Sounding of the atmosphere using broadband emission radiometry (SABER): sensor design, performance, and lessons learned

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, a 10-channel infrared (1.27 - 16.9 μm) radiometer, was launched on the TIMED (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics) satellite in December 2001 from Vandenburg Air Force Base. SABER is being used to measure earthlimb emissions and to characterize infrared radiation, allowing calculation of cooling rates and determination of composition and temperature profiles in the mesosphere, lower thermosphere, and ionosphere (60-180 km). The SABER telescope is an on-axis Cassegrain design with a picket-fence tuning fork chopper at the first focus and a clamshell re-imager to focus the image on the focal plane. The telescope was designed to reject stray light from the Earth and atmosphere outside the instrument's instantaneous field-of-view (IFOV). The baffle assembly contains a single-axis scan mirror, which permits the 2 km vertical IFOV of each detector to be scanned from the Earth to a 400 km tangent height. The telescope and baffle assembly are cooled to 220 K by a dedicated radiator. The focal plane assembly is cooled to 75 K by a miniature cryogenic refrigerator. Field programmable gate arrays are used to implement state machine algorithms for control and operation of the instrument and subsystems. Although originally designed for a two-year lifetime requirement, the SABER instrument has been in continuous operation since January 2002. This paper discusses the SABER instrument design and innovations developed to achieve the required performance, along with instrument performance and lessons learned from the program.