Can Winds/Temps be added to GPS info?

Many of our planes now automatically and continuously calculate wind velocity from aircraft and ground velocity. And they continuously measure outside air temperature. Can this data be added to the GPS track data in the APRS transmitted packets?

Suppose this were implemented in all APRS transmitters. You'd then have hundreds (eventually) of fairly accurate "measured" wind and temps aloft throughout the day over the USA. Just the raw numbers would be a help for pilots planning a cross-country trip, and the data would have to be useful to the Weather Service for forecasting.

Telemetry is Supported

Hi Ralph

APRS does support telemetry, but I think it would require some different equipment than we are running. Many details to work out. We would need to come up with formats and make sure we are not flooding the freq with too much congestion.

It is doable and would be cool. If you look at the APRS maps, you will see many WX symbols - those are weather reporting stations- weather bugs doing much of what you are suggesting for ground stations.

I think I have this right - the group will keep me honest.

APRS telemetry

If you just want to send a few reports of analog voltage values ( 0 to 5 volts, representing whatever values your gear produces) It will fit pretty easily in the comment field. You might take a look at the Byonics TT4 manual (www.byonics.com) to see if this is what you need. I hope to have a TT4 based Micro-Trak transceiver out in the next couple of months.

Allen
VHS

VHS said:

If you just want to send a few reports of analog voltage values ( 0 to 5 volts, representing whatever values your gear produces) It will fit pretty easily in the comment field.

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I'm thinking of something easier to use when reported. Seems this might require a hardware change to the encoder box: in addition to GPS inputs it would receive inputs from an AHRS or EFIS. Knowing very little how these gadgets pass data around I'm being vague, but I assume they talk to each other digitally, not analog.

I guess I'm proposing that the additional input be handled in future devices then, not in current ones. That would delay implementation but make it easier for non-expert implementers (pilots) and users of the data (pilots, weather forecasters) to set up and use the additional data.

If you guys as developers of the APRS gadgets think this is feasible I would like to contribute somehow. Might be able to do a little programming or even subsidize some modest research costs. I can work some contacts at the National Weather Service to see if they have a need for this type of data.

rfinch said:

Might be able to do a little programming or even subsidize some modest research costs. I can work some contacts at the National Weather Service to see if they have a need for this type of data.

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I don't know if this helps, but several of the major airlines sell wind data to various weather agencies and companies. At my company, the Boeing 767, 777 and 747 transmit real-time wind data at certain intervals -- I think it's every 50 NM -- via digital datalink.

Of course the vast majority of that data is collected way up in the flight levels. I suspect there could be a need for much better wind data below 18,000 feet. Perhaps our worldwide fleet of RVs or other G/A planes could produce some valuable wind data for the National Weather Service as we fly out to those pancake breakfasts, etc. Neat idea!

EFIS

Ralph,

Before I met you guys, I could not even spell EFIS! There has been discussion in earlier links about transmitting EFIS data. I understand that EFIS can send info out as serial data, but I don't know much more than that.

Our TT4/Micro-Trak will have serial and analog/digital inputs, so I suppose that sending reports from EFIS should not be too hard. Once we know what the unit spits out its serial port (everything? somethings? nothings?) and how we want to parse it out, how often to send it, etc, it needs to be converted to AX.25 format and transmitted. Not knowing how much data we are talking about is dangerous, since sending a continuous data stream on the APRS channel would be very uncool!

Allen
VHS

VHS said:

Once we know what the unit spits out its serial port (everything? somethings? nothings?) and how we want to parse it out, how often to send it, etc, it needs to be converted to AX.25 format and transmitted. Not knowing how much data we are talking about is dangerous, since sending a continuous data stream on the APRS channel would be very uncool!

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I would think the most anybody would want would be time, position, altitude (with the AHRS/EFIS would have baro altitude as well as GPS altitude), OAT, and calculated wind velocity, every, say 10 seconds during climb or descent, every minute during cruise. Surely the EFIS/AHRS generates more data than that, but it is unneeded for this purpose.

Time, position and GPS altitude are already transmitted. Baro altitude, OAT, wind direction and wind speed could each be 32 bit floats, or maybe 16 bit ints converted to float at the receiving end. We're talking 128 bits, double it for good measure, so 256 bits additional each transmission. Don't know how often the AHRS gizmotrons generate and send their data over the wire but probably at least 1 Hz, maybe more often, so that would have to be either averaged or subsampled for the APRS transmission by the encoder/controller.

I will start querying the NWS people in my agency to see if there would be interest. I'll try to find the folks who run the forecasting models if the additional data would be helpful. There's a math trick called data assimilation which takes observed data and statistically folds it into a running numerical model to improve the model results. They should be using that already so more data should help. Might have to do an experiment to see how the AHRS calculated wind velocity compares to more traditional observed data, I think with cheap little balloons (radiosondes) set loose?

Commercial enterprises and APRS

Hi Folks,

Just a reminder to everyone as we discuss this topic: Remember that APRS is a part of the Amateur Radio Service, and as such, the system may not be used for commercial enterprises. In other words, it's my understanding of the FCC regs that you cannot sell data, and no one can financially benefit from transmissions that are made in the ham bands. (There are minor exceptions to this, but the regs are pretty clear that you can't use the airwaves for commercial operations.)

So as we discuss delivering wind and other data to the National Weather Service, just keep that in mind. I'm not trying to be pessimistic at all, just keeping us going down the "straight and narrow."

BuckWynd said:

Just a reminder to everyone as we discuss this topic: Remember that APRS is a part of the Amateur Radio Service, and as such, the system may not be used for commercial enterprises.

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Yes, good reminder. Certainly I have no intention of trying to make money from this. What a shock that would be, an airplane that made money! All my flying has been the other way

Most EFIS systems calculate this data, and some even spit that data out of a port. Unfortunately, there is no standard protocol, such as NMEA for GPS data, for EFIS data. So there would need to be a unique solution for each EFIS provider.

I guess one of the largest would be Dynon, and they have their Dynon Smart Avionics Bus (DSAB). It would be interesting if they would give us the specs so we could add this:

http://www.dynonavionics.com/docs/D10_Feature_DSAB.html

--Bill

rfinch said:

I will start querying the NWS people in my agency to see if there would be interest.

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What with people on vacation, and having to start up a chain of contacts, it will be a week or two before I get further with the NWS folks. Meanwhile I wonder if the APRS developers could answer some questions.

Seems that APRS was developed for ground use, only recently being used in airplanes. Won't APRS, like cell phones, start saturating receivers when used from airplanes, because of the wide transmission coverage? And I suppose that APRS cannot be sophisticated about frequency hopping because it doesn't receive. I guess it avoids conflict by transmitting only briefly (fraction of a second) and occasionally (every minute or so)?

Just wondering how well APRS would scale to more widespread aviation use.

rfinch said:

What with people on vacation, and having to start up a chain of contacts, it will be a week or two before I get further with the NWS folks. Meanwhile I wonder if the APRS developers could answer some questions.

Seems that APRS was developed for ground use, only recently being used in airplanes. Won't APRS, like cell phones, start saturating receivers when used from airplanes, because of the wide transmission coverage? And I suppose that APRS cannot be sophisticated about frequency hopping because it doesn't receive. I guess it avoids conflict by transmitting only briefly (fraction of a second) and occasionally (every minute or so)?

Just wondering how well APRS would scale to more widespread aviation use.

Click to expand...

Ralph, these issues have been discussed in great depth on the APRS forum. Here is one such thread:

http://www.vansairforce.com/community/showthread.php?t=30126

Not sure how the present APRS net would scale to widespread GA use, but that probably won't happen due to the necessity for a license and the difficulty of installing APRS in certificated aircraft.

The APRS format...

While waiting for the NWS folks to get back to me, I started looking at the APRS 1.0.1 protocol reference, and specifically the weather reports in the AX.25 protocol.

Looking at the various formats, there is a lot of hardwiring. I guess that comes from the protocol's history. Of the various AX.25 Information Fields, the Complete Weather should work. The protocol reference says that wind gust must be reported, in addition to the desired wind direction, wind speed, and (outside air) temperature; gust could be reported as zero. Rainfall, humidity, and other optional parameters would not be reported.

Is this on the right track?

I haven't abandoned this thread. I got one reply from the NWS which referred me to another division. I sent them an email last week and am waiting a reply.