The Infrared Horizon of the Planet Earth

Abstract Horizon sensors are essential elements in the orientation systems of many space vehicles and satellites. Their design and an evaluation of their capabilities and limitations requires a knowledge of the spectral radiance emitted by the Earth. This report investigates the discontinuity between the surface, the atmosphere, and outer space for various latitudinal, seasonal, climatic, and meteorological conditions. Calculations are carried out for the following five spectral intervals—the water vapor band from 6.33 to 6.85 microns, the ozone band from 8.9 to 10.1 microns, the atmospheric window from 10.75 to 11.75 microns, the carbon dioxide band from 14 to 16 microns, and finally the rotational water vapor band from 21 to 125 microns. The superior properties of the carbon dioxide band and the rotational water vapor region for horizon sensor purposes are shown.