Author Topic: Wind Speed Adjustment  (Read 7285 times)

0 Members and 1 Guest are viewing this topic.

Offline Gerald

  • Member
  • *
  • Posts: 30
Wind Speed Adjustment
« on: December 22, 2008, 06:20:32 PM »
I thought I had read in one of the VP2/ISS manuals, though I can't find it now, that the weather service suggests a height of 30' for accurate wind speed/wind gust readings. My anemometer is mounted approximately 8' feet above the ground. Is there a console procedure to adjust for the increased wind speed found at 30'?
Jerry
Altoona, IA

Davis Vantage Pro2
VWS v15.00 p15
EW7358
CoCoRaHS: IA-PK-83
KIAALTOO4

Offline mmorris

  • Forecaster
  • *****
  • Posts: 766
  • Hope your day is full of sunshine
    • Weather and Racin
Re: Wind Speed Adjustment
« Reply #1 on: December 22, 2008, 07:39:32 PM »
Who said that the wind blows harder at 30 feet the it does a 8 feet. The wind may in fact be blowing harder at 8 feet then it is at 30 feet. The wind is blowing what it blows no matter what feet it is. And also nws 30 feet at there station my be blowing different then it is blow at my station at 30 feet. And if you got a house or a tree in the way it my be a different reading all together. That would be a hard thing to cal for.. You maybe able to make an adjustment for a tight bearing in the anemometer but for different heights I not think you can. Just my thought been wrong before   :?       
>>Miles<<  By from Portage Lakes, OH.
Been using VWS since 1996 Ver# 14.01P43
Wireless Vantage Pro2Plus Serial Data Logger, Anemo Tran Kit
Win XP, Firefox, WXSIM, Cumulus, NexStorm, Yawcam, VVP, BadBlue Web server, Quake Catcher Net
Follow me on twitter
Vietnam era Veteran USAF bb loader
Quadruple Bypass survivor

Offline racenet

  • Forecaster
  • *****
  • Posts: 1306
    • NH Weather Data
Re: Wind Speed Adjustment
« Reply #2 on: December 22, 2008, 07:43:12 PM »
Who said that the wind blows harder at 30 feet the it does a 8 feet. The wind may in fact be blowing harder at 8 feet then it is at 30 feet. The wind is blowing what it blows no matter what feet it is. And also nws 30 feet at there station my be blowing different then it is blow at my station at 30 feet. And if you got a house or a tree in the way it my be a different reading all together. That would be a hard thing to cal for.. You maybe able to make an adjustment for a tight bearing in the anemometer but for different heights I not think you can. Just my thought been wrong before   :?       

You are 100% correct.  ;)


Bob
www.theamericanflagstore.com - The American Flag Store



www.nhweatherdata.com - NH Weather Data

Offline Gerald

  • Member
  • *
  • Posts: 30
Re: Wind Speed Adjustment
« Reply #3 on: January 18, 2009, 12:11:27 PM »
Thanks for the reply. I found the basis for my question, this time in The Davis Wx Club E-Newsletter, Jan 2009, in the article "I've Fallen and I Can't Get Up".
 
"However, this might not be the best height for your anemometer. We recommend that the anemometer be placed at least 7 feet (2.1 meters) above surrounding obstructions such as trees. For many applications, the best place is on the roof. (The standard for meteorological and aviation applications is to place the anemometer 33 feet (10 meters) above the ground. We recommend professional installation in that case.)"


Jerry
Altoona, IA

Davis Vantage Pro2
VWS v15.00 p15
EW7358
CoCoRaHS: IA-PK-83
KIAALTOO4

Offline mmorris

  • Forecaster
  • *****
  • Posts: 766
  • Hope your day is full of sunshine
    • Weather and Racin
Re: Wind Speed Adjustment
« Reply #4 on: January 18, 2009, 12:24:13 PM »
No  :-)


I thought I had read in one of the VP2/ISS manuals, though I can't find it now, that the weather service suggests a height of 30' for accurate wind speed/wind gust readings. My anemometer is mounted approximately 8' feet above the ground. Is there a console procedure to adjust for the increased wind speed found at 30'?
>>Miles<<  By from Portage Lakes, OH.
Been using VWS since 1996 Ver# 14.01P43
Wireless Vantage Pro2Plus Serial Data Logger, Anemo Tran Kit
Win XP, Firefox, WXSIM, Cumulus, NexStorm, Yawcam, VVP, BadBlue Web server, Quake Catcher Net
Follow me on twitter
Vietnam era Veteran USAF bb loader
Quadruple Bypass survivor

Offline mmorris

  • Forecaster
  • *****
  • Posts: 766
  • Hope your day is full of sunshine
    • Weather and Racin
Re: Wind Speed Adjustment
« Reply #5 on: January 18, 2009, 12:41:46 PM »
Well here is some interesting info about the official recording station at the Akron Canton Airport there anemometer is only 20 feet above the ground, now I'm confused.
 found data here:
http://www.webmet.com/State_pages/SAMSON/14895_sam.htm



Thanks for the reply. I found the basis for my question, this time in The Davis Wx Club E-Newsletter, Jan 2009, in the article "I've Fallen and I Can't Get Up".
 
"However, this might not be the best height for your anemometer. We recommend that the anemometer be placed at least 7 feet (2.1 meters) above surrounding obstructions such as trees. For many applications, the best place is on the roof. (The standard for meteorological and aviation applications is to place the anemometer 33 feet (10 meters) above the ground. We recommend professional installation in that case.)"



>>Miles<<  By from Portage Lakes, OH.
Been using VWS since 1996 Ver# 14.01P43
Wireless Vantage Pro2Plus Serial Data Logger, Anemo Tran Kit
Win XP, Firefox, WXSIM, Cumulus, NexStorm, Yawcam, VVP, BadBlue Web server, Quake Catcher Net
Follow me on twitter
Vietnam era Veteran USAF bb loader
Quadruple Bypass survivor

Offline Bushman

  • Forecaster
  • *****
  • Posts: 7549
    • Eagle Bay Weather
Re: Wind Speed Adjustment
« Reply #6 on: January 19, 2009, 02:34:26 PM »
Who said that the wind blows harder at 30 feet the it does a 8 feet. The wind may in fact be blowing harder at 8 feet then it is at 30 feet. The wind is blowing what it blows no matter what feet it is. ... Just my thought been wrong before   :?       

And I will suggest you are wrong again.  :)  Seriously, wind speed does change as you approach the ground.  It drops AAMOF.
Need low cost IP monitoring?  http://wirelesstag.net/wta.aspx?link=NisJxz6FhUa4V67/cwCRWA or PM me for 50% off Wirelesstags!!

Offline Zephirus

  • Member
  • *
  • Posts: 21
Re: Wind Speed Adjustment
« Reply #7 on: January 19, 2009, 03:01:15 PM »
There is a big drop off in wind speed as you get closer to the ground.  The standard NOAA height is not best for people or plants either but is better for aviation or where the fetch is poor (better wind at 33ft than none at 3m if blocked off).  Folks just need to decide what they want their data to represent.  The two standard sensors heights are ~10 m and 3 m depending on your purpose.  I did not really get my station to support the government data collection efforts.  If I did I would have worked to set my anemometer at 33 ft.  Mine is at 3 m.  Just do some Google (or other) searches and you can read volumes on this ...... The table below is from the BC Integrated Land Management Bureau.  It is a simplification since it leaves out some important factors such as surface roughness and fetch (whats between your anemometer and the wind .  Anyway you can see the point - wind measured at 10 m does not reflect (well at all) what you would experience at 2 m or 6 ft.

For wind speed measured at a height between:   Multiply by:
0 and 2.0 m   1.5
2 and 2.9 m   1.48
3 and 3.9 m   1.35
4 and 4.9 m   1.25
5 and 6.9 m   1.15
7 and 8.9 m   1.07
9 and 11.9 m   no correction
« Last Edit: January 19, 2009, 03:40:34 PM by Zephirus »

Offline Bushman

  • Forecaster
  • *****
  • Posts: 7549
    • Eagle Bay Weather
Re: Wind Speed Adjustment
« Reply #8 on: January 19, 2009, 04:35:38 PM »
Here's more inof on wind speeed and impacting factors for those interested:  http://www.windpower.org/en/tour/wres/calculat.htm
Need low cost IP monitoring?  http://wirelesstag.net/wta.aspx?link=NisJxz6FhUa4V67/cwCRWA or PM me for 50% off Wirelesstags!!

Offline d_l

  • Forecaster
  • *****
  • Posts: 1700
  • Slide Mtn - Mt Rose
    • Thomas Creek Estates neighborhood weather
Re: Wind Speed Adjustment
« Reply #9 on: January 19, 2009, 05:49:44 PM »
Bushman, unfortunately the calculator at that link isn't set up to work on sub-10 meter anemometer heights, but the link does give the equations to calculate the correction factors that Zephirus gave.

If someone wants more continuous adjustment/correction factors than the the stepped values above, they can use the following equation:

Adjustment Multiplier Factor = ln(10/z0)/ln(z/z0)

where z = the height of your anemometer in meters

and z0 is the roughness length which can be very roughly approximated as the 1/10 the height in meters of the surrounding surface, e.g. the top of nearby buildings, the top of a forest canopy, top of surrounding scrub brush, the top of nearby crop fields, the mowing height of grassy fields, a concrete surface, water, etc.
--Dave--

Wireless VP2 w/ solar, 24hr FARS, Heater, (Envoy-WLIP)*3-Meteohub, plus custom VP2 @ 26', WL 6.0.4, WU & W4U=KNVRENO37 NetcamXL

People always talk about the weather, but they never do anything about it.  Not me.  I'm gonna measure it.  https://www.tceweather.com

blackjack52

  • Guest
Re: Wind Speed Adjustment
« Reply #10 on: January 19, 2009, 06:50:16 PM »
From CWOP, to be used as a standard;
2. Siting
The international standard for anemometer height above ground level is 10 meters (33
feet) with no obstructions at or above this level. CWOP encourages weather station
operators to place their anemometers at this level, consistent with safety considerations, if
no obstructions are at or immediately below this height.
Simple Anemometer standard (see Figure 13):
 10 meters (33 feet) above ground level (AGL).
 If there are obstructions above 8 meters, anemometer should be at least 2 meters (7
feet) above obstructions (trees and/or buildings) that are within the immediate vicinity
of weather station (20 meters horizontally).
 Anemometer mast should be absolutely vertically level.
 Anemometer should be orientated to yield wind direction values from “true north”

The way I see it, if you have a Davis, it's considered a professional system, therefore, try and get as accurate a siting as possible, especially if you're sending data to CWOP, NOAA, etc.  The reason CWOP inconsistency exists is due to deviations from the standard....and micro-climatological variations.  You spend $600 plus on station/software, set it up as such.

The previously posted conversion chart should aid those not able to site properly.  Gain adjustments?
'

Offline mmorris

  • Forecaster
  • *****
  • Posts: 766
  • Hope your day is full of sunshine
    • Weather and Racin
Re: Wind Speed Adjustment
« Reply #11 on: January 19, 2009, 07:29:51 PM »
Well as a old Vietnam war era bb loader and a person that has had open heart surgery I no longer have time to help you all worry about if you got that dam anemometer to spec.  I'm done with this thread... =D&gt;
>>Miles<<  By from Portage Lakes, OH.
Been using VWS since 1996 Ver# 14.01P43
Wireless Vantage Pro2Plus Serial Data Logger, Anemo Tran Kit
Win XP, Firefox, WXSIM, Cumulus, NexStorm, Yawcam, VVP, BadBlue Web server, Quake Catcher Net
Follow me on twitter
Vietnam era Veteran USAF bb loader
Quadruple Bypass survivor

Offline Gerald

  • Member
  • *
  • Posts: 30
Re: Wind Speed Adjustment
« Reply #12 on: January 24, 2009, 07:20:48 PM »
Thanks to all for your responses. The responses from Zephirus and  MadALwx were of particular help. Appreciate it. 
Jerry
Altoona, IA

Davis Vantage Pro2
VWS v15.00 p15
EW7358
CoCoRaHS: IA-PK-83
KIAALTOO4

Offline LIWeather

  • Senior Contributor
  • ****
  • Posts: 252
Re: Wind Speed Adjustment
« Reply #13 on: January 28, 2009, 01:19:17 AM »
Not for anything, they recommend your anemometer be 7' above any trees. Im not sure about you guys, but the trees in my neighborhood are easily 40-50' if not more. I would need a 75' tower to get 7' above the tree line or tallest obstruction. Are they serious with these recommendations?

Does it mean you are out of luck if you are not 7' higher than obstructions? I still struggle to see how you can really base your accuracy on another station. There are so many elements that impact my station compared to the closest "official" station. I guess you take your data for what its worth.

Offline Scalphunter

  • Forecaster
  • *****
  • Posts: 2314
Re: Wind Speed Adjustment
« Reply #14 on: January 28, 2009, 01:27:13 AM »
 40 to 50 foot that brush here try getting above 125 to 150 foot  Spruce and Red cedar.   But I hear you about wind and accuracy. Have a small knoll   that pushes the  wind up and over me... Can see  it  blowning on the channel  but still been 20 to 30 mph under what it is  out on the water.


Offline LIWeather

  • Senior Contributor
  • ****
  • Posts: 252
Re: Wind Speed Adjustment
« Reply #15 on: January 28, 2009, 01:33:32 AM »
That is part of my point. Whats taking place in location A could be far different than location B due to terrain, obstructions, etc. So who is to say one station is more accurate than the other? Granted if the anemometer is sitting 5 feet above the ground with a building or fence 10-15 feet away, the #'s are going to be inaccurate but the different obstructions are what makes your weather unique.

I'm not completely happy with my current anemometer location but when I put it up on the roof, there is no way im going to compete with the tree's. My information cannot be devalued b/c the station 5 miles away has different readings. Maybe the wind isnt blowing that hard by me as it is 5 miles away.

I dont think there really is a valid answer. You have to take your results for what their worth and work with what you have.

Offline d_l

  • Forecaster
  • *****
  • Posts: 1700
  • Slide Mtn - Mt Rose
    • Thomas Creek Estates neighborhood weather
Re: Wind Speed Adjustment
« Reply #16 on: January 28, 2009, 10:58:56 AM »
LIWeather and Scalphunter, if you can follow the math through all the Turbine Siting pages in this link: http://www.windpower.org/en/tour/wres/shear.htm that bushman posted, you can get a feel for how much your wind speed measurements could be reduced by the forest around you. 

I don't think the "7-foot rule" applies within a forest.  If the NWS or Forest Service establish a standard weather station in a forest, I think they just use a standard 10m mast set up in a small clearing.  A forest isn't considered an obstacle because there are so many trees.  Instead all those many trees become a very rough surface that reduces the wind speeds at that height, but that is what it is in a forest as far as standard wind measurements.

Now if someone was measuring the site for wind energy, then that would be a differnt story and they might use a hundred foot mast or higher.
--Dave--

Wireless VP2 w/ solar, 24hr FARS, Heater, (Envoy-WLIP)*3-Meteohub, plus custom VP2 @ 26', WL 6.0.4, WU & W4U=KNVRENO37 NetcamXL

People always talk about the weather, but they never do anything about it.  Not me.  I'm gonna measure it.  https://www.tceweather.com

blackjack52

  • Guest
Re: Wind Speed Adjustment
« Reply #17 on: January 28, 2009, 11:34:48 AM »
I agree.  You kind of have to make an interpretation of the siting standard for your environment.  What if you lived in a canyon :?:  For a forest or woods, you're not trying to site and provide windage [sorry, term from my ballistics days; Scalphuntret knows] as if the forest wasn't there.  That doesn't make sense. 

Unless you have Kodiak's around.  Then you can't adjust for height.  [Nice trick to play on fellow wx enthusiast in AK....toss a beef cube in the rain bucket.]

By the way, Scalphunter, Spec Ops are using Kestrel 4000s now for windage.

Offline Scalphunter

  • Forecaster
  • *****
  • Posts: 2314
Re: Wind Speed Adjustment
« Reply #18 on: January 28, 2009, 11:45:29 AM »
  That turbine chart is nice if you live in Reno or other flatland areas. Some of you need to take a cruise  up this way to get a feel for way the channels  work on wind here. It  is like living in a carburator throat. Wind goes the path of least resistants. Seen it blowing 80 knots 5 miles away and get  to where I live water and air dead calm. Now talk about a micro clime. My general wind direction is from SE and there are no trees to speak of  but a low lying point of land causes a burble so the wind goes  up and  over rather then  doing a laminar flow like you get on a car. This channel here is  fun to fly when it gets breezy. I have seen 737's have to abort  approach  because the  burbles  coming off the peaks around here was slamming them all over the place.  Yeah some people get white knuckles here.  In my 172 i have a set  route i come in at approach to minize the  bouncing around and  keep stress off the  wings.

MadAl I know they are. Have one here that I pack every where with me.....

blackjack52

  • Guest
Re: Wind Speed Adjustment
« Reply #19 on: January 28, 2009, 11:51:54 AM »
Your conditions make micro-bursts look like breezes.  Watch out for those vortexes.

Offline Scalphunter

  • Forecaster
  • *****
  • Posts: 2314
Re: Wind Speed Adjustment
« Reply #20 on: January 28, 2009, 12:05:23 PM »
 Yeah I know  been  turned around couple tmes  coming  over the ridges here. Nothing like a wing dropping  and you  turn and lose altitude at same time and you never tuen the controls. What is  fun is  being  about 50 feet up  on landing and get slapped  down on to the water.  My old instructor  went swimming when the beaver she was flying  got slapped out of the air at around 75 to  100 feet up. Tore the  floats off  the plane. Good thing she was about 100 feet off the  land/dock when it happen.

blackjack52

  • Guest
Re: Wind Speed Adjustment
« Reply #21 on: January 28, 2009, 12:15:30 PM »
I'm sorry, that's not fun.  You bush pilots are crazy.  Your own breed.
Now kicking SEAL trainees out the back of the 53, when we did 30/30s, that's fun.  Until the SEAL instructor thinks 50/50 builds character.

For others wondering what the lingo is...30/30 = Helicopter moving 30knots at 30' altitude.  The SEALS jump out, no chute.

Offline Scalphunter

  • Forecaster
  • *****
  • Posts: 2314
Re: Wind Speed Adjustment
« Reply #22 on: January 28, 2009, 12:31:45 PM »
 Just keep your feet together and you be ok...  get off balance and it a wipe out....   any time going out chopper is  a blast with rotor wash