Hans Roelofsen doctorate
Rapidly mapping nature area using remote sensing data
Hans Roelofsen defends his thesis on the use of remote sensing data to map out vegetation at VU University Amsterdam. Roelofsen carried out most of his research at KWR under the supervision of Flip Witte, professor at VU and also on-staff at KWR. Remote sensing (RS) data are produced from advanced aerial photographs (taken from a satellite or aircraft) and can help characterise an entire nature area simply, inexpensively and quickly. There is therefore less need for labour-intensive field work and for the use of (out-of-date) mapping material.
Nature in the Netherlands is threatened by fragmentation, desiccation, acidification and disturbance. Nature management is therefore desirable to safeguard the natural richness for the future. An important question is where and how abundant plant species occur in a particular area. We also need to know how species will respond to changes in their environment – for example, higher air temperature resulting from climate change, or a dryer soil caused by groundwater extraction.
The PROBE model has been developed to answer these questions. PROBE predicts the type of vegetation that is present in an area, given a certain combination of soil and vegetation characteristics. One of the challenges to the successful use of PROBE is the acquisition of precise input data. Roelofsen studied whether these input data can be derived from advanced aerial photographs taken from a satellite or aircraft, that is, from remote sensing data.
East Ameland and North Brabant were among the areas in which Roelofsen conducted his field work. He collected natural vegetation samples in several areas, and the samples were then analysed in the laboratory. He derived different types of PROBE input data from RS data, and had varying degrees of success. But his research did show that the use of satellite and aircraft data has an important advantage, namely, an entire nature area can be characterised simply, inexpensively and quickly. This is a big advantage compared to labour-intensive field work and the use of (out-of-date) mapping material.
The research represents a step toward the operationalization of PROBE. In the future, this will enable the pre-testing of the impact of nature management measures, and predictions as to how nature in the Netherlands will respond to climate change. The research is therefore of significance for nature managers, water companies and other policy-makers, among others. In light of the rapid technical development of drones, Roelofsen anticipates that these machines will soon be able to replicate the results of his work. This will make the mapping of the condition of nature easier and more readily accessible.
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