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Mission Name: Nimbus 7
Launch Date/Time: 1978-10-24 at 08:14:00 UTC
On-orbit dry mass: 832.00 kg
Nominal Power Output: 300.00 W

Experiment mass: 68.40 kg
Average experiment power: 27.00 W
Average experiment bit rate: 4.00 kbps


The objective of the Limb Infrared Monitor of the Stratosphere (LIMS) experiment was to map the vertical profiles of temperature and the concentration of ozone, water vapor, nitrogen dioxide, and nitric acid in the lower to middle stratosphere range, with extension to the stratopause for water vapor and into the lower mesosphere for temperature and ozone. This experiment was a follow-on to the Limb Radiance Inversion Radiometer (LRIR) flown on Nimbus 6. The instrument had a six-channel infrared (IR) radiometer that incorporated Hg-Cd-Te detectors cooled by a two-stage solid cryogen cooler. The LIMS instrument consisted of two electronic boxes and the radiometer unit. The radiometer unit consisted of the solid cryogen package (SCP) and the optical-mechanical package (OMP). The OMP contained the optics for the folded telescope, while the SCP contained the detector assembly and cryogen. Radiance from the earth's limb entered the OMP aperature, reflected off the scan mirror to the 18-cm diameter off-axis parabolic primary mirror where the radiation was focused and chopped at 945 Hz. The radiation was re-collimated by the secondary mirror and directed through a Lyot stop to a folding mirror and into the detector capsule assembly (DCA). The radiation was then focused through a cadmium telluride lens and through interference filters, which defined the FOVs, and onto an array of discrete mercury cadmium telluride detectors. The detectors were maintained at about 63 K temperature by the cryogen. The LIMS began a scan near 153 km altitude, taking about 12 sec to move near 38 km below the solid limb, then retraced its motion upward. After every second scan pair, the scan mirror was placed in a position to observe radiation from a small cavity blackbody for inflight warm calibration after which the instrument viewed space to obtain a cold calibration point. Calibration data was included in the LIMS output data stream. The LIMS mapped vertical profiles of thermal IR emission coming from the horizon in six bands (6.2, 6.3, 9.6, 11.3, and two at 15 micrometers) of CO2N, CO2, O3, HNO3,H2O, and NO2. Two of the channels were used to determine radiance profiles of emission by CO2. The profiles were mathematically inverted to obtain temperature versus pressure. The infrared temperature profile, together with radiance profiles in the other spectral bands, were then used to infer the vertical distribution of trace constituents. The temperature was determined to an accuracy of about 1.5 deg K. Constituent concentrations were determined with an accuracy of about 20%, with the exception of NO2 which was determined to within about 50%. Instantaneous vertical field of view at the horizon was 2 km for the temperature, ozone, and nitric acid channels, and 4 km for the NO2 and water vapor channels. For more detailed information, see Section 4 in "The Nimbus 7 Users' Guide" (TRF B30045), available from NSSDC. The instrument was turned off due to depletion of cryogen, as planned, in June 1979.

Organization: GATS
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