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ISA Atmosphere Model

Implement International Standard Atmosphere (ISA)




The ISA Atmosphere Model block implements the mathematical representation of the international standard atmosphere values for ambient temperature, pressure, density, and speed of sound for the input geopotential altitude.

The ISA Atmosphere Model block icon displays the input and output metric units.


Change atmospheric parameters

Select to customize various atmospheric parameters to be different from the ISA values.

Selecting this check box enables the parameters .

Acceleration due to gravity (m/s^2)

Enter acceleration from gravity in m/s2.

Ratio of specific heats

Enter a ratio of specific hits.

Characteristic gas constant (J/Kg/K)

Enter the characteristic gas constant in J/Kg/K.

Lapse rate (K/m)

Enter the lapse rate in K/m.

Height of troposphere (m)

Enter the height of the troposphere in m.

Height of tropopause (m)

Enter the height of the tropopause in m.

Air density at mean sea level (Kg/m^3)

Enter the air density at mean sea level in Kg/m3.

Ambient pressure at mean sea level (N/m^2)

Enter the ambient pressure at mean sea level in N/m2.

Ambient temperature at mean sea level (K)

Enter the ambient temperature at mean sea level in K.

Lowest altitude (m)

Enter the lowest altitude in m.

Inputs and Outputs

InputDimension TypeDescription


 Contains the geopotential height.
OutputDimension TypeDescription


 Contains the temperature.


 Contains the speed of sound.


 Contains the air pressure.


 Contains the air density.

Assumptions and Limitations

Below the geopotential altitude of 0 km and above the geopotential altitude of 20 km, temperature and pressure values are held. Density and speed of sound are calculated using a perfect gas relationship.


[1] U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C.

Introduced before R2006a