Meet an expert user of Copernicus Sentinel-2 data for human settlement mapping
13 December 2018
Copernicus Sentinel-2A has been in orbit since June 2015 while Sentinel-2B joined its twin in March 2017. They each have a lifespan of at least seven years and fly at an altitude of 786 km in a polar, Sun-synchronous orbit.
They both carry a multispectral imager (MSI) covering 13 spectral bands (443–2190 nm) with a swath width of 290 km and spatial resolutions of 10 m (4 visible and near-infrared bands), 20 m (6 red-edge/shortwave-infrared bands) and 60 m (3 atmospheric correction bands).
The mission mainly provides information for agricultural and forestry practices and for helping manage food security.
As well as monitoring plant growth, Copernicus Sentinel-2 can be used to map changes in land cover and to monitor the world's forests. It also provides information on pollution in lakes and coastal waters. Images of floods, volcanic eruptions and landslides contribute to disaster mapping and help humanitarian relief efforts.
Franz Schug of the Humboldt-Unversität zu Berlin, Germany, has discovered that Copernicus Sentinel-2 data is fundamental for his current project.
Born in Bad Kreuznach (Germany), Franz spent the first two decades of his life in the south-west of Germany. In 2011 he received a Bachelor's degree in business economy from the Université de Lorraine, and then moved to Berlin. There he obtained a Bachelor's degree in Geography and a Master's degree in Physical Geography of Human-Environment Systems from Humboldt-Universität.
Franz is now a doctoral researcher in the remote sensing lab at the Geography Department of Humboldt-Universität in Berlin.
The University's remote sensing lab uses satellite remote sensing data to study all kinds of Earth surface processes, from agriculture (both cropland and grassland) over forest ecosystems to urban areas, in order to better understand global change related to land systems.
Franz's research focuses on methods of optical multi-spectral remote sensing image analysis, data processing and visualisation, with a thematic emphasis on human settlements, for instance in the context of urban expansion and densification.
Analysing long and dense time series from Landsat and Copernicus Sentinel data is core for the lab's and Franz's research.
ESA: What does your work with Sentinel-2 data entail?
The research project I am contributing to aims at identifying patterns of material stock distribution through remote sensing imagery. Meaning the amount and type of materials used for human-made built-up features and infrastructure, such as concrete, metals or wood. Mapping the patterns of material usage and understanding their links to socio-economic indicators is, at the end, part of sustainability and transformation research.
Societies heavily rely on stocks, as their presence guarantees the provision of services. At the same time, we want to reduce material usage and consumption without giving up living standards.
All kinds of spatial data do - or will - play a role in this project. However, as material stocks occur mainly in human infrastructure and the built-up environment, my current everyday research focuses on land cover quantification to identify where we have to look for stocks.
Optical imagery is widely approved data in land cover mapping and this is what I also work with at the moment. The open data archives and our need to look at large areas are the key reasons for us to use Copernicus Sentinel-2A and -B and Landsat as main data sources.
Until recently, Landsat alone was the way to go for many large area applications, but the increased spatial, temporal and spectral resolution of Copernicus Sentinel-2A and -B changed that. And even though both Earth monitoring systems provide similar data in principle, data and method handling also changed.
Pre-processing procedures need to be handled, but I am not an expert in this so it is carefully managed by people who really understand what they do. We use FORCE, which is a powerful open-source software for Copernicus Sentinel-2 and Landsat data pre-processing, that is currently developed in our lab.
Data storage is a huge issue, since the data size of Copernicus Sentinel-2 exceeds the size of Landsat 8 by a factor of 10 or more. For nation-wide mapping, that might make the difference between using a local machine or a server-based or cloud-based computing environment. This applies for processing methods, too. Using the exact same approaches as for Landsat could be feasible, but might require computational optimisation. And then we also see challenges in the applications themselves. We observe that validating our products is not always possible on a 10m level provided by Copernicus Sentinel-2, because reference data may have a coarser resolution and the effect of inexact image overlays is more important.
Looking for material stocks, it is obvious that land cover information alone is not sufficient. We rather need to know about the nature of the area. Is it a settlement? Is it mainly a residential, commercial or industrial neighbourhood? Can we make a statement about its age? Can we identify traffic infrastructure? For many areas, this information exists in a very simplified way or not at all yet, but remote sensing does make progress in finding answers to such questions.
We think that Copernicus Sentinel-1 and -2 can most likely contribute to capturing the complexity of human settlements and their processes because of their high resolution and good availability. We could hardly identify a single building with Landsat, but it is possible with the Copernicus Sentinels.
I learn a lot of things working with satellite imagery. Not every part of it is academic or professional, and that's because I can discover places I have never been to. I detect features of the landscape, within cities, that look particular on the image and then I start doing research on them. I recently found an airport cut in half, not even an hour away from where I live and work. I was at first convinced that a part of the image was shifted or wrongly merged, for whatever reason. It actually turned out that this former military airfield of the German and British Air Force is a Museum of military history I didn't know about, which had been partly transformed into a residential single-family housing area.
During my work on urbanisation processes in Ouagadougou, Burkina Faso, I was particularly impressed - if this is an adequate word here - by the huge structural difference of planned and slum-like unplanned housing. Remote sensing, including low-barrier tools such as Google Earth, makes it possible to see all the places you cannot or do not go to.
The Copernicus Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to the European Union's Copernicus environmental programme.
The European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites on behalf of the European Union and ensuring the flow of data for the Copernicus services, while the operations of the Copernicus Sentinels have been entrusted to ESA and EUMETSAT.