Engineering topics

Mcpeters, R. D.

Publications and source records attributed to Mcpeters, R. D..

At least 19 records

NASA NTRS1995

Ozone trends deduced from combined Nimbus 7 SBUV and NOAA 11 SBUV/2 data

The long-term time series of global ozone from the Nimbus-7 Solar Backscatter Ultraviolet instrument (SBUV) (Nov. 1978-June 1990) are extended through June 1994 by using measurements from the NOAA-11 SBUV/2. The data sets are merged based upon comparisons during the 18-month overlap period in which both instruments were operational. During this period, the average offset between the two time series is less than 2% in total ozone, and less than 6% in Umkehr layers 1-10. A linear-regression trend model is applied to the extended time series to calculate updated trends as a function of latitude and altitude. Trends through June 1994 are 1.5-2% per decade less negative than through June 1990 in the tropical middle stratosphere (35-40 km) and in the upper stratosphere (45-50 km) at mid-latitudes. In the lower stratosphere, the trends are nearly 1.5% per decade more negative in the southern hemisphere tropical regions to 25 deg S, but remain relatively unchanged elsewhere. The seasonal structure of the total ozone trends is similar to past trend study results, but the magnitude of the seasonal trend can vary by 2% per decade depending on the length of the time series. Both Total Ozone Mapping Spectrometer (TOMS) (through April 1993) and SBUV total ozone time series show small negative trends in the equatorial region, though they are not statistically at the 2-sigma level.

Hollandsworth, S. M.↗

NASA NTRS1995

Spectral analyses, climatology, and interannual variability of Nimbus-7 TOMS version 6 total column ozone

This reference publication presents selected results from space-time spectral analyses of 13 years of version 6 daily global ozone fields from the Total Ozone Mapping Spectrometer (TOMS). One purpose is to illustrate more quantitatively the well-known richness of structure and variation in total ozone. A second purpose is to provide, for use by modelers and for comparison with other analysts' work, quantitative measures of zonal waves 1, 2, 3, and medium-scale waves 4-7 in total ozone. Their variations throughout the year and at a variety of latitudes are presented, from equatorial to polar regions. The 13-year averages are given, along with selected individual years which illustrate year-to-year variability. The largest long wave amplitudes occur in the polar winters and early springs of each hemisphere, and are related to strong wave amplification during major warning events. In low attitudes total ozone wave amplitudes are an order of magnitude smaller than at high latitudes. However, TOMS fields contain a number of equatorial dynamical features, including Rossby-gravity and Kelvin waves.

Stanford, J. L.↗

NASA NTRS1995

Application of the Langley plot method to the calibration of the solar backscattered ultraviolet instrument on the Nimbus 7 satellite

The concept of the well-known Langley plot technique, used for the calibration of ground-based instruments, has been generalized for application to satellite instruments. In polar regions, near summer solstice, the solar backscattered ultraviolet (SBUV) instrument on the Nimbus 7 satellite samples the same ozone field at widely different solar zenith angles. These measurements are compared to assess the long-term drift in the instrument calibration. Although the technique provides only a relative wavelength-to-wavelength calibration, it can be combined with existing techniques to determine the drift of the instrument at any wavelength. Using this technique, we have generated a 12-year data set of ozone vertical profiles from SBUV with an estimated accuracy of +/- 5% at 1 mbar and +/- 2% at 10 mbar (95% confidence) over 12 years. Since the method is insensitive to true changes in the atmospheric ozone profile, it can also be used to compare the calibrations of similar SBUV instruments launched without temporal overlap.

Bhartia, P. K.↗

NASA NTRS1994

Comparison of SBUV and SAGE II ozone profiles: Implications for ozone trends

Solar backscattered ultraviolet (SBUV) ozone profiles have been compared with Stratospheric Aerosol and Gas Experiment (SAGE) II profiles over the period October 1984 through June 1990, when data are available from both instruments. SBUV measurements were selected to closely match the SAGE II latitude/longitude measurement pattern. There are significant differences between the SAGE II sunrise and the sunset zonal mean ozone profiles in the equatorial zone, particularly in the upper stratosphere, that may be connected with extreme SAGE II solar azimuth angles for tropical sunrise measurements. Calculation of the average sunset bias between SBUV and SAGE II ozone profiles shows that allowing for diurnal variation in Umkehr layer 10, SBUV and SAGE II agree to within +/- 5% for the entire stratosphere in the northern midlatitude zone. The worst agreement is seen at southern midlatitudes near the ozone peak (disagreements of +/- 10%), apparently the result of the SBUV ozone profile peaking at a lower altitude than SAGE. The integrated ozone columns (cumulative above 15 km) agree very well, to within +/- 2.3% in all zones for both sunset and sunrise measurements. A comparison of the time dependence of SBUV and SAGE II shows that there was less than +/- 5% relative drift over the 5.5 years for all altitudes except below 25 km, where the SBUV vertical resolution is poor. The best agreement with SAGE is seen in the integrated column ozone (cumulative above 15 km), where SAGE II has a 1% negative trend relative to SBUV over the comparison period. There is a persistent disagreement of the two instruments in Umkehr layers 9 and 10 of +/- 4% over the 5.5-year comparison period. In the equatorial zone this disagreement may be caused in part by a large positive trend (0.8 K per year) in the National Meteorologica Center temperatures used to convert the SAGE II measurement of ozone density versus altitude to a pressure scale for comparison with SBUV. In the middle stratosphere (30-40 km), SBUV shows a 2-4% negative drift relative to SAGE II. If the actual ozone trends are considered, SBUV and SAGE II agree in showing little ozone change (less than 2%) between 1984 and 1990, except in layer 3 where SAGE II measures a large ozone decrease. But over 11 years, SBUV measured a 7% per decade ozone decrease between 40 and 50 km, decreasing in magnitude at lower altitudes, in good agreement with 11-year trends derived from the average of 5 Umkehr stations.

Mcpeters, R. D.↗

NASA NTRS1994

The solar cycle variation of ozone in the stratosphere inferred from Nimbus 7 and NOAA 11 satellites

The combined Nimbus 7 solar backscattered ultraviolet (SBUV) and NOAA 11 SBUV/2 ozone data, covering a period of more than a solar cycle (about 15 years), are used to study the UV response of ozone in the stratosphere. The study shows that about 2% change in total column ozone and about 5-7% change in ozone mixing ratio in the upper stratosphere (0.7 to 2 hPa) may be attributed to the change in the solar UV flux over a solar cycle. In the upper stratosphere, where photochemical processes are expected to play a major role, the measured solar cycle variation of ozone is significantly larger than inferred either from the photochemical models or from the ozone response to the 27-day solar UV modulation. For example, the observed solar cycle related change in ozone mixing ratio at 2 hPa is about 1% for 1% change in the solar UV flux near 200 nm. The inferred change in ozone from either the photochemical models or from the 27-day ozone-UV response is about a factor of 2-3 lower than this value.

Chandra, S.↗

NASA NTRS1994

Profile shape dependence in backscattered ultraviolet satellite retrievals of total ozone

Total ozone operational algorithms use climatological mean ozone profiles. When the actual ozone profiles have significantly different shapes versus the climatology and the solar zenith angles are large, retrieved total ozone will have an error. Recalibrated SBUV profiles are used to estimate this error. Preliminary results suggest that, on the average, the change and variation in significant profiles shapes can to a large degree be estimated by the SBUV derived profiles. Preliminary results suggest the average error in the report algorithm ozone trend (trend in reported ozone) from profile shape is relatively small during the north hemisphere winter (less than 2 percent) for solar zenith angles less than 82 degrees (for 60 degrees North Latitude).

Taylor, S. L.↗

NASA NTRS1994

External comparisons of reprocessed SBUV/TOMS ozone data

Ozone Retrievals from the Solar Backscatter Ultraviolet (SBUV) Instrument on-board the Nimbus-7 Satellite have been reprocessed using an improved internal calibration. The resulting data set covering November, 1978 through January, 1987 has been archived at the National Space Science Data Center in Greenbelt, Maryland. The reprocessed SBUV total ozone data as well as recalibrated Total Ozone Mapping Spectrometer (TOMS) data are compared with total ozone measurements from a network of ground based Dobson spectrophotometers. The SBUV also measures the vertical distribution of ozone, and these measurements are compared with external measurements made by SAGE II, Umkehr, and Ozonesondes. Special attention is paid to long-term changes in ozone bias.

Wellemeyer, C. G.↗

NASA NTRS1994

Effect of partially-clouded scenes on the determination of ozone

Differences in wavelength pair ozone values determined from Backscattered Ultraviolet (BUV) instrument measurements are directly correlated with scene reflectivity which, in turn, is a function of scene cloudiness. At low solar zenith angles (overhead sun), maximum discrepancies between pair values of 2 to 3 percent. These discrepancies are believed to be due to algorithmic behavior and imply a mean error in the final derived ozone of approximately 5 percent for cases of 50 percent reflectivity. Results using a new algorithm show a significant decrease in pair discrepancy and, therefore, in the error of the final derived ozone.

Seftor, C. J.↗

NASA NTRS1994

Procedures to validate/correct calibration error in solar backscattered ultraviolet instruments

The Nimbus 7 SBUV measures the same latitude ozone at widely different sun angle conditions at the ascent and descent part of the orbit during the summer solstice. This situation is used in a particular procedure (Ascent/Descent) to obtain the relative channel-to-channel calibration error for channels 273 nm to 306 nm. These estimated errors are combined with results from the Pair Justification procedure to correct the sun-view diffuser drift in calibration from November 1978 to February 1987 for the shorter wavelength channels that measure upper stratospheric ozone. Some preliminary re-calirated Nimbus 7 SBUV data in 1989 is compared with the first set of SBUV measurements flown on the Space Shuttle.

Taylor, Steven L.↗

NASA NTRS1994

Performance evaluation of the solar backscatter ultraviolet radiometer, model 2 (SBUV/2) inflight calibration system

The Solar Backscatter Ultraviolet Radiometer, Model 2 (SBUV/2) instruments, as part of their regular operation, deploy ground aluminum reflective diffusers to deflect solar irradiance into the instrument's field-of-view. Previous SBUV instrument diffusers have shown a tendency to degrade in their reflective efficiencies. This degradation will add a trend to the ozone measurements if left uncorrected. An extensive in-flight calibration system was designed into the SBUV/2 instruments to effectively measure the degradation of the solar diffuser (Ball Aerospace Systems Division 1981). Soon after launch, the NOAA-9 SBUV/2 calibration system was unable to track the diffuser's reflectivity changes due, in part, to design flows (Frederick et al. 1986). Subsequently, the NOAA-11 SBUV/2 calibration system was redesigned and an analysis of the first 2 years of data (Weiss et al. 1991) indicated the NOAA-11 SBUV/2 onboard calibration system's performance to be exceeding preflight expectations. This paper will describe the analysis of the first three years NOAA-11 SBUV/2 calibration system data.

Weiss, H.↗

NASA NTRS1994

Northern hemisphere total ozone values from 1989-1993 determined with the NOAA-11 Solar Backscatter Ultraviolet (SBUV/2) instrument

Determinations of global total ozone amounts have been made from recently reprocessed measurements with the SBUV/2 on the NOAA-11 environmental satellite since January 1989. This data set employs a new algorithm and an updated calibration. Comparisons with total ozone amounts derived from a significant subset of the global network of Dobson spectrophotometers shows a 0.3% bias between the satellite and ground measurements for the period January 1989-May 1993. Comparisons with the data from individual stations exhibit differing degrees of agreement which could be due to the matchup procedures and also to the uncertainties in the Dobson data. The SBUV/2 data set discussed here traces the Northern Hemisphere total ozone from 1989 to the present, showing a marked decrease from the average of those years starting in the summer of 1992 and continuing into 1993, with an apparent returning to more normal levels in late 1993.

Planet, W. G.↗

NASA NTRS1993

Effect of marine stratocumulus in TOMS ozone

The algorithm used to correct total O3 from the total ozone mapping spectrometer (TOMS) for cloud effects is based on the measured reflectivity, a climatological cloud top height, and an assumed tropospheric O3 column amount below clouds. In regions of persistent subtropical marine stratocumulus it is assumed that this introduces a positive error into total O3 because these clouds are lower than the assumed mean cloud height used in the algorithm. This appears to be confirmed by high correlation between Nimbus 7 TOMS total O3 and reflectivity data for typical regimes of persistent stratus, as identified by the international satellite cloud climatology project (ISCCP) observations. The TOMS total O3 overestimate has been computed using Nimbus 7/solar backscattered ultraviolet total O3 derived using temperature humidity infrared radiometer (THIR) data for years 1979-1984. A functional relationship between the THIR/non-THIR total O3 difference and reflectivity is used with TOMS reflectivity to modify Nimbus 7 TOMS O3 data for selected regions and periods. The correction diminishes or eliminates a number of apparent O3 maxima, with reductions of up to 20 Dobson units (DU) in total O3 on daily maps and approximately 5 DU on monthly mean O3 maps. Significant correlation between corrected TOMS O3 and reflectivity data remains because low-altitude O3 is retrieved more efficiently over a high-albedo surface. It is also possible that dynamical influences leading to stratocumulus formation bring O3-enriched air into the area. These results imply that although good arguments can be made for the use of TOMS total O3 as a proxy for tropospheric O3 in the tropics, caution must be exercised in the use of daily and even monthly O3 maps in the vicinity of clouds. Further research into the TOMS algorithm in cloudy regions is required to derive reliable estimates of tropospheric O3.

Thompson, A. M.↗

NASA NTRS1990

Ozone measurements from the NOAA-9 and the Nimbus-7 satellites - Implications of short and long term variabilities

An overview of the measurements of total ozone and ozone profiles by the SBUV/2 instrument on the NOAA-9 spacecraft relative to similar measurements from the solar backscatter ultraviolet (SBUV) and TOMS instruments on Nimbus-7 is presented. During the three-year period from March 14, 1985 to February 28, 1988, when these data sets overlap, it is shown that there have been significant changes in the calibrations of the three instruments that may be attributed to diffuser plate degradation (for SBUV/TOMS) and to the drift of the NOAA-9 orbit to later equator crossing times (for SBUV/2). Though these instrument characteristic changes have effected the absolute values of the trends derived from the three instruments, their geophysical characteristics and response to short-term variations are accurate and correlate well among the three instruments. It is seen that the total column ozone measured by the three instruments shows good agreement with respect to its day-to-day, seasonal, and latitudinal variabilities.

Chandra, S.↗

NASA NTRS1990

Nimbus 7 solar backscatter ultraviolet (SBUV) ozone products user's guide

Three ozone tape products from the Solar Backscatter Ultraviolet (SBUV) experiment aboard Nimbus 7 were archived at the National Space Science Data Center. The experiment measures the fraction of incoming radiation backscattered by the Earth's atmosphere at 12 wavelengths. In-flight measurements were used to monitor changes in the instrument sensitivity. Total column ozone is derived by comparing the measurements with calculations of what would be measured for different total ozone amounts. The altitude distribution is retrieved using an optimum statistical technique for the inversion. The estimated initial error in the absolute scale for total ozone is 2 percent, with a 3 percent drift over 8 years. The profile error depends on latitude and height, smallest at 3 to 10 mbar; the drift increases with increasing altitude. Three tape products are described. The High Density SBUV (HDSBUV) tape contains the final derived products - the total ozone and the vertical ozone profile - as well as much detailed diagnostic information generated during the retrieval process. The Compressed Ozone (CPOZ) tape contains only that subset of HDSBUV information, including total ozone and ozone profiles, considered most useful for scientific studies. The Zonal Means Tape (ZMT) contains daily, weekly, monthly and quarterly averages of the derived quantities over 10 deg latitude zones.

Fleig, Albert J.↗

NASA NTRS1989

Climatology of nitric oxide in the upper stratosphere, mesosphere, and thermosphere - 1979 through 1986

The contents of NO in the upper stratosphere, mesosphere, and thermosphere were determined as a function of time and latitude, using spectral scan data for 1979 through 1986 from the solar backscattered UV instrument on Nimbus 7. In that period, the integrated column amount of NO near the equator decreased from 6.4 x 10 to the 14th molecules/sq cm to 3.3 x 10 to the 14th molecules/sq cm. The time dependence of the decrease in NO correlated with solar activity, following the decline in solar activity from a solar maximum in 1979 to solar minimum in 1985-86. At middle and high latitudes, on the other hand, the NO concentration was found to be maximal in 1982-1983, a few years after the solar cycle maximum, and declined thereafter.

Mcpeters, R. D.↗

NASA NTRS1988

The three-dimensional morphology of the Antarctic ozone minimum

The three-dimensional morphology of the Antarctic ozone minimum was obtained by mapping ozone distribution data from Nimbus-7 solar backscatter UV instrument, obtained at different pressure levels, on a south polar projection. These maps show that a clearly defined ozone minimum relative to the local ozone field extends throughout the stratosphere from about 10 km to above 50 km, though the intensity of the ozone decrease becomes less with altitude. The examination of the behavior of the general ozone-hole area suggests the existence of at least three distinct regions: (1) the region below 33 km, where ozone follows the pattern of the ozone hole, exhibiting a strong trend since 1979 and decreasing from late August to a minimum in October; (2) the 33-43 km height region of relatively stable ozone concentration; and (3) the region above 43 km, where ozone is again fluctuating, with a decrease during September to a minimum in October.

Aikin, A. C.↗

NASA NTRS1988

The threee-dimensional morphology of the Antarctic ozone hole

The three-dimensional morphology of the spring antarctic ozone distribution as determined by the Nimbus 7 Solar Backscatter Ultraviolet (SBUV) spectrometer instrument is presented for the period 1 to 11 October in 1986. The data show that a clearly defined minimum in ozone relative to the local ozone field extends throughout the stratosphere from the tropopause to above 50 km, though decreasing in intensity with altitude. Near 18 km ozone in the ozone hole is 50 percent less than the average surrounding ozone. But even at 50 km the ozone is 20 percent less than the surrounding ozone field. The ozone minimum in the upper stratosphere is displaced about 6 degrees toward the equator so that observations at a fixed station may provide the illusion that the ozone minimum is restricted only to low altitudes. While the ozone minimum is spatially coherent throughout the stratosphere, there are differences in the behavior of ozone at different altitudes that suggest the existence of at least three distinct altitude domains. Below 30 km ozone is characterized by classic ozone hole behavior. Between 33 and 43 km ozone is more stable, actually increasing during September and October. Above 43 km ozone has always decreased during September to a minimum in October, but it has suffered a long term decrease of 7 to 12 percent since 1979 similar to that seen at low altitudes.

Aikin, Arthur C.↗

NASA NTRS1986

The intercomparison of ozone measured from the SME and Nimbus-7 satellites on short and long time scales

The spatial and temporal characteristics of ozone density measured from the SBUV (Solar Backscatter Ultraviolet) spectrometer on Nimbus-7 and the UV and the UV and the IR spectrometers on SME (Solar Mesosphere Explorer) are compared in the altitude region near 50 km where the three data sets overlap. Their temporal characteristics, when averaged over the same longitude range, are remarkably similar with respect to seasonal variations and short term fluctuations induced by transient planetary waves. The long term trends in the three data sets, however, differ significantly with each other. Over the three year period after 1982 ozone mixing ratio at 1 mb decreased by about 10 percent based on SEUV measurements but increased by 12 and 30 percent respectively based on SME-IR and SME-UV measurements. None of these estimates are consistent with the predicted decrease of about 2 percent based on solar UV flux and temperature changes during this period.

Chandra, S.↗