Solid State Rain Gauge

Sal Ammoniac

There was a thread in this forum a few months ago concerning solid state anemometers, and since I'm in the early stages of designing a Propeller-based weather station/data logger, I thought that it'd be cool to also implement a solid-state rain gauge.

Vaisala have already done this in their WXT520 (see image attachment). They measure precipitation acoustically by listening to the pitter-patter of individual raindrops on a stainless steel disk at the top of the unit. Pretty cool technology.

I'd like to implement something similar. I'm sure that the hardware that Vaisala uses to amplify and detect the sound of raindrops hitting the sensor along with the software algorithms is proprietary and very closely held. Does anyone know of any freely available references, perhaps in academia, that discuss this technology?

ElectricAye

Sal Ammoniac said...
....

I'd like to implement something similar. I'm sure that the hardware that Vaisala uses to amplify and detect the sound of raindrops hitting the sensor along with the software algorithms is proprietary and very closely held. Does anyone know of any freely available references, perhaps in academia, that discuss this technology?

If I'm not mistaken, one of USA's first rockets, Explorer 1, was equipped with a microphone that basically listened to things pinging against its hull. The idea was to log the density of micrometeoroids as the rocket went sailing through space. I suppose for rain, it's a matter of correlating rain drop counts and perhaps acoustic peak energies (to account for raindrop size) to a measured rain fall with a good ole fashioned rain gauge. Where things probably get complex is when you have wind and major downpours and then you'd need to shift to some sort of acoustic signature detection, probably taking into account the mechanical resonance of the metal plate, etc.

en.wikipedia.org/wiki/Explorer_1#Spacecraft_design

Another option might be to develop a gargoyle monitor, which listens to the gargoyle gargling and, from that, determines a total rainfall figure.

One thing you can do is look up their patent and see if they make reference to any articles.

patft.uspto.gov/netahtml/PTO/search-bool.html

TinkersALot

You may also want to check out this site. They have lots and lots of weather sensors to play with. All with One-Wire interface as well.

http://www.hobby-boards.com/catalog/index.php

Tracy Allen

The pitter-patter of raindrops in the first analysis should not be hard at all to implement, with a drumhead type of sensor. MSI piezo film would make a good detector. Counting impacts and estimates of size (volume, energy of impact) would be a cool Prop project.

It will be more complicated in the second analysis. At high rainfall rates, coincidence of impacts leads to underestimate of the rainfall volume. One of my customers did a test of the WXT520 and found that it did not do very well during intense rainfall. Even in low rainfall, the sensor's estimate of drop size can be affected by the energy and angle of impact of the drop and the effects of wind.

I helped install a rain detector in Mongolia for a project where the interest was the kinetic energy of raindrops, because that is what is important for breaking loose bare soll leading to erosion. The sensor was from the company Sensit, and the project also included sensors for the kinetic energy of windblown sand and particles to support a theory of erosion by saltation. The sensors output a pulse for each impact, and also an integrated signal for the accumulated kinetic energy of impacts.

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Tracy Allen
www.emesystems.com

Sal Ammoniac

Thanks Tracy. Based on your description of the accuracy of the WXT520 I think I'll stick with a tried-and-true tipping bucket gauge.

Tracy Allen

The tipping bucket is surely tried and true. It has to be properly sited, with a good wind screen if possible, and ants and ice kept out of the mechanism, but it can't be beat for simplicity and directness.

Here is a photo of a Sensit rain impact and energy sensor, and also a couple of the installation sites. Also a sand impact/energy sensor. The ground cover is sparse to begin with, and overgrazing had left it even more vulnerable to wind driven erosion.

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Tracy Allen
www.emesystems.com

steve_b

I remember reading about a fella that basically took a stainless steel salad bowl and mounting it to an old birdbath (I think he used stand-offs).

Anyhow, he wanted to hear the sound of rain inside....so he put small mic under the bowl and ran it inside.
I don't believe he used it for anything more than the "atmosphere"...but there's no reason you couldn't gate it and grab the peaks.

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<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

Tracy Allen

Another sidelight on disappearing rain gages in the Mongolian Steppes. We used plastic rain gages, but some other groups set out the standard Forest Service metal gages that have a nice funnel in the center. Central Asian people have a fermented beverage, kumis, or airag, that is traditionally made from mare's milk, and is kind of like kefir, low alcohol content. But it is possible to distill it to make a more potent beverage. For that one needs a distillation funnel. ahhhh, need we look further?!

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Tracy Allen
www.emesystems.com

CounterRotatingProps

Side note to E.Aye RE the micrometeors - in the late 60's I saw a NASA demo of this gadget that could count them. It was a flat metal plate connected to some electronics with a readout (I was kid, so no idea how it worked.) The guy said it could count many micrometeors quickly - and proceeded to pour a handful of sand onto the plate - in a few seconds - it counted over 100,000 grains. I was blown away.

Sal: I think the solid state anemo. was a thread I started (or at least I got deeply pulled into [noparse]:)[/noparse] ... like the micrometeor counter, I didn't understand how they worked - our good friends here straightened me out.

I have to ask my dad (a retired meterologist) what NOAA/NWS uses for automated rain gauges --- actually, it wouldn't surprise me if they still do it by hand.

cheers - and may your buckets overfloweth ...

- Howard



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Post Edited (CounterRotatingProps) : 11/27/2009 10:07:29 PM GMT

kwinn

Automated rain guages have a funnel that feeds into a "tip" bucket. When the bucket gets a certain amount of water in it it tips and empties. A counter counts the number of tips. Not sure of the exact volume to tip the bucket but it is small.

Tracy Allen

The standard tip is 0.2mm or 0.01 inch of rain collected over the area of the mouth of the rain gage funnel.

For example, the Davis instruments gage has an area of 214 square cm, which, covered to a depth of 0.2mm, accumulates 4.282 cc of water. That causes one tip. They provide a small weight that you attach to the counterarm, to change 0.2mm and 0.01 inch calibrations.



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Tracy Allen
www.emesystems.com

steve_b

I work for the NOAA/NWS equivalent up in Canada....we still use the standard copper Tipping bucket.
They used to have mercury switches (for switch bounce).

We also use weighing gauges. Some use encoders and springs....the newer ones use vibrating wires (vibrate the wire at 1kHz and as the weight of the bucket increases, so does the frequency -- think guitar string).

Other ones we have are optical and RF. Aim a police radar gun up and you can measure the falls speed of precip...do some more math with temperatures and the amount of RF reflected and it gets more accurate.
Capacitive plates....coupled with optical scatter sensors do alright.
Distrometers are the newer things....they want to measure the size of the drops/flakes. So, shine a laser beam across a fall path and the shadow created can be used to determine snow/rain size.

Lots of neat things....

Use GPS or Cell signal changes (during weather)....not sure that's sold yet!

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<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!