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56 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
Figure 2.27: The timeline of continuous novel UV/vis/NIR satellite measurements starts in April
1995 with GOME (1) on ERS-1. With its successors it will hopefully cover a total period of more
than 25 years.
Main activities
How are single projects linked, list/group the subprojects
The various projects can be classified according to their spectral range, viewing geometry, and
analysis method.
- UV/vis DOAS for Nadir viewing geometry The main target is the determination of global maps
of tropospheric trace gas distributions like NO2, BrO, H2O, HCHO, SO2, Glyoxal. Currently measurements
of GOME and SCIAMACHY are under investigation.
- NIR DOAS for Nadir viewing geometry The main target is the determination of global maps of
tropospheric trace gas distributions like CH4, CO2, and CO. Measurements in the near IR spectral
range are carried out only by SCIAMACHY.
-Cloud retrieval for Nadir viewing geometry The main target is the determination of global maps of
cloud cover (effective cloud fraction) from broad band spectral measurements. From the combination
with narrow band absorption measurements of O2 and O4, also additional parameters like cloud top
height can be retrieved.
-UV/vis DOAS for limb viewing geometry The main target is the determination of vertical profiles
of stratospheric trace gases like O3, NO2, BrO, and OClO. Measurements in limb viewing geometry
are carried out only by SCIAMACHY.
-3-D radiative transfer modelling Detailed radiative transfer modelling is the prerequisite for the
correct interpretation of the results of the spectral analysis. The full spherical 3-dimensional Monte
Carlo model is developed and operated in our group. Also a detailed scheme for the simulation of
radiative properties of aerosols is developed.
-Validation of satellite data with independent observations DOAS observations are carried out
from several ground based stations (Kiruna, Paramaribo, Neumayer) as well as from aircrafts and
ships.
Methods and results From the measured spectra, the narrowband absorption features of several
trace gases are analysed using the DOAS method. The result of the spectral analysis represents the
trace gas absorption integrated along the absorption path. In addition, also the broad band spectral
features are analysed; they yield information in particular on the cloud cover, aerosol load and ground
albedo (in particular also vegetation cover). Various algorithms for the analysis of satellite spectra
were developed in the satellite group within the last years. For the detailed interpretation of the
analysed spectral information, radiative transfer modelling is needed. A 3-D Monte-Carlo radiative
transfer model (TRACY-II) was developed in our group, which allows to simulate various complex
viewing geometries and atmospheric properties. The retrieved global data sets are further investigated
using image sequence techniques.