A precise prognosis of how the atmosphere is developing requires a thorough understanding of the entire system. This understanding is in turn based on precise observations. Satellites provide an ideal platform from which to measure the atmosphere continuously, globally and with consistent quality. Many global change processes occur on time scales measured in decades. Early and reliable detection of these climate signals therefore requires long-term, continuous, high quality and standardized monitoring and assessment of a multitude of key parameters for the most important processes known to us today which characterize the "Earth System."
By combining measurements with numerical models which reflect our current understanding of the atmosphere and how it relates to the earth's surface and outer space we can obtain a consistent picture of the atmosphere, and note any differences between the measurements and the models, thus increasing our knowledge.
In the framework of numerous basic and applied research projects we cooperate with national and international partners, and are the location of the World Data Center for Remote Sensing of the Atmosphere of the International Council for Science (ICSU).
Although ozone is only a trace gas, it absorbs almost all the sun's irradiance in the highly energetic ultraviolet (UV) part of the spectrum. In this way it filters out UV radiation which is damaging to people and animals, absorbs solar energy and releases it in the form of heat to the surrounding atmosphere. Ozone thus determines to a large extent the vertical temperature structure of the stratosphere and characterizes its large-scale circulation pattern. Because of its absorptive behaviour, ozone contributes to the natural greenhouse effect, without which the average temperature on the earth's surface would not be +15 degrees centigrade, but nearer to -18 degrees instead.
We do not yet have enough reliable UV measurements, which means that it is difficult to identify UV trends. This is especially the case because historic UV information is lacking and estimates based on models are accordingly uncertain. High UV-B radiation levels have many direct effects on people and plants (like mutation of DNA, or weakening of the photosynthesis process). UV radiation also influences the chemistry of the troposphere and thus air quality in that part of the atmosphere in which we live.
Today we know that during the past decades the ozone content of the atmosphere has significantly decreased everywhere except in the tropics. Careful, long-term measurements of global atmospheric ozone distribution are required, for example to follow the development of ozone trends.
Another issue concerns the quality of mid-term weather forecasts. The absorptive behavior of ozone also affects the weather. So DFD supplies the ewather services with up-to-date information every day about the amount of ozone in the atmosphere.
These data are also an important information source for government environmental and health authorities in estimating health risks, and they are made available to the public media.
Water vapor is the most common trace gas in the atmosphere, accounting for up to four percent of its volume. It substantially affects the climate, the weather, the chemistry of the atmosphere, and the biosphere. By absorbing both incoming solar irradiance and outflowing terrestrial irradiance, it heavily influences the atmosphere's radiation budget. Water vapor is thus responsible for 21 of the 33 degrees of the natural greenhouse effect. Only thanks to the natural greenhouse effect is there an average mean global temperature on earth beneficial for life amounting to 15 degrees centigrade. By means of the water cycle, which includes evaporation, followed by transport of latent heat, and finally precipitation, energy exchange between the earth's surface and the atmosphere, and likewise energy transport within the atmosphere, is determined. Besides this important climate function of transport agent for solar irradiance, water vapor also plays a main role in the formation of clouds, and thus in what happens with the weather.
At DFD measurements from the TOVS (Tiros Operational Vertical Sounder) and ATOVS (Advanced Tiros Operational Vertical Sounder) sensors on board the NOAA satellites over Europe are evaluated daily. In addition to the vertical profile of water vapor at 10 km (TOVS) or at 0-65 km (ATOVS) altitude, the water vapor column content and the vertical profile of temperature from 0-30 km (TOVS) and 0-65 km (ATOVS) are determined.
Scientific investigations show that the average temperature of the earth's atmosphere has risen since the beginning of the 20th century. The cause for this global trend is presumed to be an increase of so-called greenhouse gases like carbon dioxide or methane. The noticable consequence of climate changes are more storms, bad weather and natural catastrophes.
The international community of nations is attempting to stop the rise in global carbon dioxide emissions by means of international environmental agreements like the Kyoto Protocol. It is the goal of the Kyoto Protocol to reduce carbon dioxide emissions arising from human activity (industry, households, transportation). At the same time, reforestation is encouraged in order to increase the absorptive capacity of carbon dioxide by vegetation.
Among other input, models of the carbon cycle which include both the emission and absorption of carbon dioxide incorporate biophysical and geophysical parameters from current satellite data. These models make an important contribution to improving our understanding of global cycles. This knowledge also assists political decision makers to plan and implement relevant measures. DLR's applied remote sensing institutes support national and European research on the carbon cycle and on monitoring environmental agreements.
The European heat wave of 2003 affected the vegetation. This is shown in the image at left, which visualizes the change in the NDVI in 2003 compared with the average NDVI value for the previous ten years. NDVI stands for "Normalized Difference Vegetation Index" and is a mathematical ratio which identifies the existence and vitality of vegetation.
The value 0 indicates no deviation from the 10-year average. Negative values (brown) mean a decrease in vegetation and thus a possible reduction in yield. Positive values (green) show where NDVI has increased. A decrease in NDVI because of drought occured especially in agricultural areas such as Mecklenburg Vorpommern and northern Bavaria, whereas forested areas like the Black Forest or the Hartz Mountains showed an increase in NDVI.