Space-based near-infrared CO2 measurements: Testing the Orbiting Carbon Observatory retrieval algorithm and validation concept using SCIAMACHY observations over Park Falls, Wisconsin

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Read Full Article (file size: 815159 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D23302, doi:10.1029/2006JD007080, 2006 Space-based near-infrared CO₂ measurements: Testing the Orbiting Carbon Observatory retrieval algorithm and validation concept using SCIAMACHY observations over Park Falls, Wisconsin H. Bösch Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA G. C. Toon Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA B. Sen Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA R. A. Washenfelder Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA P. O. Wennberg Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA M. Buchwitz Institute of Environmental Physics, University of Bremen, Bremen, Germany R. de Beek Institute of Environmental Physics, University of Bremen, Bremen, Germany J. P. Burrows Institute of Environmental Physics, University of Bremen, Bremen, Germany D. Crisp Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA M. Christi Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA B. J. Connor National Institute of Water and Atmospheric Research, Lauder, New Zealand V. Natraj Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA Y. L. Yung Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA Abstract Space-based measurements of reflected sunlight in the near-infrared (NIR) region promise to yield accurate and precise observations of the global distribution of atmospheric CO₂. The Orbiting Carbon Observatory (OCO) is a future NASA mission, which will use this technique to measure the column-averaged dry air mole fraction of CO₂ (X_CO₂) with the precision and accuracy needed to quantify CO₂ sources and sinks on regional scales (∼1000 × 1000 km²) and to characterize their variability on seasonal timescales. Here, we have used the OCO retrieval algorithm to retrieve X_CO₂ and surface pressure from space-based Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) measurements and from coincident ground-based Fourier transform spectrometer (FTS) measurements of the O₂ A band at 0.76 μm and the 1.58 μm CO₂ band for Park Falls, Wisconsin. Even after accounting for a systematic error in our representation of the O₂ absorption cross sections, we still obtained a positive bias between SCIAMACHY and FTS X_CO₂ retrievals of ∼3.5%. Additionally, the retrieved surface pressures from SCIAMACHY systematically underestimate measurements of a calibrated pressure sensor at the FTS site. These findings lead us to speculate about inadequacies in the forward model of our retrieval algorithm. By assuming a 1% intensity offset in the O₂ A band region for the SCIAMACHY X_CO₂ retrieval, we significantly improved the spectral fit and achieved better consistency between SCIAMACHY and FTS X_CO₂ retrievals. We compared the seasonal cycle of X_CO₂ at Park Falls from SCIAMACHY and FTS retrievals with calculations of the Model of Atmospheric Transport and Chemistry/Carnegie-Ames-Stanford Approach (MATCH/CASA) and found a good qualitative agreement but with MATCH/CASA underestimating the measured seasonal amplitude. Furthermore, since SCIAMACHY observations are similar in viewing geometry and spectral range to those of OCO, this study represents an important test of the OCO retrieval algorithm and validation concept using NIR spectra measured from space. Finally, we argue that significant improvements in precision and accuracy could be obtained from a dedicated CO₂ instrument such as OCO, which has much higher spectral and spatial resolutions than SCIAMACHY. These measurements would then provide critical data for improving our understanding of the carbon cycle and carbon sources and sinks. Received 17 January 2006; accepted 30 June 2006; published 6 December 2006. Keywords: satellite remote sensing; carbon dioxide column; near-infrared measurements. Index Terms: 0394 Atmospheric Composition and Structure: Instruments and techniques; 0480 Biogeosciences: Remote sensing; 1610 Global Change: Atmosphere (0315, 0325). Read Full Article (file size: 815159 bytes) Cited by Citation: Bösch, H., et al. (2006), Space-based near-infrared CO₂ measurements: Testing the Orbiting Carbon Observatory retrieval algorithm and validation concept using SCIAMACHY observations over Park Falls, Wisconsin, J. Geophys. Res., 111, D23302, doi:10.1029/2006JD007080. Copyright 2006 by the American Geophysical Union.

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