Wind speed seems to be reading low (solved in firmware v103)

Based on other weather stations near mine and visual observation, the wind readings seem to be 2 - 3 kts low. Sky is located with a clean shot in 360 degrees right on the water.

anyone else seeing this? any way to calibrate?

there is a search function in this forum, pretty handy :smirk:

thanks for your condescending remarks ERIC, Always helpful when building a friendly community. I did a search and did not get this piece you quoted. Anyway Station has been up two weeks and I have not seen any self calibration taking place. Still reads low.

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Sorry you took it so direct, from time to time I poke someone because in my 20 years forum reading/moderating, I saw so often people ask even before doing the basic search … and you end up with about 50 threads with the same question. Even here it started and some try to merge, move things as to keep it a little clean … and sometimes, well I play the nasty one. Sorry you were the victim.

Regarding search, pretty weird as Discourse is pretty good at that compared to some other software. I used ‘sky calibration’ and the ninth topic is the one I added for you …

the difference in wind speed isn’t so big according me as measuring it is really local and even little changes can affect it quite a bit. Also the calibration isn’t just done once, it is an ongoing process that should get better and better as the process gets more and more data from us all.

But is you want @dsj David can ask to have a closer look at your data. If you could give him your station number, will help to find you quicker.

@tod.sackett

You won’t see it take place and it can take several days for the calibration to start. I have tagged David @dsj and he will reply to you as soon as he us able.

In the meantime keep an eye on your readings and hope for the best.

Gary

Station number is 4229. There is a WindAlert.com station about 200 yards from mine. This is how I can compare and know how my station is reading. I will keep an eye on it and see if things improve. Thanks All for the input

@tod.sackett Good experiment! Yes, there is a professional WeatherFlow station installed in Cleveland, OH near the Edgewater Boat Ramp. Note: this weather station is sited out in the water on a USCG navigational aide with a very clean 360deg unobstructed wind fetch. It is sited 35ft above ground level and enjoys near perfect wind capture.
Edgewater

We don’t know the meta data for your installation, but be careful as it is not likely apples to apples. Also, your station reports every 3sec, whereas the Edgewater stations updates at 5min intervals (samples continuous, updates avgs, etc) so there can be data differences due to the average intervals. That said we just took a peak at the winds at 8:10p local:

Your Station 4229: NNW 315deg Averaging 3.2 kts, Gusting 2.6-4.4 kts (8:10p timestamp, 1min avg)
WF Pro Station Edgewater: NNW 339 deg Averaging 4.4mph, Gusting 3.4-5.4 mph. (8:10p timestamp, avg from 5min data)

Obviously just one snap shot in time. Keep an eye on it and let us know. If you have a WINDmeter or WEATHERmeter to test the wind immediately next to your SKY that would be interesting as well.

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After looking at your data a bit deeper, @tod.sackett, it looks like the calibration of your SKY’s wind sensor is spot-on. Your station, at 15ft (4.6m) off the ground, will naturally read slightly lower than the station at 35ft (10.7m), thanks to friction, even though they are very close to each other horizontally. The sampling scheme also causes some of the difference, as noted above. However, when you normalize both values to the same height and sampling scheme, they match up almost perfectly!

We get this sort of question often from owners of the WINDmeter & WEATHERmeter, and have created a page with more details, some of which apply to your case. And here’s a nice graphic describing the ground effect on windspeed, from that page:

image

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@dsj @WFmarketing - It is probably worth noting in the Sky siting docs that the WMO standard for wind observations is 10 meters (~33 feet) AGL if it isn’t mentioned already.

@tod.sackett - Comparing apples to apples at about 6 meters (20 feet), my Sky and Davis VP2 have been tracking each other darn near perfectly when the winds are above 2 MPH or so:

On a slow wind day:

daywind2

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We probably should, somewhere, I agree. Although for the typical home user, it’s certainly not critical to mount the SKY at 10m.

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thanks all, I will keep an eye on this and see how the data shakes out over time. I also see from this data that I am not exactly lined up to true north as the WeatherFlow station is usually 20 degrees to the right of mine. Easy fix

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Hi Support or @WFmarketing,
I installed my weather station #4555 on 14th August and I mainly want to know an accurate wind speed. I am on the top of a hill and my Sky is approximately 4m above my tall 2 story house with a view in most directions to the horizon. My impression of the ‘out of the box’ settings are that in winds above 15 knots it reads low and I am waiting for the auto calibration self learning feature to improve it. My issue is trying to know what the wind speed calibration is and how to know when it changes. Otherwise my reading has no validity. In a personal support question Tim answered that he believed the ‘Sky’ will restart its initial learning period by opening and closing the battery door. Which suggests to me that when I change the batteries it might loose its calibration. I have also deleted the data a few times to avoid historical errors and then wonder if that restarts the learning from scratch. But even so if it is continuously learning then I really need to know what my calibration is. How long before we get to see our wind speed calibration? How will I know when the calibration has changed? Is there a detailed manual or instructions anywhere?
kind regards Ian Ladyman

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I’ve noticed the same lower than expected wind speeds on my unit (#2006) when compared with weather bureau or other Wunderground connected stations nearby. It seems to be about half the expected windspeed. We’ve had quite a few days recently with local wind speeds around 60-90 kph and my Sky reports half those figures at best. On another accuracy point, the Sky unit seems to be reporting double the rainfall amounts of other local stations. I was also wondering about calibration but ultimately accuracy. The Air unit has been spot on but the Sky unit less so unfortunately. The unit is on our roof and has clear exposure to sun and rain but there may be some shielding from nearby buildings that could affect the wind readings but I wouldn’t have thought that much. I’d appreciate any thoughts/tips to improve accuracy. Thanks.

Hi Ian. Thanks for the great questions.

As I’m sure you know, wind speed measurement is heavily dependent on siting. It’s very difficult to compare wind data between non-co-located weather stations, because so many factors can cause them to differ. To what are you comparing your SKY’s wind speed? How much lower is it from your reference standard?

That sounds good! Can you share a couple pictures?

Currently, the only wind-related self-calibration that happens is a “balancing” of the four ultrasonic sensors. This happens to all new SKY units as it collects data from each of the four cardinal directions. There is no fixed time period for this process - it depends on the wind speed and directly at your location. Each direction is balanced independently, so you don’t need to wait for the wind to pass through all four directions before your SKY benefits from it.

Once this step is complete, the balancing data is stored on the device, so restarting your SKY (by opening and closing the battery door) will not remove these settings. Tim was correct that restarting the SKY will restart the balancing process. The SKY will use the new balancing data, once collected. Normally, the new data will be identical to the initial data, but this is a way to force your SKY to go through this step again, if you suspect your SKY is “out of balance.”

Note, however, that in most cases this is a very subtle adjustment and you normally won’t notice any difference before and after this “balancing” step. Also, the need to “re-balance” your SKY is very rare, and it would be unlikely to be causing a significant error in your readings.

No, when you delete your data it removes it from our servers but it does not change the calibration on your SKY.

There is nothing to see other than your data being slightly more accurate.

You probably won’t - it’s very subtle and it only happens once (normally).

Not yet!

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Remember, wind speed measurement is heavily dependent on siting. It’s very difficult to compare wind data between non-co-located weather stations, because so many factors can cause them to differ. How high off the ground your station is, what’s upwind and downwind of it, how close to the roof of your house it is - all of these factors will affect your reading.

The rain sensor on the SKY has some well-known issues that we’re working through. Please see this thread for lots more detail!

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Thanks for your response, David. I suspect you are right regarding my wind speed measurements as there are quite a few buildings not too far from my site that likely affect and flow in the area. I may look to get a conventional weather station to determine any difference.

Thanks for providing that link to the known rain sensor issues. Much appreciated so look forward to any future updates.

Cheers,

Robert

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Hi @dsj,
I have Station 4555, 31 Bombala st, Dudley, NSW Australia (Southern hemisphere, note the sun and shadows for directions) taken 1:45pm 22nd Aug 2018. This view towards the South shows my over 5m pole and current mount:G0011626 And from Anemometer height, (Note the marker Pen highlighting the ‘N’ on the Sky): G0011655 All photos taken with a GoPro very wide angle, cropped and distorted due to wide angle lens (notice even poles and walls lean too, so it is difficult to use the photo to determine level but I now suspect my Sky leans towards NNE). I mounted it in a hurry as an experiment when I needed to know the wind one day. The streets and my house walls run roughly 45 deg from North. View towards the West: G0011670 View towards East: G0011678 View towards North: G0011721 View from about 6m (Half Sky height of 12m) above the road towards my Sky and towards North. From here the ground slopes downhill in every direction. You can see all surrounding houses roofs are lower than the horizon of the camera’s 6m. My ‘Sky’ is mounted 12m higher than the roads highest point. The roads meet at 90 degree but the wide angle lens captures wider:
G0021945
I usually compare my winds with Newcastle Nobbys Weather Station, the 4th graph on this page: https://www.seabreeze.com.au/weather/wind-forecast/nsw-mid-north or under Hunter here: http://www.bom.gov.au/nsw/observations/coastal.shtml But it is roughly 10km away in a shallow valley beside the ocean. And if it is onshore I use this unreliable Station installed by our local hang gliding club: https://holfuy.com/en/data/179 I fly a paraglider all along my coast and analyse all the different speeds and directions and wind gradients and shear layers so I do realise the wind is different everywhere within even small distances. If I had a reliable station beside me to compare, then I wouldnt have needed mine :slight_smile: There are many times I am in a different wind to Newcastle and that is why I and my gliding, surfing, and kiting friends require my station. I feel the lower than expected minimum speeds are pulling the average down but I need to do more experiments to get detailed data. It is most likely turbulence in the strong winds pulling the minimums (And average) down, but my wind sock doesnt show the lows that the Sky indicates. This is an interesting read: http://www.bom.gov.au/climate/cdo/about/observation_specification_2013.pdf I am considering attaching it above the front of my car for a high speed run?
cheers Ian

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what is that bucket like thing on the sky’s mast ??? doesn’t that vibrate to much with high winds ???

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Thanks for the photos! That’s a beautiful installation, Ian. Your SKY should give you excellent wind readings for the area around your home. Comparing it to a station 10km away is tricky, though. Local topography plays a huge role in surface winds, as I’m sure you know.

This is very likely. Turbulence close to the ground can be significant. You’d have to get your SKY up a lot higher to get out of the boundary layer. You may need to “mentally calibrate” your SKY’s readings to the corresponding values in the sky (for your paragliding) or over the ocean (for your kiting friends).

Go for it!

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It looks like a windsock. Whether it causes vibration, and whether that vibration causes “false rain,” remains to be seen. That phenomenon is not something everyone experiences - it seems to be dependent on several factors, including the resonant frequency of the mast. Time will tell…

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