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Search Results: 1 - 10 of 191310 matches for " D. Fussen "
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An efficient algorithm for the large-scale smoothing of scattered data retrieved from remote sounding experiments
D. Fussen
Annales Geophysicae (ANGEO) , 2003,
Abstract: We present a new algorithm for smoothing/interpolation of two-dimensional fields applicable to noisy data observed at scattered sites. The technique is based on a special statistics allowing one to simultaneously minimize the fit residual and the correlation between residuals of adjacent points. The principle of the method is first explained in the 1-D case and then extended to the 2-D case by adjunction of a regularization operator. The method is compared with different algorithms (Loess-Renka, Biharmonic Spline and kriging) in three test cases related to remote sounding of the Earth’s atmosphere by space-borne experiments. Key words. Atmospheric composition and structure (evolution of the atmosphere; instruments and techniques; general or miscellaneous)
Evidence of transport, sedimentation and coagulation mechanisms in the relaxation of post-volcanic stratospheric aerosols
D. Fussen,F. Vanhellemont,C. Bingen
Annales Geophysicae (ANGEO) , 2003,
Abstract: Spatio-temporal distributions of stratospheric aerosols, measured by the ORA instrument from August 1992 until May 1993, are presented in the latitude range (40° S–40° N). Particle total number density, mode radius and distribution width are derived and interpreted. The respective roles of advection, sedimentation and coagulation are discussed. We also identify clear transport/sedimentation patterns and we show the enhancement of coagulation in stagnation regions. Efficient transport of aerosol particles up to 50 km is suggested. Key words. Atmospheric composition and structure (aerosols and particles; middle atmosphere-composition and chemistry; volcanic effects)
A new regularized inversion method for the retrieval of stratospheric aerosol size distributions applied to 16 years of SAGE II data (1984–2000): method, results and validation
C. Bingen,F. Vanhellemont,D. Fussen
Annales Geophysicae (ANGEO) , 2003,
Abstract: We apply a regularization method for the optical inversion of SAGE II aerosol extinction profiles and derive the particle number density N, the mode radius r and width s of an effective lognormal aerosol size distribution. The constraint applied to the inversion scheme allows us to appreciably enhance the stability of the solution. Therefore, because of the disposal of a more stable inversion scheme and of the wide extend of SAGE II data in time and space, we were able to improve the estimation of the aerosol parameter profiles with respect to previous published retrievals and, hence, our knowledge of the aerosol distribution characteristics in space and time. After presenting the inversion method and retrieved profiles concerning the particle number density profile over the time period 1984–2000, we validate our results by means of data derived from both in situ and remote spectral measurements. We also discuss the limits of the comparison between the various types of measurements due to their respective particularities. The validation gives a satisfying agreement with other data sources for N and r as long as the mode radius is not too small compared to the shortest SAGE II wavelength, whereas s appears to be less easily retrieved with a good accuracy. Key words. Atmospheric composition and structure (aerosols and particles; middle atmosphere – composition and chemistry; volcanic effects)
Retrieval of ozone profiles from GOMOS limb scattered measurements
S. Tukiainen,E. Kyr?l?,P. T. Verronen,D. Fussen
Atmospheric Measurement Techniques Discussions , 2010, DOI: 10.5194/amtd-3-4355-2010
Abstract: The GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite measures the vertical composition of the atmosphere using the stellar occultation technique. While the night-time data of GOMOS are proved to be of good quality, the daytime observations are more challenging due to poorer signal-to-noise ratio. In this paper we present an alternative technique, which uses GOMOS limb scattered radiances instead of the stellar signal, to retrieve stratospheric ozone profiles. Like for many other limb-viewing instruments, GOMOS observations contain stray light at high altitudes. We introduce a method for removing the stray light and demonstrate its feasibility by comparing the corrected radiances against those from the OSIRIS (Optical Spectrograph & Infra Red Imaging System) instrument. For the retrieval of ozone profiles, an onion peeling method is used. The first validation results suggest that the retrieval of stratospheric ozone is possible with a typical accuracy better than 10% at 22–50 km. GOMOS has measured about 350 000 daytime profiles since 2002. The new retrieval method presented here makes this large amount of data finally available for scientific use.
A global climatology of stratospheric OClO derived from GOMOS measurement
C. Tétard,D. Fussen,F. Vanhellemont,C. Bingen
Atmospheric Measurement Techniques Discussions , 2013, DOI: 10.5194/amtd-6-3511-2013
Abstract: The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European platform ENVISAT was dedicated to the study of the atmosphere of the Earth using the stellar occultation technique. The spectral range of the GOMOS spectrometer extends from the UV to the near infrared, allowing for the retrieval of species such as O3, NO2, NO3, H2O, O2, air density, aerosol extinction and OClO. Nevertheless, OClO can not be retrieved using a single GOMOS measurement because of the weak signal-to-noise ratio and the small optical thickness associated with this molecule. We present here the method used to detect this molecule by using several GOMOS measurements. It is based on a two-step approach. First, several co-located measurements are combined in a statistical way to build an averaged measurement with a higher signal-to-noise ratio. Then, a Differential Optical Absorption Spectroscopy (DOAS) method is applied to retrieve OClO slant column densities. The statistics of the sets of GOMOS measurements used to build the averaged measurement and the spectral window selection are analyzed. The obtained retrievals are compared to results from two balloon-borne instruments. It appears that the inter-comparisons of OClO are generally satisfying. Then, two nighttime climatologies of OClO slant column densities based on GOMOS averaged measurements are presented. The first depicts annual global pictures of OClO from 2003 to 2011. From this climatology, the presence of an OClO layer in the equatorial region at about 35 km is confirmed and strong concentrations of OClO in both polar regions are observed, a sign of chlorine activation. The second climatology is a monthly time series. It clearly shows the chlorine activation of the lower stratosphere during winter. Moreover the equatorial OClO layer is observed during all the years without any significant variations. Finally, the anti-correlation between OClO and NO2 is highlighted. This very promising method, applied on GOMOS measurements, allowed us to build the first nighttime climatology of OClO.
Simultaneous measurements of OClO, NO2 and O3 in the Arctic polar vortex by the GOMOS instrument
C. Tétard,D. Fussen,C. Bingen,N. Capouillez
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: We present the first nighttime measurements of OClO from a limb-viewing satellite instrument in the Arctic polar vortex. The relationship between OClO, NO2 and O3 slant column densities in the Arctic polar vortex are analyzed from the GOMOS measurements. The retrieval process is based on a differential optical absorption spectroscopy (DOAS) method applied on the weighted median GOMOS transmittances. A study about the longitudinal distributions of OClO, NO2 and O3 above 65° north in January 2008 is presented. It shows a strong halogen activation in the lower stratosphere and a strong denoxification in the entire stratosphere inside the Arctic polar vortex. Time series of temperatures and OClO, NO2 and O3 slant column densities for the winters 2002/2003 to 2007/2008 are also presented. They highlight the correlation between temperature, OClO and NO2. The GOMOS instrument appears to be a very suitable instrument for the monitoring of OClO, NO2 and O3 in the stratosphere during nighttime.
A 2003 stratospheric aerosol extinction and PSC climatology from GOMOS measurements on Envisat
F. Vanhellemont,D. Fussen,C. Bingen,E. Kyr?l?
Atmospheric Chemistry and Physics Discussions , 2005,
Abstract: Stratospheric aerosols play an important role in a number of atmospheric issues such as midlatitude ozone depletion, atmospheric dynamics and the Earth radiative budget. Polar stratospheric clouds on the other hand are a crucial factor in the yearly Arctic 5 and Antarctic ozone depletion. It is therefore important to quantify the stratospheric aerosol/PSC abundance. In orbit since March 2002, the GOMOS instrument onboard the European Envisat satellite has provided a vast aerosol extinction data set. In this paper we present an aerosol/PSC climatology that was constructed from this data set, together with a discussion of the results.
Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT
J. L. Bertaux,E. Kyr?l?,D. Fussen,A. Hauchecorne
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-9917-2010
Abstract: GOMOS on ENVISAT (launched in February, 2002) is the first space instrument dedicated to the study of the atmosphere of the Earth by the technique of stellar occultations (Global Ozone Monitoring by Occultation of Stars). From a polar orbit, it allows to have a good latitude coverage. Because it is self-calibrated, it is particularly well adapted to the long time trend monitoring of stratospheric species. With 4 spectrometers the wavelength coverage of 248 nm to 942 nm allows to monitor ozone, H2O, NO2, NO3, air, aerosols, and O2. Two additional fast photometers (1 kHz sampling rate) allow for the correction of scintillations, as well as the study of the structure of air density irregularities, resulting from gravity waves and turbulence. A high vertical resolution profile of the temperature may also be obtained from the time delay between the red and the blue photometer. Noctilucent clouds (Polar Mesospheric Clouds, PMC), are routinely observed in both polar summers, and global observations of OCLO and sodium are achieved. The instrument configuration, dictated by the scientific objectives rationale and technical constraints, are described, together with the typical operations along one orbit, and statistics over 5 years of operation. Typical atmospheric transmission spectra are presented, and some retrieval difficulties are discussed, in particular for O2 and H2O. An overview of a number of scientific results is presented, already published or found in more details as companion papers in the same ACP GOMOS special issue. This paper is particularly intended to provide the incentive for GOMOS data exploitation, available to the whole scientific community in the ESA data archive, and to help the GOMOS data users to better understand the instrument, its capabilities and the quality of its measurements, for an optimized scientific return.
Optical extinction by upper tropospheric/stratospheric aerosols and clouds: GOMOS observations for the period 2002–2008
F. Vanhellemont,D. Fussen,N. Mateshvili,C. Tétard
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-11109-2010
Abstract: Although the retrieval of aerosol extinction coefficients from satellite remote measurements is notoriously difficult (in comparison with gaseous species) due to the lack of typical spectral signatures, important information can be obtained. In this paper we present an overview of the current operational nighttime UV/Vis aerosol extinction profile results for the GOMOS star occultation instrument, spanning the period from August 2002 to May 2008. Some problems still remain, such as the ones associated with incomplete scintillation correction and the aerosol spectral law implementation, but good quality extinction values can be expected at a wavelength of 500 nm. Typical phenomena associated with atmospheric particulate matter in the Upper Troposphere/Lower Stratosphere (UTLS) are easily identified: Polar Stratospheric Clouds, tropical subvisual cirrus clouds, background stratospheric aerosols, and post-eruption volcanic aerosols (with their subsequent dispersion around the globe). In this overview paper we will give a summary of the current results.
A global climatology of the mesospheric sodium layer from GOMOS data during the 2002–2008 period
D. Fussen,F. Vanhellemont,C. Tétard,N. Mateshvili
Atmospheric Chemistry and Physics Discussions , 2010,
Abstract: This paper presents a climatology of the mesospheric sodium layer built from the processing of 7 years of GOMOS data. With respect to preliminary results already published for the year 2003, a more careful analysis was applied to the averaging of occultations inside the climatological bins (10° in latitude-1 month). Also, the slant path absorption lines of the Na doublet around 589 nm shows evidence of partial saturation that was responsible for an underestimation of the Na concentration in our previous results. The sodium climatology has been validated with respect to the Fort Collins lidar measurements and, to a lesser extent, to the OSIRIS 2003–2004 data. Despite the important natural sodium variability, we have shown that the Na vertical column has a marked semi-annual oscillation at low latitudes that merges into an annual oscillation in the polar regions, a spatial distribution pattern that was unreported so far. The sodium layer seems to be clearly influenced by the mesospheric global circulation and the altitude of the layer shows clear signs of subsidence during polar winter. The climatology has been parameterized by time-latitude robust fits to allow for easy use. Taking into account the non-linearity of the transmittance due to partial saturation, an experimental approach is proposed to derive mesospheric temperatures from limb remote sounding measurements.
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