Abstract: A horizon sensor scans an infrared detector over the earth's horizon generating first (A) and second (B) signals of finite pulse width representing radiation from the fields of view of the infrared detector as it is scanned across the earth's horizon. Signals (A-B) and (A+B)/3 are derived from the first (A) and second (B) signals. The horizon is detected when a threshold is exceeded when the absolute value (A-B) is less than the absolute value of (A+B)/3 whereby the detected horizon is essentially independent of the radiance variations of the earth's horizon. Sun and moon signals appearing in the field of view of the infrared detector are eliminated based on the smaller pulse width of such signals in comparison with the finite pulse width of the first and second signals. The method of radiance compensation can be implemented using a dual field of view for the infrared detector in a horizon crossing indicator sensor where the scanning of the detector is provided by the rotation of the satellite.