The earth seen with electronic eyes

A virtual group language on the European remote sensing satellite Envisat

If everything proceeds according to plan, should be in the night of 28. February on 1. Marz An Ariane 5 from the European Space Station in Kourou, French-Guayana, withdrawing and the Environmental Satellites Entvisat bring in a 800 kilometer orbit.

The start was originally planned for a more earlier date. Last July, however, there was a malfunction of the Ariane upper level, which managed that the communications satellite artemis was exposed to a low orbit. The 2.3 billion euro expensive ENVISAT makes in particular the experiences that the Europeans could collect with the two processes ERS (Earth Remote Sensing Satellite) -1 and ERS-2 and is with a total of ten instruments to explore the atmosphere, the oceans and equipped the mainland.

The following text is based on three individual languages, which were combined with a virtual group interview. The talk partners were Richard Bamler, director of the Institute for Methodology of Remote Sensing at the German Center for Aerospace (DLR), Oberpfaffenhofen; Michael Bittner, scientist at the German remote sensing data center (DFD) of the DLR, Oberpfaffenhofen; And Andreas Neumann, head of the sea remote sensing at the DLR, Berlin.

The earth seen with electronic eyes

Envisat. Photos: ESA

QUESTION: On the 1. Marz is intended to finally start the most expensive and most expensive European earth observation satellite ENISAT after some delay – with a rocket that has a 20 percent error rate. Are you nervous?

Bamper: I see that optimistic: We use the best tested engine at the start. Since the malfunction of the Ariane 5 upper level last July, there have been many test runs, also on the DLR prudent in Lampoldshausen, where the error has been identified. Even now, there are still true tests that can lead to a shift of the start until the last moment. But of course we are nervous. There is always a long time for such an event, and it depends a lot of a successful start.

Bittner: When the startup on 1. Marz does not work, we have a rough problem. At the project Hang many jobs. The Federal Ministry of Education and Research has a lot of money for the scientific processing of the data within the context of the atmosphere research program, AFO-2000, and the Climate Research Program, Declimate. If no data came now, the for the research community was very unsatisfactory.

QUESTION: Envisat is equipped with ten highly complicated sensors. It would not be more sense to distribute it to several satellites, so that at a false start is not all lost?

Bittner: That’s a question of philosophy. Today, there is actually a trend to smaller satellites. However, a gross satellite like Envisat has the advantage that it provides practically a complete laboratory in the orbit with which you can make different quantities at once. The earth is a system that you have to consider as a whole. Observation only one component, such as the atmosphere, is not enough for the understanding of the system Earth. We also need to examine the biosphere, the land masses, the oceans and their interactions with each other and with the atmosphere. For this we need a variety of different instruments, whereby it is advantageous for the comparison of the measured values to gather these devices in one place. The Americans also operate despite the "Fast-better-cheaper"-Philosophy continues to grow rough earth observation satellites such as Terra, Aqua or UARS, each with six to ten sensors on board.

The earth seen with electronic eyes

NO2 load

QUESTION: I imagine myself difficult to get a hat in the construction of such a coarse satellite, different requirements for the sensors lower.

Neumann: If you combine all sensors on a satellite, compromises are unprecedented. That’s going on at Orbit. For the earth observation, almost exclusively so-called sun-synchronous orbits are used, which run in Polish and always cross the different latitudes in the same local time. Now, however, different overflight time and lighting conditions are made available depending on the question. A high sun level may be favorable for some mainland observations, but thails through the strong reflections the observation of the oceans. Another problem is the highly complex data management of all these sensitive devices, which are mutually not stewed. This is an excerpt demanding task. Therefore, it was also so important to raise the Artemis satellite despite the failure of the Ariane upper stage last July still to the planned orbit. He ibal’s relay station for the transmission of the Envisat data indispensable.

QUESTION: Alone three instruments are dedicated to the observation of the atmosphere. Why this effort? Had not enough a device?

Bittner: At the beginning of the conception of Envisat, scientists have become all of them, which are the urgent questions that must be clarified in the next ten to fifty years. In this case, three rough theme blocks have been cleared out relatively quickly: Firstly, this is the still existing ozone problem, secondly the ie of greenhouse effect and global emphasis and thirdly the increasing pollution burden in troposphare. The next step was the identification of the parameters we have to watch from space to answer these questions. There was relatively fast a list of trace substances, whose distribution in the atmosphere we have to get to know exactly, in addition to meteorological values such as temperature, prere or wind speeds. Such a variety of quantities dearly realized with the required accuracy with a sensor.

QUESTION: Let’s start with Gomos. This instrument uses the light of stars for the determination of ozone concentration?

Bittner: The short is standing for "Global Ozone Monitoring by Occultation of Stars". This is about measuring the vertical distribution of ozone very precise. For this purpose, an upstanding or undergoing star is pursued and pursued by the atmosphere during its apparent hike. This method allows a very high, vertical resolution, but has the disadvantage that only a few quantities are possible per orbit.

QUESTION: You can jump from one star to another.

Bittner: Yes, Gomos will be about 45 different stars per orbit, but also that is not enough for a flat-covering observation. We only get scattered measured values, which, however, highly accurate with a vertical resolution of about one kilometer in the high range of 15 to 80 kilometers.

The earth seen with electronic eyes

Ozone hole over the Antarctic on 26. February 2002

QUESTION: Below 15 kilometers probably comes the second sensor into the game?

BittnerExactly, these quantities we drove through with Sciamachy (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography). In contrast to Gomos measuring in the ultraviolet and visible area of the spectrum, Sciamachy also has measuring channels in the near infrared range, about 0.2 to 3 microns approximately 0.2 to 3 microns. The most interesting thing about this instrument is that it can be operated in two different modes: it can look both to the horizon as well as perpendicular downwards and measure the sunlight reflected by the molecules.

QUESTION: Accordingly, it can only be used by day?

Bittner: Yes, unlike gomos that works only at night. Due to the vertical view, the so-called NADIR mode, we also get information about trace gases in the troposphere, the lowest layer of atmosphere. Here we hope for progress in the declaration of the carbon cycle. For the implementation and verification of the Kyoto protocol, it is necessary to know exactly where carbon dioxide, the most prominent greenhouse gas, is created and where it is absorbed. Sciamacchy is the first instrument that tries to determine the distribution of carbon dioxide in the troposphere in the coarse slab from the satellite.

QUESTION: The third atmosphere instrument measures primarily in the infrared area?

Bittner: The name of this sensor is MiPAS (Michelson Interferometer for Passive Atmospheric Sounding). He observes the range between 4 and 20 microns in the infrared and thus detects the concentrations of about a dozen trace gases, sometimes the same as Sciamachy. The comparison of this data will be very interesting. MiPas does not go down to the troposphere, but may measure for day and night and to high from about 150 kilometers. Sciamaky’s upper limit is approximately 55 kilometers.

QUESTION: What causes instruments to observe the atmosphere of those, which are primarily geared to the mainland or on the oceans?

Neumann: There it goes essentially three parameters. This is, on the one hand, the room resolution: land-related sensors can nowadays still structures of a few meters roughly relosable. At the ocean sensors, structure recognition does not play such an important role. Here, the Envisat instrument Meris currently pays for the most performance at 250 to 300 meters. Atmosphere sensors, on the other hand, who look at very coarse-flat phanomena come out with a space resolution in the ten-kilometer area. The second distinguishing criterion concerns the spectral resolution: here the lowest demands are made by land observation, as it is primarily about the identification of objects. For many land applications, therefore relatively few color channels with a resolution of 50 to 100 nanometers enjoyed. In the ocean observation, there is more on the subtleties in the color gradations, here are the exploits of the sensors therefore at about 5 nanometers. The atmosphere sensors are at least a magnitude better. They can still distinguish colors that are less than 0.5 nanometers apart.

QUESTION: How high is the spectral dissolution of the human eye for comparison?

Neumann: The human eye has three color channels whose dissolution movements are at approximately 200 nanometers.

QUESTION: And the third parameter to distinction between land, sea and atmosphere observation?

Neumann: This is the spectral range in which is observed. This is essentially the visible light and the temperature measurement in the mainland and ocean the infrared. The atmosphere sensors cover a substantial coarse area between ultraviolet and infrared, depending on which substances should be detected.

QUESTION: What do you learn from the colors of the water?

Neumann: With the help of biophysical models, which describe the absorption and scattering properties of the substances in the water, we can derive the quantitative distribution of these substance groups from the observed spectra. It is essentially about three groups of ingredients: On the one hand, the phytoplankton, ie the biologically active substances, interest us. Its concentration is usually determined on the basis of chlorophyll content. The second interesting group of materials are the sediments, these are sand particles and minerals ranging in the water and typically focused in the shore area and in flow rodings. Flusses transport the main share of the sediment in the seas. Here we know where these sediments dropped and where they deposit. In addition, the observation of the sedimentation processes provides information about the constraints in the crust range and helps us pursue the spread of pollutants. As a third group, we are very interested in the olay organic substances, which often lead to a dark or even black color of the water, but not a priori are pary.

Licking olplatforms in the North Sea

QUESTION: Mr. Bamler, you have sought for ENVISAT mainly around the Asar instrument. Where was your starting point for development?

Bamper: Asar stands for "Advanced Synthetic Aperture Radar", A microwave-working, active procedure. It provides images independently of the day or night and cloud cover. This is an important motivation for the use of such devices. A second motivation is that the Synthetic Aperture radar (SAR) properties of the sea surface can very well. It reacts very sensitively to the roughness of surface: In a smooth flat, the shrinking radar beam is completely reflected away and the site appears black. A wind upstream surface, however, reflects the signals partially to the sensor. From the brightness gradations, we can therefore extend directly to the respective waveforms and highs as well as on the wind directions and wind speeds. Such data collected weather may be used, for example, can be used for the maritime prediction and optimization of ship routes.

QUESTION: You could call up to early experiences?

BamperAbove all, we build on the experiences with the two European remote sensing satellites ERS 1 and 2. We have the DLR from the beginning "Processing and Archive Facility" On behalf of ESA, one of the European centers for processing ERS data. The radar himself does not provide images, the raw data rather look like a broadcasting point on the TV and must only be converted into pictures through propagated computing processes. In order to develop and optimize these procedures, you have to know a lot about the peculiarities of the sensor and the peculiarities of the satellite aircraft. All this fell directly into the quality of the pictures. It’s about as if you were taking a photo without lens and add the effect of the lens only later in the computer in the computer.

QUESTION: How expensive is the development of such algorithms?

Bamper: Depending on the complexity, 10 to 20 people are coming up. But compared to the work that is in the satellite hardware, this is rather little.

QUESTION: And what is now "Advanced", So improved to Asar?

Bamper: We can control the radar beam for the first time. The antenna on ERS was relatively simple and has always observed the earth from the same, fixed angle of 23 degrees. If you wanted to record a picture from a certain point on earth, they had to wait for the satellite to rebuilt there. That could take up to 35 days in the most unnecessary case. At ASAR, the antenna consists of loud small stations and receivers, which can be controlled electronically so that the beam is directed into a desired directions. This reduced the repetition rate for the figure of certain areas to a few days. In addition, we can swing the ray back and forth quickly and cover such a much wider strip. With a mechanically controlled antenna that would not have been because she had to swing it up to a hundred times a second. With Asar, we can absorb up to 1000 kilometers wide strips across the flight direction, but with this extreme width then with reduced resolution. The ERS sensors were cranked to 100 kilometers.

QUESTION: To what extent can the ENVISAT data can be used military or security policy?

Bamper: Envisat is a project of ESA, and ESA has committed itself to the civil, peaceful use of space travel. This is called, all data is free accessible. Also militaric authorities you can use. But we can not provide you exclusively to you exclusively. For security applications, the satellite fleet SAR-loupe is currently being built, which, however, is considered significantly higher domestic dissolution migration and higher repeat rates than Asar.

QUESTION: How to justify the hope, with the help of the ENVISAT data the tug of the drawing to end the interpretation of the Kyoto Protocol and the trade in emission rights? The interpretation of this data scientists were able to argue again long and extensively.

Bittner: For this you first have to say that Eversat was designed, long before Kyoto was talking about. Therefore, the instruments are not optimized for the Meng Tropospharic gases to which it goes primarily in the Kyoto protocol. Whether the Sciamachy data is sufficient for checking the climate change agreement must only show. Probably additional quantities, even on the ground and aircraft, will be required. Also important is the linking of the quantities with high-performance models of atmosphere.

QUESTION: Envisat is considered an environmental satellite because it should provide valuable data to climate and environmental research. At the same time, however, a stronger commercialization of remote sensing. They did not flare that such commercialization can counteract environmental protection if, for example, remote sensing data are used to steer fishing fleets and thus effect the exploitation of the seas?

Neumann: No, I do not share the excavation. The optimization of fishing routes does not have to be bad. The data can also serve to direct the fleets where the risk of overfish is lowest. The problem of commercialization I see somewhere else. Environmental protection is primarily a sovereign task, which is perceived at the different levels of the respective public institutions, from the UN to the municipal council. I think that’s right too. Anyway, I do not see how the market alone should regulate these things. Despite all the efforts, there has yet been given a remote sensing satellite, which has born itself economically. If you look at the commercial projects that have given it to the Americans and still exist, you realize that they mainly finance themselves on the militar or government. Since I think it’s consistent and reasonable, especially the satellites for the environmental observation to be fully inspected and released the data.

QUESTION: The conversion of these raw data to tangible information, which tailored to specific customer requirements, could then be commercially interesting?

Neumann: That’s a completely different story that can work through and will increase in the future. But the total chain, construction and operation of the satellite itself to the exploitation of the data, commercially successfully operate, was not allowed to be possible for the foreseeable future. ()

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