What are ocean swells and how are they measured?
First, I should mention that wind waves are generated by local winds blowing over the surface of the water, while swell is generated by distant storms. Wind waves tend to die out as the winds diminish...but ocean swell can travel hundreds of miles (or longer). Wind waves are choppy, and often 'break' while swells are smooth and undulating (until they reach a shoreline, reef, or sudden shallow section of sea floor. We measure swell using automated ocean buoys, and typically measure the height (from crest to trough), the direction (from which the swell is moving) and the period (the time interval between individual swell).