INFRARED GRATING SPECTROMETER

Objective of the flight was to test a prototype satellite solar occultation instrument designed for monitoring the concentrations of ozone (O3), water vapor (H2O), and nitric acid (HNO3) in the stratosphere. The experiment, was developed by a collaboration between the NOAA/National Environmental Satellite, Data and Information Service (NESDIS) that designed and built the prototype grating spectrometer, NASA's Goddard Space Flight Center which provided the gondola, attitude control and stabilization systems, sun-tracking equipment, and telemetry systems and HSS, Inc. that was in charge of the optical design of the spectrometer, including the telescope and grating system.

Final goal of the project was to demonstrate the feasibility of using a multi-detector infrared grating spectrometer, operating in solar occultation mode, as a low-cost, stable, and reliable satellite sensor for long-term atmospheric monitoring. The spectrometer observed solar radiation as it passed tangentially through the atmosphere during sunset, allowing the retrieval of vertical concentration profiles of selected trace gases in the upper stratosphere between 25 and 39 km in altitude.

The apparatus consisted of a Cassegrain telescope with a 0.6-meter focal length and a fixed grating spectrometer equipped with eight discrete infrared detectors. The telescope directed sunlight through an entrance slit into the spectrometer, which had an over/under Ebert layout with a 0.5-meter focal length. Instead of scanning the spectrum, the spectrometer simultaneously measured in eight preselected spectral intervals associated with absorption bands of target gases. Two intervals were centered on the 9.6 µm ozone band, two on the 6.6 µm water vapor band, and one on the 11.3 µm nitric acid band. The remaining intervals were initially intended to detect CO2 and Freon-12, although issues with atmospheric transparency and nitrogen interference limited their usefulness in this flight. Each detector used a thermopile with a built-in filter-window to isolate the desired wavelength, and the optical signal was mechanically chopped and then processed via amplification, synchronous detection, and digitization. The data were transmitted to Earth via a 50 kbps PCM telemetry system.

Sun tracking was essential for the instrument's operation and was achieved through a combination of NASA's gondola-mounted tracking system for high solar elevations and a dedicated two-pair infrared detector system embedded in the telescope for low solar elevations. The field of view of the spectrometer was carefully controlled, and pointing accuracy was maintained to within 3 arcminutes during ground tests.

Balloon launched on: 4/16/1983 at 18:37 utc
Launch site: Columbia Scientific Balloon Facility, Palestine, Texas, US  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon SF 316.06-050-NSCHR-01
Balloon serial number: W11.59-1-01
Flight identification number: 1318P
End of flight (L for landing time, W for last contact, otherwise termination time): 4/17/1983 at 1:35 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 7 h
Landing site: 20 miles E of Jackson, Mississippi, US

This was the second flight of the instrument. The balloon was launched from the National Scientific Balloon Facility, in Palestine, Texas at 18:37 UTC on April 16, 1983. The balloon remained in flight at 130.000 feet for 7 hours. Payload was recovered 20 miles E of Jackson, Mississippi.

During the flight, an unidentified spectral feature interfered with gas absorption measurements. The researchers couldn't determine whether this interference came from atmospheric aerosols or instrument malfunction, and lacked the additional spectral data needed to isolate or remove the effect. Consequently, they decided not to report the flight's results.

• Balloon-based infrared solar occultation measurements of stratospheric O3, H2O, HNO3, and CF2C12 National Environmental Satellite, Data, and Information Service, 1987
• Data processing algorithms for inferring stratospheric gas concentrations from balloon-based solar occultation data Washington, D.C.: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service