[wxqc] Calibrating anemometers

[Victor Engel]

Thank you for the reply.

Here is a brief description of the siting. If you want, go to
http://www.wunderground.com/stationmaps/gmap.asp?zip=78757&magic=1&wmo=99999and
zoom in as far as possible while keeping North Allandale and North
Central Austin SKYWARN in the picture. Then click on Satellite to see the
buildings, trees, etc. Our stations are the two closest together on the map.
In fact, you have to zoom in considerably before the symbols stop
overlapping.

Mine is the north one, North Allandale. The anemometer is mounted on a pole
12 feet above my two storey house. The house is 28 feet tall. It's mounted
on the northernmost peak of the second storey, just northwest of a large red
oak (casting its shadow on the street). My neighbor's unit is mounted on a
taller pole over a single storey house two doors south of my house. It's
actually one house north of where the symbol indicates. His house is
surrounded by trees, but they are short trees (I'm not sure whether they
taller than the pole or not). Both our units are at 40 feet. My pole extends
farther if I want it to, but I wanted the same height for now (from the
ground -- I think the ground is slightly higher at my house).

My equipment is brand new, having been installed less than a month. In fact,
tomorrow I am reinstalling the anemometer pole, because it's slightly tilted
(perhaps by 3 degrees or so). We also both have Davis Vantage Pros, but his
is wired, and mine is wireless. And he's running different software than I
am. I don't know how much difference the software would make.

I believe my neighbor's equipment is several years old. It was installed
when I moved into the neighborhood over 3 years ago, and I think it was up
for some time before that.

You may also notice temperature differences that are significant during the
day. I have a fan aspirated shelter. I don't think my neighbor does, and he
has told me that his temperatures are too high due to a restriction in
siting caused by a limitation imposed by cable length.

Anyway, I don't intend to make any adjustments any time soon. But his will
frequently register a breeze when mine doesn't register anything. That makes
me wonder if something is adjusted too tight or if I screwed up attaching
the cups somehow. I don't see what I could have screwed up, though. Is there
a period of time before lubrication gets broken in? I wouldn't expect so.

On 7/8/06, Gerry Creager N5JXS <gerry.creager at tamu.edu> wrote:
>
> Having followed a bit of this (I've been missing in action on vacation)
> the obvious question arises: What are the similarities and differences
> in instrument siting?  Are you measuring at the same heights above
> ground? Is your anemometer shielded by buildings or trees preventing it
> from seeing higher readings (I know my station suffers from this).
> Calibrating (or making ad hoc changes to cal'd instruments) is a step
> one shouldn't undertake lightly.  Dr. Lee's comment about sending it
> back to Davis makes the most sense if you're worried  about cal.
>
> You also fail to mention the age of the instrument and whether casual
> inspection suggests the device may have suffered normal wear that could
> cause performance degradation.
>
> Gerry
>
> Victor Engel wrote:
> > What techniques do people use to calibrate anemometers? My neighbor and
> > I each have a Davis Vantage Pro anemometer, and his readings are usually
> > higher than mine. Wind gusts, especially, are stronger on his. My wind
> > direction sensor, however, seems to be more sensitive than his.
> >
> > Victor
> >
> >
> > ------------------------------------------------------------------------
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> --
> Gerry Creager -- gerry.creager at tamu.edu
> Texas Mesonet -- AATLT, Texas A&M University
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> Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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