WXforum.net
Weather Station Hardware => Davis Instruments Weather Stations => Topic started by: Sartori on May 25, 2010, 04:02:26 PM
-
Hello
I recently purchased a Vantage Vue station and am finding that the rain accuracy is quite a bit different then my cylinder gauge. This is the one I'm comparing it too:
http://www.amazon.com/All-Weather-Rain-Gauge-Official/dp/B000PHKZPS
Recently there have been three different rain storms come through here and the Vantage Vue has been consistently lower then the cylinder gauge. They are both in open areas and are about 100 feet apart. The difference varies but gets worse the more it rains, all the way from a .10 at a half inch to .20 at an inch and a half.
So, I figured I would go into the rain calibration area of the console and change the settings. I started out at -2, then went to -8, -14, and all the way to the max at -25, didn't make any difference in the readings at all....
Yes, everything is clear, clean, and its mounted spot-on level also. I did contact Davis and they are sending me a new tipping spoon assembly but thought I would post a topic here and see if anyone else has gotten or are getting a big difference in their rain readings...
Thanks for any replies!!
-
Mine has tracked really close to the CoCoRaHS collector.. usually varies .01-.04 difference between the two.
Maybe I have been really lucky :-P
-
100' is too much distance over which to compare rain gauges. If you are going to adjust the Vue to the Stratus gauge, mount them as close together as possible. My Stratus is on the opposite side of a 6x6 post from the VP2 ISS. Both are at the top, tops level with each other to avoid rain shadow. They track very closely, within 0.02" or so in most rain events, and also closely track an 8" standard gauge about 6' away sitting on the ground.
OTOH, the wireless VP2 in the back yard, perhaps 200' away, which I use for systems development, hardly ever matches the other gauges. Both VP2s have been carefully calibrated with a NovaLynx tipping bucket calibrator. I don't know what the console adjustment is for, but IMO, if you're going to calibrate a tipping bucket/tipping spoon gauge, it's best to calibrate the mechanism itself.
-
Okay, will see about getting the cylinder gauge mounted a little closer.
I didn't see anywhere on the tipping mechanism where you would calibrate it on there. The only place was within the console...
-
There's a screw you can turn by hand underneath the ISS to alter it.
Are you sure it's level first?
That makes a big difference with the vue single spoon-type bucket.
Make sure it's level including after you tighten up the clamp.
-
There's a screw you can turn by hand underneath the ISS to alter it.
Are you sure it's level first?
That makes a big difference with the vue single spoon-type bucket.
Make sure it's level including after you tighten up the clamp.
Okay, I see that now won't mess with it yet though...Yes its mounted level, made sure the pole was level and the bubble was directly in the center...
I mainly thought messing with that console calibration would change it more but guess thats not the case....
I have been reading some more on the forum, it seems the wind is going to affect the reading quite a bit too as I do have it mounted quite a ways in the air. Heres a pic:
If we ever get a rainstorm without any wind I'll see how they both read then also....
-
Yes, wind has quite an effect - that's the main reason to have them close together, if you're going to compare. If there are any houses, trees, bushes, etc. around, and/or if they are mounted at different heights, then they get different breezes.
-
I have 4 tipping bucket rain gauges along with cocorahs gauge in a line. My Rainwise gauge which is 7 years old is by far the best tipper for consistancy and staying calibrated over time.
-
Just a follow-up, and the Davis tech guy couldn't answer this....Do any of you know how much the rain calibration changes the amount on the Vantage Vue console? The amounts are in a percentage from -25 to +25 but a percentage of what amount though....of a .01, .10, 1.00, etc...
Thanks
-
It wouldn't make any difference, it would still be the same percentage.
If you think it rained an inch but vue says 0.9inch turn it up 10%
There's going to be a bit of trial and error.
-
Okay, makes sense, I guess...yes already been through the trial and error, read my first post:)
-
Well, first, this (from the Vue console manual) seemed fairly clear to me:
Enter the error. Enter a negative number if your station is under reporting; enter a
positive number if it is over reporting. For example, if your station is low by 2%,
enter -2. If your station is high by 4%, enter 4. Press the + and - keys to add or
subtract from the percent amount. The Rain Error Percentage range is -25 to 25
percent. (Not all corrections are available, so you may have to choose the closest
one.)
Now, what is it that you're calibrating?
The book says: "The Rain Error in Percent refers to the measuring error of your rain collector".
So, I figured I would go into the rain calibration area of the console and change the settings. I started out at -2, then went to -8, -14, and all the way to the max at -25, didn't make any difference in the readings at all....
What readings were you looking at?
I'm betting you were looking at daily rain, monthly rain, total rain.
I'm betting that the calibration changes the correction to what will be measured and recorded in the future..
What has already been measured and recorded in the past, can't be changed (by that method). That's why you didn't see any "change".
You can manually change the "past" (pages 28 and 29), of course.
-
I see from your picture the Vue is on the roof. Is the cylinder gauge as well? I'm guessing not, considering you don't want to climb up to dump it all the time. That right there can make a huge difference, depending on winds.
My father has 2 of the same gauges you have, and he has them about 100 feet apart. One in front of the house and one in back. He lives out in the country, so no neighbors to shield him. But even then, he can get as much as .10 inch difference.
I moved to a new house and had reception problems with my VP1, so I bought a VP2. I gave him my old VP1 hoping he can use it. I'm real curious to see how the rain gauge will compare to his manual gauges. My dad doesn't think it'll work as well. But I have a CWOP gauge mounted to the same pole as my VP2 is, and they agree within .02 inches.
-
Well, first, this (from the Vue console manual) seemed fairly clear to me:
Enter the error. Enter a negative number if your station is under reporting; enter a
positive number if it is over reporting. For example, if your station is low by 2%,
enter -2. If your station is high by 4%, enter 4. Press the + and - keys to add or
subtract from the percent amount. The Rain Error Percentage range is -25 to 25
percent. (Not all corrections are available, so you may have to choose the closest
one.)
Now, what is it that you're calibrating?
The book says: "The Rain Error in Percent refers to the measuring error of your rain collector".
So, I figured I would go into the rain calibration area of the console and change the settings. I started out at -2, then went to -8, -14, and all the way to the max at -25, didn't make any difference in the readings at all....
What readings were you looking at?
I'm betting you were looking at daily rain, monthly rain, total rain.
I'm betting that the calibration changes the correction to what will be measured and recorded in the future..
What has already been measured and recorded in the past, can't be changed (by that method). That's why you didn't see any "change".
You can manually change the "past" (pages 28 and 29), of course.
Well I'm happy that its clear for you:) I'm not worthy, I'm not worthy...
Okay, yes I know all that, I'm calibrating the rain amount! And I understand its the future amounts, that what I was looking at after I changed it and after the next storm went through. I wasn't looking at daily, past, month. I was comparing the change to the future rains! And I'm saying, changing it DID NOT change the "future rain" amounts at all comparing it too the cylinder gauge from each rain strom...
And the percentage that they are referring too in the book isn't clear on what they are comparing it too for the difference...
-
Okay, yes I know all that, I'm calibrating the rain amount! And I understand its the future amounts, that what I was looking at after I changed it and after the next storm went through. I wasn't looking at daily, past, month. I was comparing the change to the future rains! And I'm saying, changing it DID NOT change the "future rain" amounts at all comparing it too the cylinder gauge from each rain strom...
And the percentage that they are referring too in the book isn't clear on what they are comparing it too for the difference...
OK, sorry I misinterpreted what you wrote. I'm still a bit curious about your exact procedure, though.
First, although you didn't say, I'm assuming that you believe that your Vue is underreporting. That's why you would use a negative adjustment.
Recently there have been three different rain storms come through here and the Vantage Vue has been consistently lower then the cylinder gauge. They are both in open areas and are about 100 feet apart. The difference varies but gets worse the more it rains, all the way from a .10 at a half inch to .20 at an inch and a half.
So, I figured I would go into the rain calibration area of the console and change the settings. I started out at -2, then went to -8, -14, and all the way to the max at -25, didn't make any difference in the readings at all....
What was the calibration set to, when the half-inch storm happened? What was it set to when the 1.5-inch storm happened?
And you made 4 changes for 3 storms?
How about posting just the actual data for the three storms:
Calibration setting, Vue measurement, Cylinder measurement.
I think that would be a lot easier for us to understand, and perhaps help with.
-
Hello
Had another rain storm come through last night with very little wind. I have the calibration setting at -25, the cylinder showed .37 and the Vantage Vue showed .32
I still don't think that calibration setting is changing it any...
-
For the other three storms you reported:
"How about posting just the actual data for the three storms:
Calibration setting, Vue measurement, Cylinder measurement."
-
For the other three storms you reported:
"How about posting just the actual data for the three storms:
Calibration setting, Vue measurement, Cylinder measurement."
Okay, initial install of the Weather Vue station with no change in the rain calibration:
Calibration setting: 0
Vue Measurement: .40
Cylinder Measurement .54
Second Rain
Calibration Setting: -8
Vue Measurement: .25
Cylinder Measurement .38
Third Rain
Calibration Setting: -25
Vue Measurement: 1.48
Cylinder Measurement 1.70
-
Thanks for the data.
If I "back convert" the data (remove the assumed correction percentage), then the percentage differences between the Vue and the Cylinder are fairly similar, which tends to indicate that the console correction is in fact working. Of course, the sample size is relatively small.
Notice that the percentage difference from both of the samples where the setting was -25, are virtually identical. And the "error" on the other two samples is quite different.
And I don't know how far you are from Flaxville, but it looks like your cylinder readings are consistently lower than Flaxville.
At any rate, I don't think you're going to know anything for sure until you get the two rain gauges mounted close together, and at the same elevation. Until then, you'll have to assume that they are each accurately measuring the rain that they catch, where they are.
-
Flaxville?? Where the heck did you get that from? Thats pretty funny:)
-
Flaxville?? Where the heck did you get that from? Thats pretty funny:)
Well, your ISP is "North East Montana Network". I just picked a town. Should I have picked West Fork or Scobey or Wolf Point? :grin:
Billings or Missoula?
-
There's no way that you can compare my cylinder reading's to those towns if theres going to be a big difference in two gauges 100 feet apart. I'm out in the country in the middle of nowhere and the distance to those towns you listed varies from 20 miles to 500 miles:)
We had another rain event last night, it was dead calm when it was raining so wind was not a factor at all this time. I still have the rain calibration set to -25, the Vue reported .10 and the cylinder reported .13. Yes the gauges are still in the same place, I didn't move the cylinder gauge closer yet.
I really don't think that in this rain event instance that having the gauges close together would have made an difference....
I guess I'm just going to live with the difference for now and just average the two together. I had a Vantage Pro before this station and it always undereported also and the two gauges were 10 feet apart and at the same elevation. I also previously had the data uploading to wunderground and was going to do it again but am holding off for now till I change the tipper assembly with a different one just to make sure. I refuse to upload data again if its just going to be "close"...
I shouldn't have to max that rain calibration all the way to -25 right out of the box just to get the reading's "close". If they are going to have that option in there they need to do it from -100 to +100 so it will make a bigger difference, especially if wind is going to be a factor with the unit...
-
I recently post an interesting segment of a CoCoRaHS newsletter in another thread . Look at http://www.wxforum.net/index.php?topic=7899.msg76618#msg76618 (http://www.wxforum.net/index.php?topic=7899.msg76618#msg76618)
-
I noticed a discrepancy of about 25% due to wind one day early April
( http://www.wxforum.net/index.php?topic=7602.0 )
Take it to the extreme with wind blowing rain almost horizontally and clearly quite a lot will not fall inside the funnel.
Mind you that almost suggests a debate about where the missing rain does end up!
-
I really don't think that in this rain event instance that having the gauges close together would have made an difference....
You will not know for sure, until you try it. Until then, it's a guess.
What is the vertical distance between the two gauges?
"...one general conclusion is that measurements of rainfall constitute an unsolved problem in that rainfall measurements are corrupted with significant uncertainties that are difficult to quantify." That's from:
http://www.iihr.uiowa.edu/~hml/people/kruger/Publications/PDF/StMauritz.pdf
-
Thanks for the PDF, that was pretty interesting reading! I want a 2-D Video Disdrometer, yeah thats the ticket:)
-
There's also a more general PDF resume available of gauge height and other variables on rainfall measurement which I have posted before some time back, but maybe a reminder would be useful:
http://www.onerain.com/includes/pdf/whitepaper/InconsistentRainGageRecords.pdf
-
Which is why I asked Sartori about the vertical distance between gauges.
Also, Sartori's Vue is mounted about 3 or 4 ft. above a large, pitched, smooth metal roof - ideal for enhancing any disturbance of even small wind currents. And perhaps higher than the 20 ft. in the Figure 2 graph.
I've never seen a significant rain event when it was "dead calm when it was raining". I'm inclined to say that's technically impossible.
-
There's also a more general PDF resume available of gauge height and other variables on rainfall measurement which I have posted before some time back, but maybe a reminder would be useful:
http://www.onerain.com/includes/pdf/whitepaper/InconsistentRainGageRecords.pdf
Yes, very interesting read too, am learning:)
-
Hello
Just thought I would let you guys know that I did get the Vantage Vue synced up with the CoCoRahs gauge now. Every rain event now is either spot on or within a .01 or .02 of each other. And yes I did temporarily mount the gauge up by the station. After that I moved the gauge back to where it was originally....
It took quite a bit of trial and error but I got it....
I'm currently uploading my data to the NWS and the station is showing up on the MesoWest site...
Thanks for all your input and help!
-
Thanks for the update. One question: (below)
Just thought I would let you guys know that I did get the Vantage Vue synced up with the CoCoRahs gauge now. Every rain event now is either spot on or within a .01 or .02 of each other. And yes I did temporarily mount the gauge up by the station. After that I moved the gauge back to where it was originally....
So, are you saying that after you moved the gauge back to where it was originally, the Vue and the CoCoRahs gauge now read the same for every rain event?
[If not, then how much variation?]
That information will be very helpful to others, in the future.
-
Mine varies. This morning it was spot on. However for the monthly total the Vue is off by -.63" for the month of June.
8.6" CoCoRahs vs 7.97" for the Vue.
-
Mine varies. This morning it was spot on. However for the monthly total the Vue is off by -.63" for the month of June.
8.6" CoCoRahs vs 7.97" for the Vue.
Thanks - but my question was aimed at Sartori, who seems to have argued with advice, then taken some of it, and then not come back to answer questions. So, we have no idea of his real results.
Sartori's Vue and CoCoRahs are apparently very far apart vertically and horizontally.
I sometimes get really discouraged when people ask for advice, and then don't provide followup information.
-
Well, it is what it is. Mine are about 75 feet apart, Cocorahs is at 5' above ground and the Vue is 15' above ground. I report what the CocoRahs gauge says to them and that is, in my opinion the "gold standard". The Vue just tells me it's raining, about how much, and I need to check the other guage.
-
Well, it is what it is. Mine are about 75 feet apart, Cocorahs is at 5' above ground and the Vue is 15' above ground. I report what the CocoRahs gauge says to them and that is, in my opinion the "gold standard". The Vue just tells me it's raining, about how much, and I need to check the other guage.
Yes, and thanks for describing that. As I recall, Sartori's Vue is about 20 ft. up, above a metal roof - and his CocoRahs-type gauge is mounted at normal height, and he expected to be able to get them to always agree. He reported some detailed differences in readings.
After finally convincing him that he needed to calibrate with them physically "together", he said:
Just thought I would let you guys know that I did get the Vantage Vue synced up with the CoCoRahs gauge now. Every rain event now is either spot on or within a .01 or .02 of each other. And yes I did temporarily mount the gauge up by the station. After that I moved the gauge back to where it was originally....
So, I'm curious as to how "together" the readings are, now that he has done the calibration and then moved them apart.
I'm rather sure I know the answer - but it would be nice to hear from Sartori.
-
have had several storms, seems to run about 10-15% low on rainfall compared to my 4" gauge and WS-3610 tipping bucket. main difference...vue is roof mounted and gets more wind, other 2 are not on roof and pretty much wind protected most of the time. had a fairly light wind rain event overnight, 4" gauge had .22, 3610 recorded .20, and the vue reported .19 ... have yet to use the console rain correction... instead am using the rain tweak in WUHU, which is nice because you can tweak the rain after the fact, and it will correct and send updated rainfall to the servers. the vue correction only applies as the rain falls, not for past rain. anyway, not a huge issue IMHO, and since it is likely due to wind more than an inaccurate rain gauge, will continue to tweak as needed. if I can get a reliable correction over the passage of time, probably should just go ahead and use the console correction. anyone else having rainfall issues?
-
Not me, but mine is only 9' off the ground.
-
We had another rain event last night,
PMFJI but is that American for "it rained last night"? This expression is creeping into British TV weather reports. Last winter we had 'snow events' meaning it snowed. Will a hurricane be known as an extreme wind event?
I don't understand why it's used when there's a much simpler alternative. ](*,)