Probably the most sophisticated sensor onboard ENVISAT is the so-called ASAR – Ad-vanced Synthetic Aperture Radar. It’s a radar system which constantly emits radar waves which are reflected from ground and received by ASAR. From these reflected waves surface maps with 30 meters resolution can be generated. The key point is that these maps can be generated day and night, 24x7, and even at 100% cloud coverage, because radar waves are actively illuminating the surface and can penetrate clouds. This makes ASAR superior to optical sensors. These advantages are the reason why Germany currently launched a radar satellite, SAR-Lupe, with a peak resolution of below 1 m for military surveillance purposes.How do we get the data from ENVISAT? ENVISAT transmits the data in two ways to ground. One is directly to a ground station in Kiruna in Sweden. Though this is the easiest link it works only when ENVISAT flies over Kiruna. In order to have constant data access ENVISAT also transmits via the European relay satellite ARTEMIS, which is located in a geostationary orbit, to the ground station ESRIN in Italy. From there the data are distributed to five different data processing facilities in Europe, so called PACs (Processing & Archiving Centers), where the data are exploited and made available to the researchers. This is just the first step: Compiling the status of our atmosphere. We also need to know how much trace gases and aerosols our atmosphere can stand without too much warming. And finally, what can we do to lower these unwanted constituents? We need at least to withdraw the same amount of substances we release into atmosphere until we arrive at a closed loop cycle maintaining garbage concentrations well below their critical limits. Plants helps us to withdraw CO2. It’s up to us to reduce burning CO2 to the same emission rate. We are far from that. But we have an alternative: Switching from CO2 emission to H2O emission. There are no H2O emission limits. Earth bathes in water. So let’s be pioneers: Don’t burn carbon, let’s burn hydrogen!

What does ENVISAT do for us? To understand we have to recall that “seeing” garbage trace gases means that electromagnetic waves from the atmospheric constituents are received, whereby each constituent emits waves with very special wavelengths which can be taken as fingerprints of this constituent. So what the sensors of ENVISAT do is to point obliquely to the horizon, so that the light arriving stems from the atmosphere at the horizon and not from ground, and scan the arriving light at different wavelengths. Because ENVISAT circles Earth every 1 hour and 40 minutes, global atmospheric trace gas and aerosol maps can be gener-ated about once a day. But ENVISAT does much more. With nine different sensors it analyzes also clouds and atmospheric temperatures. It meas-ures land surface temperatures vegetation characteristics and surface elevation. It determines ocean colors, sea surface temperatures and surface topography in particular wave characteristics. It determines the extent of polar ice, its topography and the ice temperature. So in every aspect ENVISAT is a truly environmental satellite. These measurements give answers to today's crucial questions concerning climate changes: Is the ozone hole still growing? How much rain forest is deforested each year? What is the reason for the rise of the sea level? We know today that it’s NOT the melting of the ice! What are the effects of air pollution? Will natural disasters increase and intensify in the future and if yes, how much?

So what we need is atmosphere control. Controlling means sensing and actuating. We need to know the actual state of the atmosphere, compare it with an established standard and to have the means to modify it accordingly. This sounds easy, but is awfully difficult. Atmosphere is a global system. How can we measure atmospheric constituents entirely? What are acceptable limits for garbage constituents? And once we know the unwanted constituents and their wanted levels, how can nations ensure that every one sticks to reducing the un-wanted garbage? Let’s start with the first step: How can we measure garbage concentrations globally? Take a probe here, take a probe there? Even if we would do that at thousands of sampling stations worldwide, would this give us the overall concentrations? No, because we would also have to climb mountains and even would have to go much higher at any place to sample the entire atmosphere. What we rather need is a globally integrating sensor. We do have sensors like this. They are called environmental satellites. The most sophisticated of these is the European Environmental Satellite, ENVISAT. ENVISAT constantly monitors our atmosphere and Earth’s surface properties from space since March 2002. It is the biggest one as well, com-parable with a truck: 10 meters long, 3 meters wide, and weighting 8 tons. With 2.3 Billion Euros it was also by far the most expensive.