CONTRIBUTION OF MULTITEMPORAL SPOT DATA TO THE MAPPING OF A SOIL-EROSION INDEX - THE CASE OF THE LOAMY PLATEAUS OF NORTHERN FRANCE

Loamy soils of the northern European loess belt commonly are exposed t o erosion caused by concentrated runoff. Such runoff generates mud flo ws that, when strong, may create major problems because of the damage they cause to infrastructure. Using multi-temporal SPOT data and GIS t echnologies, a method is proposed and tested for mapping surfaces affe cted by runoff, as well as for evaluating the effectiveness of such re motely sensed index to infer erosion. This work is part of a major res earch effort, jointly undertaken by BRGM and INRA, which develops a pr edictive approach for monitoring erosion at a regional scale. Results have shown that the method for estimating surfaces affected by runoff, is quite reliable for areas underlain by loamy soil. However, the cor relation between such surfaces and effective erosion, i.e. soil loss q uantitative measurements, remains low, even though it confirms the pos sibility of using satellite data rather than other sources of informat ion. It became clear that the conditions of low erodibility during the period of our study were a handicap for this type of validation; anot her problem is caused by the choice of the optimum observation period, which can vary as a result of winter rainfall events.