Intercomparison of Global Total Ozone Measurements Retrieved from ENVISAT/SCIAMACHY Using Different State-of-the-art Algorithms
Christophe Lerot(1), Michel Van Roozendael(1), Jos Van Geffen(1), Caroline Fayt(1), Robert Spurr(2), Henk Eskes(3), Ronald Van der A(3), Astrid Bracher(4), Lok Nath Lamsal(4), Mark Weber(4), Thomas Schroeder(5), Klaus Kretschel(6) and Albrecht Von Bargen(6)
(1) Belgian Institute for Space Aeronomy (BIRA-IASB), 3 Avenue circulaire, B-1180 Brussels, Belgium
(2) RT Solutions, Inc., 9 Channing Street, MA 02138 Cambridge, United States
(3) Royal Netherlands Meteorological Institute (KNMI), 10 Wilhelminalaan, NL-3732 GK De Bilt, Netherlands
(4) Institute of Environmental Physics (IFE), PO Box 330440, D-28334 Bremen, Germany
(5) Remote Sensing Technology Institute (IMF-DLR), PO Box 1116, D-82230 Wessling, Germany
(6) Remote Sensing Technology Institute (IMF-DLR), P.O. Box 1116, D-82230 Wessling, Germany
The SCaning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) is an imaging spectrometer launched in March 2002 on the ESA ENVISAT platform. Its primary objective is to achieve global measurements of a number of important atmospheric trace gases, among which ozone. Combined with measurements from ESA’s Global Ozone Monitoring Experiment (GOME), which was launched in 1995 but lost is capability for global coverage in June 2003, SCIAMACHY provides an opportunity to accurately monitor the state of the ozone layer over a period of more than a decade. However, this requires that the accuracy of the SCIAMACHY total ozone retrieval matches the one recently achieved for GOME as a result of algorithmic developments carried out at BIRA-IASB, KNMI and IFE-Bremen during 2003 under ESA/ESRIN funding.
In this work, we compare the results from three established state-of-the-art total ozone algorithms developed for GOME and applied to nadir backscattered light observations from SCIAMACHY, namely: SDOAS, the SCIAMACHY version of the GDOAS algorithm developed at BIRA-IASB for GOME and currently implemented at DLR in the ESA operational system of both GOME and SCIAMACHY; TOSOMI, an adaptation of the total ozone algorithm developed at KNMI for the Aura/OMI instrument; and WF-DOAS, an advanced modified-DOAS algorithm developed at IFE-Bremen. Although in principle trivial, the transfer of algorithms designed for GOME to the SCIAMACHY instrument comprises some difficulties mainly related to spectral calibration and reference data issues. In order to reach a target accuracy of 1% on total ozone retrievals, these issues must be carefully addressed. We focus on assessing the consistency between the aforementioned algorithms including the ESA SCIAMACHY off-line operational processor (SGP L12) after optimization to both GOME and SCIAMACHY observations. The latitude, solar zenith angle, cloud fraction and temporal dependences of the retrieved ozone columns are characterized. We concentrate on conditions where largest and/or systematic discrepancies are observed (e.g. Polar Regions and high solar zenith angle conditions). The aim is to improve the understanding of these discrepancies and thereby consolidate the data products. It is expected that the study will lead to a better understanding of the limits of the physical models and help to increase the quality of future algorithms.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,