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Radiation Shield accuracy

Discussion specific to Davis weather stations
RayProudfoot
Posts: 2404
Joined: Wed May 06, 2009 6:29 pm
Weather Station: Davis VP2 with Daytime FARS
Operating System: Windows XP SP3
Location: Cheadle Hulme, Cheshire, England
Contact:

Re: Radiation Shield accuracy

Postby RayProudfoot » Fri Jun 25, 2010 10:24 pm

Hi Pete,

It's possible you have already ordered your daytime FARS unit and if so I hope it helps with your station accuracy.

OTOH, you might be recording accurate temperatures for your garden. I emphasise the last bit because of earlier discussions on this very thread about variations of temperature in a short distance not meaning any of them are wrong.

To clarify, Mark in Wilmslow, 4 miles south of me and 2-3 miles south of Manchester Airport consistently records higher maxima than both the airport and my station. But his station is always in the shade. How is this possible? It's probably just a sheltered garden. Just like yours is becoming.

That doesn't make your temperatures wrong and it's quite possible that adding a daytime FARS won't make much difference if the whole garden is warmed by its sheltered location. I had a similar thought thinking my garden - surrounded on three sides by houses - was in a local hot spot. But by raising the ISS by about 2 feet to around 6ft has made my readings more accurate. Comparing my maxima today to that of my reference station shows mine as 24.7C and his as 24.4C and his is still on his roof! Manchester Airport recorded a high of 24C but they only record to whole numbers. So with little wind today I'm still within 1C of an official Met Office station and with no daytime FARS.

I suppose I could add one before the VAT rise in January but it would only marginally improve my accuracy for an outlay of £150. Ouch!

Looking at your station photos I would say you're in the same position as Mark in Wilmslow in that your sheltered garden is warming the air but that your ISS is accurately recording the ambient temperature.

Tomorrow and Sunday will be interesting as they look to be the year's warmest days. Keep us posted on how your readings compare to surrounding stations. BTW, did you contact the owner of the nearby station who's readings were close to yours?
Cheers,
Ray, Cheshire.

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Pete B
Posts: 28
Joined: Mon Mar 08, 2010 9:59 am
Weather Station: Davis VP2 Wireless
Operating System: Windows XP Home SP3

Re: Radiation Shield accuracy

Postby Pete B » Wed Jun 30, 2010 10:59 pm

Hi Ray

I haven't ordered the FARS unit yet but plan to do so very soon.

I have been doing a bit of research looking through postings on the various groups I mentioned and it is quite likely that a FARS will add that bit more accuracy to my still, hot day max temp readings. As we've discussed before, we all agree that the temperatures measured by our stations are essentially those of our localities and so may not be exactly the same as reasonably local 'official' stations without the very local siting problems we all have. Because of the nature of my garden 'variable shielding', I don't think raising the ISS to 2m, the highest point of the official range will make much difference as the rapidly growing boundary hedge heights are well above that now.

I haven't made contact yet with the conventional Stevenson Screen holder, mainly because I'm not sure about doing it 'cold' on the basis of seeing the station equipment (anemometers on the roof etc) rather than approaching officially by purchasing the Climatological Observers Link directory, probably the 'proper' way to do it as there is no other open electronic link or otherwise.

Regarding my weekend readings, something I was awaiting with interest, my hottest day still remains as Sun May 23rd!. On Sat pm, my station very briefly recorded one reading via the datalogger (10 min interval) of 30.1C, all others were below 30C. That is well below the period of over 1hr on the May date where readings higher than 30C was continually logged.

My station records are shown here so the max temps for Sat, Sun & Mon can be seen as the brief 30.1C, 28.1C & 27.9C respectively. Subsequent days have been that bit cooler, mainly due to more cloud. My closest what I would call well set up station to me is here and his max temps for the same days were 27.2C, 27.2C & 26.1C respectively but it's a difficult comparison as he is somewhat higher than me up the side of the Malvern Hills and there will be a difference due to that. That station also has a lot of greenery around it but the ISS is on a pole above his roof so well above the ground.

gemini06720
Posts: 1700
Joined: Mon Aug 10, 2009 10:16 pm
Weather Station: No weather station
Operating System: No operating system
Location: World...

Re: Radiation Shield accuracy

Postby gemini06720 » Thu Jul 01, 2010 4:09 am

Here are some ISS location information that might be useful to everyone:

    Wind Speed and Direction

    Wind sensors should be located over open level terrain. The EPA
    recommends the wind sensor be a distance of at least ten times
    the height of nearby buildings, trees, or other obstructions.

    Standard measurement heights:
    - 3.0 m ± 0.1 m recommended (AASC)
    - 2.0 m ± 0.1 m, 10.0 m ± 0.5 m optional (AASC)
    - 10.0 m (WMO and EPA)

    Temperature and Relative Humidity

    The sensor should be housed in a ventilated radiation shield. The
    EPA recommends the sensor be no closer than four times an
    obstruction’s height, at least 30 m from large paved areas, and
    located in an open level area that’s at least 9 m in diameter. The
    open areas should be covered by short grass, or where grass does
    not grow, the natural earth.

    Avoid these:
    • large industrial heat sources
    • rooftops
    • steep slopes
    • sheltered hollows
    • high vegetation
    • shaded areas
    • swamps
    • areas where snow drifts occur
    • low places holding standing water after rains

    Standard measurement heights:
    - 1.5 m ± 1.0 m (AASC)
    - 1.25 to 2.0 m (WMO)
    - 2.0 m temperature (EPA)
    - 2.0 m and 10.0 m for temperature difference (EPA)

    Precipitation

    The AASC and EPA suggest tipping buckets be no closer than
    four times the height of an obstruction. The orifice of the gage
    must be in a horizontal plane, open to the sky, and above the level
    of in-splashing and snow accumulation. Typically, tipping buckets
    are sited on level ground covered with short grass or gravel. Wind
    shields, such as those used by the National Weather Service, are
    recommended for open areas.

    Standard measurement heights:
    - 1.0 m ± 1.0 cm (AASC)
    - 30.0 cm minimum (WMO, EPA)

    Definitions:

    • EPA = Environmental Protection Agency
    • AASC = American Association of State Climatologists
    • WMO = World Meteorological Organization

The information was copied from the Campbell Scientific, Inc. 'Weather Station Siting and Installation Tools' brochure.

And, please, remember, this whole weather data gathering is just a hobby... :roll:

RayProudfoot
Posts: 2404
Joined: Wed May 06, 2009 6:29 pm
Weather Station: Davis VP2 with Daytime FARS
Operating System: Windows XP SP3
Location: Cheadle Hulme, Cheshire, England
Contact:

Re: Radiation Shield accuracy

Postby RayProudfoot » Sat Jul 03, 2010 12:44 pm

Pete B wrote:Hi Ray

I haven't ordered the FARS unit yet but plan to do so very soon.


I hope it helps give you more accuracy with your temps. It's a sizeable investment.

I have been doing a bit of research looking through postings on the various groups I mentioned and it is quite likely that a FARS will add that bit more accuracy to my still, hot day max temp readings. As we've discussed before, we all agree that the temperatures measured by our stations are essentially those of our localities and so may not be exactly the same as reasonably local 'official' stations without the very local siting problems we all have. Because of the nature of my garden 'variable shielding', I don't think raising the ISS to 2m, the highest point of the official range will make much difference as the rapidly growing boundary hedge heights are well above that now.


Our gardens are quite different. Your's appears quite closed in so temperatures are bound to build up. I suppose the chainsaw option is a non-starter? :mrgreen: Above 6 feet mine is still reasonably open despite being surrounded on 3 sides by houses.

I haven't made contact yet with the conventional Stevenson Screen holder, mainly because I'm not sure about doing it 'cold' on the basis of seeing the station equipment (anemometers on the roof etc) rather than approaching officially by purchasing the Climatological Observers Link directory, probably the 'proper' way to do it as there is no other open electronic link or otherwise.


I would just go for it. You have a common interest. I'm sure if you just knocked on his door he would enjoy sharing the hobby with a fellow enthusiast.

Regarding my weekend readings, something I was awaiting with interest, my hottest day still remains as Sun May 23rd!. On Sat pm, my station very briefly recorded one reading via the datalogger (10 min interval) of 30.1C, all others were below 30C. That is well below the period of over 1hr on the May date where readings higher than 30C was continually logged.


Coincidentally my hottest day remains May 22nd - 28.6C. And that was after the ISS was raised. Your high of 30.1C is feasible given you're further south but significantly is 3C warmer than your reference stations 2010 high. That was the sort of difference I was getting when my station was in its former position compared to Manchester Airport. Its high on 22 May was 27C but they only record to whole C number so that could be 27.4. Mine is higher but I still feel it's accurate for my environment.

Anyway, once the daytime FARS is fitted it will be interesting to see how your temps compare to your ref station. But if his ISS is above his roof I wouldn't lose any sleep where there are significant differences. There's no way you're going to get similar temps except on cloudy, windy days.
Cheers,
Ray, Cheshire.

Image

djwiktor
Posts: 1
Joined: Wed Aug 23, 2017 9:17 am
Weather Station: Davis VP2
Operating System: Win 8

Re: Radiation Shield accuracy

Postby djwiktor » Wed Aug 23, 2017 9:23 am

Hi guys, sorry t o write to quite an old topic, but I would like to give to my station a new sensor extra in a shield and would like to pinpoint a kind of a new on market shield called MeteoShield from Barani company. I have ordered it several weeks ago and did a lot of tests in low wind and high sun conditions, where it shows significant reduction of the error in ambient temperature measurement compared to Davis stations VP2.

Those findings lead me out to let you know, that there seems to be a good and not so expensive solution, if anybody needs to accurately measure the temperature of air. As based on my tests, and also on results found on their websites here: https://www.allmeteo.com/radiation-shield-comparisons/
and here https://www.allmeteo.com/maximum-radiat ... eld-error/ the shield looks just fine :clap: hope to see more positive results later this year.

User avatar
yv1hx
Posts: 221
Joined: Mon Apr 05, 2010 10:40 pm
Weather Station: WX-200 / WS-2310
Operating System: Win XP Professional
Location: Cabimas, Zulia, Venezuela
Contact:

Re: Radiation Shield accuracy

Postby yv1hx » Thu Aug 24, 2017 3:38 am

djwiktor wrote:Hi guys, sorry t o write to quite an old topic, but I would like to give to my station a new sensor extra in a shield and would like to pinpoint a kind of a new on market shield called MeteoShield from Barani company. I have ordered it several weeks ago and did a lot of tests in low wind and high sun conditions, where it shows significant reduction of the error in ambient temperature measurement compared to Davis stations VP2.

Those findings lead me out to let you know, that there seems to be a good and not so expensive solution, if anybody needs to accurately measure the temperature of air. As based on my tests, and also on results found on their websites here: https://www.allmeteo.com/radiation-shield-comparisons/
and here https://www.allmeteo.com/maximum-radiat ... eld-error/ the shield looks just fine :clap: hope to see more positive results later this year.


Very interesting, Thanks for the update, I will look closer the results for sure.
Marco-Luis
YV1HX
Cabimas, Zulia, Venezuela
http://www.twitter.com/meteoven


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