Weather Software > Station Software Development
Rain and Rain Rate
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iisfaq:
I have a Davis Vantage Pro II
I am interested in thoughts about the rain rate per hour (which is bucket tips per hour not mm or inches)
Here is an example of rain for 100 minutes at 1 minute intervals:
DateTime Rainfall RainRateHighest
2011-06-13 13:00:00.000 1.000000 0.000000
2011-06-13 13:01:00.000 0.000000 0.000000
2011-06-13 13:02:00.000 0.000000 0.000000
2011-06-13 13:03:00.000 0.000000 0.000000
2011-06-13 13:04:00.000 0.000000 0.000000
2011-06-13 13:05:00.000 0.000000 0.000000
2011-06-13 13:06:00.000 0.000000 0.000000
2011-06-13 13:07:00.000 0.000000 0.000000
2011-06-13 13:08:00.000 0.000000 0.000000
2011-06-13 13:09:00.000 0.000000 0.000000
2011-06-13 13:10:00.000 0.000000 0.000000
2011-06-13 13:11:00.000 0.000000 0.000000
2011-06-13 13:12:00.000 0.000000 0.000000
2011-06-13 13:13:00.000 0.000000 0.000000
2011-06-13 13:14:00.000 0.000000 0.000000
2011-06-13 13:15:00.000 0.000000 0.000000
2011-06-13 13:16:00.000 0.000000 0.000000
2011-06-13 13:17:00.000 0.000000 0.000000
2011-06-13 13:18:00.000 0.000000 0.000000
2011-06-13 13:19:00.000 0.000000 0.000000
2011-06-13 13:20:00.000 0.000000 0.000000
2011-06-13 13:21:00.000 0.000000 0.000000
2011-06-13 13:22:00.000 0.000000 0.000000
2011-06-13 13:23:00.000 0.000000 0.000000
2011-06-13 13:24:00.000 0.000000 0.000000
2011-06-13 13:25:00.000 0.000000 0.000000
2011-06-13 13:26:00.000 0.000000 0.000000
2011-06-13 13:27:00.000 0.000000 0.000000
2011-06-13 13:28:00.000 0.000000 0.000000
2011-06-13 13:29:00.000 0.000000 0.000000
2011-06-13 13:30:00.000 0.000000 0.000000
2011-06-13 13:31:00.000 0.000000 0.000000
2011-06-13 13:32:00.000 0.000000 0.000000
2011-06-13 13:33:00.000 0.000000 0.000000
2011-06-13 13:34:00.000 0.000000 0.000000
2011-06-13 13:35:00.000 0.000000 0.000000
2011-06-13 13:36:00.000 0.000000 0.000000
2011-06-13 13:37:00.000 0.000000 0.000000
2011-06-13 13:38:00.000 0.000000 0.000000
2011-06-13 13:39:00.000 0.000000 0.000000
2011-06-13 13:40:00.000 0.000000 0.000000
2011-06-13 13:41:00.000 0.000000 0.000000
2011-06-13 13:42:00.000 0.000000 0.000000
2011-06-13 13:43:00.000 0.000000 0.000000
2011-06-13 13:44:00.000 0.000000 0.000000
2011-06-13 13:45:00.000 0.000000 0.000000
2011-06-13 13:46:00.000 0.000000 0.000000
2011-06-13 13:47:00.000 0.000000 0.000000
2011-06-13 13:48:00.000 0.000000 0.000000
2011-06-13 13:49:00.000 0.000000 0.000000
2011-06-13 13:50:00.000 0.000000 0.000000
2011-06-13 13:51:00.000 0.000000 0.000000
2011-06-13 13:52:00.000 0.000000 0.000000
2011-06-13 13:53:00.000 0.000000 0.000000
2011-06-13 13:54:00.000 0.000000 0.000000
2011-06-13 13:55:00.000 0.000000 0.000000
2011-06-13 13:56:00.000 0.000000 0.000000
2011-06-13 13:57:00.000 0.000000 0.000000
2011-06-13 13:58:00.000 0.000000 0.000000
2011-06-13 13:59:00.000 0.000000 0.000000
2011-06-13 14:00:00.000 0.000000 0.000000
2011-06-13 14:01:00.000 0.000000 0.000000
2011-06-13 14:02:00.000 0.000000 0.000000
2011-06-13 14:03:00.000 0.000000 0.000000
2011-06-13 14:04:00.000 0.000000 0.000000
2011-06-13 14:05:00.000 0.000000 0.000000
2011-06-13 14:06:00.000 0.000000 0.000000
2011-06-13 14:07:00.000 0.000000 0.000000
2011-06-13 14:08:00.000 0.000000 0.000000
2011-06-13 14:09:00.000 0.000000 0.000000
2011-06-13 14:10:00.000 0.000000 0.000000
2011-06-13 14:11:00.000 0.000000 0.000000
2011-06-13 14:12:00.000 0.000000 0.000000
2011-06-13 14:13:00.000 0.000000 0.000000
2011-06-13 14:14:00.000 0.000000 0.000000
2011-06-13 14:15:00.000 0.000000 0.000000
2011-06-13 14:16:00.000 0.000000 0.000000
2011-06-13 14:17:00.000 0.000000 0.000000
2011-06-13 14:18:00.000 0.000000 0.000000
2011-06-13 14:19:00.000 0.000000 0.000000
2011-06-13 14:20:00.000 2.000000 4114.000000
2011-06-13 14:21:00.000 0.000000 30.000000
2011-06-13 14:22:00.000 0.000000 20.000000
2011-06-13 14:23:00.000 0.000000 15.000000
2011-06-13 14:24:00.000 0.000000 12.000000
2011-06-13 14:25:00.000 0.000000 10.000000
2011-06-13 14:26:00.000 0.000000 9.000000
2011-06-13 14:27:00.000 0.000000 8.000000
2011-06-13 14:28:00.000 0.000000 7.000000
2011-06-13 14:29:00.000 0.000000 6.000000
2011-06-13 14:30:00.000 0.000000 5.000000
2011-06-13 14:31:00.000 0.000000 5.000000
2011-06-13 14:32:00.000 0.000000 5.000000
2011-06-13 14:33:00.000 0.000000 4.000000
2011-06-13 14:34:00.000 0.000000 4.000000
2011-06-13 14:35:00.000 0.000000 4.000000
2011-06-13 14:36:00.000 0.000000 4.000000
2011-06-13 14:37:00.000 0.000000 0.000000
2011-06-13 14:38:00.000 0.000000 0.000000
2011-06-13 14:39:00.000 0.000000 0.000000
I am quite amazed at the 2 bucket tips at 14:20 producing a rate rate per hour of 4114 tips.
The Potential rate per hour (which is what RainRateHighest) is 4114.000000 (that must mean it really pelted down for 1 minute)
Now these are not MM or Inches but tips of the bucket and in my case 0.2 mm per tip
so 4114 * 0.2 = 822mm per hour (but it only lasted 1 minute or less)
How would you average this out? I am trying to write my own software and these sort of readings are pretty strange. We have had some heavy rain but not anything much as far as I would be converned.
Could this be the bucket almost full and sitting waiting to tip and then it tips and it tips again and that is it? Maybe in a few seconds?
Rather weird data..
chris
tobyspond:
Hi Chris,
Maybe this will be of help....?
Are you sure the 2 refers to number of tips rather than total rain (2 mm)?
From http://www.davisnet.com/product_documents/weather/app_notes/AN_28-derived-weather-variables.pdf
RAINFALL RATE
Parameters Used: Rain Total (actually, rain rate is a measured variable in the sense that it is
measured by the ISS and transmitted to the display console, whereas all other calculated
variables are determined by the console from data received from the ISS.)
Formula:
Under normal conditions, rain rate data is sent with a nominal interval of 10 to 12 seconds.
Every time a rain tip or click occurs, a new rain rate value is computed (from the timer values)
and the rate timers are reset to zero.
Rain rate is calculated based on the time between successive tips of the rain collector. The rain
rate value is the highest rate since the last transmitted rain rate data packet. (Under most
conditions, however, a rain tip will not occur every 10 to 12 seconds.)
If there have been no rain tips since the last rain rate data transmission, then the rain rate based
on the time since that last tip is indicated. This results in slowly decaying rate values as a rain
storm ends, instead of showing a rain rate which abruptly drops to zero. This results in a more
realistic representation of the actual rain event.
If this time exceeds roughly 15 minutes, than the rain rate value is reset to zero. This period of
time was chosen because 15 minutes is defined by the U.S. National Weather Service as
intervening time upon which one rain "event" is considered separate from another rain "event".
This is also the shortest period of time that the Umbrella will be seen on the display console
after the onset of rain.
Kerry
iisfaq:
--- Quote from: tobyspond on July 01, 2011, 06:35:07 PM ---Are you sure the 2 refers to number of tips rather than total rain (2 mm)?
--- End quote ---
Yes they are bucket tips - as I am reading the data from the archive data record myself using my own code.
Chris
wuhu_software:
The reason that you are seeing such rates is because it is projected from one minute to the next and does not consider the data from the past hour. This is then the instantaneous rate of change, not the hourly rate. The instantaneous rate would assume that the change seen from one minute to the next would continue for the next hour at the rate from 0 to .4mm. I think you are also multiplying by 60 which is not correct. (.4 * 3600) = 1440. I think this would really be .4 * 60 = 24 mm/hr if that same rate continued for an entire hour (always at the same .4mm per minute for an entire hour).
To determine an hourly rainfall rate, the change in time is 60 minutes, the change in total from one hour ago to the time the calculation is made is the "distance" in the formula:
distance (mm) = rate (mm/hr) * time (hr)
rate = distance / time
rain rate = ((total now - total one hour ago)) / 60 mins.
rate = (.4mm - 0) / 60
rate = 0.0066 mm/hr, which rounds to 0.01 mm/hr.
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