# pvl_absoluteairmass

Determine absolute (pressure corrected) airmass from relative airmass and pressure

## Contents

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

## Syntax

`AMa = pvl_absoluteairmass(AMrelative, pressure)`

## Description

Gives the airmass for locations not at sea-level (i.e. not at standard pressure). The input argument `AMrelative` is the relative airmass. The input argument `pressure` is the pressure (in Pascals) at the location of interest and must be greater than 0. The calculation for absolute airmass is:

## Inputs

- `AMrelative` - The airmass at sea-level. This can be calculated using the PV_LIB function `pvl_relativeairmass`.
- `pressure` - a scalar or vector of values providing the site pressure in Pascal. If pressure is a vector it must be of the same size as all other vector inputs. pressure must be >=0. Pressure may be measured or an average pressure may be calculated from site altitude.

## Outputs

- `AMa` - Absolute (pressure corrected) airmass

## Example

Adjust airmass for elevation

    AM = 1;
    pressure = 80000; %Approximate air pressure at 2000 meters above sea level
    AMa = pvl_absoluteairmass(AM, pressure)

    AMa =

        0.7895

## References

[1] C. Gueymard, "Critical analysis and performance assessment of clear sky solar irradiance models using theoretical and measured data," Solar Energy, vol. 51, pp. 121-138, 1993.

## See Also

`pvl_relativeairmass`

Copyright 2014 Sandia National Laboratories