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Search Results: 1 - 10 of 582937 matches for " D. A. Degenstein "
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Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra
A. E. Bourassa, D. A. Degenstein,E. J. Llewellyn
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with two coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.
Application of tomographic algorithms to Polar Mesospheric Cloud observations by Odin/OSIRIS
K. Hultgren,J. Gumbel,D. A. Degenstein,A. E. Bourassa
Atmospheric Measurement Techniques Discussions , 2012, DOI: 10.5194/amtd-5-3693-2012
Abstract: Limb-scanning satellites can provide global information about the vertical structure of Polar Mesospheric Clouds. However, information about horizontal structures usually remains limited. This is due to both a long line of sight and a long scan duration. On eighteen days during the Northern Hemisphere summers 2010–2011 and the Southern Hemisphere summer 2011/2012, the Swedish-led Odin satellite was operated in a special mesospheric mode with short limb scans limited to the altitude range of Polar Mesospheric Clouds. For Odin's Optical Spectrograph and InfraRed Imager System (OSIRIS) this provides multiple views through a given cloud volume and, thus, a basis for tomographic analysis of the vertical/horizontal cloud structure. Here we present algorithms for tomographic analysis of mesospheric clouds based on maximum probability techniques. We also present results of simulating OSIRIS tomography and retrieved cloud structures from the special tomographic periods.
Retrieval of stratospheric aerosol size information from OSIRIS limb scattered sunlight spectra
A. E. Bourassa,D. A. Degenstein,E. J. Llewellyn
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: Recent work has shown that the retrieval of stratospheric aerosol vertical profiles is possible using limb scattered sunlight measurements at optical wavelengths. The aerosol number density profile is retrieved for an assumed particle size distribution and composition. This result can be used to derive the extinction at the measured wavelength. However, large systematic error can result from the uncertainty in the assumed size distribution when the result is used to estimate the extinction at other wavelengths. It is shown in this work that the addition of information obtained from the near infrared limb radiance profile at 1530 nm measured by the imaging module of the OSIRIS instrument yields an indication of the aerosol size distribution profile that can be used to improve the fidelity of the retrievals. A comparison of the estimated extinction profile at 1020 nm with coincident occultation measurements demonstrates agreement to within approximately 15% from 12 to 27 km altitude.
The red-sky enigma over Svalbard in December 2002
N. D. Lloyd, D. A. Degenstein, F. Sigernes, E. J. Llewellyn,D. A. Lorentzen
Annales Geophysicae (ANGEO) , 2005,
Abstract: An anomalous red glow due to scattered sunlight was observed at Longyearbyen (78° N, 15° E) on 6 December 2002 from 07:30 UT to 13:30 UT when the solar zenith angle varied between 100.7° and 104°. A model for this red sky event using sunlight scattered in a two stage process by Polar Stratospheric Clouds (PSC) at 25km is presented and demonstrated to be feasible. The model requires a significant fraction of the polar vortex, which is cold enough for the formation of ice PSC, to be occupied with PSC with an integrated vertical extinction of approximately 0.037 at 845nm. Given these conditions, the model is able to predict, within an order of magnitude, the spatial distribution of intensities measured by meridional scanning photometers located at Longyearbyen across the visible and near infra-red spectrum. Keywords. Aerosols and particles; Transmission and scattering of radiation; Polar Meteorology Full Article (PDF, 497 KB) Special Issue Citation: Lloyd, N. D., Degenstein, D. A., Sigernes, F., Llewellyn, E. J., and Lorentzen, D. A.: The red sky enigma over Svalbard in December 2002: a model using polar stratospheric clouds, Ann. Geophys., 23, 1603-1610, doi:10.5194/angeo-23-1603-2005, 2005. Bibtex EndNote Reference Manager XML
Odin-OSIRIS stratospheric aerosol data product and SAGE III intercomparison
A. E. Bourassa, L. A. Rieger, N. D. Lloyd,D. A. Degenstein
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: The scattered sunlight measurements made by the Optical Spectrograph and InfraRed Imaging System (OSIRIS) on the Odin spacecraft are used to retrieve vertical profiles of stratospheric aerosol extinction at 750 nm. The recently released OSIRIS Version 5 data product contains the first publicly released stratospheric aerosol extinction retrievals, and these are now available for the entire Odin mission, which extends from the present day back to launch in 2001. A proof-of-concept study for the retrieval of stratospheric aerosol extinction from limb scatter measurements was previously published and the Version 5 data product retrievals are based on this work, but incorporate several important improvements to the algorithm. One of the primary changes is the use of a new retrieval vector that greatly improves the sensitivity to aerosol scattering by incorporating a forward modeled calculation of the radiance from a Rayleigh atmosphere. Additional improvements include a coupled retrieval of the effective albedo, a new method for normalization of the retrieval vector to improve signal-to-noise, and the use of an initial guess that is representative of very low background aerosol loading conditions, which allows for maximal retrieval range. Furthermore, the Version 5 data set is compared to Stratospheric Aerosol and Gas Experiment (SAGE) III 755 nm extinction profiles during the almost four years of mission overlap from 2002 to late 2005. The vertical structure in coincident profile measurements is well correlated and the statistics on a relatively large set of tight coincident measurements show agreement between the measurements from the two instruments to within approximately 10% throughout the 15 to 25 km altitude range, which covers the bulk of the stratospheric aerosol layer for the mid and high latitude cases studied here.
Odin-OSIRIS stratospheric aerosol data product and SAGE III intercomparison
A. E. Bourassa,L. A. Rieger,N. D. Lloyd,D. A. Degenstein
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012, DOI: 10.5194/acp-12-605-2012
Abstract: The scattered sunlight measurements made by the Optical Spectrograph and InfraRed Imaging System (OSIRIS) on the Odin spacecraft are used to retrieve vertical profiles of stratospheric aerosol extinction at 750 nm. The recently released OSIRIS Version 5 data product contains the first publicly released stratospheric aerosol extinction retrievals, and these are now available for the entire Odin mission, which extends from the present day back to launch in 2001. A proof-of-concept study for the retrieval of stratospheric aerosol extinction from limb scatter measurements was previously published and the Version 5 data product retrievals are based on this work, but incorporate several important improvements to the algorithm. One of the primary changes is the use of a new retrieval vector that greatly improves the sensitivity to aerosol scattering by incorporating a forward modeled calculation of the radiance from a Rayleigh atmosphere. Additional improvements include a coupled retrieval of the effective albedo, a new method for normalization of the retrieval vector to improve signal-to-noise, and the use of an initial guess that is representative of very low background aerosol loading conditions, which allows for maximal retrieval range. Furthermore, the Version 5 data set is compared to Stratospheric Aerosol and Gas Experiment (SAGE) III 755 nm extinction profiles during the almost four years of mission overlap from 2002 to late 2005. The vertical structure in coincident profile measurements is well correlated and the statistics on a relatively large set of tight coincident measurements show agreement between the measurements from the two instruments to within approximately 10% throughout the 15 to 25 km altitude range, which covers the bulk of the stratospheric aerosol layer for the mid and high latitude cases studied here.
Improving Langley calibrations by reducing diurnal variations of aerosol ngstr m parameters
J. T. Wiensz, D. A. Degenstein, N. D. Lloyd,A. E. Bourassa
Atmospheric Measurement Techniques (AMT) & Discussions (AMTD) , 2013,
Abstract: We present a technique for estimating the optical thickness of subvisual cirrus clouds detected by OSIRIS (Optical Spectrograph and Infrared Imaging System), a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Cross-sections and phase functions from an in situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is shown that the retrieved extinction profile, for an assumed effective cloud particle size, models well the measured in-cloud radiances from OSIRIS. The greatest sensitivity of the retrieved optical thickness is to the effective cloud particle size. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.
Optical property retrievals of subvisual cirrus clouds from OSIRIS limb-scatter measurements
J. T. Wiensz,D. A. Degenstein,N. D. Lloyd,A. E. Bourassa
Atmospheric Measurement Techniques Discussions , 2012, DOI: 10.5194/amtd-5-5313-2012
Abstract: We present a technique for retrieving the optical properties of subvisual cirrus clouds detected by OSIRIS, a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Optical properties from an in-situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is demonstrated that the retrieved extinction profile models accurately the measured in-cloud radiances from OSIRIS. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.
Limb scatter ozone retrieval from 10 to 60 km using a Multiplicative Algebraic Reconstruction Technique
D. A. Degenstein,A. E. Bourassa,C. Z. Roth,E. J. Llewellyn
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: The OSIRIS instrument onboard the Odin spacecraft routinely measures vertical profiles of spectrally dispersed, limb scattered sunlight from the upper troposphere into the lower mesosphere. These measurements are used to retrieve the ozone number density vertical profile over the altitude range from 10 to 60 km using the SaskMART Multiplicative Algebraic Reconstruction Technique, which is a one dimensional modification of an existing two-dimensional tomographic retrieval algorithm. This technique allows for the consistent merging of the absorption information from radiance measurements at wavelengths in the Chappuis and the Hartley-Huggins bands at each iteration of the inversion. The effectiveness of the retrieval is demonstrated using a set of coincident SAGE II occultation measurements that show a mean bias of less than 2% from 18 to 53 km.
Limb scatter ozone retrieval from 10 to 60 km using a multiplicative algebraic reconstruction technique
D. A. Degenstein,A. E. Bourassa,C. Z. Roth,E. J. Llewellyn
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: The OSIRIS instrument onboard the Odin spacecraft routinely measures vertical profiles of spectrally dispersed, limb scattered sunlight from the upper troposphere into the lower mesosphere. These measurements are used to retrieve the ozone number density vertical profile using the SaskMART Multiplicative Algebraic Reconstruction Technique, which is a one dimensional modification of an existing two-dimensional tomographic retrieval algorithm. The retrieved profile extends from the cloud top to 60 km. In the absence of clouds the retrieval extends down to 10 km. This technique allows for the consistent merging of the absorption information from radiance measurements at wavelengths in the Chappuis and the Hartley-Huggins bands at each iteration of the inversion. The effectiveness of the retrieval is demonstrated using a set of coincident SAGE II occultation measurements that show a mean bias of less than 2% from 18 to 53 km.
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