less than 10 seconds. Swell on the other hand, is defined as wind-generated waves that are propagating away or are outside their generating area. Swell characteristically exhibits more regular and longer period and has flatter crests than seas. Swell is classified as wave events over 10 seconds.
Now that we have discussed some background and terminology to understanding wave measurements, CDIP data can be used to view wave events as they relate to local surf conditions on the CDIP website.