Tracking landslide evolution over decades: application of aerial digital photogrammetry to the Oudenaarde area (W Belgium)

In order to include some kinematic information within landslide hazard
prediction models, we estimated landslide motion in the medium term (i.e. a few decades) by
comparing precise landslide topography reconstructions at different dates. Precise
multitemporal 3D data of the 13 old deep-seated landslides developed on two hills close to the
town of Oudenaarde (W Belgium) were obtained by digital stereophotogrammetry using
aerial photographs of three different periods (1996, 1973 and 1952). From these data, six
DTMs (3 different dates for each investigated hill) were produced with an overall RMS error
of ~50 cm. The obtained DTMs were subtracted from each other in order to determine the
vertical displacement of each pixel during the considered time interval. Globally, movements
are observed in all the landslides and they generally correspond to a rotational pattern.