Donald F. Heath

Solar Proton Event: Influence on Stratospheric Ozone

Large-scale reductions in the ozone content of the middle and upper stratosphere over the polar cap regions were associated with the major solar proton event of 4 August 1972. This reduction, which was determined from measurements with the backscattered ultraviolet experiment on the Nimbus 4 satellite, is interpreted as being due to the catalytic destruction of ozone by odd-nitrogen compounds (NOx) produced by the event.

The Nimbus-4 Backscatter Ultraviolet (BUV) atmospheric ozone experiment — tow years' operation

SummaryIn April 1970 the Backscatter Ultraviolet (BUV) experiment was placed into orbit aboard the Nimbus-4 satellite. This double monochromator experiment measures ultraviolet terrestrial radiance at twelve discrete wavelengths between 2550 Å and 3400 Å. Approximately 100 scans covering a 230 km 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. An increase has been observed in equatorial radiance at 2550 Å relative to 2900 Å, which seems to indicate that the amount of ozone in the upper stratosphere is related to the eleven-year solar cycle.

The retrieval of O3 profiles from limb scatter measurements:Results from the Shuttle Ozone Limb Sounding Experiment

Two instruments were flown on Shuttle flight STS-87 to test a new technique for inferring the ozone vertical profile using measurements of scattered sunlight from the Earths limb. The instruments were an ultraviolet imaging spectrometer designed to measure ozone between 30 and 50 km, and a multi-filter imaging photometer that uses 600 nm radiances to measure ozone between 15 km and 35 km. Two orbits of limb data were obtained on December 2, 1997. For the scans analyzed, the ozone profile was measured from 15 km to 45 km with approximately 3 km vertical resolution. Comparisons with a profile from an ozonesonde launched from Ascension Island showed agreement mostly within ±5%. The tropopause at 15 km appears to have been detected in this comparison. A comparison with two HALOE ozone profiles showed that on average ozone measured by SOLSE was lower by 9%±5% in the 30 km to 45 km range.

Effects of a simulated high-energy space environment on the ultraviolet transmittance of optical materials between 1050 A and 3000 A.

Transmittances of LiF, MgF(2), CaF(2), BaF(2), Al(2)O(3), and fused SiO(2)were measured from 1050 A to 3000 A before and after irradiation by 10(14) electrons/cm(2) first at 1.0 MeV and then at 2.0 MeV. Similar measurements were made with 10(14) electrons/cm(2) at 2.0 MeV using A1(2)O(3) to shield fused SiO(2), ADP, calcite, and Corning glass filters 9-54 and 7-54 from the direct electron beam. The electron energy and dose represent what one might expect to encounter in the artificial radiation belt after one year in a circular, near polar orbit at 1400 km. From these measurements it is concluded MgF(2), BaF(2), and A1(2)O(3) have the greatest potential for space applications in the uv.

Estimation of Total Ozone from Satellite Measurements of Backscattered Ultraviolet Earth Radiance

Abstract 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

Variations in the stratospheric ozone field inferred from Nimbus satellite observations

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. Comparison 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.

Observed Ozone Response to Variations in Solar Ultraviolet Radiation

During the winter of 1979, the solar ultraviolet irradiance varied with a period of 13.5 days and an amplitude of 1 percent. The zonal mean ozone values in the tropics varied with the solar irradiance, with an amplitude of 0.25 to 0.60 percent. This observation agrees with earlier calculations, although the response may be overestimated. These results imply changes in ozone at an altitude of 48 kilometers of up to 12 percent over an 11-year solar cycle. Interpretation of ozone changes in the upper stratosphere will require measurements of solar ultraviolet radiation at wavelengths near 200 nanometers.

Characterization of the Nimbus-7 SBUV Radiometer for the Long-Term Monitoring of Stratospheric Ozone

Abstract Precise knowledge of in-orbit sensitivity change is critical for the successful monitoring of stratosphere ozone by satellite-based remote sensors. This paper evaluates those aspects of the in-flight operation that influence the long-term stability of the upper stratosphere ozone measurements made by the Nimbus-7 SBUV spectroradiometer and chronicles methods used to maintain the long-term albedo calibration of this UV sensor. It is shown that the instruments calibration for the ozone measurement, the albedo calibration, has been maintained over the first 6 yr of operation to an accuracy of approximately ±2%. The instruments wavelength calibration is shown to drift linearly with time. Knowledge of the SBUV wavelength assignment is maintained to a 0.02 mm precision.

Satellite Ozone Measurements

Three classes of ozone sounders have been developed since the first Echo Satellite measurements in 1960. They are the (1) backscatter ultraviolet (b.u.v.), (2) infrared limb and nadir radiance, and (3) stellar and solar occultation methods. With these techniques, ozone has been measured from 20 to 100 km. Tropospheric ozone measurements are beyond present technology, bu t total ozone is determined with the b.u.v. and nadir infrared methods.

Rayleigh scattering attitude sensor

A new instrument has been developed to measure spacecraft attitude which utilizes ultraviolet radiation scattered in the Earths limb. The sensor consists of a very stable UV bandpass filter with a center wavelength at 355 nm, imaging optics, and a linear diode array detector. The radiance of the limb at this wavelength is dominated by Rayleigh scattering and typically decreases by 15% per kilometer above 20 km. The theoretical resolution at the limb of this device is 0.39 km per pixel for a nominal orbital altitude of 306 km (approximately equals 0.012 degree(s)) and represents a significant improvement over typical infrared-based attitude sensors which have an accuracy of approximately equals 0.1 degree(s). This system was integrated with the Shuttle Solar Backscatter Ultraviolet experiment and flown on STS-72 in January of 1996. The calibration and optical characterization of the device will be presented. Results from the first flight of this instrument, showing an agreement with available shuttle pointing data of +/- 0.05 degree(s), will also be discussed.