Ultraviolet Photometer

Description

The objective of this experiment was to study the properties of Venus' upper atmosphere by obtaining measurements of the ultraviolet emissions from resonance scattering of solar radiation by atmospheric atoms. The densities of the atmospheric species, and the temperature of the high atmosphere could be determined from the measurements and from the variation of the measured densities with height above the surface. The flight sensor was a UV photometer that consisted of three photomultiplier tubes with different spectral responses. All three photomultipliers had cesium iodide photocathodes and lithium fluoride windows, and responded to radiation in the wavelength interval from 1050 to 2200A, with greatly reduced sensitivity at the longer wavelength. Filters of calcium fluoride and barium fluoride were added to the second and third tubes, respectively. The tube with no filter measured in the wavelength interval from 1050 to 2200 A, the tube with the calcium fluoride filter measured from 1250 to 2200 A, and the tube with the barium filter measured from 1350 to 2200 A. The difference in signal between the lithium fluoride and calcium fluoride channels represented a measurement of the 1216-A hydrogen Lyman-alpha radiation. A measurement of the atomic oxygen emission at 1304 A could be obtained from the difference in signal between the calcium fluoride and barium fluoride channels. The field of view of the lithium fluoride channel was 3.0 deg, while the other two channels had fields of view of approximately 1.2 deg. All three channels of the photometer were aligned and looked in the same direction. More experiment details and some measured results can be found in C.A. Barth, et al., "Ultraviolet emissions observed near Venus from Mariner V," Science, v. 158, December, 1967 (TRF B02060).