Your SKY / Tempest leaves the factory with a wind sensor calibration in place. To ensure in-situ accuracy, the sonic wind sensors in SKY / Tempest are designed to self-calibrate over time once installed in the field. The initial in-field process requires collecting a certain amount of data at all four cardinal points. This initial process runs through a check to ensure all four sonic sensors are balanced properly.
For those of you with access to a calibrated wind tunnel, or reliable testing equipment, you may notice slight directional variation out of box. This is normal. Once you have it on the roof for a few weeks and confirm you’ve had some significant wind (12 mph or more) from each direction, put it back in your wind tunnel and see if you don’t get better numbers at all points on the compass.
edit : June 2020 - added Tempest since both use same sensors
My location does not receive wind from all directions due to terrain configuration. I normally get south-eastern and some north direction. How will device calibrate?
@petercek Each cardinal direction will calibrate independently. Therefore, your SKY will collect initial data from the exposed directions and calibrate accordingly.
If you never have any wind input from a certain cardinal direction – ie. West – your SKY won’t have enough data to balance the sensors for only that direction…which seems like a mute point if your exposure is blocked due to terrain.
Had my SKY for a few weeks now. Tonight had a strong rain storm with lightning. Storm is over, but wind is showing 10-16 km, yet the trees and leaves have zero movement, and my Davis wind gauge right next to Sky isn’t moving at all.
There is zero wind right now but Sky is showing fair amount of strong winds… is this normal after a heavy storm ? Something isn’t right,.
Thanks much. That would explain it. Wind measurements back down to normal this morn.
… so it means that during big windy wet storms, the sensor measurements will be off. After the storm, it was measuring very gusty winds despite not having even a puff of air going on out there. Such is life for the moment. Love the Sky and Air despite these things - they are sexy weather meters.
I wonder if we could apply some sort of hydrophobic coating (never-wet?) to the flat surface that the ultrasonic transducers face to try to keep water from pooling in there?
Thanks Sam. Actually, our solution is a bit more technical than you might imagine. All sonic anemometers face the challenge of dealing with obstructions in the sonic path. Even slight changes in the sonic path distance can throw off the timing of the return sonic signal. To deal with obstructions like rain drops, we have developed an algorithm that inspects all wind data in real-time. Any data that looks suspect (by virtue of algorithmic rules, which will get better and better with more data) gets disqualified and thrown out immediately. Rational values are maintained. Again, this algorithm is young and will get better over time as we run more and more data scenarios through it and fine tune.
Just the opposite. A hydrophobic coating causes the water to bead into drops and skew the sonic path even further. (Note: our first designs included a hydrophobic coating matched with a downward angle on the sonic reflecting plate, theoretically encouraging droplets to form and roll off. This did not work in field testing for a variety of reasons.) Whereas a hydrophilic coating such titanium dioxide inhibit drops from forming resulting in far less skew of the sonic path. To date we have only conducted initial experiments with titanium dioxide coatings, but it looks promising when combined with the wind inspection algorithm.
Just another finding of what’s been reported here before by me and others. Sky wind sensor got wet in storm and it’s reporting wildly strong winds here even though there’s not even a whisper of wind outside.
I know you’re working on it… just another of the must-fix projects on the list.
As I am still waiting for my delivery, could you tell me (or post an image) the behavior of the top edge of the wind measuring slit?
Due to the physics of surface forces I would expect a sharp edge with overlap and / or back taper to prevent the forming of drops wich stick or to promote a quick release of those.
Is the top (rain detector) cover a little wider in diameter then the footer of
the wind slit ? @GaryFunk : is your sky normal to ground ? Would it be an option to be slightly out of angle ?
Fingers crossed!
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