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78 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
2.5.7 Satellite validation using the airborne multi axis DOAS instrument
Participating scientists Klaus-Peter Heue, Thomas Wagner, Andreas Richter 2 , Marco Bruns 2
Ping Wang 2 ( 2 Institut für Umweltphyisk, Universität Bremen)
Abstract The Airborne Multi AXis DOAS instrument designed to separate the tropospheric from
stratospheric absorptions of several Trace gases e.g. NO2. Due to the long range of the aeroplane
it is ideal for validation measurements of tropospheric NO2 observed by the new satellite instrument
SCIAMACHY on ENVISAT.
Figure 2.41: AMAXDOAS measurements along the flight track on 19/02/2003 overlaid to SCIA-
MACHY observations from the same day. The scientific SCIAMACHY data from the IUP in Bremen
were taken.
Background With the SCIAMACHY instruments
slant and vertical columns of many trace
gases can be measured. Here we concentrate on
tropospheric NO2. Based on the observed spectra
from SCIAMACHY several scientific DOAS
products exist at different scientific groups (e.g.
in Heidelberg, Bremen, Harvard). Nitrogen dioxide
is known to be harmful and plays an important
role in the tropospheric chemistry of ozone. Most
of the tropospheric NO2 is produced by anthropogenic
emissions.
Funding See satellite group overview.
Methods and results Tropospheric NO2 vertical
and slant columns from the new satellite instrument
SCIAMACHY on ENVISAT are validated
by measurements of the AMAXDOAS instrument
on board the DLR Falcon. The results
presented here were obtained in February
2003 on a flight over the Alps, the Po-Valley and
the Mediterranean ( figure 2.41). Due to the
similar measurement system of AMAXDOAS and
SCIAMACHY both tropospheric slant and ver-
tical columns can be compared. However, the
stratospheric absorption has to be separated from
the tropospheric signal first. In the Troposphere
the local variation in the NO2 columns are very
high caused by the anthropogenic emissions. The
stratospheric signal shows rather smooth spatial
variations. Different methods for the separation
of tropospheric and stratospheric signal for both
instruments were investigated. Independent information
about aerosol optical thickness and mixing
layer height were considered for the calculation of
the AMF. The TVCD measured by AMAXDOAS
varied between 16.2 and 35.2·10 15 molec/cm 2 over
the Po-Valley where SCIAMACHY data resulted
in 19.9 to 37·10 15 molec/cm 2 . Over less polluted
areas a similarly good agreement was found. The
linear correlation between the two datasets results
in a slope of 0.93. The slight differences observed
can be attributed to the different spatial resolution
and the temporal mismatch between the measurements
over the Po-Valley.
Main publications Heue [2005], Heue et al.
[2005]