What height to install a weather station?

[moylanr]

Any advice of how high to install a weather station measuring Humidity, Air pressure, Wind direction, Wind speed, Wind chill, Dew point, Global radiation and Temperature please?

Its to be located in north west Christchurch (a few hundred metres west of Wairakei/Roydvale roundabout) on an aerial mast next to a 2 storey building. I'm guessing a couple of metres above roof height but the mast is high enough that it could be much higher if warranted.

[snowstormwatcher]

Best to have your temp/humidity sensor over grass 1.5m of the ground and inside a screen or radiation shield of some sort, this avoids radiated heat from surrounding buildings or concrete effecting readings.

Anemometer should be high enough to clear all surrounding Trees building etc.

[moylanr]

Thanks snowstormwatcher. What if we only have one sensor, and are interested in temperature and wind?

(I have a sinking feeling you could feel like or or but that is the current restriction being given to me...)

Maybe a couple of metres above roof height (there are no trees) and add some sort of screen to minimise/eliminate radiated heat from building room?

[NZstorm]

Unless the temperature sensor has the correct exposure its not worth recording temperature. Its actually a difficult parameter to measure accurately.

[Tornado Tim]

Its actually a difficult parameter to measure accurately.

I agree with that. Temperature readings are very subjective to where you site the the thermometer/weather station.

If you can, get the sensor exposed in the open so wind can blow over the sensor (in all directions), if this isn't available I would consider purchasing a FARS (Fan Aspirated Radiation Shield).

Never mount Thermometers across any object or body that can directly reflect heat back on the sensor (such as Concrete or any metallic object).

Of note: different sensors have better site placements:
Eg: Rainfall readings ideally should be taken at ground level (with no shadows to be cast on it)
Temp/Hum: 1.3-1.5 meters above grass away from nearby objects.
Wind: 10+ meters ideally (according to WMO) with no objects around it in a 360° angle.

[moylanr]

Thanks Steven & Tim.

Will see if we can compromise on wind and aim to get the best temperature readings. Our current temporary central city site probably suffers from reflected radiation (shown on second chart half way down: http://www.oriongroup.co.nz/load-manage ... board.aspx).

If you hover cursor over the line on the chart it shows the value - temperature has dropped a couple of degrees in the last half hour.

[TonyT]

Richard, if you are really serious about wanting valid data, you need to get the wind and temperature sensors at different heights. Thats where a station like the Davis Vantage as it over the all in one units, you can separate out the temp and wind sensors. It might be a small extra set up cost to start with, but the quality of the data you get back will be well worth it.

[moylanr]

Turns out the weather station was bought many moons ago when we needed something post earthquake as we'd lost the link to the Botanic Gardens temperature sensor. So we have this all in one unit that interfaces directly into our existing systems , which is at our central city site temporarily.

So we'll reinstate the Botanic Gardens temperature for a good central city reading and when we move to Wairakei Rd, we'll aim to use the new one for solar radiation. That will give us the best indication of cloud cover which is the key parameter we're currently missing and cant find elsewhere.

I'm guessing the best position on the aerial mast will be 2 or 3 m above surrounding buildings/trees, mounted stood off the north side of the mast to minimise shadow effect from the mast. (Realising this compromises wind readings but putting it on top of the mast isn't an option).

Thanks.