The German satellite duo TerraSAR-X and TanDEM-X have consistently delivered one-of-a-kind Earth observation data since 2007 and 2010, hence shaping the international research landscape. TanDEM-X is being implemented on behalf of DLR using funds from the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie). It is a Public Private Partnership (PPP) project operated in conjunction with Airbus Defence and Space.
Radar sensors are particularly important in the field of Earth observation, as they can deliver images irrespective of cloud cover and at any time of the day or night. From space, they are able to capture expansive areas of more than 100 kilometres in length. Moreover, the civilian radar satellites TerraSAR-X and TanDEM-Xhave measured the Earth with unprecedented accuracy over the course of their missions, contributing significantly to the scientific exploitation of the data. The satellites are still in operation and may indeed continue to be in the service of science for many years.
Users in the area of environmental protection have shown, among other things, that they can utilise the radar satellites to observe systematic deforestation or illegal felling of woodland areas. This applies in particular to rainforests, as their sheer magnitude and the prevailing weather conditions mean they can only be satisfactorily monitored using radar sensors.
Impact on future research
The view from space can provide precise information on the changes taking place in glaciers and ice shelves. The sometimes dramatic developments require regular monitoring and must be viewed in context with global warming. Here, the TanDEM-X elevation model is a true treasure trove of data; never before have Greenland and the Antarctic been surveyed so comprehensively and in such immense detail. Until now, the ice masses have been, from a scientific perspective, ‘expanses of white’ on a map of the world.
Looking ahead: HRWS and Tandem-L
Successful operation of the satellites in formation flight and the outstanding quality of data yielded by the TerraSAR-X and TanDEM-X missions represent a new milestone in the history of Earth observation. Seeking to expand the German radar satellite programme, DLR has set its sights on a successor programme, HRWS (High Resolution Wide Swath), to ensure continuity in Earth observation within the proven X-band frequency range. HRWS is scheduled for launch in 2022, and DLR is also involved in intense work on a revolutionary Earth observation system with the Tandem-L mission proposal.
Tandem-L, the highly innovative radar mission, aims to acquire important environmental and meteorological data on a global scale and in high temporal resolution.
Tandem-L will operate in a longer wavelength compared with the two current missions. An approximately 24-centimetre wavelength permits penetration through the vegetation, hence revealing surface structures in the subsoil. New technologies and imaging methods such as polarimetric SAR interferometry also enable three-dimensional mapping of forests. This could be used to calculate forest elevation and hence to produce an indirect estimate of biomass, a factor that is currently beyond the reach of science on a global scale.