NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

Infrared Radiometer (LIR)

NSSDCA ID: 1978-078D-05

Mission Name: Pioneer Venus Large Probe
Principal Investigator:Dr. Robert W. Boese


The objectives of this experiment were to measure the atmosphere thermal flux profile, detect cloud layers and infer their composition, and estimate the atmospheric water vapor content as it descended through the atmosphere. This experiment used a 4-channel infrared radiometer looking down from the probe. Two internal blackbodies were used to allow absolute measurements of the flux in each channel. The primary measurement was the difference in upward and downward infrared flux at different wavelengths. The instrument weighed about 2 kg and used about 3 W of power.

The instrument had two components, an optical head and an electronics box. The electronics box was 17.5 x 13.0 x 10.7 cm, built primarily of magnesium, and contained voltage regulators, power supply, amplifiers, A/D converters, data acquisition timers, and sequencers. The optical head extended 7.6 cm from the electronics box. It had a cylindrical shape, and was surrounded by a wider, shorter cylinder containing phase change heat sink material. The instrument had two 25 x 25 degree fields of view, one centered at 45 degrees upward of the probe horizon, and one centered at 45 degrees downward. A stepper motor rotated a movable light pipe between the two views, and also occasionally orthogonally to black body calibration targets, looking through the same diamond window. The diamond window was heated to prevent contamination from the clouds. Held outside the cylinder, situated at 90 degrees from the instrument up/down positions, were a heated black body and an ambient temperature black body for calibration. The instrument was mounted on the aft side of the forward shelf on the large probe.

Infrared radiation entered the instrument through a type IIa diamond window. It was transmitted through the light pipe through collimator baffles, to a pyroelectric detector array. The detector array holds six detectors, each with a different filter, backed by detector Field-Effect Transistor (FET) preamplifiers. The six filters, feeding six diferent channels, covered different wavelength ranges. Channel A covered 3.0 to roughly 50 microns to measure net thermal flux. Channel B covered 6.0 to 7.0 microns, and channel C 7.0 to 8.0 microns to look for water and determine its abundance. Channel D (8.0 - 9.0 microns) was for cloud opacity, channel E (14.5 - 15.5 microns) covered a strong carbon dioxide band (to determine if there was any obscuration of the window), and channel F (4.0 - 5.0 microns) was centered on the diamond lattice vibration band to determine window temperature consistency. The outputs from channel E and F were expected to be zero in the absence of any problems.

During large probe descent, the instrument started operations at about 67 km altitude. The difference in flux between upward and downward positions was measured at a 2 Hz scan rate, integrated over a 6 second period. digitized data were transmitted to Earth during the following integration period. The sampling continued for 174 seconds, at which point the instrument performed 12 seconds of radiation calibration and 6 seconds of electronic calibration. It would then return to the scanning sequence. This would continue right up to impact on the surface. The vertical resolution at 67 km would be about 250 m and would improve to 90 m at the slower speed near the surface.

Alternate Names

  • LIR
  • PioneerVenusLargeProbe/LIR
  • urn:nasa:pds:context:instrument:pvmp.lp.lir

Facts in Brief

Mass: 2 kg
Power (avg): 3 W

Funding Agency

  • Unknown (United States)


  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Mr. Jacob H. MillerOther InvestigatorNASA Ames Research Center
Dr. James B. PollackOther InvestigatorNASA Ames Research Center
Mr. Lawrence P. GiverOther InvestigatorNASA Ames Research
Dr. Robert W. BoesePrincipal InvestigatorNASA Ames Research Center

Selected References

  • Boese, R. W., et al., The infrared radiometer on the sounder probe of the Pioneer Venus mission, IEEE Trans. Geosci. Rem. Sens., GE-18, No. 1, 97-99, doi:10.1109/TGRS.1980.350289, Jan. 1980
  • Boese, R. W., et al., First results from the large probe infrared radiometer experiment, Science, 203, No. 4382, 797-800, doi:10.1126/science.203.4382.797, Feb. 1979.
  • Colin, L., Ed., and D. M., Ed. Hunten, Pioneer Venus experiment descriptions, Space Sci. Rev., 20, No. 4, 451-525, doi:10.1007/BF02186463, June 1977.
[] NASA Logo -