Search NASA⌕ Search

Engineering topics

Simon, P. C.

Publications and source records attributed to Simon, P. C..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Combined Characterisation of GOME and TOMS Total Ozone Using Ground-Based Observations from the NDSC

Several years of total ozone measured from space by the ERS-2 GOME, the Earth Probe Total Ozone Mapping Spectrometer (TOMS), and the ADEOS TOMS, are compared with high-quality ground-based observations associated with the Network for the Detection of Stratospheric Change (NDSC), over an extended latitude range and a variety of geophysical conditions. The comparisons with each spaceborne sensor are combined altogether for investigating their respective solar zenith angle (SZA) dependence, dispersion, and difference of sensitivity. The space- and ground-based data are found to agree within a few percent on average. However, the analysis highlights for both Global Ozone Monitoring Experiment (GOME) and TOMS several sources of discrepancies, including a dependence on the SZA at high latitudes and internal inconsistencies.

Lambert, J.-C.↗
NASA NTRS1996

Observations of the Solar Irradiance in the 200-350 nm Interval During the ATLAS-1 Mission: A Comparison Among Three Sets of Measurements-SSBUV, SOLSPEC and SUSIM

The SOLSPEC, SSBUV, and SUSIM spectrometers simultaneously observed the solar spectral irradiance during the ATLAS-1 mission flown on board the Space Shuttle Atlantis in March 1992. The three instruments use different methods and means of absolute calibration and were each calibrated preflight and postflight. The three data sets are reported from 200 to 350 nm at 1.1 nm resolution. The method of comparing the three independent data sets is discussed. The importance of a common, precise wavelength scale is shown when comparing the data in wavelength regions of strong Fraunhofer lines. The agreement among the solar irradiance measurements is better than plus or minus 5%. The fact that the calibrations of the three instruments were based on three independent standards provides confidence that the absolute solar spectral irradiance in the range 200-350 nm is now known with an accuracy better than plus or minus 5%. The mean ATLAS-I solar spectrum is compared with simultaneous solar observations from the UARS SOLSTICE and UARS SUSIM instruments. The two mean solar spectra agree to within plus or minus 3%.

Cebula, R. P.↗
NASA NTRS1994

Long path monitoring of tropospheric O3, NO2, H2CO and SO2

Concentrations of tropospheric O3, NO2, H2CO, and SO2 have been measured on the Campus of the 'Universite Libre de Bruxelles' on a routine basis since October 1990. The long path system consists of a source lamp, a first 30 cm f/8 Cassegrain type telescope which collimates the light onto a slightly parabolic mirror placed on the roof of a building situated 394 m away from the laboratory. The light is sent back into a second 30 cm Cassegrain telescope. This telescope has been modified so that the output beam is a 5 cm diameter parallel beam. This beam is then focused onto the entrance aperture of the BRUKER IFS120HR fourier transform spectrometer. The two telescopes are mounted on alignment devices and the external mirror is equipped with a driving system operated from the laboratory. The choice of the light source (either a 1000 W high pressure 'ozone free' xenon lamp or a 250 W tungsten filament) and of the detector (either a solar blind UV-diode or a silicon diode) depended on the spectral region studied. These regions lie respectively from 26,000 cm(exp -1) to 30,000 cm(exp -1) (260-380 nm) and from 14,000 cm(exp -1) to 30,000 cm(exp -1) (330-700 nm). The spectra have been recorded at the resolution of 16 cm(exp -1) and with a dispersion of 7.7 cm(exp -1). They have been measured during the forward and the backward movements of the mobile mirror, in double sided mode; each spectrum is an average of 2000 scans. The time required to record a spectrum is about 45 minutes. The shape of the raw spectra in the two investigated regions are represented.

Vandaele, A. C.↗
NASA NTRS1994

Temperature dependence of ultraviolet absorption cross-sections of alternative hydrochlorofluorocarbons

Ultraviolet absorption cross-section of six alternative hydrochlorofluorocarbons (HCFC-21 HCFC-22, HCFC-123, HCFC-124, HCFC-141b and HCFC-142b1) have been measured between 170 and 260 nm for temperature ranging from 210 to 295 K. These data are compared with other available determinations performed at room temperature and their temperature dependence is discussed. Photodissociation coefficients are estimated and their temperature dependence is discussed. Impact of the photodissociation on the total atmospheric destruction of these compounds is illustrated.

Gillotay, D.↗
NASA NTRS1994

Ultraviolet absorption cross-sections of some carbonyl compounds and their temperature dependence

Ultraviolet absorption cross-section of phosgene (CCl2O), trichloroacetylchloride (CCl3-CClO) and trichloroacetaldehyde (CCl3-CHO) have been measured between 170 and 320 nm for temperature ranging from 210 to 295 K with classical double beam equipment. These data are compared with other available determinations performed at room temperature. Photodissociation coefficients are estimated and their temperature dependence is discussed. Impact of the photodissociation on the total atmospheric destruction of these compounds is illustrated.

Gillotay, D.↗
NASA NTRS1989

Spacecraft instrument calibration and stability

The following topics are covered: instrument degradation; the Solar Backscatter Ultraviolet (SBUV) Experiment; the Total Ozone Mapping Spectrometer (TOMS); the Stratospheric Aerosol and Gas Experiment 1 (SAGE-1) and SAGE-2 instruments; the Solar Mesosphere Explorer (SME) UV ozone and near infrared airglow instruments; and the Limb Infrared Monitor of the Stratosphere (LIMS).

Gille, J. C.↗
NASA NTRS1988

Solar Spectrum (SOLSPEC) measurement from 180 to 3000 nanometers

The SOLSPEC experiment, planned for the Atmospheric Laboratory for Applications and Science (ATLAS 1) NASA mission, is described. The purpose of this experiment is the measurement of the absolute solar irradiances in the wavelength range from 180 to 3000 nm and the variabilities of the solar irradiances in this wavelength range. Measurements of the irradiances and variabilities are used in: (1) solar-terrestrial/planetary relationships, in particular aeronomy of the stratosphere and mesosphere; (2) climatoglogy; and (3) solar physics.

Thuiller, G.↗
NASA NTRS1983

Ozone profile intercomparison based on simultaneous observations between 20 and 40 km

The vertical distribution of stratospheric ozone has been simultaneously measured by means of five different instruments carried on the same balloon payload. The launches were performed from Gap during the intercomparison campaign conducted in June 1981 in southern France. Data obtained between altitudes of 20 and 40 km are compared and discussed. Vertical profiles deduced from Electrochemical Concentration Cell sondes launched from the same location by small balloons and from short Umkehr measurements made at Mt Chiran (France) are also included in this comparison. Systematic differences of the order of 20 percent between ozone profiles deduced from solar u.v. absorption and in situ techniques are found.

Aimedieu, P.↗
NASA NTRS1983

Report on the Workshop on Intercomparison of Solar UV Irradiance Measurements and Related Instrument Calibration

The knowledge of the absolute value of the solar ultraviolet irradiance did not improve very much during the rising phase of the solar cycle 21. The variations associated with the solar rotation period were observed by means of three satellites, namely, the Atmospheric Explorer E (AE-E), Nimbus 7 and the Solar Mesospheric Explorer (SME). Long-term variations related to the solar activity cycle are not well known. Values were deduced during the solar cycle 21 from the AE-E satellite and the rocket program performed by the Laboratory for Atmospheric and Space Physics leading to variations of about a factor of 2 around 150 nm but definitely less than 20 percent beyond 175 nm. Such low level of variation is still masked by the current uncertainties and reproducibility of the observations performed since 1976. The uncertainties of recent observations are reported with their discrepancies. The gaps between the current accuracy goals and the achievements are still very important. The challenge for the next three years is to improve both the accuracy and the precision of future observations at the level of the available irradiance standards and to measure quantitatively long-term variations of the order of a few percent. The main causes of these gaps are identified.

Simon, P. C.↗
NASA NTRS1983

MSG-7: Molecular absorption processes related to the penetration of ultraviolet solar radiation into the middle atmosphere

The information presently available on the absorption cross sections of O2 and O3 with attention to the application of these data in middle atmospheric science is reviewed. The cross sections values reported by different groups are intercompared in tabular form where feasible, and specific values are recommended when there is a basis for preferring a particular set of results over other available data. When no such basis exists, the differences among published cross sections then serve to indicate a range of uncertainty. In these cases the need for additional work is indicated. Specific topics addressed are the absorption of molecular oxygen at Lyman alpha, in the Schumann-Runge continuum, in the Schumann-Runge bands, and in the Herzberg continuum. For ozone, the Hartley and Huggins bands are considered.

Frederick, J. E.↗
NASA NTRS1981

An instrument to measure the solar spectrum from 170 to 3200 nm on board Spacelab

This instrument, at the present time in development, will fly on board Spacelab I in May 1983. Other flights are foreseen during the following missions. The instrument is composed of three double monochromators covering the range 170 to 3200 nm. The spectrometers have bandpasses of 1 nm up to 900 nm and 20 nm from 850 to 3200 nm with an accuracy 1/100 nm. Calibration lamps are included in the instrument to monitor any change of its sensitivity and wavelength scale.

Thuiller, G.↗