Currently archived ozone data from the Solar Backscatter Ultraviolet (SBUV) spectrometer experiment on the Nimbus 7 satellite has been reported to show large global decreases in the amount of atmospheric ozone, both total content and as a function of altitude, for the period from 1978 to 1987. Analysis of atmospheric albedo data leading to these reported trends was based on empirical models of the SBUV spectrometer and diffuser plate degradation with time. Their combined degradation can be obtained from apparent decreases in measured solar irradiance at wavelengths where little or no long‐term intensity changes are expected. The central problem in analyzing SBUV data is to separately specify the diffuser plate degradation [Husdon et al., 1988]. Ratios of radiance to solar irradiance used to obtain ozone amounts are proportional only to diffuser reflectivity and independent of any spectrometer degradation. Even observations of relatively short‐term solar irradiance changes with time must be based on a model of diffuser plate degradation, since the SBUV data provide no internal means to uniquely specify diffuser plate reflectivity changes at ail wavelengths. A new class of explicitly empirical models have been developed that produce a better fit to all of the SBUV solar flux data. The models have a single free parameter to separately specify the diffuser plate and spectrometer degradation. This parameter must be within a narrow range to bring the calculated ozone trend into approximate agreement with data from the Dobson network, Solar Mesospheric Explorer (SME) and Stratospheric Aerosol Gas Experiment (SAGE) satellites, or with the different trends reported from the Umkehr ground stations. It is shown that outside sources of ozone data must be used to obtain a unique solution from SBUV radiance data within the precision necessary to determine the existence of a global annual ozone decrease. A correction factor is given as a function of time and altitude that brings the SBUV data into approximate agreement with SAGE, SME, and Dobson ozone trends. The total ozone results also agree with a recently developed wavelength pair justification method of internal calibration for the SBUV instrument. In our opinion, the currently archived SBUV ozone data should be used with caution for periods of analysis exceeding 1 year, since it is likely that the yearly decreases contained in the archived data are too large.
The solar backscattered ultraviolet spectral radiometer on the Nimbus 7 satellite routinely measures fluorescence emissions from the nitric oxide (1, 4) gamma band that are imposed on the large Rayleigh‐scattered signal in the wavelength range 255–256 nm. The gamma band feature, when isolated from the background radiance, provides information on the seasonal and latitudinal variations in the nitric oxide column abundance over the altitude region from 40 to 45 km upward through the thermosphere. At latitudes from 30° to 45° in the northern hemisphere the measurements show an annual cycle with maximum nitric oxide abundance in summer. The southern hemisphere pattern is qualitatively similar to this, although the amplitude of the seasonal variation is substantially smaller. The most prominent feature of the data base is a large maximum in nitric oxide emission that develops poleward of 45° latitude in both hemispheres during late autumn and early winter. These maxima dissipate rapidly as spring approaches and are no longer evident in the data for northern hemisphere March and southern hemisphere September.
The mid‐latitude upper stratospheric ozone profiles obtained by the solar backscatter ultraviolet instrument on the Nimbus 7 satellite show a clear annual cycle both in the absolute ozone amounts between 0.98 and 15.6 mbar and in the magnitude of disturbances that reveal themselves as longitudinal structure. At the lowest pressures analyzed a winter maximum in ozone exists, but as one progresses downward in altitude a shift in the temporal phase of the annual cycle occurs in the vicinity of 3 to 4 mbar. Comparison of the observed behavior with the predictions of a one‐dimensional photochemical model shows a systematic tendency for calculated ozone amounts to be 20–27% below the data for pressures less than 7.8 mbar. The chemical model successfully predicts the change in phase of the annual cycle, although at a pressure greater than observed. Diagnosis of model results shows the observed shift to be closely coupled to the magnitude of the ozone column density near 3–4 mbar. The wavelength‐dependent attenuation of the solar radiation field by ozone alters the relative magnitude of the molecular oxygen and ozone dissociation rates, leading to a change in the temporal phase of the annual cycle.
The Sea-viewing Wide Field-of View Sensor (Sea-WiFS) Mission has initiated a new era of ocean color remote sensing and has established performance benchmarks that will be emulated by subsequent missions. An integral element of the SeaWiFS mission is the data component, performed by the Goddard Earth Sciences Distributed Active Archive Center (GES DAAC), NASA Goddard Space Flight Center, Greenbelt, MD. Since the beginning of data distribution in September 1997, the GES DAAC has managed the data archive and improved data distribution capability. SeaWiFS data products are archived in a primary, secondary, and tertiary archive structure, ensuring data preservation. Data distribution utilizes a World Wide Web (WWW)-based ordering interface, allowing distribution either electronically or on magnetic tape media. Automatic data subscriptions, supplying user-tailored data product selections, have yielded a high archive-to-distribution ratio. System improvements have increased efficiency and redundancy. The user interface has added features designed to facilitate data access and data usage, enhanced by WWW information resources and comprehensive online dataset documentation. As SeaWiFS enters the latter half of its five-year mission, a system performance assessment provides useful information for other Earth remote sensing missions and allows consideration of future usage objectives for the SeaWiFS data archive.
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