The unofficial Australian standard atmosphere, 2000 (UASA2000) is the same as USSA1976, except for the upper atmosphere. The upper atmosphere is divided into 15 regions. Logarithms of the pressure and density values of the 16 levels from the USSA1976 tables are used to construct pressure and density curves using cubic spline interpolation. The procedure init_atmosphere is used to initialise the lower and upper atmosphere parameters. The procedure atmosphere currently outputs pressure, density, and speed of sound given Z. The local Earth radius Re and local acceleration of gravity gs are global variables used to determine H. The output from USSA1976 was used to confirm the upper atmosphere from UASA2000.