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Backscatter Ultraviolet (BUV) Spectrometer

NSSDCA ID: 1970-025A-05

Mission Name: Nimbus 4
Principal Investigator:Dr. Donald F. Heath


The Nimbus 4 Backscatter Ultraviolet (BUV) spectrometer experiment was designed to monitor the vertical distribution and total amount of atmospheric ozone on a global scale by measuring the intensity of UV radiation backscattered by the earth/atmosphere system during day and night in the 2500- to 3400-A spectral band. The primary instrumentation consisted of a double monochromator containing all reflective optics and a photomultiplier detector. The double monochromator was composed of two Ebert-Fastie-type monochromators in tandem. Each monochromator had a 52- by 52-mm grating with 2400 lines per mm. Light from a 0.05-sr solid angle (subtending approximately a 222-sq-km area on the earth's surface from a satellite height of approximately 1100 km) entered the nadir-pointing instrument through a depolarizing filter. A motor-driven cam step rotated the gratings to monitor the intensity of 12 ozone absorption wavelengths. The detector was a photomultiplier tube. For background readings, a filter photometer measured the reflected UV radiation in an ozone-free absorption area near 3800 A. Signals from both units were read by separate range-switching electrometers with seven ranges. A BUV experiment cycle required 6144 s. Each cycle, in turn, was divided into 192 BUV frames of 32-s duration. Calibration by onboard light sources was performed in 26 of the 192 frames. The other frames were used for experimental data. During each of these data frames, the monochromator measured the intensity of the UV radiation in each of the 12 wavelength bands, while the photometer measured the UV intensity in a single wavelength band. The dwell time at each wavelength was 1.8 s, and, during this interval, four analog UV intensity measurements were taken at 400-ms intervals in addition to an integrated pulse count measurement of the UV intensity and energetic particle flux. Once each orbit, the field of view was changed to monitor the sun or moon directly. The measurement range of the signal current was from 0.2 to 3000 microamps. The vertical distribution of ozone was obtained by mathematical inversion techniques. For a complete description of the BUV experiment, see Section 7 in "The Nimbus IV User's Guide" (TRF B06861). For an index of the data, see "User's Guide to the Nimbus-4 Backscatter Ultraviolet Experiment Data Sets" (TRF B30067). Both documents are available from NSSDC.

Alternate Names

  • BUV
  • Nimbus4/BUV

Facts in Brief

Mass: 14.5 kg
Power (avg): 7 W

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Earth Science: Atmospheric Chemistry

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Arlin J. KruegerOther InvestigatorNASA Goddard Space Flight
Mr. J. V. DaveOther Investigator
Dr. Carlton L. MateerOther InvestigatorEnvironment Canada
Dr. Donald F. HeathPrincipal InvestigatorNASA Goddard Space Flight Center
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