Sandaysoft

Been looking into this myself as the air temperature at 4 or 5 ft above ground is a fair bit higher than the ground temperature. There have been several days in the last fortnight when the ground has been freezing hard but air thermometers have shown a couple of degrees above freezing. So far the only thing I've found has been indoor/outdoor digital thermometers or very expensive temperature probes. Extending the cable to the external probe could be a problem if it uses a thermocouple as any change in metal will cause errors. I doubt thermistors would be accurate enough. If the measuring electronics could be put outdoors it might be possible to use a thermocouple type.

I'd be very interested in any other thoughts on this

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Gina

Sorry, no banner - weather station out of action. Hoping to be up and running with a new home-made one soon.

Maplin do an indoor/outdoor digital thermometer http://www.maplin.co.uk/Module.aspx?ModuleNo=34932 It just might be possible to get inside this and bring out digital data to interface with a computer. They also do other similar thermometers.

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Gina

Sorry, no banner - weather station out of action. Hoping to be up and running with a new home-made one soon.

This brings me to a point I have been discussing with Dave -Laindon Weather. Many of us set up our weather stations on poles or rooves - all of different heights. Shouldn't we try to get some uniformity with our sensors so that the data recorded is comparable.The met. Office suggests a height of 1.25 Metres above ground level (approx. 4 feet) for temperature sensors.I haven't worked out if height above sea level is another factor to take into account although I think it probably is.Hands up if your temperature sensor is 4 feet above ground level & also if you live at the top of Mount Everest! This however brings problems of numerous wires going from different parts of the weather station to different locations in the garden.

If this is in the wrong place - apologies.

Cheers,

Chris

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http://www.burnhamthorpeweather.co.uk

My Danish Met. Office recommends 2 metres above ground level for temperature and humidity sensors, and 1.5 metres for rain sensors (and 10 metres for wind instruments).
So much for 'standards'

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Ib http://www.ibtest.dk/vejr/

Oddly, UK MetO height standard is for the enclosure (expecting a big wooden box and a stick thermometer), so you will see variations in 'standard' height.

Again - the standards were brought in as windchill was beginning to be appreciated, and so was equal to average head height.

.... but, we've all been on a better diet since then ... and so it goes on

Temp sensor should be 1.5 => 1.7m above grass. (Sea Level is not a consideration unless you are floating on it)

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......................Imagine, what you will KNOW tomorrow !

Mine is inline with Met Office Guidelines (Thanks to Beteljuice) at 1.5m above Ground Level.
Anno is around 10m above Ground Level.
Rain Bucket is on Flat Surface around 5m above Ground Level (Not recommended but due to Location and Wiring).

I think I did read somewhere, that When the air is 2.8C the Ground is 0.0C. So, you could in theory use a formula based script where, when Temp is (Whatever) subtract 2.8 and output is Ground Temp (Whatever Temp is -2.8C) - So in short -- <#temp> - 2.8 = <#groundtemp>

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Jason Duncombe
La-Crosse WS2300 (Wired & Serial) - Cumulus V1.9.3
Check out the Weather Blog

An example of a PHP Solution:

Ground Temperature: <?php $sum_total=$temp-2.8; print(sum_total); print ($tempunit); ?>

An example of a JavaScript Solution:

Will be available very soon

Enjoy

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Jason Duncombe
La-Crosse WS2300 (Wired & Serial) - Cumulus V1.9.3
Check out the Weather Blog

Warning - Danger Will Robinson !

That is a very rough approximation for a gauge at 'standard' height, above grass, and clear night temperatures

Any and every site will be different, and will be affected by cloud cover.

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......................Imagine, what you will KNOW tomorrow !

Ah yes -- Thank you Beteljuice for the 'Heads Up'

As Beteljuice has said, The -2.8C Approximation & My Php Script is 'Very Rough' and depends on a number of Variables - Clear Night, Temperature Sensor Height and Site.

Hopefully through this MAYBE we can come up with SOMETHING but the real answer is a Purpose Built Device.

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Jason Duncombe
La-Crosse WS2300 (Wired & Serial) - Cumulus V1.9.3
Check out the Weather Blog

It is a VERY complicated subject, all to do with thermal dynamics, boundary layers etc.etc.

.. and the rules change for eg. lying snow (like now) and even more devious for permafrost !

However, under 'normal' cold / frost a good general explanation (and pointing the difference reverses in daylight) is here: http://www.bbc.co.uk/weather/features/u ... rost.shtml

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......................Imagine, what you will KNOW tomorrow !

I wouldn't worry about the differences...

You do the best you can do with the equipment and sitting you have available.

It is likely more important that you maintain the same configuration and location so that you have good relative data from day to day, month to month over the seasons that you can compare like type settings when the year rolls around.

Many "Official" sites are not what one would consider perfect sitting locations (like over concrete for example) but they are the same as they have been for years and are the record of that area.

You might find that the accuracy of your instrument isn't within the difference anyway.

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Kevin

All you need is Time, Aptitude and Desire ... and you can build just about anything...
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