How researchers use the latest Earth observation data – Part two
In the second part of the series on the TerraSAR-X and TanDEM-X Science Meeting in Oberpfaffenhofen, we present further applications for satellite data. This time, for example, biomass is determined with the help of 'Earth observers from space'. Up until Thursday, 20 October 2016, international scientists will use the congress to show their research results on satellite-based Earth observation and to exchange ideas.
High above the swamp
Wet, warm and salty – the perfect habitat for mangroves. These tropical trees only feel at home in seawater or the brackish water of rivers. Together with other water-loving plants and shrubs, they can spread across entire forests or swamps. They offer protection against land loss through coastal erosion along seaboards and act as buffers to block storm surges and tsunamis. Around the world, mangrove forests account for an expanse of roughly 150,000 square kilometres. This equates to an enormous quantity of biomass – plant constituents that act as natural carbon reservoirs and that influence the climate. But exactly how much biomass is stored in these forests? And what about the inaccessible areas? ##markend##To get answers to these and other questions, Seung-Kuk Lee from NASA Goddard Space Flight Center selected a starting point located at an altitude of 514 kilometres. The scientist used TanDEM-X to survey the world’s largest mangrove forest region, the Sundarbans, which stretch from the Indian state of West Bengal across Bangladesh, and determined the height of the tree crowns with a 90 percent accuracy. Speaking at the science meeting, Lee summarised: "The TanDEM-X dataset is a fantastic opportunity to measure the height of large swathes of mangrove forest on a global scale and to obtain a more precise estimation of the biomass they contain."
Radar and laser in top form
The determination of biomass continues – researchers from Sweden are enthusiastic about the results achieved by TanDEM-X. While the far north of Europe may not be home to many mangroves, the region is well populated by spruce, pine and birch trees. Forests cover more than 50 percent of the country. The volume of forested areas in Sweden has grown by over 80 percent in the last century. This is a good reason for scientists from the Chalmers University of Technology and the Swedish University of Agricultural Sciences to take a closer look. The research group tested the suitability of the TanDEM-X dataset to calculate the climate factor biomass in Sweden at both regional and national levels. To do this, they conducted comparative measurements in the test region of Krycklan in the north of Sweden. First they performed an aerial laser scan (LIDAR) – a highly precise measurement method, but one whose coverage is strongly dependent on environmental conditions; they then analysed the TanDEM-X data. The surprising result was that the precision of the radar measurements is equivalent to the best results recorded in the LIDAR scan, yielding a mean square error of 16 percent. This number describes how much the prediction differs on average from observed values, so a lower number is equivalent to a better performance. This means that Swedish environmental and forestry researchers will now be able to survey all of the country's forested areas with unprecedented precision – using the comprehensive digital elevation model created using TanDEM-X and their previously acquired data as references.