%% $Date: 2012-07-06 17:42:54#$
%% $Revision: 156 $
\index{altitude\_pressure\_raf}
\algdesc{Pressure altitude
}
{ %%%%%% Algorithm name %%%%%%
altitude\_pressure\_raf
}
{ %%%%%% Algorithm summary %%%%%%
Calculates pressure altitude given static pressure using US Standard Atmosphere definitions. Sea
level conditions in the US Standard Atmosphere are defined as having a pressure of 1013.25 hPa and
a temperature of 15 degC at an altitude of 0m.
}
{ %%%%%% Category %%%%%%
Thermodynamics
}
{ %%%%%% Inputs %%%%%%
$P_s$ & Vector & Static pressure [hPa] \\
}
{ %%%%%% Outputs %%%%%%
$H$ & Vector & Pressure altitude [m]
}
{ %%%%%% Formula %%%%%%
For pressures greater than or equal to 226.3206:
\begin{displaymath}
H = \frac{T_0}{L} \left[1-\left(\frac{P_s}{P_0}\right)^{\frac{R_a L}{g}} \right]
\end{displaymath}
%
where the lapse rate $L$ is 0.0065 K/m. For pressures less than 226.3206:
\begin{displaymath}
 H = H_1 + \frac{R_a T_1}{g} \ln{\left(\frac{P_1}{P_s}\right)}
\end{displaymath}
%
where $H_1$ is 11000m, $T_1$ is  216.65 K and $P_1$ is 226.3206.

}
{ %%%%%% Author %%%%%%
NCAR EOL-RAF
}
{ %%%%%% References %%%%%% 
US Standard Atmosphere 1976 (NASA-TM-X-74335), 241 pages. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539\_1977009539.pdf
}
