Satellite Wind Measurement

Magicseaweed builds its long range forecasts from a swell model that aims to predict exactly how waves will be created and then travel. To predict wave growth we need to know what the wind is doing. The more accurately we can gauge this the more accurate your surf forecast becomes. But we’ve a big task in hand. The swell arriving on the beach in Oregon could have originated thousands of miles away in the Southern Pacific, so we need to know exactly what the wind is doing over the whole globe. How do we figure this out?

A fascination with weather is an age old part of the human condition, the ancient Greeks were enthusiastic weather forecasters and by the middle of the 17th Century systematic weather observations were being made across the US. It was the advent of the telegraph that allowed this information to be pooled for early storm tracking and as early as 1848 the US had a robust network of weather observers sharing reports. The birth of aviation made accurate weather reporting even more critical and led to the wide spread use of the weather ballon. By measuring the track of a released ballon (by theodolite, radar or more recently with built in GPS) you can accurately gauge wind speed and direction. In fact this method is still used routinely today with over 800 stations around the globe releasing ballons on schedule twice daily and feeding the results into a shared network of reports. It’s pretty humbling to understand that this information, in part, still feeds into the surf forecast we all take for granted. 75,000 balloons are released each year in the US alone at a cost of $150 a piece as just a tiny part of gathering the information that we use to create your surf forecast.

However the issue with this method is that it limits your sampling to those locations that allow for the release and tracking of balloons, in our case of particular issue given the need for us to understand the wind speed in some of the most inhospitable and remote areas of the worlds oceans.

NOAA's QuikSCAT satellite (c) NASA / JPL

Since 1978 we’ve had a solution in the form of satellites. Using an instrument called a scatterometer an orbiting satellite beams microwave radiation (which penetrates cloud cover) at the surface of the ocean. By measuring the amount of this radiation reflected back from the surface at different angles the Satellite can deduce (via a complex bit of maths) the direction and speed of travel of the tiny wind generated capillary waves on the surface of the ocean. Knowing how these waves are moving in turn allows the Satellite to calculate the strength and direction of the wind at the sea surface – the critical bit of information we need to then forecast the generation of waves, swell and ultimately, surf.

QuikSCAT satellite winds from Hurricane Katrina (c) NASA / QuikSCAT Science Team JPL

So here’s an overview:

  • Weather ballons and ground observations are collected twice daily.
  • Satellites orbit the earth every hour and a half collect surface measurements.
  • Observed data is gathered together to build a comprehensive picture of the current state of the atmosphere.
  • These starting observations are used to run a forecast the predicts the wind speed over the next couple of weeks.
  • The swell model is run using the observed winds initially, and the forecast winds into the future.
  • MSW interprets this swell model data to predict your local surf.