NSSDCA ID: 1971-024A-12
Mission Name: ISIS 2A two-channel photometer was used to measure directly and to map the intensity of the atomic oxygen red line at 6300 A in day, twilight, and night airglow and aurora. Each channel had its own optical input, and the two inputs were mounted at the same end of the spacecraft, separated by 180 deg, with their axes at 90 deg to the spacecraft's spin axis. One optical input was characterized by a spectral bandwidth of 12 A centered around the 6300-A line of atomic oxygen, and the other input was used for white-light measurements. The spinning satellite caused the photometer to alternately view the earth and then the sky; i.e., when one sensor viewed the earth, the other sensor saw the dark sky. Both sensors had a 2.5-deg circular field of view. With the use of a beam-combiner arrangement, the same photomultiplier accepted the two inputs. The dynamic range of intensity measurements was from about 1.E11 photons/(sq m-s) (10 rayleighs) to more than 1.E16 photons/(sq m-s). Sunlight could enter the optical systems directly in addition to earth-reflected light. The instrument baffle was illuminated by the sun only for the off-axis angles less than 47 deg. Outside this limit, the data were not degraded by sunlight, permitting normal operation in the region of the orbit where the spacecraft was in sunlight, but the portion of the earth beneath it was dark. An external light source "saw" the filter only when it was 7.5 deg or less off axis. In the range 7.5 to 47 deg, good data were still obtained when the sunlit earth was the origin of the contamination. To perform the data analysis, it was necessary, among other operations, to evaluate different geometrical situations, and to locate the point at which the 12-A bandpass photometer's FOV crosses the earth's leading limb so that the data could be organized into spin maps. For more details see G. G. Shepherd et al. "ISIS-II atomic oxygen red line photometer," Applied Optics, v. 12, n. 8, pp. 1767-1774, August 1973.
Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Gordon G. Shepherd | Principal Investigator | York University | gordon@windii.yorku.ca |