Rain affecting signals and sensing rain.

[Poxy]

richardghole@yahoo.com wrote:

Hi

Thanks for the letters.

We get a lot of drizzle in our area which does not get detected by
radar or audiably by sound on a roof. Also the radar covers a large
area and does not detect small amounts of rain. The frames are also
only updated every 10 minutes. However, the drizzle we get is still
enough to wet things. I am on the Atherton Tableland at 737 meters
altitude.

So is there any other signals or radiation apart from lazar light that
would have their strength reduced by such precipitation so that their
strength could be easily measured?

As others have said, the problem is that pretty much anything in the air
(dust, pollen, haze, smoke) is going to attenuate a beam.

My suggestion is to try the circuit at the bottom of this page:

http://www.emesystems.com/lwet_dat.htm

It's a simple circuit - you can just use a standard 555 and regulator rather
than the specialised versions they use, it is hella-sensitive, the sensor is
a simple grid - you could use veroboard as someone suggested, or maybe make
up something finer, and you can interface the output a number of ways,
voltage, current or frequency - the latter being a very easy way to
interface to a micro.

 

[Ken Taylor]

Pete wrote:

How about a large collector (think *big* funnel, or possibly even the
existing roof drainage system) and in the output pipe, either a flow
sensor (to give a range of outputs depending on actual rainfall), or a
simple continuity test to detect rain/no rain.

Rethinks: perhaps the "dynamic range" of the existing guttering and
downpipes might be just a *little* too large between "barely raining"
and "extreme storm"

Peter

If you use too big a collector, light rain (an undefined variable) may
evaporate before getting tot he sensor. But in principle a good idea.

Cheers.

Ken

 

[Ray]

In article <1142467926.344986.120880@j33g2000cwa.googlegroups.com>,
richardghole@yahoo.com says...

Hi

Thanks for the letters.

We get a lot of drizzle in our area which does not get detected by
radar or audiably by sound on a roof. Also the radar covers a large
area and does not detect small amounts of rain. The frames are also
only updated every 10 minutes. However, the drizzle we get is still
enough to wet things. I am on the Atherton Tableland at 737 meters
altitude.

Your help is appreciated,
Regards Richard.


The radar is most likely able to detect the rain.

There is one proviso though, it has to be able to see it from it's point
of view.

The lowest threshold is actually a fair bit higher than light drizzle.
It is also possible that the radar is detecting it, but the signal is
being suppressed.
The level 1 threshold of 12dBz is roughly equivalent to 0.2mm/hour.

Which radar are you using? Cairns?

If it is light drizzle on the hills, it is also possible that the radar
is gating the signal off due to massive permanent echo contamination.

Cheers, Ray

 

[richardghole@yahoo.com]

Hi

Thanks for your letter.

I would be interested in getting a leaf wetness sensor made. However, I
do not have much electronics experience or time. Could you or do you
know of anyone who could make one up for me or are there any made up
units for sale. If so, how much would it cost to either buy one or get
one made? How long do they take to make? I am about to make an order
from Electus Distribution so I could purchase the parts.

I have a data logger that collects data so that the weather can be
graphed out. It is then automatically uploaded on to a public site
linked to http://www.weather.org.au/tolga/ The logger requires
between 0 and 5 volts. The voltage values are saved in a text file and
pasted into Microsoft Excel to be converted into the values I need and
graphed out. It would be good if very light drizzle registered at
perhaps the lowest voltage and heavier drizzle was logged at a higher
voltage so that a graph could be created. Also it would be good to put
an alarm on the wetness sensor so it would buzz even when light drizzle
is falling on it. The buzzer could be switched off and separate to the
computer and data logger.

Could you also please contact me by email if possible. The address is
weather@truesolutions.info or you can go to the website above.

Your help is appreciated,
Regards Richard.

 

[Poxy]

richardghole@yahoo.com wrote:

Hi

Thanks for your letter.

I would be interested in getting a leaf wetness sensor made. However,
I do not have much electronics experience or time. Could you or do you
know of anyone who could make one up for me or are there any made up
units for sale. If so, how much would it cost to either buy one or get
one made? How long do they take to make? I am about to make an order
from Electus Distribution so I could purchase the parts.

I have a data logger that collects data so that the weather can be
graphed out. It is then automatically uploaded on to a public site
linked to http://www.weather.org.au/tolga/ The logger requires
between 0 and 5 volts. The voltage values are saved in a text file and
pasted into Microsoft Excel to be converted into the values I need and
graphed out. It would be good if very light drizzle registered at
perhaps the lowest voltage and heavier drizzle was logged at a higher
voltage so that a graph could be created. Also it would be good to put
an alarm on the wetness sensor so it would buzz even when light
drizzle is falling on it. The buzzer could be switched off and
separate to the computer and data logger.

I'm not sure whose you are replying to, but the leaf wetness sensor on this
page
http://www.emesystems.com/lwet_dat.htm
is available from them for US$65
It's listed about 3/4 down on this page:
http://www.emesystems.com/prices.htm

The base unit puts out 0.2-1v but it looks like you can get one with a more
suitable voltage output for an extra $10. I'd suggest you send them an email
if you're interested.

 

[richardghole@yahoo.com]

Hi

Thanks for your letter.

I have written to them. However, I am not sure if the sensor is heated
so that it will evaporate the moisture quicker. I think it would need
to be heated to give a more accurate reading of when the rain stopped.
If it is not heated the water will take a long time to evaporate and it
will still be registering rain when there is none.

Chris Jones mentioned that he has one with a heater. I would be
interested in a diagram of it when he can post it. I am not sure where
he got it or if he made it up.

So do you think these sensors will be able to tell you when there is
light drizzle and when it stops?

Many years ago I also heard of a sensor that had some sort of salt or
mineral coating so that when it was wet it would conduct electricity
better. This could overcome the problem that water has a very high
resistance and also make the sensor more accurate. However, a problem
could be that the salt or whatever is used may wash off. Do you know
any of them like this?

Your help is appreciated,
Regards Richard.

 

[richardghole@yahoo.com]

Hi

Thanks for your letter.

So is the sensor just a circuit board or does it have some chemical on
the surface to increase the conductivity of water?

I would also be interested in how the other ones mentioned by other
people compare to the sensor at http://www.emesystems.com/lwet_dat.htm

For example, Chris Jones said he would send some info. Does anyone know
his contact email address?

Your help is appreciated,
Regards Richard.

 

[GB]

"richardghole@yahoo.com" <richardghole@yahoo.com> wrote in
news:1142725417.694308.203540@i39g2000cwa.googlegroups.com:

Sorry Chris. Actually it was Match who wrote the letter. It is just
[...]

What are you replying to?

GB

 

[Simone Merrett]

There is another kind of senor no one has mentioned, that may be worth
considering...
VIBRATION / SOUND.
If you are only considering droplets moving largely under gravity, then a
tallish un-resonant column with a sound-absorbtive inner surface (to reduce
wind noise even more) may nicely complement ( a resistive sensor) , or even
suffice as a 'drizzle' detector. It could/would work by having a
large-surface area thin 'plate' connected directly to either a piezo or
speaker-type tranducer. Fed straight into a low-noise high gain audio amp,
the output would be super-amplifyed 'pings' of dirzzle landing on the
'rain-microphone'. The problem then of course is decoding this into amount
of drizzle. I suggest putting output straight into sound card of PC, simple
bit of SW would be able to separate out wind noise from droplet pings,
provided some calibration work is done before hand.
An active bandpass filter after LNA would be wise too.

In your kind of problem, it may not be a simple matter of "drizzle or not?".
One might consider there to be a 2 dimensions of atmospheric water : droplet
size, and droplets / volume (density) , where drizzle free, high humidity
represents very small droplets, but a high density, and a shower in a dry
southern area might be large drops, but low density.
I only say this, because it is likely that for good accuracy, it is often
better to combine detections of 2 or more sensors (eg radar and resistance)
to increase probability of correct output. (EG With resistance detector, How
do know the difference between high humidity and drizzle? ..(without also
knowing humidity) .)

Another thing that has not been discussed is droplet resonance, where at a
particular radio or sound frequency, the absorbtion of energy by the droplet
rapidly increases.
There should be science literature (esp at BOM) available that discusses
droplet size for drizzle, and any decent sound or radar book will have a
small section (or refs at least) on radio / sound properties wrt drop-size.

If you are lucky, drizzle droplets will all be roughyly the same size,
meaning that a simple ultrasonic path-loss measurment at a narrow band
centred on the resonant frequency will reveal drizzle.

Obviously a good topic, with so many responses!
Good luck.
David Merrett.

<richardghole@yahoo.com> wrote in message
news:1142368728.491174.263800@j33g2000cwa.googlegroups.com...

Hi

I am thinking of making a rain sensor to detect light rain as the BOM
radar is often not accurate at measuring light rain in my local area. I
have an Internet weather station linked to http://weather.org.au .

I heard some wireless transmissions can be affected greatly by rain so
if I set up a transmitter and receiver, the signal would get weaker in
the rain and the strength of it could be measured. The distance between
the transmitter and receiver could be experimented with. Perhaps I
could set up one for the very local area where the distance between the
transmitter and receiver is only about 50 or 100 meters. However,
another one could be set up so that it spans a distance of a kilometer
or more. The signal could extend between my house and someone else's
place in the direction where the prevailing weather comes from. This
would alert us when rain is about to arrive.

It would be good if the sensor detected even light drizzle. Ideally it
would be nice to see or measure the signal reduce as the drizzle or
rain became heavier between the transmitter and receiver.

Is there a simple way to do this, such as by using an infa red
transmitter and receiver? The receiver could be housed in a pipe to
block out as much background interference as possible and so it only
received signals from the direction of the transmitter.

Another alternative could be a low cost radar if one is suitable.

What sort of transmitters and receivers could be used and would the
setup be affordable?
How accurate would the system be?

Your help is appreciated,
Regards Richard.

 

[richardghole@yahoo.com]

Hi

Thanks for your letter.

Sorry not to reply sooner.

We had a cyclone which you should have heard about on the news.

How difficult or expensive could this be to set up? Could one of the
options you said be transmitted over a couple of miles to determine if
there is any drizzle over that distance?

Your help is appreciated,
Regards Richard.

Simone Merrett wrote:

There is another kind of senor no one has mentioned, that may be worth
considering...
VIBRATION / SOUND.
If you are only considering droplets moving largely under gravity, then a
tallish un-resonant column with a sound-absorbtive inner surface (to reduce
wind noise even more) may nicely complement ( a resistive sensor) , or even
suffice as a 'drizzle' detector. It could/would work by having a
large-surface area thin 'plate' connected directly to either a piezo or
speaker-type tranducer. Fed straight into a low-noise high gain audio amp,
the output would be super-amplifyed 'pings' of dirzzle landing on the
'rain-microphone'. The problem then of course is decoding this into amount
of drizzle. I suggest putting output straight into sound card of PC, simple
bit of SW would be able to separate out wind noise from droplet pings,
provided some calibration work is done before hand.
An active bandpass filter after LNA would be wise too.

In your kind of problem, it may not be a simple matter of "drizzle or not?".
One might consider there to be a 2 dimensions of atmospheric water : droplet
size, and droplets / volume (density) , where drizzle free, high humidity
represents very small droplets, but a high density, and a shower in a dry
southern area might be large drops, but low density.
I only say this, because it is likely that for good accuracy, it is often
better to combine detections of 2 or more sensors (eg radar and resistance)
to increase probability of correct output. (EG With resistance detector, How
do know the difference between high humidity and drizzle? ..(without also
knowing humidity) .)

Another thing that has not been discussed is droplet resonance, where at a
particular radio or sound frequency, the absorbtion of energy by the droplet
rapidly increases.
There should be science literature (esp at BOM) available that discusses
droplet size for drizzle, and any decent sound or radar book will have a
small section (or refs at least) on radio / sound properties wrt drop-size.

If you are lucky, drizzle droplets will all be roughyly the same size,
meaning that a simple ultrasonic path-loss measurment at a narrow band
centred on the resonant frequency will reveal drizzle.

Obviously a good topic, with so many responses!
Good luck.
David Merrett.

richardghole@yahoo.com> wrote in message
news:1142368728.491174.263800@j33g2000cwa.googlegroups.com...
Hi

I am thinking of making a rain sensor to detect light rain as the BOM
radar is often not accurate at measuring light rain in my local area. I
have an Internet weather station linked to http://weather.org.au .

I heard some wireless transmissions can be affected greatly by rain so
if I set up a transmitter and receiver, the signal would get weaker in
the rain and the strength of it could be measured. The distance between
the transmitter and receiver could be experimented with. Perhaps I
could set up one for the very local area where the distance between the
transmitter and receiver is only about 50 or 100 meters. However,
another one could be set up so that it spans a distance of a kilometer
or more. The signal could extend between my house and someone else's
place in the direction where the prevailing weather comes from. This
would alert us when rain is about to arrive.

It would be good if the sensor detected even light drizzle. Ideally it
would be nice to see or measure the signal reduce as the drizzle or
rain became heavier between the transmitter and receiver.

Is there a simple way to do this, such as by using an infa red
transmitter and receiver? The receiver could be housed in a pipe to
block out as much background interference as possible and so it only
received signals from the direction of the transmitter.

Another alternative could be a low cost radar if one is suitable.

What sort of transmitters and receivers could be used and would the
setup be affordable?
How accurate would the system be?

Your help is appreciated,
Regards Richard.