Author Topic: CWOP Quality Control  (Read 3549 times)

Blicj11

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CWOP Quality Control
« on: March 09, 2015, 04:09:47 PM »
I have never received the CWOP quality control thumbs up for barometric pressure. One of the reasons is that I am 3,000 feet higher than the closest airport and there aren't really any good nearby stations against which to check my readings.

Here are two quotes from a Davis article about calibrating for CWOP:

CWOP prefers to receive barometer data in the form of altimeter. Altimeter is the CWOP pressure standard because it is the simplest pressure reduction format that most CWOP members can reliably deliver. The National Meteorological Services use this information to determine the uncorrected pressure value at your location, called station pressure. Altimeter uses only elevation to determine a sea-level pressure value. Sea-level pressure is determined from temperature and humidity also, making it more difficult to determine station pressure. Davis Instruments weather stations normally report sea-level pressure.

WeatherLink versions 5.7 and later automatically convert Vantage Pro and Vantage Pro2 barometer data to altimeter. Vantage Pro barometers only need the elevation to be set once to report properly.

I don't use WeatherLink but Davis provides a method of calibrating the pressure reading to be altimeter-based. Basically you set you altitude to 0 on the console and then adjust it until it is within a pressure difference of less than ?0.03 inches (?1.0 mb) of the nearest airport.

1. I think it is better to have your elevation accurate so that you get a true pressure reading even if CWOP rejects that reading in its quality control algorithm. I'm curious if you think it's better to get a green thumbs up from CWOP quality control?

2. Does WeatherCat report altimiter-based pressure readings to CWOP?
Blick


Randall75

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Re: CWOP Quality Control
« Reply #1 on: March 09, 2015, 06:30:37 PM »
Hi Blick
 I have the same problem I am the highest weather station in my area and the during the winter months i never get two thumbs up but as the temperature get warmer then I get 2 thumbs up I did calibration and found out that it did not do any good. I have checked with 2 airports that both within 20 miles on my house and my readings are usually the same as theirs but I have PWS around me that are reading lower than me but are also 200 to 300 ft lower than me I emailed them and they gave me a bull that my new station is not calculated right so i contacted Davis and we went through the calculation process and they at CWOP still give bad thumbs up during the winter months so I quit wearing about it


But if it is bugging you you can set you barometer .03 lower and after a week or two get better thumbs up but then to me your are sending out uncorrect values out other stations.


Go here and change the numbers to your station and they say ever thing is OK or and X if there is something wrong : http://www.wrh.noaa.gov/mesowest/getobext.php?sid=C6734 that is out of Salt Lake City, Utah


hopes this helps you understand.
 about what the  the"http://weather.gladstonefamily.net/site/xxxx I have questions about it.


cheers [cheers1]

Bull Winkus

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Re: CWOP Quality Control
« Reply #2 on: March 09, 2015, 07:26:01 PM »
Here's my thoughts on the matter. I completely disagree with the premise of calibrating a sensor to a quality monitoring service. Calibration is the process of adjusting the output of a sensor to a known standard. The CWOP service is determining the quality by comparing your reading to those of others using the same service. If several users start to adjust their station to conform to the perceived correct reading, then the perceived correct reading becomes corrupted by the adjustments resulting in a positive or negative feedback error in CWOP as a standard, which it is not.

I find their report useful for communicating the consistency of my pressure sensor. It revealed to me that my first console had a tendency to drift. However, I wont use it to determine the accuracy. What is know about their reference signal is that it's accuracy is not known, and this is especially true for your station location.

Herb

elagache

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Doesn't sound like your fault (Re: CWOP Quality Control)
« Reply #3 on: March 09, 2015, 08:48:10 PM »
Dear Blick, Randall, Herb, and WeatherCat data submission junkies,

I have never received the CWOP quality control thumbs up for barometric pressure. One of the reasons is that I am 3,000 feet higher than the closest airport and there aren't really any good nearby stations against which to check my readings.

Seems to me that the real problem is as you describe it.  Without other stations to compare your against, CWOP simply cannot know if your barometric pressure is accurate or not.  It is a bit annoying that their ignorance is being held against you, but effectively this is a kind of bureaucratic bad call.  Unless you actually have a reason to suspect your station has a problem . . . . . as they used to say in the "good old days of TV:"

No adjustment of your screen is necessary.

Cheers, Edouard  [cheers1]

xairbusdriver

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Re: CWOP Quality Control
« Reply #4 on: April 26, 2015, 09:05:48 PM »
I've just spent (wasted?) an hour looking for a way to adjust my position as reported in/by/on APRS, as reported by CWOP. The "registered" location is about 10 feet from the actual location in my yard. The APRS position is ~0.1 miles ESE, on the green of the golf course south of me. [rolleyes2]

I registered my location on 4/17/15 and modified it three days later making moving it 0.0001?N and -0.0002?W. I had five different altitude numbers from various sites averaging to 354.66 feet (108.1 meters).

First WC data was: 35? 04'.13N, 89? 44'.10W, 108 metres.
I changed that to: 35? 04'.13N, 89? 44'.11W, 108.1 metres.

I have a two "thumbs up" CWOP rating with the following "error" message:
Average barometer error:   -0.5 milliBars
Error standard deviation:   0.6 milliBars

TwoThree questions:
  • Where did APRS get its location info?
  • Will a tenth of a meter/metre really make a difference in the baro pressure?!
  • Should I care?
[removed link to the now castly photobucket.com site]
« Last Edit: December 30, 2017, 05:54:28 PM by xairbusdriver »
THERE ARE TWO TYPES OF COUNTRIES
Those that use metric = #1 Measurement system
And the United States = The Banana system


Randall75

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Re: CWOP Quality Control
« Reply #5 on: April 26, 2015, 09:56:29 PM »
Hi xairbusdriver
 You can go to:http://weather.gladstonefamily.net/site/XXXXX (XXXXX are your call letters)
 And adjust the location on the map to give you the best location possible.


A few degrees are not going to change your pressure readings and I don't think that their readings are that acturate with my Old LaCrosse I had 100% all the time since i got my VP2 I don't get 100% on my pressure readings tried everything to get 100% and couldn't get ti [banghead]


Cheers


 [cheers1]

xairbusdriver

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Re: CWOP Quality Control
« Reply #6 on: April 26, 2015, 10:08:19 PM »
That's how I adjusted the LAT/LON. My main question is how the altitude is created at APRS. If all the stations around me aren't any more exact than mine, it would seem to be the infamous "Garbage IN, Garbage OUT". ;)
THERE ARE TWO TYPES OF COUNTRIES
Those that use metric = #1 Measurement system
And the United States = The Banana system


Felix

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Re: CWOP Quality Control
« Reply #7 on: April 27, 2015, 01:14:57 AM »
I live in a valley and there's a small regional airport some five miles away on a plateau. During lengthy rainy periods, especially when accompanied by lots of fog in the valley (temp/dew point spread very close), I frequently get dinged by CWOP for dew point deviations. I stopped worrying about it since the CWOP algorithm clearly has no way to figure out that fog collects in valleys and the RH is going to be higher than at the airport on a plateau. When things dry out, I'm back to a green check and two thumbs up. But it is irritating when CWOP includes a message that I likely have a station siting problem (which I don't, it's in a wide open area meeting the NWS criteria) yet all other tracked parameters are green check and two thumbs up. It's a case of CWOP giving too much preference to the airport station just because it's an airport and presumed to be correct. Yet I went out there once and found they are not certified by NWS and have no established periodic calibration plan in place. At that point, I stopped being concerned with CWOP's QC ratings. I figure my data is likely just as accurate as the airport's data. But the next time I send a station back to Davis for refurbishing, I'm going to see how much extra they charge to calibrate and certify the sensors.