Best way to calculate altitude?

[Dr. Quigley]

My friend and I are making an Arduino-powered altimeter, and I'm wondering what the best way to calculate altitude is. I know that this can be determined with a pressure sensor, but I also thought that pressure varies with temperature and other weather phenomena as well. Is it accurate enough with just a barometer, or should I also add some other components?

 

[ClayD]

Yes,

there is a standard model of atmospheric pressure used on most altimiter altitude calculations. This isnt just rocket guys, but if you have one of those hanglider guy hiking watches, they have barometers that give altitude.

GWIz partners wrote this excelent article. https://www.gwiz-partners.com/Flight_Computers.pdf

https://www.marsa4.com/jmla/index.php?option=com_content&view=article&id=52&Itemid=57

Discusses some math for altimeters.

and the Altusmetrum.com guys Bdale, and Kieth, have an open source gps altimeter.


The Raven Featherweight.com, has a "temperature corrected" barometer.

Carefull if using a IY: altimeter for deployment. Barometers sense supersonic shock waves that simulate decending while under boost and will deploy your parachute. you have to specify a filter for airspeed, or a time duration before it can deploy.

 

[Dr. Quigley]

Yes,

there is a standard model of atmospheric pressure used on most altimiter altitude calculations. This isnt just rocket guys, but if you have one of those hanglider guy hiking watches, they have barometers that give altitude.

GWIz partners wrote this excelent article. https://www.gwiz-partners.com/Flight_Computers.pdf

https://www.marsa4.com/jmla/index.php?option=com_content&view=article&id=52&Itemid=57

Discusses some math for altimeters.

and the Altusmetrum.com guys Bdale, and Kieth, have an open source gps altimeter.


The Raven Featherweight.com, has a "temperature corrected" barometer.

Carefull if using a IY: altimeter for deployment. Barometers sense supersonic shock waves that simulate decending while under boost and will deploy your parachute. you have to specify a filter for airspeed, or a time duration before it can deploy.

Thanks! Will do.

We won't be using this for deployment JUST yet, we wanted to be sure data was accurate before using for that. Thanks for the tip, though! Any good reads for filters?

 

[Adrian A]

The Raven's baro temperature compensation is just to adjust for the sensor temperature to make sure that it has accurate pressure readings. The conversion from pressure to altitude just uses the standard atmosphere model with no attempt to correct for ambient atmospheric temperature. Note that there are actually 3 different standard atmosphere equations, for roughly 36kft and below, 36 to 66 kft, and 66 to about 100 kft. Those are from memory so don't quote me on those. Wikipedia has a good entry on it if you think your unit might be used that high.

A simple and effective filter is the recursive filter: new filtered value = (new reading- old filtered value)/gain factor. It basically adjusts the filtered value part way to the new reading at each step.

Powers of 2 are popular for the gain factors for computational efficiency. This isn't an estimating filter like a Kalman filter, but it's still useful for smoothing out noise (or Mach transients) if you can live with some time lag.

 

[Dr. Quigley]

*snip*

A simple and effective filter is the recursive filter: new filtered value = (new reading- old filtered value)/gain factor. It basically adjusts the filtered value part way to the new reading at each step.

Powers of 2 are popular for the gain factors for computational efficiency. This isn't an estimating filter like a Kalman filter, but it's still useful for smoothing out noise (or Mach transients) if you can live with some time lag.

Yes, I can live with some time lag. As long as it isn't over a second, I'm fine. Thanks!