Topic: Weather Stations at Airports

[LIWeather]

Just curious to know if there is a specific brand/model that the airports use. Do they utilize FARS?

Being that some warm, sunny weather is approaching, I've been thinking more and more about about a Daytime FARS or home made project as I've seen on here to keep the temperature readings more accurate. I am currently over 10 degrees warmer then the local airport and I'm sure its b/c of the sun beating down on the station. I was more curious about the way airports keep their readings accurate and whether it was the brand of weather station, location, extra equipment, etc.

[METARMan]

All Weather and Vaisala make automated weather stations installed at airports:

http://www.allweatherinc.com/meteorological/toc_temperature.html

http://www.vaisala.com/weather/products/humiditytemperature.html

[METARMan]

ASOS is probably the most popular airport weather station in the U.S. today.  Here is the ASOS User's Guide (published in the 1990s):

http://www.nws.noaa.gov/asos/pdfs/aum-toc.pdf

The description of the temperature sensor and housing begins in Chapter 3.  While ASOS still uses the HO-83 to measure temperature, the chilled mirror dewpoint sensor was unreliable & inaccurate.  ASOS units currently measure dewpoint using the Vaisala DTS 1.

A criticism of the HO-83 can be found here:

http://wattsupwiththat.com/2008/01/10/inside-the-asos-ho83-tempdewpoint-sensor/

and a paper can be found here:

http://ams.allenpress.com/archive/1520-0442/8/5/pdf/i1520-0442-8-5-1394.pdf

[wxtech]

Just curious to know if there is a specific brand/model that the airports use. Do they utilize FARS?

Being that some warm, sunny weather is approaching, I've been thinking more and more about about a Daytime FARS or home made project as I've seen on here to keep the temperature readings more accurate. I am currently over 10 degrees warmer then the local airport and I'm sure its b/c of the sun beating down on the station. I was more curious about the way airports keep their readings accurate and whether it was the brand of weather station, location, extra equipment, etc.

The temperature that your sensor is exposed to is more a function of where it is located than how much air flow it experiences.
If your temp sensor is close to a street/asphalt, to a house/roof, or in a grassy area will affect the air temperature.  Directing more of that temperature of air won't appreciably affec the temperature of the sensor.
If the sensor is near a street and the air temperature in that area is 85º then you'll measure 85º regardless how much of that 85º air you push across the sensor.  Pushing more air across the sensor won't lower the temperature of the air.
Look at the height of the sensor from the grass, how close is it to a building, how close is it to pavement?  The sensor device inside the radiation shield should not be able to "see" anything black that is hotter than the soil/grass. 
I worked at airports, the sensors were on towers in grassy areas.  The temp/dew point sensors were aspirated.
Increased air flow will across the sensor cause the sensor to respond quicker to changes in air temperature.
Don't try to make your temperature the same as at your nearest airport.  What you got is what you got.  We want to know what the temperature is at your house.

[DanS]

"The temperature that your sensor is exposed to is more a function of where it is located than how much air flow it experiences.
If your temp sensor is close to a street/asphalt, to a house/roof, or in a grassy area will affect the air temperature.  Directing more of that temperature of air won't appreciably affec the temperature of the sensor.
If the sensor is near a street and the air temperature in that area is 85º then you'll measure 85º regardless how much of that 85º air you push across the sensor.  Pushing more air across the sensor won't lower the temperature of the air.
Look at the height of the sensor from the grass, how close is it to a building, how close is it to pavement?  The sensor device inside the radiation shield should not be able to "see" anything black that is hotter than the soil/grass."

Well said Wxtech! May I also add, temp sensors inside a solar radiation shield will not only measure the surrounding air temperature but also the additional heat from the direct sun on the shield's plates. The fan aspiration helps to pull the outside air across the plates cooling them closer to the surrounding temperature. With your example of the 85 degree street, the sensor in a radiation shield exposed to direct sun senses the 85 degrees plus whatever is absorbed by the shield from the sun. A FARS will draw this 85 degree air through and keep the shield temperature closer to the outside 85 degrees. Placing the shielded sensor(s) in a location out of direct sunlight will give better results.

Dan

[LIWeather]

Understood about the direct sunlight and drawing in ambient air. How well does the solar sensor work being out of direct sunlight? I'm not sure I want to be replacing the battery all year long.

In order for me to be out of direct sunlight, I would have to move the ISS to an area that would be over concrete instead of grass and far closer to the house which would add more indirect rain to the rain collector as well as add radiant heat to the temperature readings. I'm trying to find the solution that will allow more accurate readings. The ISS being baked in the sunlight is definitely giving me noticeably higher readings then PWS's around me.

[wxtech]

Well said Wxtech! May I also add, temp sensors inside a solar radiation shield will not only measure the surrounding air temperature but also the additional heat from the direct sun on the shield's plates. The fan aspiration helps to pull the outside air across the plates cooling them closer to the surrounding temperature. With your example of the 85 degree street, the sensor in a radiation shield exposed to direct sun senses the 85 degrees plus whatever is absorbed by the shield from the sun. A FARS will draw this 85 degree air through and keep the shield temperature closer to the outside 85 degrees. Placing the shielded sensor(s) in a location out of direct sunlight will give better results.

Understood about the direct sunlight and drawing in ambient air. How well does the solar sensor work being out of direct sunlight? I'm not sure I want to be replacing the battery all year long.
In order for me to be out of direct sunlight, I would have to move the ISS to an area that would be over concrete instead of grass and far closer to the house which would add more indirect rain to the rain collector as well as add radiant heat to the temperature readings. I'm trying to find the solution that will allow more accurate readings. The ISS being baked in the sunlight is definitely giving me noticeably higher readings then PWS's around me.

Dan is absoultely correct.  I disagree, respectfully, however in that it should be in the sun.  Don't try to lower the high temps by moving the sensor out of the sun.  You may need to invest in/build a more efficient solar radiation shield.  Build on what Dan said, put your shield within a new shield. 
I can't find your type of wx station listed.   
I'll post my backyard photo again.  It's mostly Davis VP2 with a mingling of everything I can afford.  Direct Sun exposure all day.
One of the two shields in the photo is an NWS max/min temp system.  Sited and installed by the NWS Region Coop Manager.  He was trying to get it 100 feet from the nearest street, but in a town, that wasn't possible.

[LIWeather]

Is your shield within a shield all the way to the right in the right picture?

I too have a Vantage Pro2. I just want the temps to be as accurate as possible. I want to know when I look at the temps and walk outside, thats the temp. I know that the sunlight is heating it up and increasing the temps.

What is the outer shield consist of? What materials? I am not the most handy of the bunch so keep it simple if you don't mind...haha

[wxtech]

Is your shield within a shield all the way to the right in the right picture?

I too have a Vantage Pro2. I just want the temps to be as accurate as possible. I want to know when I look at the temps and walk outside, thats the temp. I know that the sunlight is heating it up and increasing the temps.

What is the outer shield consist of? What materials? I am not the most handy of the bunch so keep it simple if you don't mind...haha

I don't have any modified radiation shields.  The Davis is used as it came and runs +1.5º higher than the National Weather Servcie Max/Min Temperature System that is in this picture.

I added the daytime aspiration and it didn't change any temperature comparing the VP2 with the MMTS.  I put in a -1.5º temp offset in the Davis console to make it equal with the NWS system which is at the same height and 30 inches laterally.
See the discussion with Mason on http://www.wxforum.net/index.php?topic=3868.0 "Seperating senors on the VP2"

[LIWeather]

So is the consensus that I need to adjust my temperature offset on the console to -1.1 to -1.5 to be accurate? Is that offset something that is standard across the board? What is the best way for me to compare this without having any other PWS or NWS running in conjunction with my setup?

[wxtech]

So is the consensus that I need to adjust my temperature offset on the console to -1.1 to -1.5 to be accurate? Is that offset something that is standard across the board? What is the best way for me to compare this without having any other PWS or NWS running in conjunction with my setup?

This topic is only a few days old.  Mason and I are the only ones that I know of that compares to the NWS eqpt and puts in this offset.  Lets see if others use a temperature offset correction factor.
I've used other thermometers to find the most accurate temperature.  I have a sling  psychrometer but that just adds another number to the mix.  I built a 1-wire thermometer using a DS1620 IC which has a digital output and an accuracy of 1ºF. 

[Anthony]

I do not use a temperature offset. I do however use a dewpoint/humidity offset. As the OS stations are notorious for reporting low humidity. Notmally my temps track to withing 1 or 2 degress of the METAR station at the airport about 3 to 5 ground miles away, abros 2 air miles & at a higher elevation. So my guess would be if the NWS were to place one of their temp stations and I wish they would. I think the thems would be prety much spot on.

But the way wxtech. How did you end up getting a NWS temp station placed in your yard?

[wxtech]

But the way wxtech. How did you end up getting a NWS temp station placed in your yard?

Volunteered.
Actually, I sent an email putting my name on the list of volunteers.  When he received my email, the Coop manager was closing the station closest to me.  He then just moved the station from that house to mine.
It's nice to be able to say "The official National Weather Service temperature in Lexington is - ".  It's OK with NWS for me to title my station, "The Lexington NWS Cooperative Weather Station".

[LIWeather]

This topic is only a few days old.  Mason and I are the only ones that I know of that compares to the NWS eqpt and puts in this offset.  Lets see if others use a temperature offset correction factor.
I've used other thermometers to find the most accurate temperature.  I have a sling  psychrometer but that just adds another number to the mix.  I built a 1-wire thermometer using a DS1620 IC which has a digital output and an accuracy of 1ºF. 

So would my best bet be to put up a mercury thermometer along side of the ISS being that's all I have? I am not sure how I can compare temperatures and verify the accuracy. I don't think using PWS around my area would be a valid comparison as you never know how their station is set up. I don't claim to have the best set-up but I did do my best to follow the "rules."

[George Richardson]

Your Weather is what it IS. You have a GOOD weather station. If you did your best to follow the "rules", then don't worry about it. Look at your console Manual for the Weather Data Specifications. Each variable has a nominal accuracy. If you think your rainfall is incorrect, buy a 4" rain gauge and adjust to that. If you think your Barometer is off, there are procedures involving waiting for a stationary high pressure and adjusting to a nearby airport. If you think your wind speed is off, I dont know what you can do if your anemometer is 20 or more feet in the air. You could buy a Krestrel hand held and climb a ladder to take readings at the same location. If you think your temperature, dew point, or relative humidity are off, buy a sling psychrometer for testing. A mercury thermometer adjacent to the ISS would be useless.

I remember, with some distaste, when I first set my station and started reporting to the internet databases. My barometric pressure was "WRONG". I questioned the situation and was immediately told to enter an offset. I balked. I had a Davis VP2. I paid good money for it. It should be better than it was reporting. I persued the situation and found out that in actuality, it was the software (which I also paid good money for) that was reporting the wrong data. Got another reporter software and everything is cool. Had I entered that offset, the data would have been skewed forever. FWIW, I did eventually enter a very small barometric pressure offset.

I find this thread very interesting. WXTECH has an official NWS Thermometer 30" from the Davis and the difference is only 1 1/2 degree. I see no reason NOT to enter that offset but if the NWS station was 100' away, I would personally think it questionable. Remember, the Davis accuracy is +/- 1 degree F and the NWS unit must have an accuracy range so 1 1/2 degree is VERY close to tolerance.

JMO

George

[LIWeather]

George, I agree with what you are saying. My other readings are now on par with local airports and PWS's but my temperature is at least 10 degree's hotter then surrounding areas. This is because of the direct sunlight on the ISS. I'm just trying to get the readings down to a more accurate level.

I'm not a fan of playing with the offsets as it will make the temp readings off even more when the sunlight is not beaming down on the ISS (overcast days & nighttime hours). I'm just looking for the best way to bring my temps into a more accurate range.

[George Richardson]

Davis # 7747 from Ambient Weather = $112.50 + shipping. I really don't understand this. Davis designs their 6152 series to sit in the sun and be a LOT more accurate than 10 degrees unless you are mounted over concrete in a shielded area with no breeze.

Look on Davis' web site for the studies of accuracies of 6152 vs 6153. I didn't think there was a $200.00 difference when I purchased.

JMO
George

[Anthony]

But the way wxtech. How did you end up getting a NWS temp station placed in your yard?

Volunteered.
Actually, I sent an email putting my name on the list of volunteers.  When he received my email, the Coop manager was closing the station closest to me.  He then just moved the station from that house to mine.
It's nice to be able to say "The official National Weather Service temperature in Lexington is - ".  It's OK with NWS for me to title my station, "The Lexington NWS Cooperative Weather Station".

Don't guess I will ever have that happen. I don't think the NWS would ever move the METAR from the airport.

[wxtech]

But the way wxtech. How did you end up getting a NWS temp station placed in your yard?

Volunteered.
Actually, I sent an email putting my name on the list of volunteers.  When he received my email, the Coop manager was closing the station closest to me.  He then just moved the station from that house to mine.
It's nice to be able to say "The official National Weather Service temperature in Lexington is - ".  It's OK with NWS for me to title my station, "The Lexington NWS Cooperative Weather Station".

Don't guess I will ever have that happen. I don't think the NWS would ever move the METAR from the airport.

How to become a Cooperative Observer.
http://www.weather.gov/om/coop/become.htm

Beckley has an ASOS station at the airport.  There is listed a coop station at the VA Hospital in Beckley; call sign BCKW2 station 460580 in operation from 1948 to present.  Can't locate any data from that station.  Is this station still operating?

Raleigh County Coop stations found
Beckley Va Hospital
Beckley, WV, United States
Type: AB COOP-A COOP
COOP ID: 460580
Climate Division: WV-04 - Central
In Service: 01 Aug 1948 to Present
Elevation: 710.2m (2330') above s/l
Lat/Lon: 37°46'N / 81°12'W
County: Raleigh

Dry Creek
WV, United States
Type: COOP-A COOP B 
COOP ID: 462462 
Climate Division: WV-04 - Central 
In Service: 01 Dec 1961 to Present 
Elevation: 385.3m (1264') above s/l 
Lat/Lon : 37°52'N / 81°28'W 
County: Raleigh
 
Search for NWS Cooperative stations;
http://www.ncdc.noaa.gov/oa/climate/climateinventories.html

[d_l]

LIWeather, so your VP2 has no FARS now, right?  Have you read this application note by Davis?: http://www.davisnet.com/product_documents/weather/app_notes/apnote_24.pdf  It reports that the Davis passive shield could give a temp error of 8-9 degrees during the maximum insolation portion of the day.  Even the probably very expensive R M Young passive radiation shield had errors of about 10-11 degrees higher than the reference-aspirated shield.

I think this excessive insolation heating of passive radiation shielding during low wind periods is a dirty little secret that affects ALL weather stations.  The LaCrosse stations in my area are especially affected by the problem. As soon as the sun comes up and starts to heat them, their temps will climb 10-20 degrees higher than the other stations on Wunderground.  By mid day they seem to cool off relative to the other stations and are only 5-10 degree hotter.  Their insolation heating is so distinctive that I can readily pick them out on the weather map off my area during the day.  I think they could all be made more accurate if their owners added home-made FARS like Axelvold and DanS have put together.

[Sigdigit]

I noticed the same temp spikes you did d l.  You're right, you can pick 'em out on the map!  When I added daytime FARS to my Davis, it did help smooth out the afternoon temps.  Once my solar radiation sensor reads around 400, the little fan kicks on.  Been running over a year now without problems, despite some of the other members having the fan motor quit prematurely.

[Anthony]

But the way wxtech. How did you end up getting a NWS temp station placed in your yard?

Volunteered.
Actually, I sent an email putting my name on the list of volunteers.  When he received my email, the Coop manager was closing the station closest to me.  He then just moved the station from that house to mine.
It's nice to be able to say "The official National Weather Service temperature in Lexington is - ".  It's OK with NWS for me to title my station, "The Lexington NWS Cooperative Weather Station".

Don't guess I will ever have that happen. I don't think the NWS would ever move the METAR from the airport.

How to become a Cooperative Observer.
http://www.weather.gov/om/coop/become.htm

Beckley has an ASOS station at the airport.  There is listed a coop station at the VA Hospital in Beckley; call sign BCKW2 station 460580 in operation from 1948 to present.  Can't locate any data from that station.  Is this station still operating?

Raleigh County Coop stations found
Beckley Va Hospital
Beckley, WV, United States
Type: AB COOP-A COOP
COOP ID: 460580
Climate Division: WV-04 - Central
In Service: 01 Aug 1948 to Present
Elevation: 710.2m (2330') above s/l
Lat/Lon: 37°46'N / 81°12'W
County: Raleigh

Dry Creek
WV, United States
Type: COOP-A COOP B 
COOP ID: 462462 
Climate Division: WV-04 - Central 
In Service: 01 Dec 1961 to Present 
Elevation: 385.3m (1264') above s/l 
Lat/Lon : 37°52'N / 81°28'W 
County: Raleigh
 
Search for NWS Cooperative stations;
http://www.ncdc.noaa.gov/oa/climate/climateinventories.html

Never realized there was a coop station at the VA hospital. If you can't find any data for it, I guess it either is not operating or no one is sending in the data.

[METARMan]

MMTS radiation shields don't have fans, do they?  How do they stay "cool"?

[d_l]

MMTS radiation shields don't have fans, do they?  How do they stay "cool"?

A good question.  I just started wondering about that. 

What material is used to make the rings? A highly reflective, highly insulating, low thermal mass material?  White plastic-coated styrofoam?

[wxtech]

MMTS radiation shields don't have fans, do they?  How do they stay "cool"?

A good question.  I just started wondering about that. 

What material is used to make the rings? A highly reflective, highly insulating, low thermal mass material?  White plastic-coated styrofoam?

They are non-aspirated, molded from white plastic.  Only the indicator is powered.  The sensor is an RTD (resistance temperature detector), connected by two low resistance wires to the indicator panel.  For a picture of my Nimbus panel, see my site http://www.lexingtonwx.com/  Scroll halfway down to see the Nimbus Digital Thermometer with a green panel. 

Three photos of the Nimbus PL Digital Thermometer (MMTS) sensor.  To the right of the MMTS sensor is a Davis VP2 Plus ISS.