Author Topic: Tripod mount distance above roof line?  (Read 15603 times)

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Offline jjocsak

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Re: Tripod mount distance above roof line?
« Reply #25 on: January 22, 2009, 01:09:18 PM »
Yes I agree. That is why I am separating the ISS from the anemometer (separate transmitter) and putting it in a more favorable location.

Jeff

Offline MoradaWx

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Re: Tripod mount distance above roof line?
« Reply #26 on: January 22, 2009, 09:05:23 PM »
I have not read about  perfect locations in about 2 years, but I seem to remember that you were not to place the ISS close to sprinklers or pools also. When California "has water", we water our lawns which effects the humidity and temp that may higher on the roof. I have several temp sensors of various types and brands around the house and except for direct sunlight or the afternoon sun on a concrete door step they all track very close to each other. My ISS is on the roof with a tripod. The ISS is at eye level so I can maintain it with the anemometer at the top of the 10 foot pole. There is an A/C unit about 10 feet away. The exhaust from the heater is on the opposite side away from the ISS and the fan from the A/C condensing blows up and over the ISS with no effect. On several different days with different weather, heating and cooling loads I saw no change or spikes in the reported data.

my $.02

Rick

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jwyman

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Re: Tripod mount distance above roof line?
« Reply #27 on: January 22, 2009, 11:15:49 PM »
See SlowModem's post on the CWOP guide. It gives great insight to why things are placed where they should...

Jim

Offline jjocsak

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Re: Tripod mount distance above roof line?
« Reply #28 on: January 23, 2009, 05:21:03 AM »
I was amazed to see the Rain Gauge Precipitation
Under-Catch and Wind Speed chart.

Loss is incredible at just slightly higher wind speeds.

Jeff

jwyman

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Re: Tripod mount distance above roof line?
« Reply #29 on: January 23, 2009, 08:10:07 AM »
Jeff,
  If you could see the rain collection devices at AWOSs (stationed at airports), they have a large wind deflection barrier around them to minimize the effect of wind on rain/precip collection.....

Jim

Offline d_l

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Re: Tripod mount distance above roof line?
« Reply #30 on: January 23, 2009, 09:45:08 AM »
Thank guys for bringing that rain under catch subject up!  :grin:

That may be exactly what I was seeing yesterday when I could hear very light rain on the skylight, but hardly had any increase in the tipping bucket. The winds were 2 to 5 m/s at the time.  My ISS is in some native brush, but about 2-3 feet above the top of it.  I had thought when I set it up that the brush would cut the wind down over the rain cone, but apparently it is not enough to eliminate the under catchment possibility.  I estimated that for a while my ISS was only seeing 30-70% of the rain all the other rain gauges in the area were reporting.  This is in incredibly good aggreement with the charts! Due to the dry climate here, I don't often have tests of the ISS's rain collection and this is really the first in five months.

It looks like I either need to lower the ISS slightly (it is ~6' high) to get it better sheltered by the surrounding brush or devise some sort of wind shield that can be installed within all the bush back there.
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blackjack52

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Re: Tripod mount distance above roof line?
« Reply #31 on: January 23, 2009, 10:48:59 AM »
I would think if you surround it by brush that your DP, HUM, CloudBase, HeatIndx, etc data will then be affected.

Offline d_l

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Re: Tripod mount distance above roof line?
« Reply #32 on: January 23, 2009, 11:58:02 AM »
Maybe in the fall and winter months.  The brush is native high-desert, vegetation that doesn't exhale moisture like non-desert plants might. Certainly the RH would be much higher (and totally artificial) in the summer over an open, watered lawn than over native bare dirt, rocks, sage and bitter brush, and dried grass.

One function of my station is to accurately measure the ET rates needed for my plants/lawn in order to minimize the expensive watering of them.  This would be for the air after the wind has blown it across this surrounding native enviroment.
--Dave--

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People always talk about the weather, but they never do anything about it.  Not me.  I'm gonna measure it.  https://www.tceweather.com

blackjack52

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Re: Tripod mount distance above roof line?
« Reply #33 on: January 23, 2009, 01:37:29 PM »
Good point.  The other factor to consider would be to ensure shading where the temp sensor is.

Offline Cienega32

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Re: Tripod mount distance above roof line?
« Reply #34 on: January 24, 2009, 03:17:45 PM »
Jeff,
  If you could see the rain collection devices at AWOSs (stationed at airports), they have a large wind deflection barrier around them to minimize the effect of wind on rain/precip collection.....

Jim
Is there a source for info/details on that? I think using something like that would be a helpful addition for us in the monsoon belt.

Too many times watching torrents of rain coming down in 30+MPH winds! I always wonder just how much is missed because of the impact, let alone the angle.

Pat ~ Davis VP2 6153-Weatherlink-Weather Display-StartWatch-VirtualVP-Win7 Pro-64bit
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blackjack52

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Re: Tripod mount distance above roof line?
« Reply #35 on: January 24, 2009, 03:53:56 PM »
Good point.  The other factor to consider would be to ensure shading where the temp sensor is.

Let me correct myself;
The other factor to consider would be to ensure there is no shading where the temp sensor is.

Offline tomcj2

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Re: Tripod mount distance above roof line?
« Reply #36 on: January 24, 2009, 03:56:29 PM »
Why should the wind velocity have any effect on the rain measurement.  The rain drops that land in my gauge during a 50 mph wind may have landed in my neighbour's yard had it been calm. Sooner or later all rain will hit the ground;  I want to know what is landing on my property.  

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blackjack52

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Re: Tripod mount distance above roof line?
« Reply #37 on: January 24, 2009, 04:16:43 PM »
If the rain is being blown horizontally, it will measure less.  Won't the wind affect rain rate :?:


Offline jjocsak

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Re: Tripod mount distance above roof line?
« Reply #38 on: January 24, 2009, 04:36:54 PM »
Why should the wind velocity have any effect on the rain measurement.  The rain drops that land in my gauge during a 50 mph wind may have landed in my neighbour's yard had it been calm. Sooner or later all rain will hit the ground;  I want to know what is landing on my property.  

Taken from the Citizen Weather Observer Program Guide:



Jeff

Offline Bushman

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Re: Tripod mount distance above roof line?
« Reply #39 on: January 24, 2009, 04:41:44 PM »
That is interesting.  Top speed of ~17 MPH is only 12% catch!
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Offline tomcj2

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Re: Tripod mount distance above roof line?
« Reply #40 on: January 24, 2009, 04:44:42 PM »
Where does the other 88% go?

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Offline jjocsak

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Re: Tripod mount distance above roof line?
« Reply #41 on: January 24, 2009, 04:48:28 PM »
Here



Jeff

blackjack52

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Re: Tripod mount distance above roof line?
« Reply #42 on: January 24, 2009, 05:03:37 PM »
Measured RainRate decreases with increased wind, unless the volume of water increases.  But what you would feel if you were outside would be an increase in rainrate with the increase in wind.  I guess the wx station doesn't compute for increase in wind increasing the rainrate.  Now that's deep.

jwyman

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Re: Tripod mount distance above roof line?
« Reply #43 on: January 24, 2009, 05:04:09 PM »
Great Data jjocsack! I will try to find some airport photos about the rain gauage and wind deflection unit...

Jim

Offline Bushman

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Re: Tripod mount distance above roof line?
« Reply #44 on: January 24, 2009, 05:59:39 PM »
Here's some info on one deflection screen:  http://www.novalynx.com/manuals/260-952-953-manual.pdf
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Offline SlowModem

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Re: Tripod mount distance above roof line?
« Reply #45 on: January 24, 2009, 09:06:37 PM »
I want to know what is landing on my property.

It's those spaceships full of illegal aliens that you have to worry about!

 :o

Greg Whitehead
Ten Mile, TN USA

Offline SlowModem

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Re: Tripod mount distance above roof line?
« Reply #46 on: January 24, 2009, 09:19:29 PM »
Now that's deep.

Oh, so now you're adding an element of time in addition to the increase in rainfall rate! 

How long does it take to get deep?

 UU
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blackjack52

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Re: Tripod mount distance above roof line?
« Reply #47 on: January 24, 2009, 09:26:06 PM »
Now that's deep.

Oh, so now you're adding an element of time in addition to the increase in rainfall rate! 

How long does it take to get deep?

 UU

No, just that since the measured rain rate at the bucket will decrease when winds increase, there should be a variable computed by the software to compensate. But that might be too difficult.

blackjack52

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Re: Tripod mount distance above roof line?
« Reply #48 on: January 24, 2009, 09:32:03 PM »
Here's some info on one deflection screen:  http://www.novalynx.com/manuals/260-952-953-manual.pdf

I could understand going to those lengths if you have a couple k wrapped up in the wx sys, but not for a Davis.

Online SLOweather

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Re: Tripod mount distance above roof line?
« Reply #49 on: January 24, 2009, 10:45:05 PM »
No, just that since the measured rain rate at the bucket will decrease when winds increase, there should be a variable computed by the software to compensate. But that might be too difficult.

Hmm... That's an interesting idea. The curve on the graph in the post up above is almost linear, close enough that the slope could be used for a velocity to rainfall compensation factors.

There are a couple of things that complicate applying a compensation. The first is velocity. Storm winds are, in my experience, almost never steady. They vary by quite a bit. So, they'd have to be averaged out. The slope of the curve is almost linear, so that might actually work.

However, the next problem is that rainfall is always measured in arrears. That is, the gauge only tells you how much has fallen in the past. For compensation to be useful, you'd have to know the time between the latest rain gauge tip and the one before it. That time will almost always vary as the storm progresses.

Then, you'd have to calculate the average wind speed for that time period, and use that to calculate or look up the rainfall compensation factor for that wind speed, multiply that times the rainfall in the period (probably 0.01") and then add that to the current rainfall.

It could be done, but that's a lot of work.