[wxqc] Calibrating anemometers

[Dan Crooks]

Victor,

Wind is a funny beast influenced by friction of what it passes over/around.
I don't think you should expect your stations to match, be it direction,
gust, or other.  Same with rain amounts.  There are so many things that
influence the any particular stations readings that it's impossible to say
one station is wrong or right.

Your best bet is to get other instruments to cross-check your
readings, ie. rain
gauge <http://www.ambientweather.com/loraga.html>, sling psychrometer, etc.
Here is an example of an
instrument<http://www.testequipmentdepot.com/extech/thermometers/rh390.htm>I
just purchased for use with my station - note that it can be purchased
with NIST certification.  It doesn't do wind but there are other 'toys' that
will measure that for you.


Dan

On 7/9/06, Victor Engel <brillig at gmail.com> wrote:
>
> After preliminary data analysis, it seems my initial impressions may have
> been faulty. Here are the results of my analysis.
>
> In this first report, I list mean DIFSPEED (my neighbor's reported speed
> minus my reported speed) for each of the coded directions. Apparently, my
> wind readings are actually higher than his. Units are miles per hour.
>
> DIFSPEED WindDirection
>    -1.46         North
>     -.36           NNE
>     -.37            NE
>     -.33           ENE
>     -.69          East
>     -.16           ESE
>    -1.17            SE
>    -1.01           SSE
>     -.84         South
>     -.33           SSW
>     -.37            SW
>     -.91           WSW
>    -1.17          West
>      .13           WNW
>    -1.16            NW
>     -.29           NNW
>     -.70       AVERAGE
>
> On the other hand, his speeds are higher for wind gust data. I think that
> is where I got the impression his readings were higher.
>
>     1.83         North
>     1.57           NNE
>     1.55            NE
>     1.38           ENE
>     1.69          East
>     1.72           ESE
>     1.03            SE
>     1.49           SSE
>     1.47         South
>     1.49           SSW
>     1.59            SW
>      .35           WSW
>     -.04          West
>      .40           WNW
>     1.79            NW
>     1.82           NNW
>     1.47       AVERAGE
>
> Finally, here is a count of total data points used for these statistics.
>
> North 83
>   NNE 96
>    NE 119
>   ENE 176
> East 166
>   ESE 98
>    SE 147
>   SSE 270
> South 169
>   SSW 45
>    SW 46
>   WSW 34
> West 23
>   WNW 15
>    NW 43
>   NNW 99
> TOTAL 1629
>
> Something that probably skews the top chart a little bit is that I only
> selected data for which windspeed was nonzero at my station. Here is the
> procedure I used:
>
> I downloaded all weatherunderground data (CSV charts) for our two weather
> stations over the period of time my station has been active. Since the times
> are sometimes every minute and sometimes every five minutes, I took only the
> first data points on or after 5 minute boundaries. Then, I selected only
> data for which both stations had values for the timeframe.
>
> I wonder if my setup is missing wind gusts for some reason or other. If
> the Davis WIND station itself does not keep track of gusts, then gusts would
> have to be captured by software, and gaps between readings could possibly
> miss gusts.
>
> Victor
>
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