To trust the data, you need to understand where it comes from. At WindTrackr, we connect to various types of weather stations. We explain how the tools that "catch" the wind work.
1. The Anemometer (Speed)
It is the instrument that measures wind speed. There are mainly three types:
- Cup Anemometer (Robinson): The classic 3-cup rotating device. Robust and reliable, but has inertia (takes a moment to slow down when the gust stops).
- Propeller Anemometer (Windmill): Like a small airplane. Very accurate if properly oriented to the wind.
- Ultrasonic: No moving parts. Measures the time a sound pulse takes to travel from one point to another. Most accurate and expensive, ideal for measuring instant gusts without inertia.
Ultrasonic sensors are the latest generation and offer significant advantages: no mechanical wear, instant response to wind changes, and simultaneous measurement of speed and direction. However, they are more expensive and require periodic electronic calibration.
2. The Weather Vane (Direction)
Indicates where the wind comes from. Must be perfectly calibrated with geographic or magnetic North.
Fun fact: In very light winds, direction can be erratic. Quality sensors have a minimum threshold before recording direction changes to avoid "noise" in the data.
Modern vanes usually incorporate digital encoders that provide much more accurate readings than traditional analog vanes. These systems can detect direction changes of up to 1 degree, essential for sports like windsurfing where exact direction makes the difference between being able to go upwind or not.
3. Location, Location, Location
The best sensor in the world is useless if poorly placed.
- Standard height: WMO recommends 10 meters height in open terrain.
- Obstacles: A nearby building or tree creates turbulence ("wind shadow").
At WindTrackr, we strive to catalog well-located stations, or warn you if any have "dirty" readings due to obstacles.
The general rule is that the sensor should be at least 10 times higher than any obstacle within a 100-meter radius. For example, if there is a 5-meter building nearby, the sensor should be at 50 meters height. In practice, this is almost impossible in urban areas, which is why coastal stations in open spaces are much more reliable.
4. Maintenance and Calibration
A poorly maintained sensor is as useless as a poorly located one. Mechanical anemometers require regular bearing cleaning, cup balance verification, and periodic lubrication.
Ultrasonic sensors, although they have no moving parts, also need transducer cleaning to prevent accumulation of sea salt, dust, or insects that could affect measurements.
Calibration should be done at least once a year. In professional stations like AEMET, it is done every 6 months. Incorrect calibration can make you see 15 knots when there are actually 20, leading you to go out with inadequate gear.
5. How to Interpret Sensor Data
Knowing the sensor type of your favorite station helps you better interpret the data:
- Mechanical sensor: Gusts may be smoothed by inertia. If you see 25 knots gust, it was probably 27-28 knots real.
- Ultrasonic sensor: Readings are instantaneous and very accurate. A 25-knot gust is exactly that.
- Sensor height: If at 3 meters, add 10-15% to estimate wind at 10 meters. If at 15 meters, subtract 5-10%.
At WindTrackr we show sensor information when available, so you can make these mental corrections.
