Hannover 2010 – wissenschaftliches Programm
UP 2.16: Poster
Dienstag, 9. März 2010, 16:30–18:30, Lichthof
Cloud effects on tropospheric NO2 measurements from satellite — •Achim Zien, Andreas Richter, Andreas Hilboll, and John P. Burrows — Institut für Umweltphysik, Universität Bremen, Deutschland
The signal of UV/vis remote sensing of trace gases in the troposphere by satellite instruments is strongly affected by clouds. It can be either enhanced or diluted depending on the relative altitudes of cloud and trace gas, the optical thickness of a cloud, and the surface albedo.
The sensitivity of the measurements as function of altitude can be expressed as block-airmass factor (BAMF) which is dependent on parameters such as the viewing geometry, the sun position, the surface albedo and which is strongly affected by clouds. As a result, the distribution of clouds affects the observed shape and magnitude of tropospheric distributions of a trace gas.
It is common practice in tropospheric satellite retrievals to exclude pixels with a cloud cover of more than 20%, thus significantly reducing the spatial and temporal coverage of the measurements. In addition, selection of clear sky scenes biases the observations and will lead to non-representative averages.
Here, we investigate the effects of clouds on satellite data with radiative transfer calculations for different cloud scenarios and an analysis of GOME-2 NO2 measurements. In addition, we evaluate how data can be corrected for with the knowledge of cloud properties and the trace gas profile and why clouds may help the detection of trace gases over bright surfaces.