Finding out height above Sea Level

[rosecottage]

I have had a Heavy Weather - Lacrosse 3600 for the last couple of years. Having just broken the cble for the anemometer I was told tha new cable is not an option because the Heavy Weather station is a 'consumer item' and no spares are available. On checking in here, I have decided to buy a Davis VP2 which should be here tomorrow. However I have a question abut pressure.

This is directed at UK people really, I know that pressure varies according to height above sea level. How do I find out my location height?

Thoughts?

Thanks

David
in cold and wet Tuddenham St Martin, Suffolk

[Clanger]

Hi,
 I use http://www.earthtools.org/
Or a good old paper map 

[rosecottage]

Google Earth was the way to go. I found Tuddenham St. Martin and hovered the cursor over my house and - bingo - 31m!

Interestingly though, our cottage was completely refurbished 6 years ago and extended - the image on Google Earth is of the previous form which means its at least 6 years out of date!

Thanks for your comments.

David

[jwwd]

Hi

Im not from UK but Denmark.

I called the technical department in our municipality - and they could tell me the excact elevation, where our house is build. (75,15 meters above sea)

Best regards,

Henrik

[Kojack]

Google Earth was the way to go. I found Tuddenham St. Martin and hovered the cursor over my house and - bingo - 31m!

David

You posted whilst I was checking Google Earth 
Not knowing you house location, I centred and found:
52^o 05" 28.23'N   1^o 11"  51.4' E    Elevation24m

When I set mine up on the original WS I had at the time, I found that there was a conflict between Google Earth and the good old OS map. (nearly 6m difference)
I certainly trust the OS more FWIW

[rosecottage]

We are half way up the hill below the church. Interesting if there is a difference. Mind you will 6m make mach difference to the pressure reporting? I don't know the adjustment calculation

[aviva]

We are half way up the hill below the church. Interesting if there is a difference. Mind you will 6m make mach difference to the pressure reporting? I don't know the adjustment calculation

At lower altitudes the atmospheric pressure changes approximately 0.125 hPa/m.
So the 6m amounts to a difference of approx. 0.75 hPa on your barometer reading.

In an aircraft an error of 6m of the altimeter makes the difference of landing on or under the runway  .

[SandhurstWX]

Atmospheric pressure changes by approximatly 1hPa (1mbar) for every 10 meters of altitude change (decrease for increase in altitude and visa-versa). So for example, if the barometric pressure at sea level was 1000hPa, then at an altitude of 10 meters, the pressure would be 999hPa.

A simplified conversion, which should only be used for stations at elevations below a few hundred meters, is:

Station Pressure = Sea Level Pressure – (elevation/9.2)

or re-arranged

Sea Level Pressure = Station Presure + (elevation/9.2)

(Note: pressure in hPa (or mbar) & elevation in meters)

The correction factor of 9.2 in the above formula is very nearly the change in elevation (vertically) that will
correspond to a 1 millibar change in pressure.

[aviva]

Atmospheric pressure changes by approximatly 1hPa (1mbar) for every 10 meters of altitude change (decrease for increase in altitude and visa-versa). So for example, if the barometric pressure at sea level was 1000hPa, then at an altitude of 10 meters, the pressure would be 999hPa.

I kindly beg to differ with this oversimplistic approach  .
It's been awhile, but when I was invoved in aircraft instruments the following was the "rule of thumb" for altimeters (=barometers): "Air pressure decreases with an increase of altitude about one hPa (0.03 inches of mercury) per 27 feet (8.23 m) near sea level (@ 288°K = 15°C)". This translates to 0.1215 hPa/m (which I rounded to 0.125 as a more practical figure).

My station is situated 139m above sealevel, so the difference between the two calculations would add up to 3hPa, which I think is quite substantial.

[SandhurstWX]

I did say that it was an approximation, and the information was obtained from the National Physical Laboratory (NPL) website at www.npl.co.uk/pressure/pressure.html (in the second paragraph under NOTES).

I do have some fairly complicated formulas for calculating Station Pressure from Sea Level Pressure & the other way around, and they all agree to within less than 0.5hPa of each other (see screenshot).

See also barometric.pdf below.

[TokKiwi]

It is 6.167HPa for the first 50m - it is not quite linear as there are temperature affects as well as elevation... to make up the mass of air in the height (or volume equivalent since we cannot visualise a slim column of air with no width or depth but only helight...   I have a polynomial equation at work but it has been corrected and not sent home.  Sorry - I will post next week with the correct formula.

[aviva]

It is 6.167HPa for the first 50m

6.167hPa/50m= 0.12334 hPa/m  .

I've not yet found my (old) textbooks on altimeter calibration but on the web this looks closely what I remember.

Other than searching I performed a simple experiment.
My Davis VP2 shows presently 1019.4 hPa compensated for 139m altitude. Setting my station altitude to 0m shows the pressure as 1002.5. Difference 16.9hPa. Gradient used by Davis: 16.9/139= 0.1216 hPa/m. Not very scientific, but the results are quite close to what I thought it would be...