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Orbiting Carbon Observatory (OCO)

Orbiting Carbon Observatory (OCO). Vijay Natraj. Mission Overview. CO 2 is the principal atmospheric component of the global carbon cycle Processes governing carbon cycle not well understood

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Orbiting Carbon Observatory (OCO)

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  1. Orbiting Carbon Observatory (OCO) Vijay Natraj

  2. Mission Overview • CO2 is the principal atmospheric component of the global carbon cycle • Processes governing carbon cycle not well understood • OCO will measure column-averaged CO2 vmr (XCO2) with more complete global coverage to better understand geographic distribution of the sources and sinks

  3. Measurement Strategy • High resolution spectra of reflected sunlight taken simultaneously in NIR CO2 (1.58 μm and 2.06 μm) and O2 (0.76 μm) bands • 3 grating spectrometers • Data acquired in nadir, glint, target modes

  4. Retrieval Algorithm • Radiative Transfer Model • Instrument Response Model • Inverse Method

  5. Radiative Transfer Model • Spectrum-resolving, multi-stream, multiple-scattering model for scattering, absorbing atmospheres • BDRF at the lower boundary to characterise surface reflectance • Together with ILS, called the forward model

  6. Inverse Method • Based on optimal estimation theory (Rodgers, 2000) • Minimises cost function involving computed and a priori states, measured and computed spectra, a priori and measurement error covariances • Simultaneously retrieves several properties of surface and atmospheric state, such as XCO2, temperature, humidity, aerosol, surface pressure, albedo, etc.

  7. Retrieval of Oxygen A-Band Spectra from Airborne Measurements • High-precision, high-resolution O2 A-band spectra of sunlight reflected from the sea surface (O’Brien et al., 1996) • Sample spectrum retrieved to within an rms error of 1.5% • Wavelength scaled to match the calculated spectrum • Continuum level, tilt and zero level offset fitted

  8. Retrieval of Oxygen A-Band Spectra (contd) • Objective is to retrieve column O2 with precisions between 0.1-0.3% from this data set • Next logical step in demonstrating the feasibility of retrieving XCO2 from space with precision near 0.3%

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