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

[Martin Mueller]

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
> 
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> 

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