Re: [Paparazzi-devel] RE: distance measurement for landing. (Chris)

[Christophe De Wagter]

Using an extra barometer on the ground station is nice (when the weather is changing), but will not readily give you the 14cm precision. The temperature (rate) differences, differences in vibration and pressure influences in an inflight airframe makes 2 identical sensors (1 in aircraft and 1 as reference) still vary.

If you want to use barometric pressure, the first thing to do would be to use it to augment the low frequency GPS. Together they can realistically be merged into an altitude estimation that is 10 times faster than GPS, while significantly reducing GPS outliers, hopefully should get you pretty far. 

I have seen nicely calibrated temperature compensated barometers landing at minus several meters due to hysteresis effects in the temperature calibration. (avionics cooling down during flight, while temperature calibration is slow)

 
Christophe

On Sat, Nov 14, 2009 at 12:12 PM, gisela.noci <address@hidden> wrote:

Yes, I did mention doing this, and it works well, but you still need the
resolution (in both sensors) in you want to try landing with Baro-Alt.No
point in knowing accurately the altitude every 2 meters..

Joe

-----Original Message-----
From: paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org
[mailto:paparazzi-devel-bounces+gisela.noci=ate-international.com@nongnu.org

] On Behalf Of Chris
Sent: Saturday, November 14, 2009 9:57 AM
To: address@hidden

Subject: [Paparazzi-devel] RE: distance measurement for landing. (Chris)

I think that i good, simple and feasible idea (someone i think mentioned
it) would be to use two barometers, calibrated together of course, and
have the ground station automatically transmitting a correction for the
airborne altimeter (effectively change the ground altitude or pressure
variable ).
With a precision barometer we can then set the ground pressure the same
for both the ground station and the airplane thus allowing precise
altitude measurement.
Since the precise altitude of the take off point will be known from SRTM
or from an accurate gps and cannot change unless there is a big
earthquake or a volcano erruption :-) the plane will always have an
accurate barometric altitude for short missions.
AFAIK real pilots do the same by getting the ground pressure from the tower.
Chris



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