Disdrometer
From Wikipedia, the free encyclopedia
A disdrometer is an instrument used to measure the drop size distribution and velocity of falling hydrometeors. Some disdrometers can distinguish between rain, graupel, and hail.
That’s a little more involved than my initial project, which is just to continuously measure and quantify the instantaneous intensity of rainfall. I already have an idea of how to try to do it, and have done a proof-of-concept prototype of some hardware. Rain gauge tips can tell you how hard it WAS raining by bucket tips, but we all know that a light drizzle can take forever to tip it once. If mine works properly, you might be able to see the sheets of rain fall in a downpour, if trended fast enough, as well as see drizzle before the bucket tips.
I already asked about this on the Ambient forum a few months ago and received a resounding yawn of interest. However, now that I’ve started to explore Weather Display, the members of this forum seem to be a lot more active in projects like this, and I suspect a successful project could easily be integrated into WD for display purposes.
So, if you have any experience with audio frequency analysis and quantification on PCs, and are interested in this project, PM me here, or use my contact page at http://wx.sloweather.com/contact.php .
And if you know of something like this already made and affordable for the hobbyist, please point me to it. I’d rather not reinvent it.
It sounds like an interesting project. Rather than a PC, you might like to investigate a microcontroller (PIC) like the dsPIC30F6014A. It’s got DSP capabilities which might be useful for doing the kind of calculations and processing you’ll need to do. I’ve just got a development kit with one of those in to have a play with the technology, so I’m not an expert yet!
That was suggested by another friend. However, I’m trying to keep the hardware costs down, at least in the beginning, by using a PC’s sound card input, rather than adding more hardware. It may turn out, though, that the dynamic range in question is such that it winds up requiring more hardware. I won’t know until I play a little more with the transducer design.
I’d sacrifice some of the fancy abilities of the Viasala device to make it affordable for most people on this list to afford.
I’m with Chris on this one although I have seen some pretty amazing things done with soundcards too. There are also eval boards from e.g. Analog or TI that might be worth considering.
I would think a soundcard would have the bandwidth and dynamic range for a large plate kind of transducer… and external devices usually have a much lower noisefloor when it comes to the cheaper ones…
maybe find some scope capture software for a starting place to look for useful signatures when experimenting with transducers? before getting into custom dsp/analysis
Be very interested to hear how it all goes!
I think I’ll have to start banning everyone else called Chris from the forum to avoid such problems
PIC based solutions don’t need to be expensive. MAX187 ADC ($20), dsPIC30F6014A MCU ($20), MAX232 for RS232 I/O ($10), plus a few resistors/capacitors mounted on a board…$60 for a programmable solution giving easy connectivity to a PC. You might even be able to find a cheaper ADC or be able to use a cheaper PIC model. With a dsPIC MCU you also have lots of other potential connectivity options (CAN1/2, RS485, USB, Ethernet, 1-wire). With 1-wire you could probably even dispense with the MAX232 chip.
One thing that I suspect will be tricky with this project is tuning it for individual disdrometer builds. I assume that unless manufactured to very tight tolerances, the ‘impact plate’ will produce quite different sound patterns for identical rain patterns. The problem is that creating a standard pattern of rain drops for calibration will also be tricky. So repeatably converting a specific sound pattern for a specific impact plate into a rain rate won’t be easy.
For the initial project, I’ll be happy to get qualitative rather than quantitative results; mist, drizzle, light rain, moderate rain, heavy rain, etc., rather than aim for a calibrated “inches per hour” (or “mm/hour”).
FWIW, Rev A is a Rat Shack piezo transducer epoxied to the center of a Lexan window pane from Home Depot, perhaps 11 x 9 (?), stuck to a wooden frame made of 1" x 4" lumber with foam glazing tape.
The transducer is connected to a shielded RCA cable which is connected to an old Rat Shack mixer to control gain, and then to an old BSR audio spectrum analyzer to look at the spectrum.
In my limited experience, the high impedance signal from the transducer might be rolled off more for longer runs of cable.
I have a couple of wav files recorded of a moderate rain last spring, if anyone wants to listen.
One other concern about the flat plate transducer is that the response of the plate changes with the amount of water accumulated on it. I wonder if a hemisphere or shallow pyramid might be better?
