Radiation Shield accuracy

[RayProudfoot]

Hey Ray,

Just took a look at the pictures of your temp/sensor placement. I guess I didn't realize just how close it is to that dark fencing. I would speculate that a day of good sunshine on that fence might just add a few degrees to your temps. If it were me, I would seriously consider getting your sensor farther out into the yard...if that is even an option for you. Some folks simply do not like the idea of sinking a post in a more open part of their yard.

Hi Brian,
I thought long and hard before choosing that spot. I chose it because that point is furthest from the house and gets the most sun. If I brought it closer to the house it would be close to the stone patio and although it would be well away from any fencing the patio would have a worse effect I think. Another compromise might be to move it towards me on that right hand border so it's away from the corner but that right-hand fence gets the sun all afternoon whereas the taller one doesn't get any in the afternoon (on my side) when the highest temperatures occur.

As far as the daytime fan is concerned, given your current setup...a tough call. On one hand a fan will certainly keep the sensor aspirated and remove any build up of "heat" inside the shield, particularly on calm wind days. On the other hand a fan will pull in more air from around the sensor which could potentially be warmer due to that fence

That was my main concern. That the air immediately around the ISS would be warmed by the enclosed space so using a fan would make no difference at all. Unfortunately I have a small garden which is 80% lawn surrounded on 3 sides by fencing. But if I move it towards the camera position along that right-hand border I think that would make it more open and even though that fence gets the sun all afternoon it's not as high and any warmed air might not extend to the sensor. How far from a fence do you think it needs to be?

In the end all you can do is strike the best balance between your space limitations, sensor exposure, and minimizing sources of artificial heating. Not always an easy task as you can see.
-Brian

It's proving extremely difficult Brian as you can see. I will take some photos over the weekend and they may give you a better idea of my garden layout. I also placed it there as it has line of sight to the console aerial but the anemometer transmitter on the front of the house sends a signal through a brick wall and an internal one without problem so I can probably move it elsewhere without compromising the signal. I just don't want it in the lawn because it would be liable to being knocked as well as being a pain to mow around.

I have a Oregon Scientific thermometer sensor which I can place in various parts of the garden and come the spring I will use that to determine which places might be better. It's all about compromises in urban areas as you say.

[RayProudfoot]

Ray,
A hobby isn't any good unless you can throw money at it so maybe you should get the fan. Actually, you will never know if it actually helps unless you buy a complete 6153 and mount it side by side and compare the readings. Whatever you decide to do it looks as if your grounds are in good enough condition to stand a couple of months inattention. Would you be willing to come over and spruce mine up?!

The more I think about it, I think a fan would pick up stagnant air from the fenced in corner and adversely affect your readings, both cold and hot.

JMO

George

LOL! How right you are George! But I don't want to waste it by having the ISS in a bad spot. It will be fun trying to extracate that Metapost! You should do what I do and employ a gardener. He comes every fortnight and it makes life so much easier.

That's two of you who have suggested that spot could be a hotspot so come the spring I think I will have to move the ISS. A few beers for my mate sounds like a good deal. I'll give him lots of encouragement!

[RayProudfoot]

Sun on a wet / frosty fence will also increase the (local) humidity

The least of my problems perhaps but I take your point.

[RayProudfoot]

I've given the ISS location a lot of thought over the last 24 hours. When I selected the location it wasn't obvious to me that temperatures would be significantly higher (2-3C) than nearby official stations on hot sunny days. It's now obvious to me that they are and I see no point in buying the daytime FARS until I have the ISS in a better position.

This shot taken from a bedroom shows half of my small garden and the current and 3 possible positions but in all honesty I don't think A,B or C would change things very much.

Ray_Garden1.jpg

However, in one of those Eureka moments I thought about creating a small circular flower bed in the lawn that would be just large enough to prevent acccidental contact when mowing the lawn if the ISS was located in the centre.

Ray_Garden2.jpg

This seems to offer the best solution but I'd welcome comments on whether the path and house are sufficiently far away. I hope they are as I can't see any other solution.

[beteljuice]

The all important compass bearing !

How about in the soil, house side of the bench ?

Immediate surrounding are predominately shade, the fence will be 'hot' on the other side, and any 'left over' fence effect will be masked by the conifer and shrub.

In open air the radiation from the house wall and the few slabs should be tolerable.

[RayProudfoot]

Cheers beteljuice. The camera is pointing west in that second shot. Although you can't see it there is a house on the other side of that fence that is due south of the location you suggest.

On my side that's a unheated garage where the brickwork is just visible so that shouldn't affect the temperature. Interesting point you make that the ISS being close to the side of the fence that receives no sunshine is not a problem.

I'd previous only considered positoning the ISS where it will get as much sunshine as possible to minimise battery use but station accuracy is obviously more important.

Here's another shot of the area you suggest. The camera is pointing due south and you can see how close my neighbour's house is. That's a 6ft+ fence and the rain guage would be within a couple of feet of it. I hope that doesn't put the kybosh on your suggestion.

Once spring arrives and the garden is getting good amounts of sunshine I'll take some temperature readings around the garden including the centre of the lawn for reference and see how they compare to the current location prior to removing the Metpost.

Ray_Garden3.jpg

[beteljuice]

There may be a rain 'shadow' problem with wind driven rain from the South, but I suspect that would be a minority event, even then aerodynamics suggest that rain would actually be pulled 'down' over the top of the fence.

I think that is going to be your best comprimise location, and ... won't spoil SHMBO view from the bench

[RayProudfoot]

There may be a rain 'shadow' problem with wind driven rain from the South, but I suspect that would be a minority event, even then aerodynamics suggest that rain would actually be pulled 'down' over the top of the fence.

I think that is going to be your best comprimise location, and ... won't spoil SHMBO view from the bench

When it rains here more often than not the wind comes from the south. If it's even a moderate breeze it could affect what goes in the gauge. I'd feel happier with the ISS further away from that fence.

There isn't a SWMBO so I can locate it where I like providing it doesn't look too out of place and won't get knocked. I can't do anything until spring anyway so I still have time to consider all suggestions.

Funny, it's dark and overcast but Manchester Airport is 1C warmer than my station. Shows that even when there's no sun you will still get temperature differences. Perhaps my enclosed sheltered garden really is 2-3C warmer than an open field. How often do you see Heathrow as the warmest place in the UK on a hot day? All that concrete but the station will be a Met Office certified one! Urban areas will also be warmer than the countryside.

[adam5]

Hi Ray,

Boy, that is a tough call...and I tend to agree with you that it may not make a whole lot of difference no matter what. But given everything, I might seriously consider getting the ISS more into the center part of the yard. Will you get some "heating" from the house/walkway? Maybe, but given your choices, that may well be the best compromise location. But also keep in mind that no matter what...I still think a daytime fan still might help shave off a degree or so in full sun by eliminating any heat "buildup" in the radiation shield itself. But you have a point, you might want to try a new location first.

But to be honest...these are just "educated guesses" if you will. I think someone already made the comment...the only way to really know would be to devise some sort of experimentation with a couple identical thermometers and enclosures placed strategically around the yard...and just see what readings you get on a full sun day.

Just my 2 cents,

-Brian

[RayProudfoot]

Hi Brian,

Thanks for your views. Your educated guesses - coming from a professional - carry significant weight. My garden is a meteorological nightmare! Oh to have something a bit bigger.

I will do as you suggest and take temperature readings from various parts of my garden to establish which are hot spots and which aren't. Once that is established then I'm sure a daytime fan will close the gap to a reasonable level. Thereafter any temperature differences between my station and that at Manchester Airport will be down to local conditions and not erroneous sensor siting.

Going back to a reply by beteljuice he remarked that a daytime fan could cut temps by 2C. If that is a reasonable assumption then that would place my readings very close to Manchester Airport's without moving my station. I will take some readings close to the shorter fence to see how much heat it's radiating. I might be surprised.

Many thanks.

[adam5]

Not a problem, good luck with that sensor.

My garden is a meteorological nightmare! Oh to have something a bit bigger.

I know what you mean. While I do not have the space issue for siting my temp/hum sensor, I am surrounded by 70+ foot maples. As such, getting a good siting for the rain gage was tricky (and still not perfect) and my wind speeds are substantially reduced compared to the open areas, as you might guess. That is one of the reasons I started using Cumulus...since it does a great job in averaging wind speeds and especially the weighted direction averaging. That goes a long way in reducing or eliminating spurious wind directions brought on by the trees...and thereby plucking out the true wind.

As a side note...Steve, any news on the 2-minute average speed and direction possibilities for Cumulus?

Anyway, as you can see, not many sites are completely perfect for weather station siting, unless of course you live in a wide open area with lots of land. Just remember, you bought the weather station for the fun of the hobby and to measure conditions where you live, and not to simply mirror the weather conditions reported at the local airport or Met office. Just do the best you can at siting the instruments, and have fun.

-Brian

[RayProudfoot]

Not a problem, good luck with that sensor.
I know what you mean. While I do not have the space issue for siting my temp/hum sensor, I am surrounded by 70+ foot maples. As such, getting a good siting for the rain gage was tricky (and still not perfect) and my wind speeds are substantially reduced compared to the open areas, as you might guess. That is one of the reasons I started using Cumulus...since it does a great job in averaging wind speeds and especially the weighted direction averaging. That goes a long way in reducing or eliminating spurious wind directions brought on by the trees...and thereby plucking out the true wind.

Fortunately I don't have any large trees near my house so my wind readings won't be too bad although again, my max gust will nearly always be less than an official site but isn't it funny that I don't see that as a problem? It's good though that you can adjust Cumulus to compensate for your sheltered location.

Anyway, as you can see, not many sites are completely perfect for weather station siting, unless of course you live in a wide open area with lots of land. Just remember, you bought the weather station for the fun of the hobby and to measure conditions where you live, and not to simply mirror the weather conditions reported at the local airport or Met office. Just do the best you can at siting the instruments, and have fun.
-Brian

Good advice Brian and I wish I wasn't such a stickler for accuracy because it can drive you bonkers. Interesting today as the moderate westerly wind has levelled out the temp differences. A bit like a huge FARS over the area! My next step is to get a website up and running. WU is good but I want more than it can give me. And yes, having a weather station has enhanced my interest in the weather. Never get the same weather two days running over here.

[RayProudfoot]

Hi chaps,

Me again. I know I've posted some photos of my station in my back garden but they don't really show the garden in relation to surrounding houses. Then I remembered Microsoft Bing Maps and the 3D option.

Have a look at this picture and maybe you'll agree with me that I will get higher temperatures on fairly calm days compared to more open sites because the whole garden is so sheltered. Although I still intend to take temperatures in different parts of the garden when it gets some decent sunshine I'm not convinced they will be that different.

X marks the spot where my ISS is located. South is directly behind the camera position.

Ray_House.jpg

[RCE]

Looking at that you aerial shot probably have the best compromise location, building a small Stevenson Screen would be worth while, and fan aspirating it.

The shot near the house shows a gas boiler flue in your neighbours house that under certain conditions could influence an instrument located near by.

[RayProudfoot]

Looking at that you aerial shot probably have the best compromise location, building a small Stevenson Screen would be worth while, and fan aspirating it.

The shot near the house shows a gas boiler flue in your neighbours house that under certain conditions could influence an instrument located near by.

The Davis ISS can't be installed in a Stevenson Screen. This thread is all about shield accuracy and I'm happy with the design of the Davis. I am considering a daytime fan but my only reservations are that the whole garden and surrounding area might be a hot spot and not just the location of my station. Hence why I need to take temperature readings in several parts of the garden to establish if a daytime fan is necessary.

Good point about my neighbours flue and one reason I'm reluctant to relocate the ISS to that end of the garden.