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Re: [Paparazzi-devel] Critical conditions for IR thermopiles


From: Marc Schwarzbach
Subject: Re: [Paparazzi-devel] Critical conditions for IR thermopiles
Date: Mon, 23 Aug 2010 19:00:34 +0200

Hi,

I can affirm what Martin just said and have to add things to consider.

We did some test flights in the recent weeks to test the capabilities of the 
thermopiles. 

Flights over the ocean are no problem, the difference in temperature is lower 
but not much.

We had one incident with an aircraft getting off course because of sensor 
problems. It performed well 10 minutes and suddenly headed in one direction 
instead of turning. Analysis of the data indicates that a drop of water hit the 
front left sensor and made it sense a 30° right and up angle. Since this was 
what the navigation would command (right circle), the plane headed straight.
The weather was light fog, which did not disturbe general flying but the 
humidity was sufficient to hit one of the sensors.

In summary, IR is a very robust system if you take care on the limitations.

Marc


-------- Original-Nachricht --------
> Datum: Mon, 23 Aug 2010 18:27:36 +0200 (MEST)
> Von: "Martin Mueller" <address@hidden>
> An: address@hidden
> Betreff: Re: [Paparazzi-devel] Critical conditions for IR thermopiles

> Hi Reto,
> 
> yes, there could be problems. The IR sensors use the temperature
> difference between sky and earth. If there is no difference you can not fly. 
> Water
> slightly emits infrared radiation and if e.g. fog is dense enough you will
> measure the same temperature all around. If clouds are too low and warm it
> will not work. This happened on one day at the competition in India where
> very warm clouds cancelled IR flights. As a rule of thumb in worst case the
> temperature gets about 1°C colder per 100m and you need at least 5°C
> difference so that you can operate. An IR surface-thermometer for about 20 
> Euros
> can help to measure that. Terrain is less critical, there was a
> competition right next to steep mountains in the Alps.
> 
> There have been reports of flying Paparazzi airplanes from many different
> climate zones. They flew on Iceland or in the Arctic and there is no
> general problem with that. The ground will be much colder there (coldest 
> surface
> temperature was -30°C) but the sky/clouds will also be a lot colder,
> especially as cold air can hold a lot less water (it does not go linear). For
> the radiation the absolute humidity is important.
> 
> The big advantage of the IR system is that it works extremely reliable and
> deterministic if weather permits. There are no glitches. It is fairly easy
> to estimate the infrared temperature difference and check if flights will
> be possible. More than 100 flights were done in the Arctic within two
> weeks, only flying in the morning and evening due to the permission. The 
> system
> is robust so that it can be operated by payload scientists with little
> training (plus an experienced safety pilot).
> 
> If you are not keen on operating your aircraft in foggy November rain
> there should be no issue to use Paparazzi IR. IMUs will play a bigger role in
> the future but for our campaigns they still have to prove that the have the
> same reliability.
> 
> Martin
> 
> ----- original Nachricht --------
> 
> Betreff: [Paparazzi-devel] Critical conditions for IR thermopiles
> Gesendet: Mo, 23. Aug 2010
> Von: Reto Büttner<address@hidden>
> 
> > Hello all,
> > 
> > has anyone experienced problems with IR thermopiles in flight?
> > 
> > I am thinking of exotic meteorological conditions where the IR
> > contrast between sky and earth might be to small. Or when flying in
> > fog or clouds. Or when flying in mountains close to terrain. My
> > paparazzi planes with IR thermopiles have worked fine until now, but I
> > just have been flying in nice weather conditions. I have read a lot
> > how robust IR thermopiles are to various meteorological conditions,
> > including flights in the arctic.
> > 
> > On the other hand many people in the community are not quite sure,
> > prefer IMU solutions and there are rumors of projects that have not
> > worked due to IR thermopile issues. I appreciate the efforts of
> > numerous people to integrating an IMU into paparazzi, but for my
> > project I am not sure if it is worth the effort.
> > 
> > Has anyone experienced the limitations of IR thermopiles?
> > 
> > Reto
> > 
> > _______________________________________________
> > Paparazzi-devel mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/paparazzi-devel
> > 
> 
> --- original Nachricht Ende ----
> 
> 
> _______________________________________________
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> http://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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