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46 CHAPTER 2. ATMOSPHERE AND REMOTE SENSING
• the absolute spectral solar irradiance (320 - 650 nm) and its temporal variation (see 2.3.3)
• the measurement of UV/visible actinic fluxes (e.g., of JNO2) and of the limb radiance near
horizon
• the detection and characterization of unknown, overlooked, or yet poorly characterized atmospheric
absorbers, such as the H2O continuum absorption, meta-stable and stable H2O − H2O
dimers, or the collisional complex O2 − O2, .... (see 2.3.4)
• the measurements of the stratospheric aerosol extinction and its relation to volcanic eruptions.
• the validation of level 1 products (spectral solar irradiance, and limb radiances) of the SCIA-
MACHY instrument deployed on the European research satellite ENVISAT (see 2.3.1).
Arguably all these activities aim at a better understanding of the primary driving force of the
climate system e.g., the solar radiation and its deposition in Earth’s atmosphere. The research thus
contributes to better quantify and assess man’s impact on the past, present and future global climate.
Methods used for the investigations of the radiative transfer involve (1) spectroscopic measurements
of the absolute spectral solar irradiance in the UV/vis/near-IR and of corresponding near horizon
skylight limb radiances from different spectrometers (grating and Fourier-Transform) deployed on
high altitude (∼ 40 km) balloon platforms including on-side absolute radiometric calibration to NIST
(National Institute of Standard and Technology, USA) and PTB (Physikalische Technische Bundesanstalt)
radiometric standards (2) ground-based high spectral resolution spectroscopic measurements
of zenith scattered skylight around the oxygen A-band (767 - 771 nm) (see Figure 2.19, upper panel),
that aim at the detection of photon path length distribution of solar photons for a variety of cloudy
skies (see Figure 2.19, lower panel) and (3) long-path spectroscopic absorption measurements near
surface in wavelength intervals ranging from the UV to the near-IR. All the different instruments
are deployed on internationally organized field campaigns that address a wider range of scientific
objectives (see below). The interpretation of these measurements also involves sophisticated radiative
transfer modelling (ray-tracing, Monte Carlo, discrete ordinate models, DISORT) that e.g., account
for the sphericity of the atmosphere, refraction, time and space dependent trace gas and aerosol
concentrations and cloud cover. Activity (1) is performed within a French/German collaboration with
the Laboratoire de Physique Moléculaire et Applications, Université Pierre et Marie Curie, Paris,
France and (2) within a collaboration with the IUP at the University of Bremen, Germany.
Field Campaigns & Studies
1. March 04: a high latitude balloon campaign at Kiruna/Sweden (67.9 o N, 21.2 o W) within the
ENVISAT/SCIAMACHY validation
2. Nov./Dec./Jan. 2004/05: a tropical balloon campaign at Teresina/Brazil (5.1 o S, 42.9 o W) within
the ENVISAT/SCIAMACHY validation and at Alcantara/Sao Luis/Brazil (2.39 o S, 44.38 o W).
3. June 2005: a tropical balloon campaign at Teresina/Brazil (5.1 o S, 42.9 o W) within the EN-
VISAT/SCIAMACHY validation
International Cooperation The research group closely cooperates with the following institutions
as, e.g., documented in joint peer-review publications.
(1) Laboratoire de Physique Moléculaire pour l’Atmosphere et l’Astrophysique (LPMAA), Université
Pierre et Marie Curie, Paris, France, (2) Meteorologisches Institut, Freie Universität Berlin, Berlin,
Germany, (3) European Space Agency (ESA), Nordwijk, The Netherlands, (4) Institut für Umweltphysik
und Fernerkundung, University of Bremen, Bremen, Germany, (5) Los Alamos National Laboratory,
Space and Remote Sensing Sciences Group, Los Alamos, USA, (6) Royal Netherlands Meteorological
Institute (KNMI), De Bilt, The Netherlands, (7) Meteorological Institute, University of
Bonn, Bonn, Germany, (8) Meteorological Institute, University of Munich, Munich, Germany, (9)
GKSS Research Centre, Geesthacht, Germany.
Future work will concentrate on studies (1) of the inter annual variation of the spectral solar
irradiance and its relation to climate change, (2) improved measurements of path length distribution
of solar photons during the life-time of cloud systems, (3) high resolution spectroscopic studies of the
visible and near-IR spectrum of water vapor and (4) 2-D imaging spectroscopy of radiative properties
of the atmosphere.