Abstract
Abstract. New generations of space-borne spectrometers for the retrieval of atmospheric abundances of greenhouse gases require unprecedented accuracies as atmospheric variability of long-lived gases is very low. These instruments, such as GOSAT and OCO-2, typically use a high spectral resolution oxygen channel (O2 A-band) in addition to CO2 and CH4 channels to discriminate changes in the photon path-length distribution from actual trace gas amount changes. Inaccurate knowledge of the photon path-length distribution, determined by scatterers in the atmosphere, is the prime source of systematic biases in the retrieval. In this paper, we investigate the combined aerosol and greenhouse gas retrieval using multiple satellite viewing angles simultaneously. We find that this method, hitherto only applied in multi-angle imagery such as from POLDER or MISR, greatly enhances the ability to retrieve aerosol properties by 2–3 degrees of freedom. We find that the improved capability to retrieve aerosol parameters significantly reduces interference errors introduced into retrieved CO2 and CH4 total column averages. Instead of focussing solely on improvements in spectral and spatial resolution, signal-to-noise ratios or sampling frequency, multiple angles reduce uncertainty in space based greenhouse gas retrievals more effectively and provide a new potential for dedicated aerosols retrievals.
Highlights
The Greenhouse Gases Observing Satellite (GOSAT) (Hamazaki et al, 2005; Kuze et al, 2009) and the Orbiting Carbon Observatory (OCO) (Crisp et al, 2004) are new missions dedicated to the retrieval of greenhouse gas column averaged mixing ratios
We have only focused on the ability to retrieve aerosol properties, but not on the impact of this capability on the greenhouse gas retrieval itself, which is the primary focus of the missions under consideration in this study
This study quantifies the potential of multi-angle highspectral resolution retrievals to both improve aerosol retrievals and reduce interference errors in trace gas retrievals
Summary
The Greenhouse Gases Observing Satellite (GOSAT) (Hamazaki et al, 2005; Kuze et al, 2009) and the Orbiting Carbon Observatory (OCO) (Crisp et al, 2004) are new missions dedicated to the retrieval of greenhouse gas column averaged mixing ratios (denoted XCO2 or XCH4 ). A full-physics retrieval, only represents a subset of potential aerosol properties and even those can be under-constrained Dedicated aerosol imagers such as the POLarization and Directionality of Earth Reflectances (POLDER, Leroy et al, 1997) and the Multi-angle Imaging SpectroRadiometer (MISR, Diner et al, 1998) use intensities (and polarization) measured at various viewing angles along the flight direction to improve their aerosol retrieval capability. They sample the aerosol phase function at various scattering angles, providing insight into their microphysical properties such as particle size distribution or refractive index
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