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Rain Gauge Install Height and Location

Talk about the weather
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Buford T. Justice
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Rain Gauge Install Height and Location

Post by Buford T. Justice »

I have a Fine Offset weather station. Yesterday, I received my Stratus rain gauge for use with CoCoRaHS.

I was going through the CoCoRaHS online training and they say to mount the rain gauge between 2-5 feet (0.6-1.5 meters). I have always had my FO rain gauge near the FO wind instruments. I would guess the FO rain gauge is perhaps around 25 feet (7.62 m) in the air.

Does it matter how high the rain gauge is installed? Should I buy a post to get the FO rain gauge closer to ground level? I have a lot of trees in my area so getting it out to a clearing is going to be difficult. Where it is now and its height keep it away from any obstructions.
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Re: Rain Gauge Install Height and Location

Post by steve »

The standard height for the rim of a rain gauge varies by country. In the UK it is 30cm above ground. In the US it is between 3 and 4 feet. The placement is a compromise; lower placement reduces loss due to wind which may occur at higher levels, but increases the chance of heavy rain splashing in off the ground, and of being buried by snow, where applicable.

The WMO recommend that a rain gauge be placed away from any nearby obstacle a distance of at least twice the height of the obstacle.
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Re: Rain Gauge Install Height and Location

Post by geoffp »

Maybe you could find some information that may help in the CWOP manual, url below:-

http://www.comptus.com/PDF/CWOP_Guide.pdf
Regards,

Geoff

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Buford T. Justice
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

Damn. I can't do two feet. I have dogs that like to mark their territory and items. I guess I will go 4-5 feet.
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Re: Rain Gauge Install Height and Location

Post by beteljuice »

Get smaller dogs :lol:
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

beteljuice wrote:Get smaller dogs :lol:
I am not a fan of those little yap-yapity, cat-sized breeds. A big dog is a good dog.
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

I decided to relocate all of my sensors. The picture with everything on the roof was before. I would say the rain and temperature sensors were about 14' in the air and the wind sensors were about 16' in the air.

I installed a longer mast into the tripod roof mount and installed just the wind sensors. I had to buy a telephone line coupler and 50' extra cable. Those sensors are now around 20' in the air. I noticed the wind vane doesn't turn in different directions as much as it did before.

I installed an 8' wooden post I painted white 3' into the ground surrounded by concrete. I then installed my weather station senors on to it. The rain gauge is 47.5" from the bottom of it to the ground. The temperature sensor is at 40". The Stratus rain gauge for use with CoCoRaHS is at 43.5".

We had a rather heavy rain storm this morning. The Stratus and the small rain gauge installed into the ground both reported 1.24" of rain. The rain sensor said 0.84". I made higher walls for it last night using a piece of cardboard wrapped in duck tape, but there is some spacing inside of it so I guess the rain dripped out of it.
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Re: Rain Gauge Install Height and Location

Post by beteljuice »

Not quite right, but much better :clap:

Once you can start comparing time of day / date figures you should quite surprised at the differences.
Especially wind and temperature.
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Re: Rain Gauge Install Height and Location

Post by Super-T »

You will get the temperature problems with the transmitter exposed to direct sun.
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

beteljuice wrote:Not quite right, but much better :clap:

Once you can start comparing time of day / date figures you should quite surprised at the differences.
Especially wind and temperature.
Not quite right? What am I missing or did I do something wrong?
Super-T wrote:You will get the temperature problems with the transmitter exposed to direct sun.
It's always been in the Sun occasionally in the different places it has been mounted. I have trees nearby that usually cast a shadow on it. I need a better shield though.
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Re: Rain Gauge Install Height and Location

Post by beteljuice »

Temp / humidity just below head height (and adequately radiation sheilded but ventilated).
Anemometer / wind vane - 30 feet above ground (but ridiculously far away from buildings and trees)
Hygrometer - 2 feet up, (to avoid splatter) in the open but wind shielded (good one that !)
One of the 'official' designs has them on a pedestal in the middle of a semi-circular cut out of a terrace the same height. - and here is a variation of an official 'pit' design:
Even though wind turbulence is important in reducing rain gauge accuracy, the use of windshields can generally be discounted. Their main aim is to reduce wind speed, turbulence and splash over the gauge and allow siting close to the ground, but in practice they are not easy to make locally and increase problems of interference by people and animals. Research has shown that differences in shielded and unshielded gauges are relatively small (2-8%)....

...
The UK Met Office and US Weather Bureau recommend that rain gauges in exposed positions be located within a circular turf wall to negate the effects of wind turbulence. Figure 4.3 illustrates the construction of the protective wall which should be kept in a good, clean condition. Note that the rain gauge orifice is level with the top of the wall. It should be stated that in many circumstances, recourse to such a structure will be very difficult.
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Buford T. Justice
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

Doesn't sound entirely right beteljuice. It seems like those links I posted earlier say 2-5' from the top is acceptable for rain gauges (2' if out in the open to help get rid of wind turbulence and up to 5' in developed areas as open area wind turbulence is less of an issue. 3-5' seems to be the norm for temperature sensors above grassed ground.

I know the wind is suppose to be at least 30', but I read something on NOAA that down to 20' is acceptable. Even at 20', my wind vane is not dancing around as much as it was earlier at less of a height. I am actually pretty close to 22' at the moment. I will probably get a longer mast soon, but getting hundreds of feet away from nearby buildings and trees is impossible.

I just went outside and measured from the tops of the gauges...

57" (4' 9") = Stratus Rain Gauge
51" (4' 3") = FO Rain Gauge
46" (3' 10") = Temperature Sensor
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Buford T. Justice
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Re: Rain Gauge Install Height and Location

Post by Buford T. Justice »

Another good article about this subject:

http://www.rmets.org/sites/default/file ... -guide.pdf
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Re: Rain Gauge Install Height and Location

Post by sfws »

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Last edited by sfws on Mon 03 Aug 2015 1:36 pm, edited 1 time in total.
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