[aprssig] APRS Weather hops and rates

[Gerry Creager]

 From an operational perspective, a lot (but not all) NWSWFO's use APRS 
Weather data.  In general, those that do would like to see updates as 
frequently as possible.  There's been a fair bit of discussion about an 
optimal sample rate (terms like Nyquits have arisen in these discussion, 
but so have autocorrelation and Fourier...).  1 hour rates such as AWOS 
are a bare minimum and high frequency rates such as 15- 10- and 5-min 
updates are very useful.

If one thinks back to the Baltimore Water Taxi incident (2004), NWS had 
limited data from radar and ASOS/AWOS updates.  Had they had more access 
to high frequency APRS and CWOP updates, the gust front responsible for 
the accident could have been detected sooner and better warning 
strategies developed.

At this time NOAA/ESRL/GDS (the folks who run MADIS) collect APRS-Wx 
data every 15 minutes.  We've been talking to them about collecting and 
processing more frequently but so far they're saying they are limited by 
systems and hardware issues.  They *want* to get the data more 
frequently, but that's not an option.  We are looking at alternatives to 
allow faster retrieval and potentially preprocessing their QC using 
their algorithms to facilitate faster updates, but nothing's been 
finalized.  Nowhere close yet.

The optimal timing right now, because of the data collection limitation, 
is every 15 minutes, as anything going to APRS-ISwould see the 
occasional dropout with a 10 min update cycle and some of the data 
collection logic.  Alternately, a 5 minute rate would ensure that the 
latest data would always make it into MADIS via APRS-IS and CWOP, which 
would be an operational benefit.

Does this help?

gerry n5jxs

Robert Bruninga wrote:
> I need to make sure I am best representing the Weather
> contingent in APRS.
> 
> Does the following statement best capture the best interests of
> both the weather guys and all the rest of APRS users combined?
> 
> "Generally WX stations should transmit weather data once every
> 10 minutes in the local area only.  A Weather station should
> transmit using a local path either direct or at most one hop.
> Under the unusual situation where 2 hops may be required, then
> the update rate should be reduced to once every 30 minutes.  If
> two hops are needed just to get to a NWS station or an Igate,
> then a generic/directed path of WIDE2-1,DIGIX should be used in
> that one direction."
> 
> I recognize that early on stations tended towards a 5 minute
> rate, and I am not making any suggestion that they be taken off
> the air.  But for the basis of new designs, is the above
> statement fair to everyone?
> 
> I assume that if a specific WX station is that important, then
> there should be an igate nearby to get the data direct rather
> than reducing the reliability of all other users and wather
> stations by using long hops.
> 
> Is the above generally agreed by all parties?
> Bob
> 
> 
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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.862.3982 FAX: 979.862.3983
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