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# How to calculate the altitude from the pressure sensor data? Long-established Member

can you please explain how to get altitude measurement from pressure data from the sensor

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#### Accepted Solutions (1) Long-established Member

The altitude in meters can be calculated with the international barometric formula:

H = 44330 * [1 - (P/p0)^(1/5.255) ]

H = altitude (m)
P = measured pressure (Pa) from the sensor
p0 = reference pressure at sea level (e.g. 1013.25hPa) New Poster
Well This formula is not givving accurate results. Contributor
The reference pressure at sea level needs to be adjusted according to the current weather. This varies between 870 to 1084 (based on current maximums ever recorded) New Poster
So it means that for a day when pressuere at the ground level (lets say 78m above mean sea level) is lets say 1016 hPa it should be pyt as p0 in the formula? Contributor
The p0 is the equivalent pressure at sea level. If the current pressure is 1018mbar and altitude of the weather station is 78m, then the p0 is ~1027,5mbar New Poster
How you do the math from my 1016hPA at 78m above Mean Sea Level to Your 1018hPa at weather station level (78m above ground ) and than to 1027.5hPa at the mean sea level = p0 New Poster

Also there is a bit different formula in ISA model in this publication: https://www.eurocontrol.int/publication/revision-atmosphere-model-bada-aircraft-performance-model
see page 22.

these formuals gives different reasult in comparision to one provided in this answer on the top of discussion Contributor
If you isolate p0, the equation becomes : p0 = (2.62057x10^24 * p) / ( (44330 - H)^5.255 ). With p= 101800 and H=78, then the p0 is 102746. With p=101600, the p0 would be 102545. This simplified formula assumes a sea level temperature of 15 celsius and a standard temperature gradient. It is important to note 2 things: 1) All altitude calculation from pressure formulas are estimations, and 2) Aircrafts use a standardized formula to calculate pressure altitude, which is not necessarily the true altitude of the aircraft, so that they do not collide regardless of where their altimeter was calibrated. New Poster

The formula that you provided will give the different results to the one in the cited eurocontrol document.

The result form the sensor (on of the popular Bosh sensors)   is a pressure - we convert it to altitude using International Standard Atmosphere model (formula is different than the one presented here). And that result is a proof of beating some World record.

There is no other technical way to use different sensor (GPS altitude indication is not correct on these altitudes and also not correct by the definition).

radar could not be used same as Lidar or laser measurement.

How the formula should be used?

1. conditions at the object take off

altitude above mean sea level = 78 m - from digital terrain model

temperature measured by termometer in the car 8deg C

temperature indicated by the ventusky (weather forecast) 11degC

pressure indicated by the ventusky (weather forecast) 1016hPa

pressure indicated by one of the altimeters (not conatining pressure sensor that we are talking about) = 1005hPa

Which pressure should be used and feed to the formula as p0 (p0 is present in formula presented here as well as in eurocontrol document as pb)?

Shall i take pressure at altitude 76m and find pressure at the Mean Sea Level  = 0m and use that pressure  from mean sea level in the formula or something else.

From that what I see the idea is to adjust pressure at the sea level and than calculate altitude.

Regarding airplanes yes they switch altimeters around some altitude (i belive 12 000 feet) and switch their mean se level pressure to 1013 hPa in their altimeters.

That pressure is different in comparison to the altimeter that has been zeroed at QFE = 1025 hPa theses 12hPa is around 12*9m for low altitudes but for high altitudes it will even more like 12*30m).

So from perspective of people thatare setting the  "word record " it is very important what to put in the fomula and correct it by ground level.
Also theere is one more what if altitude is 11km (tropopause) and accoridng to ISA model the p0 is around 226mbar.  