Hi Arduino Community!
I am planning to create an acoustic rain gauge using a piezo sensor. The problem is I do not know how to convert loudness to rain rate. Can you suggest a way on how to do this?
Interesting - I guess its a problem of calibration, and I wouldn't even begin
to know where to find a calibrated instantaneous rain sensor to compare with.
Collecting data alongside a rain-fall guage in various weather conditions would
allow comparing total rain over a period against average loudness reading, which
would need to be done in both heavy, medium and light precipitation to get a feel
for the response curve.
A literature search might turn something up. sleet, hail and snow are going to
confound things! Also some clouds drop larger drops than others (thunderstorms
particularly), which is a confounding variable I suspect.
Perhaps there's a calibrated rain-making machine somewhere for testing roofing
materials and leak-testing vehicles?
Here is a link that discusses acoustic rain gauges that function underwater. In addition to rainfall amount calibration there is the need to distinguish sounds produced by rain from sounds produced by wind, hale, etc. and this will take careful analysis. Scroll down the page on the link below to look at the frequency spectrum (labeled "Summary Spectra") of the sound produced by some of these disturbances, which gives a strong hint for how to proceed. http://www.dosits.org/technology/currentstemperature/acousticraingauge/
While I have not tried this, I would assume 2 things. 1) the piezo sensor will help you generate spikes that you can capture since it is more unlikely that you get simultaneous drops 2) bigger drops (or combined drops) means louder volume. The way I would approach it is to measure the low(ish) frequency of spikes and then measure the overall strength of the signal (size/quantity of water). Only with both those values, in my opinion, it is possible to make a gauge. The frequency of spikes measurement is more about "is it raining light or heavy or not at all" and volume intensity can only give a rough idea about how much water "weight" is hitting the sensor. (IE assuming you are using Piezo glued to the underside of a sheet of glass, for example).
Personally, I would start experiments on this using a quick and dirty pre-amp with DC output and feed DC to a digital pin using the frequency measure library from PJRC...
http://www.pjrc.com/teensy/td_libs_FreqMeasure.html
and to an Analog input for relative volume.
I can see how it would work underwater as it deals with a uniform surface and uniform surrounding water body.
In the above acoustic rain gauge at sea link, they have identified the rain sound pattern, to distinguish between hail or rough waves.
Never heard of anything like this on land, except for Dopplers, yet they do use them in weather monitoring.
Might be worth looking into.