[wxqc] Sea Level Pressure

[Gary Oldham]

WeatherLink reports the same data that's shown on the Vantage Pro 
console.  If the user has set his altitude on the console (or via the 
WeatherLink software, which then makes the adjustment on the console), 
then that value (adjusted for altitude only) is what is reported by 
WeatherLink.  As far as I know, that's the same way it works with all 
the third party software as well, including VWS.  VWS will allow a user 
to use their station pressure (meaning an altitude value of "0" on the 
Vantage Pro console) and will do the adjustment within VWS; I don't know 
whether this adjustment goes to altimeter value or sea level. 

Confusingly, the VWS manual makes the following statement: "An air data 
calculator is included in Virtual Weather Station. Virtual Weather 
Station uses the same formulas used in airplane data computers flying 
throughout the world.The altitude and air data information provides air 
density, pressure altitude, corrected temperature and pressure to 
sea-level conditions."  The "air data calculator" on the Station 
Settings window in VWS does show both the temperature and weather 
station-reported pressure, so perhaps VWS *is* including temperature in 
its pressure corrections.  WeatherLink, to the best of my knowledge, 
does not.

Gary Oldham
www.ag-weather.com
www.weatherforum.net

Mike Barth wrote:

> I don't know very much about the Davis data, so I might be wrong, but the
> impression I had was that the calculation of sea level pressure 
> (instead of
> the desired altimeter) is done by the Davis Weather Link software.  If 
> this
> is correct, then VWS might be reporting the correct quantity.  Can 
> someone
> who knows more about Davis and/or VWS comment on this question?
>
> Mike
>
> On Wed, 7 Sep 2005 rich.taft at att.net wrote:
>
>> I also have a VP2 using VWS.  I've been getting 97 of 97 errors on my 
>> QC report. Doesn't this mean that the pressure data that we VP2 users 
>> paid big bucks to collect is also being ignored by NOAA MADIS?
>>
>> I'm sure the VWS can provide both corrected and uncorrected data. If 
>> it?s putting the wrong data into the packet then that needs to be 
>> addressed with the Author of VWS.
>>
>> I'm a little unsure of what the problem with the data is.  Are you 
>> saying that VP2 does Temperature & Humidity compensation on the raw 
>> Pressure data prior to sending it to the Data logger, or is it 
>> something else?
>>
>> -- 
>> Richard Taft
>> www.taftphoto.com
>> CW3815
>>
>> -------------- Original message ----------------------
>> From: Mike Barth <Michael.F.Barth at noaa.gov>
>>
>>> John,
>>>
>>> Sorry I didn't reply sooner...
>>>
>>> I'm afraid the QC processing doesn't have the ability to take into 
>>> account
>>> that some APRSWXNET stations are reporting SLP instead of 
>>> altimeter.  I suggest
>>> you contact Davis about fixing this -- the APRSWXNET protocol requires
>>> altimeter.  In the meantime, you should ignore the QC results.
>>>
>>> Mike
>>
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