def get_absolute_airmass(airmass_relative, pressure=<NUM_LIT>):
if airmass_relative is not None:<EOL><INDENT>return airmass_relative * pressure / <NUM_LIT><EOL><DEDENT>else:<EOL><INDENT>return None<EOL><DEDENT>
Determine absolute (pressure corrected) airmass from relative
airmass and pressure.

Gives the airmass for locations not at sea-level (i.e. not at
standard pressure). The input argument airmass_relative 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
.. math::
    absolute airmass = (relative airmass)*pressure/101325

Note:
    [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.

Args:
    airmass_relative: numeric
        The airmass at sea-level.
    pressure: numeric, default 101325
        The site pressure in Pascal.

Returns:
    airmass_absolute: numeric
        Absolute (pressure corrected) airmass