New Zealand Local Weather Forum
Weather Discussion => Hardware Software and Technology => Topic started by: Deano on June 20, 2012, 04:57:11 PM
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I would like to find out if I have set my Barometer correctly.
My nearest Metar is NZAA Auckland. This is 87kms SE
I have set my height above sea level via GPS.
I viewed the Isobaric charts from Metservice and found when the pressure gradient was the same between the 2 places.
I then set my station Barometer to the same value.
Was this correct?
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As far as I know, GPS altitude measurement isn't necessarily the most accurate - I'd do a double check on NZ Topographic Maps http://www.nztopomaps.com/ (http://www.nztopomaps.com/), just keep zooming in and read off the height contours for your location, 10 metres extra height is about a -1 hPa difference (if I remember it right)
The only other thing I'd recommend is that the time to do a barometric pressure calibration like this is when there is a very stable and static high pressure system covering the region - ie without isobars between you and the place you're setting to.
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I know some station breeds have different gradients for the values - our three La Crosse stations follow each other very closely, but the other unit, a Davis, always headed higher as the pressure went higher, and was possibly the more correct value - I don't know. And as there was not an official station here and our Company's station did not even have a barometer (more concerened with wind, temp and rain for environmental issues and unwanted discharges) - we just had to rely on each other and the Metservice weather maps. So Arthur always chided us for having cheap weather stations... we just took it on the chin and let him gloat!
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I took the height of my station off Google Earth.
A month ago a farmer from the district came by with an aircraft altimeter from his plane calibrated at sea level. It turned out that Google was 4 metres out.
I then realised that it wasn't the height of the station I should have measured, but where the console is, so I had to add another 4 metres (which is a bit of a guess). Kicking myself that I missed the chance of being 100% accurate with the altimeter while I had the chance.
cheers
TC
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Thanks for all your answers.^-^
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