urn:nasa:pds:context:instrument:pvo.ouvs 2.0 1.20.0.0 Product_Context 2020-08-26 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model 2024-04-02 2.0 Updated to IM 1.20.0.0 urn:nasa:pds:context:instrument_host:spacecraft.pvo instrument_to_instrument_host Stewart, A.I, 'Design and Operation of the Pioneer Venus Orbiter Ultraviolet Spectrometer', IEEE Transactions on Geoscience and Remote Sensing, GE-18, 65-70, 1980. reference.STEWART_1980 PIONEER VENUS ORBITER ULTRAVIOLET SPECTROMETER (OUVS) for PIONEER VENUS Spectrometer not applicable not applicable INSTRUMENT OVERVIEW =================== The Orbiter Ultraviolet Spectrometer (OUVS), or Airglow Ultraviolet Spectrometer, was designed to map and make spectroscopic analyses of ultraviolet light scattered and emitted by the clouds and gases in the Venus atmosphere, in order to detect and measure airglow, scattered sunlight, and hydrogen Lyman-alpha emissions in the thermosphere, mesosphere, and exosphere of Venus. These measurements are used to establish and map the composition, temperature, and photochemistry of the thermosphere and ionosphere, to determine the pressure at and above the visible cloud tops, and to establish the distribution and escape rate of atomic hydrogen. The OUVS used a 250 mm Cassegrain telescope on a 125 mm focal length Ebert-Fastie monochromator with a programmable grating drive. The instrument operated in the 1100-3400 A region. The telescope had a lightshade assembly and a 5 cm aperture. It had a 1.83 x 0.16 degree field of view, 60 degrees from the spin axis. and focused the incoming light onto the monochromator. The Ebert-Fastie monochromator had a 3600 line/mm diffraction grating, with 15 Angstrom spectral resolution and 4.4 angstrom grating steps. The grating is driven by a commandable step motor, which can select a desired wavelength, and has a scan mode, or can be set in one of 512 positions. It had two exit slits, which passed the dispersed light to two photomultiplier tubes, to convert the light into electrical impulses. One tube had a cesium iodide cathode with a lithium fluoride window, and was sensitive to UV wavelengths from 1100 to 1900 Angstroms. The other tube had a cesium telluride cathode and silicon dioxide window, and covered wavelengths from 1900 to 3600 angstroms. Counting could be done up to 2 Hz, it could store up to 256 words of data, and an integration period of 4, 8, 16, or 32 ms, determined by ground command. The instrument had a mass of 3.1 kg and required 1.7 W power. The instrument had three primary modes of operation. In spectral mode, the entire spectrum is scanned in four 256-word sections. Each section is scanned in 1 second, stored, and read out to the telemetry stream over one or more spacecraft spins. In wavelength mode, the grating position, and thus the wavelength, is selected by ground command. An approximately 30 degree arc of data is collected in this mode for each spacecraft spin. This mode is used for mapping and imaging. In Lyman-Alpha mode, individual measurements at a fixed wavelength are made on command. In a typical orbit, the OUVS makes measurements from 150 to 35 minutes prior to periapsis, to make airglow measurements and do cloud imaging. It makes observations again starting 15 minutes before periapsis until 10 minutes after to study limb airglow profiles and limb hazes. Spectra are recorded at periapsis. It can observe bright, hot starts for calibration and Lyman-alpha throughout the rest of the orbit.