Atmosphere

Clouds 

Cloud detection and measurements are derived from AVHRR and MSG-SEVIRI measurements in near-real-time on a daily basis by the University of Bern’s Remote Sensing Group. They produce 3 types of products: cloud masks, cloud type and cloud-top temperature and height. Ongoing research is focused on improvements in the cloud-masking algorithm and the inclusion of probability estimates for each pixel. To achieve this, a fusion of existing approaches (PPS, CASPR, SPARC) is performed, combining the advantages of each. The extensive validation process is performed by means of atmospheric profiles from CALIPSO and CloudSat, as well as SYNOP weather reports obtained from terrestrial and ship observations. Further studies will aim at discrimination of fog cover on the basis of cloud-top height, as well as cloud properties such as cloud optical depth and effective droplet radius. 

Cloud distribution and cloud top height
Cloud distribution and cloud top height derived over Europe from NOAA-19 AVHRR data acquired on September 30, 2010 12:28 UTC. Corresponding data is available in near real-time on the saturn data portal (image by RSGB/NOAA)


Nitrogen Dioxide 

Nitrogen dioxide (NO2) is an important trace gas in the troposphere since it directly and indirectly (as an aerosol or ozone precursor) affects human health and ecosystems. Satellite derived maps of NO2 allow a spatially continuous monitoring of air pollutants and their trends. Most atmospheric gases absorb solar electromagnetic radiation in well-defined narrow spectral bands, which can be used to retrieve information about their atmospheric abundance from satellite measurements. Empa has developed EOMINO, a high-quality NO2 product for OMI, which is adapted to the specific conditions in Europe and the Alpine region (Zhou et al., 2010). The data set is freely available on ESA’s TEMIS web site.

NO2 tropospheric vertical column density distribution
NO2 tropospheric vertical column density distribution (2005-2009 summer mean) over Switzerland (image by Empa/ESA).


Aerosols 

Tropospheric aerosols play an important role in the climate system. They affect cloud physics, as well as the optical and radiative properties of the atmosphere. The most important parameters for the derivation of visibility are the optical properties of aerosols, in particular the aerosol optical depth, which are connected to the extinction of electromagnetic radiation in the atmosphere. The Remote Sensing Research Group of the University of Bern makes use of data from SEVIRI and AVHRR to obtain high temporal and spatial resolution, respectively. The retrieval methods are able to generate aerosol maps over a wide range of surface types. AVHRR also provides an archive dating back to 1981, opening the possibility to analyze long-term changes in visibility.

Aerosol optical depth
Aerosol optical depth derived from AVHRR on August 19, 2011 13:08 UTC showing the high aerosol load at the Po valley, Italy. Corresponding images are available from the saturn portal (image by RSGB/ NOAA)