Studying the effects of climate change from space enters the Big Data era

A new method developed by CREAF and UAB allows the automatic processing of thousand of satellite images taken by Landsat without using manual interventions or the need for atmospheric data.

02/10/2014

For 40 years Landsat satellites have photographed all Spanish territory every 16 days at a resolution of 30 meters (or every 18 days at a resolution of 60 meters in the case of older photos). These images now allow us to contrast the changes undergone in the past decades. To do so, the images must be as comparable as possible and they must be corrected in terms of atmospheric effects and exposure to light. These corrections are known as radiometric corrections and until now were carried out manually using algorithms. In hands of an expert, each image took approximately 30 minutes to be corrected. Now, CREAF and the Universitat Autònoma de Barcelona have published a new method in the International Journal of Applied Earth Observation and Geoinformation which can correct satellite images without the need of manual interventions. “This new method allows the machines to correct a large series of images while experts can dedicate more time to the less mechanical and more interesting parts of the analysis”, states Lluís Pesquer, CREAF researcher and member of the Grumets group (CREAF-UAB). This new method represents a change in paradigm because it can correct terabytes of images without the need of human resources, and therefore can carry out projects which were previously impossible.

Moreover, the algorithm developed by CREAF does not need the atmospheric data of the moment in which the image was taken. That gives it an advantage over other correction algorithms which do need such information, and allows it automatically to correct older Landsat images and those from moments and regions in which there is no data.

Big Data Projects Study Climate Change

Until now, manual methods and limits in time and resources caused the projects on climate change or other environmental issues to be largely based on products with lower spatial resolution (MODIS 500m for example) or in some cases with a limited number of images, and thus a reduced selection. “This new correction method allows us to work in Big Data information volumes, a new scenario which radically changes and expands our research possibilities and work methods”, says Xavier Pons, professor of the Department of Geography of the UAB and head researcher of the Grumets group (CREAF-UAB). In fact, this new method is already being applied to the DinaClive project with the objective of taking thousands of satellite images and evaluating how ground covers and land use in the Iberian Peninsula have evolved in the past 40 years, what processes modified the landscape (urbanisation, draught, biological invasions, etc.), and the real impacts of climate change on the land.

Leaders in Remote Sensing Research

GRUMETS (Research Group on Methods and Applications in Teledetection and Geographical Information Systems) is a consolidated and publicly funded research group recognised by the Government of Catalonia and formed mainly by members of the UAB and CREAF. The group is directed by Dr Xavier Pons, professor of the UAB Department of Geography. Its members began working in the field of remote sensing at the end of the 1980s and throughout the years have collaborated with leading institutes such as the Catalan Institute of Cartography (ICC), the Spanish National Institute of Geography (IGN) and the European Space Agency (ESA).

GRUMETS also has participated in several applied research projects; one of the most important projects is SatCat, the largest repository of satellite images of Catalonia. Others include the management of Catalonia's waters through remote sensing, which won them the Environmental Prize 2007 and which was conducted jointly with the Government of Catalonia (Catalan Water Agency and the Department of Agriculture). In terms of research, the group has participated in international projects such as Geo-Pictures, devoted to providing images in emergency situations, when communication networks are down, and in the GeoViQua project, focusing on the visualisation and parametrisation of the quality of geographic data, led by GRUMETS and in which the European Space Agency also participated.