On Fri, 2010-08-27 at 20:52 +1000, Luke O'Donnell wrote: > I wonder if a more feasible approach to thermal detection is using IR > cameras pointed at the ground. From what i can gather, air is a poor > medium for producing IR radiation, whereas presumably any solid object > (anything on the ground) would be much, much easier to detect. > I think the problem is not to find hot spots that might act as thermal generators, but to know where the thermal is. For example, a flat black concrete roof or car park is going be be bright in IR on a sunny day, but there is unlikely to be a continuous standing thermal above it. Similarly, a thermal travelling across a hayfield will certainly be fed by hot air pooling among or just above the grass stems, but it probably will have little effect on the temperature of the dry grass it crosses, so how can your camera see where the thermal is in a large field or even if there is one?
> A real life example is the police helicopters following suspects at > night with ease, they light up like a Christmas tree. > They also have quite a large temperature difference to work with. The back of my hand is currently 28.5C in a room at 21.3C, a 6.2C difference. Here its a cold, damp overcast day for summer and my heating is off. Outdoors at night the ground temp is going to be around 10-15C, and a moving perp is unlikely to be colder than my hand, so we're looking at a 13-18C temp difference for the camera to spot. The air temp of a thermal is somewhere between 0.2-2.0C above the surrounding air, so I suspect its impossible to pick out against the natural variations in daytime ground temperature: it would be hard enough to spot against the background air temperature looking horizontally. I'd well believe that an IR camera can see the hot air column above a candle flame with the ambient room temperature as background, but again that's a big temperature difference. You don't leave your hand above a candle flame for long! Martin ------------------------------------------------------------------------------ Sell apps to millions through the Intel(R) Atom(Tm) Developer Program Be part of this innovative community and reach millions of netbook users worldwide. Take advantage of special opportunities to increase revenue and speed time-to-market. Join now, and jumpstart your future. http://p.sf.net/sfu/intel-atom-d2d _______________________________________________ Xcsoar-user mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/xcsoar-user
