Author Topic: ASOS visit with VP2 in hand  (Read 6368 times)

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Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #25 on: July 10, 2017, 09:13:38 AM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #26 on: July 10, 2017, 01:37:16 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Very nice...Hadn't heard that before. 
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Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #27 on: July 10, 2017, 01:50:21 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Very nice...Hadn't heard that before.
Here's VTN for June.

ftp://ftp.ncdc.noaa.gov/pub/data/asos-onemin/6406-2017/64060KVTN201706.dat

You have p-type there, precip, the 3 station pressure sensors, and then the raw temp and dew. Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
« Last Edit: July 10, 2017, 01:52:40 PM by dendrite »

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #28 on: July 10, 2017, 03:44:58 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
My WFO told me that to be "official" each 5 minute obs is used then the average algorithm must be met for 3 of those 5 minutes.

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #29 on: July 10, 2017, 04:16:34 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
My WFO told me that to be "official" each 5 minute obs is used then the average algorithm must be met for 3 of those 5 minutes.

Some material was posted in another thread about humidity I started when the ASOS was reading low 90's humidity with soupy fog,  they use a 5 minute running average. I'm pretty sure my nearby ASOS humidity is running low because of what it read in the fog and compared to the SHT31 I see 3-4 difference. I'm not sure I trust the new sensors as much as I did the chilled mirrors with DP.   
« Last Edit: July 10, 2017, 04:18:06 PM by ValentineWeather »
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Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #30 on: July 10, 2017, 05:22:51 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
My WFO told me that to be "official" each 5 minute obs is used then the average algorithm must be met for 3 of those 5 minutes.

Some material was posted in another thread about humidity I started when the ASOS was reading low 90's humidity with soupy fog,  they use a 5 minute running average. I'm pretty sure my nearby ASOS humidity is running low because of what it read in the fog and compared to the SHT31 I see 3-4 difference. I'm not sure I trust the new sensors as much as I did the chilled mirrors with DP.
Frankly, I'd trust your 31. I don't know what kind are used here, but when the two ASOS's and one RAWS I always compare to "catch up" my humidity is "usually" no more than a percent off, plus or minus (usually plus) if not exact, and dew no more than two or three degrees, if not exact also. I never had this accuracy with my 11 or 15.

Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #31 on: July 11, 2017, 11:12:57 AM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
My WFO told me that to be "official" each 5 minute obs is used then the average algorithm must be met for 3 of those 5 minutes.
Can you clarify what you mean by this?

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #32 on: July 11, 2017, 02:00:30 PM »
This section may explain the ASOS 5 minute running average.

3.1 Ambient and Dew Point
Temperature
Ambient and dew point temperature reports are among
the most widely disseminated of all the weather elements
in the surface observation. Because of keen public interest,
nearly all radio and most television stations report temperature
and humidity at least once an hour. Ambient and
dew point temperature are vital in determining aircraft performance
and loading characteristics and are critical for
accurate weather forecasts. To meet these needs, ASOS
provides a 5-minute average ambient air and dew point
temperature every minute
Randy

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #33 on: July 11, 2017, 03:24:02 PM »
heh...love this thread. Let's revisit this in a few weeks when the raw 1-min numbers come out for July. Then you can make better comparisons. Did you try this in June at all?

Keep in mind that if you want the actual reported temp or dew for any particular minute that you have to take a 5-min average (that minute ob and the previous 4).
My WFO told me that to be "official" each 5 minute obs is used then the average algorithm must be met for 3 of those 5 minutes.
Can you clarify what you mean by this?
I just spoke to my WFO again and he stated that it's a running two minute average. Either way, ASOS's average things out, we obviously don't.

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #34 on: July 11, 2017, 04:57:33 PM »
See 3.1.2 http://www.nws.noaa.gov/asos/aum-toc.pdf
Other good stuff included too.

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #35 on: July 11, 2017, 05:44:58 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.


« Last Edit: July 11, 2017, 05:46:37 PM by ValentineWeather »
Randy

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #36 on: July 11, 2017, 05:54:43 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.
Ha, true. Only thing is ASOS's are "supposedly" calibrated on a regular basis. The equipment I used was checked every six months.

Offline WxLover16

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Re: ASOS visit with VP2 in hand
« Reply #37 on: July 11, 2017, 07:37:56 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?
Davis Wireless VP2 SHT31 24hr 24CFM FARS

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #38 on: July 11, 2017, 07:49:42 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?

Yes, here are the 31 specs showing typical and maximum tolerance. Specs are much tighter than what the ASOS publication claims.
Randy

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #39 on: July 11, 2017, 07:58:56 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?
Not necessarily, they just happen to have a fairly wide berth of acceptable range. A properly maintained/sited ASOS is about as good as it gets for public consumption. Remember, their basic function is for safety of the flying public so it's "suppose' to be accurate.

Offline WxLover16

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Re: ASOS visit with VP2 in hand
« Reply #40 on: July 11, 2017, 08:47:20 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?
Not necessarily, they just happen to have a fairly wide berth of acceptable range. A properly maintained/sited ASOS is about as good as it gets for public consumption. Remember, their basic function is for safety of the flying public so it's "suppose' to be accurate.

Also a properly maintained/sited VP2 AC fan with 31 is about as good as it gets for us  :grin:

BTW, off-topic but after a brief torrential downpour today, my AC fan beats on!!!
« Last Edit: July 11, 2017, 08:50:13 PM by WxLover16 »
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Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #41 on: July 11, 2017, 08:50:10 PM »
My conclusion for now unless I learn more after seeing ASOS specs in print, I'll just no longer look at ASOS as the absolute in accuracy as I once did.
Even the (.9F) which I assume is typical is more than SHT31 (.4C) (.72F) max tolerance on the SHT31. Typical on the 31 is just (.2-.3C) throughout.
Randy

Offline CW2274

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Re: ASOS visit with VP2 in hand
« Reply #42 on: July 11, 2017, 09:08:02 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?
Not necessarily, they just happen to have a fairly wide berth of acceptable range. A properly maintained/sited ASOS is about as good as it gets for public consumption. Remember, their basic function is for safety of the flying public so it's "suppose' to be accurate.
BTW, off-topic but after a brief torrential downpour today, my AC fan beats on!!!
I thought you gave up? Send me a PM so as not to gum up the thread.

Online jgentry

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Re: ASOS visit with VP2 in hand
« Reply #43 on: July 11, 2017, 09:50:27 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?

Yes, here are the 31 specs showing typical and maximum tolerance. Specs are much tighter than what the ASOS publication claims.

Maybe the sensors changed since that publication? NWS in Birmingham, AL says that they believe the ASOS uses the HO-1088 for temperature & DTS-1 for DP
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Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #44 on: July 11, 2017, 10:58:58 PM »
What I find most interesting are the specs.
They aren't as tight as the sensirion SHT31. So much for comparing with ASOS. They should be calibrating with our instruments.

So the SHT31 is more accurate than ASOS climate sites?

Yes, here are the 31 specs showing typical and maximum tolerance. Specs are much tighter than what the ASOS publication claims.

Maybe the sensors changed since that publication? NWS in Birmingham, AL says that they believe the ASOS uses the HO-1088 for temperature & DTS-1 for DP

I knew they changed the humidity sensor.  I can't find much information on the new sensors even from the Allweatherinc who makes the ASOS. They seem to have the specs unavailable on the site.
Randy

Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #45 on: July 12, 2017, 08:45:40 AM »
ASOS is definitely still a 5-min running average...not 2-min. I've confirmed this just by comparing official high temps with the 1-min readings. I've seen times where a peak stretch of 94-94-95-95-94 resulted in a high of 94 rather than a high of 95.

And those specs are outdated...that was published in 1998. Anything ASOS is still superior (I guess we could argue the definition of superior) to the SHT3x.

Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #46 on: July 12, 2017, 09:07:51 AM »
I found this 2012 publication claiming +/- 2 also. https://www.weather.gov/media/lmk/pdf/educational_pages/ASOSandClimateObservations__What_Is_ASOS.pdf

WIKI has information on changeover from the :The current ASOS thermometer is designated the HO-1088, though some older systems still utilize the HO-83.

And new dew Point sensor: Due to problems with the chilled mirror sensor, NWS ASOS sites now use Vaisala's DTS1 sensor, which measures humidity only via capacitance. The sensor is based on a solid state capacitive relative humidity element that incorporates a small heater so that the sensing element is always above the ambient temperature, eliminating the formation of dew or frost. The sensor reports directly in dew point through a calculation based on measured relative humidity and the measured temperature of the heated capacitive element.[11]

https://en.wikipedia.org/wiki/Automated_airport_weather_station

allweatherinc has this sensor also: Accuracy .01C
http://www.allweatherinc.com/meteorological-sensors/temperature-sensor/#tabs=1151
 
« Last Edit: July 12, 2017, 03:40:28 PM by ValentineWeather »
Randy

Offline dendrite

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Re: ASOS visit with VP2 in hand
« Reply #47 on: July 12, 2017, 10:25:18 AM »
+/- 0.01C sounds about right. Most of those higher end sensors run about +/-  0.01-0.05C

Offline kcidwx

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Re: ASOS visit with VP2 in hand
« Reply #48 on: July 12, 2017, 11:11:41 AM »
The ASOS humidity sensor is made by Vaisala. It's the DTS-1 which is based on the HMP243 probe utilizing the Humicap 180 sensor.

Relative humidity measurement: Measurement range: 0-100%RH; Accuracy at 68F: +-1.0% RH (0-90%RH), +-1.7%RH (90-100%RH); Sensor: Vaisala HUMICAP 180 Vaisala HUMICAP 180R

Also the HO-1088's chilled mirror was not decommissioned with the installation of the DTS-1. They are still in use as a backup should the DTS-1 fail or go out of tolerance. The HO-1088 was made by Technical Services Laboratory.

http://tslinc.com/systems/instruments-hygrothermometer/

//edit: adding diagram of the DTS-1 sensor shield for reference.
« Last Edit: July 12, 2017, 03:34:29 PM by kcidwx »
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Online ValentineWeather

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Re: ASOS visit with VP2 in hand
« Reply #49 on: July 12, 2017, 11:21:22 AM »
The ASOS humidity sensor is made by Vaisala. It's the DTS-1 which is based on the HMP243 probe utilizing the Humicap 180 sensor.

Relative humidity measurement: Measurement range: 0-100%RH; Accuracy at 68F: +-1.0% RH (0-90%RH), +-1.7%RH (90-100%RH); Sensor: Vaisala HUMICAP 180 Vaisala HUMICAP 180R

Also the HO-1088's chilled mirror was not decommissioned with the installation of the DTS-1. They are still in use as a backup should the DTS-1 fail or go out of tolerance. The HO-1088 was made by Technical Services Laboratory.

http://tslinc.com/systems/instruments-hygrothermometer/

Thanks for that information... =D>
Randy