# The Naked Scientists Forum

### Author Topic: How does a rain gauge work?  (Read 22211 times)

#### chris

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##### How does a rain gauge work?
« on: 21/04/2012 08:20:53 »
Rain gauges record rainfall. But they come in a range of shapes and sizes. So how is the volume of water in the gauge standardised, and how does this equate to the actual amount of water that falls?

#### chris

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##### Re: How does a rain gauge work?
« Reply #1 on: 25/04/2012 08:20:22 »
The reporting standard for rainfall is in millimetres; this may sound counter-intuitive, because what we're actually interested in is the volume or amount of water surely?

Well that's certainly true, but recording rainfall as a depth of water simplifies the process because it removes surface area from the equation. So if two millimetres of rain have fallen, then your pond, swimming pool, bird-bath will all increase in depth by two millimetres. And if you want to calculate the actual volume of water you still can by multiplying the surface area of the body of water by the depth increase. But don't be caught out by your water-butt. These are collecting the rainfall from a large roof-area, so their apparent depth increase will be much greater!

Water butts are good for finding micrometeorites though, which land on the roof and are washed off during a rainstorm! The iron-rich ones can be recovered by dunking a magnet into the sludge at the bottom of the tank...

#### Geezer

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##### Re: How does a rain gauge work?
« Reply #2 on: 25/04/2012 23:13:32 »
Is it OK if we use inches, or does that muck everything up?

#### Don_1

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##### Re: How does a rain gauge work?
« Reply #3 on: 26/04/2012 09:19:10 »
Is it OK if we use inches, or does that muck everything up?

Could cause a bit of confusion if you don't make it clear you are using inches. Forecasting 30mm of rainfall would cause havoc if you accidentally replaced the (mm) with ("). You'd have everyone running for the hills.

Here in the UK you can be beheaded for using feet, inches, pounds, ounces, pints and gallons. They are evil and outlawed, so sayeth the EU Grandees.

#### Mazurka

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##### Re: How does a rain gauge work?
« Reply #4 on: 26/04/2012 16:09:54 »
Unles I have the wrong end of the stick,  Strictly speaking rainfall is measured in litres per square metre, however, it is conventionaly expressed as a linear measurement per unti area.  Make that unit area 1 and it all makes sense (even if this explanation does not).  Thankfully as metric is nice and straightforward lm-2 equates directly to mm.

Why any civilised nation would cling to arbitary units is beyond me.

#### Geezer

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##### Re: How does a rain gauge work?
« Reply #5 on: 26/04/2012 18:20:28 »

Why any civilised nation would cling to arbitary units is beyond me.

Who said we are civilised, and the meter is just as arbitrary as the foot :)

#### Mazurka

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##### Re: How does a rain gauge work?
« Reply #6 on: 27/04/2012 16:22:08 »

Why any civilised nation would cling to arbitary units is beyond me.

Who said we are civilised, and the meter is just as arbitrary as the foot :)
Ahh, it was a sweeping generalisation not necesarily aimed at people with a heritage such as yours  :P

and fair comment - the distance that light travels in 1/299792458 of a second is, on reflection, pretty arbitary.

#### Geezer

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##### Re: How does a rain gauge work?
« Reply #7 on: 28/04/2012 00:41:47 »

the distance that light travels in 1/299792458 of a second is, on reflection, pretty arbitrary.

It's a shame they didn't pick 1/300000000 a second. Then it would not have been arbitrary. Oh! Hold on a minute...
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I just got a call from an extremely irate person who says that the decimal system is prejudiced against people who do not happen to have ten fingers (which is not all that unusual).

#### Mazurka

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##### Re: How does a rain gauge work?
« Reply #8 on: 30/04/2012 10:36:28 »
A quick straw poll of friends and collegaues has turned up the surprise result that more people have 10 fingers than have 9, 12, 14 or 16 put together!  The same poll came up with the shock result that no one knows how many chains make a furlong; no ones feet are exactly 12 inches long and no one knows why there are 112 (imperial) pounds in an (imperial) hundredweight.

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##### Re: How does a rain gauge work?
« Reply #8 on: 30/04/2012 10:36:28 »