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UP: Fachverband Umweltphysik

UP 1: Poster Session

UP 1.15: Poster

Dienstag, 15. März 2011, 18:30–20:30, P2

Remote sensing trace gas observations by satellite instruments over bright surfaces — •Achim Zien, Andreas Richter, Andreas Hilboll, and John Burrows — Institute of Environmental Physics, University of Bremen, Germany

Clouds strongly affect the remote sensing signal of trace gases in the troposphere when measuring with satellite instruments. The air-mass factor (AMF) is used to convert slant columns of a trace gas – from nadir absorption spectroscopy – into vertical column values. The AMF is a function of the radiative transfer and depends on the vertical profile of the observed species and the block-AMF, which denotes the measurement sensitivity at varying altitudes and depends on viewing geometry, albedo, aerosol, and cloud influence.

For a given amount of a trace gas in the atmosphere, the absorption signal observed at the satellite under cloudy conditions varies strongly depending on the relative altitudes of clouds and trace gas, the optical thickness of a cloud, and in particular the surface albedo. Between a cloud and a bright surface, the effects of diminished light intensity and enhanced light path compete, leading to either an attenuated or an amplified absorption signal from this region.

In this paper, we discuss the effects clouds over bright surfaces have on the AMF under different conditions. In particular, we show that over bright surfaces it is possible to detect trace gases below clouds from satellite in the uv/vis wavelength region. We illustrate the effects with GOME-2 measurements of O₂ ·O₂ and NO₂ at high latitudes and compare these to results from radiative transfer calculations.