Allow me, Sciamachy
Mountains and valleys are measured with centimeter precision, there are pin-sharp maps of algal blooms, and we know how the Prile change on the mud flats every day: "satellite data" is the magic word. They also show us how greenhouse gases are distributed in the atmosphere.
"And here you can see the corrected and recalculated CO2 values for the last three years"
(Michael Buchwitz) "And here you can see the corrected and recalculated CO2 values for the last three years…", Michael Buchwitz from the University of Bremen looks in the direction of amazed screen. Because there is a yawning emptiness. Just as he is preparing to present freshly evaluated data from the European environmental satellite Envisat, the technology goes on strike.
The researcher took it easy, as he occasionally has to deal with technical failures in his everyday life. After initial problems with the cooling system, the Envisat instrument Sciamachy (Scanning Imaging A, which is maintained by the Bremer and his colleagues, transmits bsorption Spectro meter for Atmospheric Chartograph y) but reliable earth data. With its help, Buchwitz and his colleagues want to track down the interactions between human air pollution, global warming and stratospheric chemistry and physics.
The satellite orbits the Earth once in just 100 minutes, allowing its atmospheric sensors to fully capture the entire Earth's atmosphere within a few days. How does the satellite instrument actually collect its data?
We use what we always get for free
(Michael Buchwitz) "We use what we can always get for free", says Buchwitz, "namely sunlight". Because Sciamachy registers the rays scattered and reflected from the atmosphere and the earth's surface.
In doing so, its sensors examine the layers of air from different perspectives: in the "nadir" direction they look through the atmosphere perpendicularly at the earth, while in the "limb" arrangement they lens tangentially past the earth. Since the sensors observe the same volume of air first in the limb direction and about seven minutes later in the nadir direction, this even results in three-dimensional information.
In addition, the instrument looks at the sunrise and the moonrise. Similar to the Limb geometry, the sensors look along the edge of the earth, but measure direct sunlight through the atmosphere.
Sciamachy captures the light using his mirrors and feeds it into a telescope, which bundles the beam and focuses it onto the entrance slit of the actual measuring apparatus. Now the light is split twice: once by a prism and then again by a grid in front of the actual detectors. That's why scientists refer to the instrument as a "double spectrometer".
Finally, the detectors convert the intensities of the incident light waves into electrical signals. But simply because they are switched on and working, the detectors disturb the measurement with so-called "dark current noise". The detector electronics generate a particularly large amount of heat, and the sun also heats up the satellite. Despite the fact that it is very cold in space, a separate cooling unit has to cool down the receivers to between minus 45 and minus 123 degrees Celsius in order to suppress the interference values.
Its sophisticated optics enable Sciamachy to split radiation from 240 to 2380 nanometers into almost 8000 wavelength ranges - a much larger spectrum than its predecessor system Gome (GlobalO zone M onitoring E xperiment) and far more extensive than the light visible to us with its wavelengths of about 380 to 780 nanometers.
The wide range is interesting because the air filters out certain wavelengths from the sunlight to a greater or lesser extent depending on its composition. Carbon dioxide, for example, absorbs infrared at multiple wavelengths - Sciamachy, for example, measures the gas at 1600 nanometers. The more of the greenhouse gas in the air, the less light of this wavelength reaches the satellite. In this way, the environmental scout distinguishes umpteen substances and maps the chemistry of the earth's atmosphere down to the ground.
Meanwhile, the Bremen team has a lot of experience in calculating disturbances caused by wind, clouds or dust from the raw data. With each passing year, the readings become more valuable to the scientists. Today they can already distinguish very precisely what we humans blow into the air and what corresponds to the natural exchange.
"We didn't develop Sciamachy to point the finger at Kyoto," says Buchwitz, "we do basic research." The latest data will again provide important building blocks for this.
