The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four experiments that will fly on the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission to be launched in May, 2000. The primary science goal of SABER is to achieve major advances in understanding the structure, energetics, chemistry, and dynamics, in the atmospheric region extending from 60 km to 1 80 km altitude. This will be accomplished using the space flight proven experiment approach of spectral broadband limb emission radiometry. SABER will scan the horizon in 10 selected bands ranging from 1.27 im to 17 tm wavelength. The observed vertical horizon emission profiles will be processed on the ground to provide vertical profiles with 2 km altitude resolution, of temperature, 03, H20, and CO2 volume emission rates due to O2(1i), OH(u=3,4,5), OH(i=7,8,9), and NO; key atmospheric cooling rates, solar heating rates, chemical heating rates, airglow losses; geostrophic winds, atomic oxygen and atomic hydrogen. Measurements will be made both night and day over the latitude range from the southern to northern polar regions. The SABER instrument uses an on-axis Cassegrain design with a clam shell reimager. Preliminary test and calibration results show excellent radiometric performance.

Over the past 60 years, ground-based remote sensing measurements of the Earth's mesospheric temperature have been performed using the nighttime hydroxyl (OH) emission, which originates at an altitude of ∼87  km. Several types of instruments have been employed to date: spectrometers, Fabry-Perot or Michelson interferometers, scanning-radiometers, and more recently temperature mappers. Most of them measure the mesospheric temperature in a few sample directions and/or with a limited temporal resolution, restricting their research capabilities to the investigation of larger-scale perturbations such as inertial waves, tides, or planetary waves. The Advanced Mesospheric Temperature Mapper (AMTM) is a novel infrared digital imaging system that measures selected emission lines in the mesospheric OH (3,1) band (at ∼1.5  μm) to create intensity and temperature maps of the mesosphere around 87 km. The data are obtained with an unprecedented spatial (∼0.5  km) and temporal (typically 30″) resolution over a large 120° field of view, allowing detailed measurements of wave propagation and dissipation at the ∼87  km level, even in the presence of strong aurora or under full moon conditions. This paper describes the AMTM characteristics, compares measured temperatures with values obtained by a collocated Na lidar instrument, and presents several examples of temperature maps and nightly keogram representations to illustrate the excellent capabilities of this new instrument.

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The SABER instrument on the National Aeronautics and Space Administration Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite continues to provide a long‐term record of Earth's stratosphere, mesosphere, and lower thermosphere. The SABER data are being used to examine long‐term changes and trends in temperature, water vapor, and carbon dioxide. A tacit, central assumption of these analyses is that the SABER instrument radiometric calibration is not changing with time; that is, the instrument is stable. SABER stratospheric temperatures and those derived from Global Positioning System Radio Occultation measurements are compared to examine SABER's stability. Global Positioning System Radio Occultation measurements are inherently stable due to the accuracy and traceability of the measured phase delay rate to the Système Internationale definition of the second. Differences in global annual mean SABER and COSMIC lower stratospheric temperatures show little significant change with time in the 11 years spanning 2007–2017. From this analysis we infer that SABER temperatures are stable to better than 0.1 to 0.2 K per decade.

This paper describes the design of a 10-channel infrared (1 .27 to 16.9 jim) radiometer instrument known as SABER (sounding of the atmosphere usingbroadband emissionradiometry) that will measure earth-limb emissions from the TiMED (thermosphere-ionospheremesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray. light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop and a window) is cooled to 75 Kby a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Keviar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detectOr airay consists ofdiscrete IJgCdTe, JnSb and InGaAS detectors. Two InGaAS detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoffof2.33 im at 77 K.1. IPTRODUCTION SABER (sounding ofthe atmosphere using broadband emissionradiomelry) is an earth-limb-scanning radiometer that has been selected as one of the four payload instruments on TIMED (thermosphere-ionosphere-mesosphere energetics and dynamics) satellite to be launched in OctOber 1998. The TIMED orbit altitude is 600 km and the orbit inclination is 74.4 degrees. SABER will look 90 degrees to the ram. The mission life is 2 years.The SABER systems requirement review(SRR) and the conceptual design review (CoDR) were held in April 1 995, and the preliminaiy design review is scheduled for April 1996. Significant modifications to the SABER design described in the literature3 have been made in the last year. Many ofthese modifications resulted because the previous optical design required filters that were impractically thick to correct for chromatic focal shifts across the very wide spectral band covered by SABER. A new optical design that solved this problem and resulted in a much more rugged instrument was developed and is described in this paper. The stray light performance of this new design is excellent. This paper is intended to provide a comprehensive overview ofthe new SABER design. SYSTEM DESIGN -A functional diagram ofthe SABER instrument is shown in Figure 1. A high off-axis rejection telescope collects wanted light and discriminates against unwanted light. The scan mirror scans the instrument field ofview vertically across the earth limb. In orbit the telescope is oriented so the nadir_zenith line is vertical in Figure 1 and local depression angles are measured relative to the horizontal. The baffle opening allows the center of SABER's 1 .4 degree wide field ofview to be scanned across depression angles from 11.148 to 26.168 degrees. Thi...

The stray light analysis of the sounding of the atmosphere using broadband emission radiometry (SABER) instrument on the thermosphere-ionosphere-mesosphere energetics and dynamics (TIMED) mission is discussed. Relevant mission objectives and operating conditions are stated to define the stray light problem. Since SABER is an earth limb viewing sensor, the telescope must be designed for large off-axis rejection. Described are the key design features which make the instrument well suited for its mission. Representative point source transmittance (PST) curves computed using the commercial stray light program APART are presented. Non-rejected radiance (NRR) values computed using APART generated PST curves and LINEPACK generated curves for the total radiance from the earth aixi the afinosphere are given. A method for computing NRR from the earth and the atmosphere using lineof-sight radiance profiles versus tangent height is described. Computed NRR values demonstrate that the effect of stray light on SABER's measurement capability is negligible.

The Sounding of the Atmosphere using Broadband Emission Radiometiy (SABER) instrument is a 10-channel earth limbviewing sensor that is to measure atmospheric emissions in the spectral range of 1.27 jm to 16.9 iim. Presented in this paper is the stray light design and analysis of SABER Unwanted radiation from the eaith and atmosphere are suppressed by the use of stiay light features that are Critical to mission success. These include the use ofan intermediate field stop, an inner and outer Lyot stop, and super-polished mirrors. The point source normalized irradiance transmission (PSNIT) curve, which characterizes the sensor's off-axis response, was computed using the stray light analysis program APART. An initial calculation of the non-rejected radiance (NRR) due to emissions and scatter from the earth and atmosphere was made using the PSNTT data. The results indicate that stray light will not impede the mission objectives.

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