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The Backscatter Ultraviolet (BUV) experiment aboard the Nimbus-4 satellite is discussed. This double monochromator experiment measures ultraviolet terrestrial radiance at 12 discrete wavelengths between 2550 A and 3400 A. Approximately 100 scans covering a 230 kilometer square are made between terminator crossings on the daylight side of the earth. A colinear photometer channel with the same field of view is used to derive the Lambert reflectivity of the lower boundary of the scattering atmosphere. The extraterrestrial solar irradiance is measured at the northern terminator. The instrument has currently produced almost three years of nearly continuous data which are being used to infer the high-level ozone distribution and total ozone on a global basis. The high-level ozone data have been verified by independent coincident rocket ozone soundings, and the total ozone values show good agreement with Dobson spectrophotometer determinations as well as those made with the Infrared Interferometer Spectrometer also on Nimbus-4.

The results of 21 rocket flights of Arcas optical ozonesondes were combined to produce estimates of the mean ozone distribution and its variability; these estimates apply to a broad range of latitudes. The flights were launched from sites near the equator to 58 S and to 64 N, in the years from 1965 to 1971. The local-noon mean ozone densities in molecules/cubic centimeter are 7.0 to the 10th power at 50 km, 6.7 x 10 to the 11th power at 40 km, 3.1 x 10 to the 12th power at 30 km, and 3.1 x 10 to the 12th power at 20 km. The range of observed densities is about + or - 30 percent of the mean value at 50 km; + or 40 percent at 40 km; + or - 40 percent at 30 km; and +200 percent, -66 percent at 20 km. The variabilities in this set of observations are much smaller than those indicated by previous measurements.

The ultraviolet earth radiance data from the Backscatter Ultraviolet Experiment on Nimbus 4 have been inverted to infer ozone profiles using a single Rayleigh scattering model. Two methods of solution give essentially the same results. Comparisons of these profiles with simultaneous rocket sounding data shows satisfactory agreement at low and middle latitudes. Vertical cross sections of ozone mixing ratio along the orbital tracks indicate that while the gross characteristics of the ozone field above 10 mb are under photochemical control, the influence of atmospheric motions can be found up to the 4 mb level.

Total ozone is estimated from Nimbus IV satellite measurements of the attenuation of backscattered radiances at wavelengths between 3100 and 3400 A. A measurement of the backscattered radiance at 3800 A, outside the O3 absorption band, is used to determine an equivalent Lambert albedo for the cloud-ground-haze surface viewed by the instrument. The measured relative attenuation at two wavelengths is compared with such values pre-computed for a series of standard O3 profiles and corrected for the equivalent Lambert

Observations of total ozone from 38°N to 60°S were made during the NASA Mobile Launch Expedition No. 1 aboard the USNS Croatan. These are compared with the upper atmospheric meteorological data obtained on the expedition. It was found that total ozone increases markedly south of the demarcation (30°S–35°S) between the high-level easterlies and westerlies. An ozone maximum was located near 47°S in the area where the polar stratosphere begins.

Rocket-borne radiometer determinations of ozone distributions by absorption of ultraviolet sunlight show anomalous eflects near 3000 angstroms. The instrument uses four 40-angstrom filters in the spectral region between 2650 and 3300 angstroms. At altitudes below 40 kilometers, signals from filters centered near 3000 angstroms appear reduced at least 25 percent below calculated values. However, at higher altitudes an unpredicted sharp increase in signals is observed. These effects are inconsistent with ozone absorption and cannot be ascribed to instrument characteristics. A previously unobserved absorption band of an atmospheric constituent, possibly the metastable excited states of molecular oxygen O(2)((1)Delta(g)) or O(2)((1)Sigma(g)+) can account for the anomalous effects.

The SBUV/TOMS measures the atmospheric ozone vertical profile and the solar ultraviolet spectrum, and provides a total ozone map by means of a mechanical scan across the Nimbus track. While the SBUV/TOMS instrument has noteworthy design features such as a state-of-the-art double monochromator and fixed optical components on a nonmetallic structure, its most significant characteristic is an optimum system design based on technology proven on the BUV instrument.