# Atmosphere

International Standard Atmospheric (ISA) model

Only metric units are used.

Functions

T Atmospheric temperature [K]

p Air pressure [Pa]

ρ Air density [kg/m³]

a Speed of sound [m/s]

Vcas2Vtas True airspeed Vtas [m/s] as a function of the calibrated airspeed Vcas [m/s]

Vtas2Vcas Calibrated airspeed Vcas [m/s] as a function of the True airspeed Vtas [m/s]

M2Vtas True airspeed Vtas [m/s] as a function of the Mach number

Vtas2M Mach as a function of the True airspeed Vtas [m/s]

M2Vcas Calibrated airspeed Vcas [m/s] as a function of the Mach number

Vtas2M Mach as a function of the True airspeed Vtas [m/s]

Hp_trans Transition altitude [m]

θ temperature ratio

δ pressure ratio

σ density ratio

Constants

- T₀ Standard atmospheric temperature [K] at Mean Sea Level (MSL)
- p₀ Standard atmospheric pressure [Pa] at Mean Sea Level (MSL)
- ρ₀ Standard atmospheric density [kg/m³] at Mean Sea Level (MSL)
- a₀ Speed of sound [m/s] at Mean Sea Level (MSL)
- κ Adiabatic index of air []
- μ constant used for Vtas<->Vcas conversion
- R Real gas constant for air [M²/(Ks²)]
- g₀ Graviation acceleration [m/s²]
- βT∇ ISA temperature gradient [K/m] with altitude below the tropopause
- Hp_trop Geopotential pressure altitude [m] of Tropopause

Source: EUROCONTROL BADA 4 User Manual Chapter 2.2 Atmosphere Model