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New rain rate calculation

Discussion specific to Fine Offset and similar rebadged weather stations
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steve
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Re: New rain rate calculation

Post by steve »

dane wrote:I think I understand what you are trying to do.
And I think my problem is basically the "mm/hour" annotation when what we are really talking about is "tips per station interval". (48 secs)
So the "rainfall rate" on the main display is your sliding average of no. of tips over some (?) period?
And the "All time high rain rate" is basically "highest no. of tips in one station interval"?
Yes, well that sort of thing. I'm just trying to emulate what Davis have done in their weather stations, and Davis seem to know a thing or two, so it seems like a reasonable thing to do.
If so, I'd very much prefer to see something like: "All time high rain rate: 0.3 mm in 48 seconds" rather than "22.5 mm per hour" - giving the impression that it rained heavily for a whole hour!
Displaying rain rate in mm/hr (or in/hr) seems to be standard. It's a rate, after all. Rates don't give any information about the length of time they apply to. If I told you I drove my car at 100 mph yesterday, there's no implication that I drove at that speed for an entire hour, nor even that I drove for more than 5 minutes.
You know when the station updates (new buffer address), so picking up the no. of tips per interval should be no problem?
The station updates at 48 second intervals, the address changes according to what you've set the station logger interval to.

Steve
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Re: New rain rate calculation

Post by dane »

About rates: you are right, of course :oops:

But I hope we can agree, at least, that an All time High of 108 mm/hr is incorrect for 1 tip (0.3mm) in a 48 sec. interval?
Ib
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Re: New rain rate calculation

Post by steve »

dane wrote:But I hope we can agree, at least, that an All time High of 108 mm/hr is incorrect for 1 tip (0.3mm) in a 48 sec. interval?
Oh yes. As you spotted, I was taking the 0.3 mm over a 10 sec interval (but not for the first tip, after that). It should actually come out as about 22mm per hour.

I've modified my code now to stop that happening, and I've had to change the way it works to avoid this problem of not knowing exactly when the station updates. What I do now is check the rain total once a minute, and compare it with the total a minute earlier, and calculate the rate based on that. So there tends to be a delay of a minute or so before it reacts to any rain tips. And it's not just 'amount of rain in last minute' * 60 to give mm/hr, it also does the 'gradually return to zero over a period of 15 minutes if no more rain falls' thing that the Davis stations do.

It's not perfect, and I know it won't please everybody. But I think it's better than just using the amount of rain that fell in the last hour, and it's really just to give an indication of how heavily it's raining over a short period. I'm doing the best I can with a station that has a resolution of 0.3mm and an update rate of 48 seconds. It may need a bit of tweaking still.

Steve
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Re: New rain rate calculation

Post by dane »

not knowing exactly when the station updates
You know - down to your resolution of 10 secs - when the station registers a new tip.
Or is that not the problem :?:

(Just ran a Cumulus debug log for a short while. Bucket tips incremented in the 3rd and 2nd last bytes of data line 6)
Ib
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Re: New rain rate calculation

Post by steve »

I know when it's tipped, yes, but I don't know when it hasn't tipped. Or something. I'm tired.

Anyway, give the new build a try and see what happens.

Steve
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Re: New rain rate calculation

Post by dane »

I restarted Cumulus build 575 from 11:10 today (before rain started here).
Rain rate never got above 1.8 mm/hour.
Thanks.
Ib
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Re: New rain rate calculation

Post by steve »

But that's from the history data, I haven't changed the way I calculate rain rate from that, there's just not enough data to do anything better. It just takes the amount of rain in each history entry, and works out a rate based on the history interval (so, you presumably have the station set to log at 10-minute intervals, and no entry had more than one rain tip - 0.3mm in 10 minutes = 1.8mm/hr). The new algorithm only operates on 'live' rain.

Steve
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Re: New rain rate calculation

Post by dane »

You're right, of course. Silly me :oops:
It stopped raining before I got the new build up and running, so will just have to wait for more rain.
Ib
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Re: New rain rate calculation

Post by dane »

Steve,
hate to tell you this - but it started raining at 21:17, and so far rainfall rate is 0.0, both on main display and in graphs (build 575)
Ib
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Re: New rain rate calculation

Post by steve »

How hard can this be? :(

I've found a bug in the code - I'll upload a new version later today.

Thanks,
Steve
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Re: New rain rate calculation

Post by Super-T »

I'm running 575 and we've had 2.1mm today....seems about right
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Re: New rain rate calculation

Post by steve »

Super-T wrote:I'm running 575 and we've had 2.1mm today....seems about right
Yes - but that rain you had at about 2030 hasn't shown anything on the rain rate graph :(

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Re: New rain rate calculation

Post by Samuel »

About rainrate calculation
I have 1.84 build 575
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steve
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Re: New rain rate calculation

Post by steve »

Now that's impressive. I have no idea where that figure came from.

Maybe I should give up and go back to the 'rain in last hour' = 'rain rate' calculation :(

Steve
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Re: New rain rate calculation

Post by Samuel »

I look at my website and it was updated 2008-12-01 19:26:47 and the value there was "3,6 mm at 08:27 on 26 oktober 2008"
and I looked at the computer at 19:30 and find "71373,0 mm/hour" and its not raining outside now but it rained 0,6 mm around 16:44
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