Standardatmosphäreprofil

Standard atmosphere is a set of reference atmospheric conditions used to estimate air properties as a function of altitude. It serves as a baseline in aviation, aerospace engineering, meteorology, and related fields for calculating performance, designing equipment, and calibrating instruments. The most widely used version is the International Standard Atmosphere (ISA), defined by international bodies such as ISO and ICAO. In the United States, a closely related US Standard Atmosphere is also used.

A standard atmosphere specifies temperature, pressure, density, and other properties at different heights, based on a simplified model of the real atmosphere. At sea level, it adopts standard values such as a temperature of 15°C and a pressure of 1013.25 hPa. The model then describes how temperature changes with altitude through several layers. In the lower atmosphere, the troposphere, temperature decreases with height at a lapse rate of about 6.5 K per kilometer. Above about 11 kilometers, the model moves into layers where the temperature changes more slowly or remains nearly constant, and then may increase in some higher strata. Pressure and density are derived from the assumed temperature profile using the hydrostatic equation and the ideal gas law.

Applications of the standard atmosphere include estimating engine thrust and fuel consumption, determining lift and drag for performance charts, calibrating flight instruments, and converting between altitude, temperature, pressure, and air density. While useful for design and planning, real atmospheric conditions vary with location, season, and weather, so deviations from ISA are common. Variants and amendments, such as ISA+ or ISA−, express these departures for specific calculations.