# pvl_pres2alt

Determine altitude (m) from site pressure (Pa).

## Contents

- Syntax
- Description
- Assumptions
- Inputs
- Outputs
- Example
- References
- See Also

## Syntax

`altitude = pvl_pres2alt(pressure)`

## Description

`altitide = pvl_pres2alt(pressure)` determines the altitude (in meters above sea level) of a site on Earth's surface given its atmospheric pressure (in Pascals).

## Assumptions

- Pressure at mean sea level = 101325 Pa.
- Temperature at zero altitude = 288.15 K.
- Gravitational acceleration = 9.80665 m/s^2.
- Lapse rate = -6.5E-3 K/m.
- Gas constant for air = 287.053 J/(kg*K).
- Relative Humidity = 0%.

## Inputs

- `pressure` - atmospheric pressure (in Pascals) of a site on Earth's surface given its altitude

## Outputs

- `altitude` - altitude (in meters above sea level) as a vector of the same size as `pressure`.

## Example

    Alt1 = pvl_pres2alt(101325) % Sea level, result should be near zero
    Alt2 = pvl_pres2alt(80000) % Approximate pressure near 2,000 meters abobe sea level

    Alt1 =

        0.1243

    Alt2 =

       1.9491e+03

## References

Portland State Aerospace Society, 2004. A Quick Derivation relating altitude to air pressure, Version 1.03, http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf.

## See Also

`pvl_alt2pres`, `pvl_makelocationstruct`

Copyright 2014 Sandia National Laboratories