Loughman

Information about Loughman

Published on February 20, 2008

Author: Panfilo

Source: authorstream.com

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The SOLSE/LORE-2 Experiment: Ozone profiles retrieved from limb scattering measurements:  The SOLSE/LORE-2 Experiment: Ozone profiles retrieved from limb scattering measurements 3rd International Atmospheric Limb Workshop Montréal, Canada, April 25, 2006 R. Loughman1, R. McPeters3, D. Flittner2, E. Hilsenrath3, S. Janz3, T. Brown3, D. Rault2, M. Hill1, S. Petelina4, and C. von Savigny5 1 Center for Atmospheric Science, Hampton University, Hampton, VA 2 Radiation and Aerosol Branch, NASA Langley Research Center, Hampton, VA 3 Atmospheric Chemistry and Dynamics Branch, NASA Goddard Space Flight Center, Greenbelt, MD 4 Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, SK, Canada 5 Institute of Environmental Physics and Remote Sensing, University of Bremen, Bremen, Germany Outline:  Outline Relationship to OMPS limb profiler instrument Description of SOLSE/LORE instruments and data Discussion of key challenges Pointing Stray light Algorithm description Comparison of ozone retrievals to correlative data Conclusions Slide3:  Future Applications of Limb Scattering for Ozone Retrieval The Ozone Mapper Profiler Suite (OMPS) includes a limb scattering instrument to provide stratospheric ozone profile information. The tri-agency Integrated Program Office (NASA, NOAA, Dept. of Defense) has committed to limb scattering to provide ozone profile retrievals, beginning in 2009. The main purpose of the SOLSE/LORE-2 and SAGE III limb scattering research efforts is to test our current knowledge of instrument design and retrieval algorithms for this relatively unproven technique. SOLSE’s Role as an OMPS Limb Profiler Predecessor:  SOLSE was the model for the instrument design of the OMPS limb profiler (LP) instrument, and they share many key design features (e.g., measuring a simultaneous image of all wavelengths and tangent heights). SOLSE and LORE were re-flown primarily as a risk-reduction measure for OMPS. But the SOLSE design differs from the OMPS LP design in two key areas: Indirect derivation of pointing information (using LORE data) Introduction of neutral density filters to reduce stray light SOLSE’s Role as an OMPS Limb Profiler Predecessor SOLSE/LORE instrument characteristics:  SOLSE/LORE instrument characteristics Imaging spectrometer, 533-863 nm, at 0.8 to 1.2 nm resolution A small subset of spectral data (9 groups of 12 pixels, each covering 3-4 nm) was downlinked during the mission Filter wheel instrument, with observations made at 322, 350, 603, 675 and 1000 nm (slit width 3-4 nm) SOLSE-2 and LORE-2 flew on the Space Shuttle (STS-107) in January 2003. The instruments were redesigned (relative to the instruments that flew on STS-87 in 1997) to focus on O3 retrievals in the lower stratosphere. LORE-2: SOLSE-2: Altitude resolution is 1 km at the tangent point for both instruments. Triplet ozone retrieval (Flittner et al., 2000) is currently implemented. Available data sets:  1/9 of the SOLSE-2 images and 3/4 of the LORE-2 images were downlinked during the flight. The remaining images were stored only on the instrument hard drives and were therefore lost in the shuttle tragedy. The surviving data set includes 536 LORE and 168 SOLSE images, taken between Jan. 19 and Jan. 27, 2003. Surviving SOLSE super-pixels are centered at 555, 585, 603, 612, 643, 675, 688, 719, 755, 761, 780, and 823 nm Available data sets Tangent Height Registration:  Tangent Height Registration Done by the “RSAS” method (Janz et al., 1997), which uses the shape of the LORE 350 nm radiance profile. But the LORE 350 nm filter measurement and the SOLSE measurement often are not simultaneous (and are frequently separated by > 30 s). Shuttle attitude information (PATH data) can be used to interpolate the pointing between LORE 350 nm filter measurements, but: This interpolation introduces a significant (but difficult-to-quantify) error in the SOLSE tangent height registration (see next page). The relative alignment of the SOLSE and LORE instruments apparently changed during the flight. Transferring tangent height registration from LORE to SOLSE by assuming that the instrument boresight alignment remains unchanged would introduce additional error. A correction has been applied, but the accuracy of the correction is uncertain. Slide8:  Uncertainty in SOLSE Pointing Disagreement between PATH-interpolated and time-interpolated altitude registration is often > 1 km, and differences can be as large as 30 km. Slide9:  Green line = SOLSE data, Black line = LORE data, at 675 nm These two frames are well-synchronized at 675 nm (to 1 s and 2 s, respectively). Instrument misalignment for observations through the Jan. 21 frames is nearly negligible (-0.15 ± 0.53 km); after Jan. 21 frames, a noticeable misalignment appears (2.26 km ± 0.22 km). A “thermal event” that followed the Jan. 21 measurements may be the culprit. Slide10:  SOLSE Neutral Density Filters The influence of the ND filter boundaries extends over several spatial pixels. Analysis of flight data also suggests significant stray light whose spatial and spectral characteristics are not captured in the laboratory instrument characterization. Without the entire SOLSE spectrum, deconvolution is not practical. Slide11:  SOLSE Ozone Retrieval Validation Procedure Use only the middle range of the ND filter. Concentrate on cases for which middle ND filter includes 15-35 km tangent heights (62 usable frames of data remain). From that subset, focus on cases for which the SOLSE and LORE 350 nm measurements are synchronized to within 1 s (27 usable frames remain). Retrieval uses GSLS model (Loughman et al., 2004). Use SAGE II weekly zonal mean aerosol profiles, and climatological T, p, and ozone data as a priori information. Compare retrieved ozone profile to independent data sources. Slide12:  Description of coincident data OSIRIS (V1.2, pointing adjusted by +0.4 km, as suggested by Petelina) SAGE II (V6.2) SAGE III LS SCIAMACHY (V1.63) SONDE (obtained from the WOUDC archive) The following plots show all cases for which t < 12 hrs,  < 5,  < 20, and  < 20 DU. Of the 27 remaining SOLSE frames, 8 have correlative data, but 3 were excluded because the SOLSE-2 algorithm did not converge satisfactorily (sometimes a large apparent pointing error appears to exist). Slide13:  SOLSE Frame 41 (Jan. 20, Japan) Comparison to: Naha O3 sonde Slide14:  SOLSE Frame 84 (Jan. 21, Alabama) Comparison to: Huntsville O3 sondes Slide15:  SOLSE Frame 125 (Jan. 24, Cameroon) Comparison to: OSIRIS and SCIAMACHY O3 profiles Slide16:  SOLSE Frame 128 (Jan. 27, Sudan) Comparison to: OSIRIS and SCIAMACHY O3 profiles Slide17:  SOLSE Frame 130 (Jan. 27, Dubai) Comparison to: OSIRIS, SAGE III LS, and SCIAMACHY O3 profiles Illustration of the SOLSE Frame 130 coincidence (Jan. 27, 2003) :  Illustration of the SOLSE Frame 130 coincidence (Jan. 27, 2003) The SAGE III and SOLSE/ LORE-2 lines of sight are aligned to within 7 in azimuth, the tangent points coincide to better than 2 in both latitude and longitude, and the observation times are separated by < 20 min. However, The SAGE III 1017 nm channel observation shows a sharp feature (cirrus cloud?) at 12 km, while the SOLSE/LORE-2 data shows a similar feature at 5 km. Despite their close proximity in space and time, this suggests that the scenes are not identical. Conclusions:  Conclusions Comparison of the SOLSE-2 ozone retrievals with correlative data shows generally good results (agreement to within 25% with SAGE II, OSIRIS, SAGE III LS, and SCIAMACHY, and ozonesonde data, allowing for apparent tangent height registration differences). Stray light characterization and tangent height registration of the SOLSE radiance profiles remain major challenges. Acknowledgements: This work was made possible by the tireless efforts of the SOLSE/LORE-2 instrument team, and by the consistent support and advocacy provided by the IPO. We thank the SAGE II, SAGE III, OSIRIS and SCIAMACHY teams for producing high-quality data and making it available for comparison. We also greatly appreciate the groups that provided ozonesonde data, and acknowledge the WOUDC for archiving it. Finally, we recognize the supreme sacrifice made by the crew of STS-107, and appreciate the opportunity to contribute to their legacy through analysis of the SOLSE/LORE-2 data. Slide20:  BACKUP SLIDES Slide24:  SOLSE Validation

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