The remote sensing of CO2 from satellites
is an exciting new and rapidly developing field in carbon cycle research. Satellite
sensors have the potential to provide a wealth of information on atmospheric CO2,
covering many regions that are scarsely monitored the ground based
observational networks. Satellite measurements could significantly strengthen
the power of inverse modelling computations in tracing sources and sinks of CO2.
The main challenge, however, is to reach the measurement accuracy needed to
resolve the important CO2 concentration gradients. The current
generation of satellite instruments from which CO2 can be retrieved
is expected to meet the requirements only partly, as the instruments were not
originally designed to measure CO2. Nevertheless interesting results
come out as we will show for the Sciamachy instrument. A particularly difficult
aspect is the determination of the airmass factor, which is needed to translate
the observed optical thickness into a column averaged dry air mixing ratio. The
airmass factor is influenced by e.g. clouds, aerosols, air pressure, and
orography. So far the uncertainty assessments have mainly relied on theoretical
investigations and ground-based measurements. The measurements from Sciamachy
allow us to verify these studies, and some of the methods that have been
proposed to reduce or eliminate the errors. We will demonstrate this with the
main focus on aerosols. Error assessments using in-flight data will be
indispensable for improving future instruments.
Author: S. Houweling, W. Hartmann, I.Aben, H. Schrijver, et al (S dot Houweling at sron dot nl)
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