资源环境科技发展态势分析平台

The Environmental Mapping and Analysis Program (EnMAP) satellite sees the world very differently from the way the people who live there do. The German environmental satellite measures the solar radiation that is reflected by Earth's surface. EnMAP not only captures visible light, but also short-wave infrared. These data allow precise conclusions to be drawn about conditions and changes on Earth's surface. The German Space Agency at DLR in Bonn is leading this unique mission on behalf of the German Federal Ministry for Economic Affairs and Climate Action. Multiple institutes and facilities at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) are involved in the preparations for and operation of the mission, as well as scientifically evaluating the data.

The EnMAP hyperspectral satellite is scheduled to lift off from NASA's Kennedy Space Center in the USA on Friday 1 April 2022 aboard a Falcon 9 rocket from the US space company SpaceX. The German Space Operations Center (GSOC) in Oberpfaffenhofen will be responsible for operating the satellite on behalf of the German Space Agency at DLR. GSOC employees have been conducting space missions from the centre's control rooms since 1969. GSOC has now successfully operated more than 70 missions, including the TerraSAR-X and TanDEM-X satellite system, which has been observing Earth using radar since 2007. The resulting data can be used for purposes including the generation of location maps for disaster management in the event of flooding and earthquakes. EnMAP data will help to address current issues in the fields of environment, agriculture, land use, water quality and geology.

242 channels go well beyond red, green and blue

DLR's Earth Observation Center (EOC) will be responsible for processing EnMAP data: "We receive and process the mission data, before making them available to scientists worldwide free of charge via a web portal," says Günter Strunz of the German Remote Sensing Data Center (DFD). The satellite transmits the data to DLR's receiving stations in Neustrelitz (Germany) and Inuvik (Canada). These are then calibrated, corrected and displayed as image maps. "The EnMAP data are not images in the conventional sense, but spectral measurements," adds Strunz. In visible light, all colours can be generated from the three primary colours red, green and blue. Like human eyes, conventional cameras only perceive light in the three primary colours: red, green and blue. A hyperspectral system like EnMAP distinguishes between a wide variety of hues, even in parts of the infrared spectrum, which are invisible to the human eye. Overall, the satellite maps Earth’s surface in spectra divided over 242 channels.

Disruptive atmospheric influences corrected

The processing of the data enables meaningful results. The last standardised processing step at EOC is atmospheric correction. "The reflected signal is altered by the atmosphere, so the effects of things such as water vapour and aerosols have to be corrected so that we only get the exact reflectance at the Earth's surface," says Peter Reinartz of the DLR Remote Sensing Technology Institute (IMF), which forms the EOC together with the DFD. "We can establish physical, chemical and biological soil parameters on the basis of the results. We might want to find out how much carbon the soil has absorbed, for example, or whether methane is leaking from a pipeline."

DLR's Center for Satellite-based Crisis Information (ZKI) will also use the data from EnMAP. The ZKI is involved in global networks such as the International Charter Space and Major Disasters. In the event of major natural disasters, the ZKI obtains and analyses Earth observation data with the aim of providing up-to-date information on the situation for public authorities and emergency services. This situational information was used, for instance, during the flooding in the German regions of North Rhine-Westphalia and Rhineland-Palatinate in July 2021.

Technology for the satellite's 'eye'

The DLR Institute of Optical Sensor Systems in Berlin was commissioned by OHB System AG to develop one of EnMAP's focal plane (or 'eye'). The focal plane is comparable to the retina of a human eye. In the case of optical satellites, the light arrives at the focal plane, is converted into electrical signals and transmitted onwards. The module for the visible and near-infrared range (VNIR for short) is only approximately 12 by 12 by 4 centimetres in size and weighs 1050 grams. The entire satellite weighs 950 kilograms. "The focal plane that the Institute developed for EnMAP is the latest in a long line of successful projects," says Institute Director Heinz-Wilhelm Hübers. This also includes the DLR-developed DESIS hyperspectral instrument on the International Space Station (ISS), which provides data on the state of vegetation on Earth. Like DESIS, the focal plane of EnMAP also facilitates technology transfer.