Mediterranean Landsurface Processes Assessed From Space

Abstract

Observations from space have been an important component in a number of research projects of the European Commission aiming, in the context of "Global Change", at the assessment of land-surface processes and their changes in the Mediterranean area. With the new generation of satellites, carrying improved instrumentation, these observations will gain in importance in the future. Changes in the Mediterranean environment are linked to the global climate system which is characterized by a strong inherent interannual variability but may, in addition, undergo trends that develop slowly in time. To assess, to which degree Mediterranean land-surface processes such as aridification, desertification, soil quality and changes of water resources are affected by the development of the global climate system, it is necessary to extend such studies over long time periods which would allow to average over the "noise" in the signals caused by its natural variability. Presently time series of thirty years are found adequate to distinguish shorter term fluctuations from long term trends and to draw reliable conclusions from those data.For two reasons it seems now timely to summarize recent experience in dealing with satellite data when studying changes at the land surfaces. Firstly, to document the results obtained so far and secondly to pave the ground for a smooth transition from old sensor systems to the advanced ones which are already available or will soon become operational. From the new sensor systems, reliable long time series will become available only thirty years from now. In combination with existing data sets this goal can be accomplished in fifteen years from now. To create a coherent data set of the required length it is mandatory to fit the new measurements with their different instrumental parameters to the present data series.The information content of measurements made from space can only fully be understood and applied if the physical and -in the case of vegetation -also the biological limitations are kept in mind. This knowledge sometimes gets lost as the applications diverge from the objective of original data. It was therefore found formative to combine in one volume background information of both the measuring systems and the objects of investigation with the methodology that leads to applications. Newcomers and students in this field may also be interested in how research can be organized to validate and support the inferred information by corroborative measurements made at the surface. Experiences gained during field experiments therefore are described to some detail and useful supplemental information is given in appendices. The research community participating in the European activities is deeply indebted to the EC for sponsoring this research into which in addition substantial national funds were invested from the participating countries. More than 35 research groups, including one of the U.S.A., participated in this research of which about one half used satellite data. The book is a recognition of the ...

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