The Platform

There are two such satellites in operation at any time (currently NOAA-11 and NOAA-12) in sun-synchronous orbits; one overhead at about 0200 LST and 1400 LST, and the other at about 0730 LST and 1930 LST. The satellites are about 840 km above the surface and have orbital periods of about 100 min. The satellites are three-axis stabilized so that the instruments on board have a pointing accuracy of 0.125, i.e., 1.7 km on the Earth's surface (Schwalb 1978). The payload includes the TIROS Operational Vertical Sounder (TOVS) suite of sensors made up of High-Resolution Infrared Radiation Sounder Mk. 2 (HIRS/2), the Microwave Sounding Unit (MSU) and the Stratospheric Sounding Unit (SSU). Starting with NOAA-9 the satellites have also carried the Solar Backscatter Ultraviolet System Mk. 2 (SBUV/2) to measure atmospheric ozone, and Earth Radiation Budget Experiment ERBE radiometers on NOAA-9 and NOAA-10. (A fuller description of the spacecraft and sensors is given by Rao et al. 1990.)