Calibration Issues? wmr88

[starman316]

took a photo of my anemometer

Pole is 6 foot

it is the top anemometer

https://dl.dropboxusercontent.com/u/297 ... 114059.jpg

is it ideal?

i know in my previous post i said it doesnt clear the house, but according to this pic it does in most directions other than north west (toward chimney)

[callum91]

Hello

I can't see from your photo whether there other houses or tall trees nearby which could be affecting the exposure of the anemometer.

I have paraphrased the following guidance from the Met Office Observer's Handbook:

At standard synoptic stations the anemometer will be 10 metres above level ground with no significant obstacles within 300 metres.

If there are obstacles within 300 metres then the anemometer needs to be 10 metres + the height of the tallest of the various obstacles. If there are large obstacles (12 metres or more high) with a height of h at various distances then the anemometer will need to be at a minimum height shown on the following table:

Distance of............Minimum height of anemometer
Obstruction

h............2 h
5 h............1.67 h
10 h...........1.5 h
20 h...........1.25 h
25 h...........1.13 h
30 h...........h


When the anemometer needs to be mounted on an isloated building, the building itself will disturb the wind flow to some extent depending on its size and shape. As a rough guide, a mast or tower erected on the roof needs to be at least half, and probably about three-quarters, of the height of the building, assuming that the building has some considerable horizontal extent (which excludes things such as towers, lighthouses, etc.) Thus, with a building 12 metres high, a roof-top mast at least 6 metres and preferably 9 metres should be used.

Therefore I think it's clear to see that unless you are in a very open rural setting or very high up, wind speed readings will differ significantly from those obtained at synoptic stations/airports or in more exposed areas.

Kind regards

Callum

[starman316]

ok thanks callum

my location

https://dl.dropboxusercontent.com/u/297 ... cation.jpg

bungalows to my south and south west, east, north

houses directly west

image faces south ish!

[callum91]

Even that tree there will reduce the wind speed slightly due to friction, as will the surrounding buildings. The only way you'd be able to tell that the instrument is under reading would be to compare the data from two different anemometers in the same location but I think we just have to trust the manufacturer.

I don't bother trying to apply corrections for the exposure, I just have the anemometer mounted as high as practical and accept that surrounding trees and buildings will mean that my readings will be less than those at the nearby official weather stations.