WH1080 wind speed comparison

[grumpazoid]

I have been playing around (I mean experimenting) with the WH1080 the last few weeks and have a question about the wind speed.
I have noticed that the wind speed uploaded to weather underground is the average reading. However some other local stations data on weather underground seem to match my latest gust speed and are about twice my average value.
Also the met office wind speeds for my area are greater than the average speed on my station.

The wind sensor is mounted on a scaffold pole about 15ft in the air and about 7ft from the house.
I cannot work out if these big differences are due to poor siting of the sensor or the fact I should be using the latest gust value?

Thanks
Rupert

[daj]

I am not the most technical person to answer this, and I am sure others will be along shortly to offer advice. However some basic reading, in the Wiki, as a starting point

http://wiki.sandaysoft.com/index.php?ti ... easurement

[steve]

For Wunderground, Cumulus sends two of the possible values, as defined by Wunderground:

windspeedmph - [mph instantaneous wind speed]
windgustmph - [mph current wind gust, using software specific time period]

For the first, it sends 'latest', and for the second, it sends the 'recent max gust', i.e. the peak gust in the last 10 minutes. These were my best attempts at fitting what various stations supply and what Cumulus calculates, to the Wunderground descriptions. And actually, this has got me thinking. Wunderground also define:

windgustmph_10m - [mph past 10 minutes wind gust mph ]

So Cumulus should probably be sending the 'recent max gust' for that, instead of (or as well as?) the windgustmph parameter.

It doesn't send any average speeds; Wunderground require a 2-minute average, and Cumulus doesn't currently calculate that.

This may or may not help you to make sense of your comparisons with nearby stations. It's a very difficult thing to do for wind, as the various types of station all measure and report wind in different ways, and then you have the siting of the anemometer and your local surroundings to take into account.

[Repairman77]

Hi Rupert,

The site of your anemometer is not ideal; it needs to be above the house preferable with no other objects higher close by.
There are vortices created around houses that can alter the wind-speed readings dramatically. It can give totally erroneous wind direction readings as well. It could be the reason for low readings; however I don't know how accurate the WH1080 is; I've only had mine a month or so and haven't had a chance to check it yet, not having another calibrated instrument to check it against.

Is there a chance that you can get it installed on a TV mast above the house?
The recommended height is 10M above ground in the clear, but of course you can only place it where practical.
I'm lucky in the fact that I've got an aerial tower up the side of my house and it's mounted 10M up on that.

Hope that helps,

Mike.

[grumpazoid]

Thanks Daj, I had not spotted that in the wiki. That is very useful.

Steve, you say that it does not send any average speeds to WU.
This is where I am confused.

At present the readings on Cumulus are Average 9.8 Gust 19.7 Latest 17.4 (mph)
WU is showing 10mph which can only relate to average?

I agree my site is poor at present Mike. I am hoping to move it further away from the house in due course.

[steve]

I guess WU must calculate the average from the data it's given. You can see exactly what data is being sent to WU if you turn on the debug log.

[grumpazoid]

I have carried out some further observations this morning.
The average speed on Cumulus (speed on Fine offset), when rounded up or down matches the figure on WU exactly every time. I can't see how they could calculate this so accurately from the gusts.
I will turn on debug when I can and have a look.

Thanks
Rupert

[grumpazoid]

I have now ran the debug.

Here is a sample of what was in the log:
09:18:24&winddir=150&windspeedmph=4&windgustmph=9

The 4mph is the average speed shown on Cumulus not Latest.

I can therefore conclude that when comparing to other local sations my wind figure is low either because my station is sending the average and not latest, or my anemometer should be high above the roof tops.

[Repairman77]

I have now ran the debug.
I can therefore conclude that when comparing to other local stations my wind figure is low either because my station is sending the average and not latest, or my anemometer should be high above the roof tops.

I don't think it's anything to do with the hardware or software grumpazoid; just the fact that the anemometer is not above any surrounding objects. The only possible difference with software could be the period from which averages are taken and calculated.

The wind speed will never be as high as in open ground when it's sheltered behind buildings or even trees.

Averages from other stations in your area within a few miles should all show approximately the same values (not like rain where it can vary within a few yards).

Mike.

[steve]

I have now ran the debug.

Here is a sample of what was in the log:
09:18:24&winddir=150&windspeedmph=4&windgustmph=9

The 4mph is the average speed shown on Cumulus not Latest.

Having checked the changelog, this is something I changed in one of the 1.8.8 builds, so I guess you're using 1.8.7?

[grumpazoid]

Many thanks.
I have upgraded to 1.8.8 and wind now showing "latest" on WU. Like the extra features also.