SHADED-RELIEFS MATCHING AS AN EFFICIENT TECHNIQUE FOR 3D GEOREFERENCING OF HISTORICAL DIGITAL ELEVATION MODELS

Traditional methods using aerial photographs for shoreline measurement often involved non-stereo photography with no vertical information. However, digital elevation models (coastal elevation models or CEMs in our case) are widely used in GIS to predict the impact of coastal flooding and Sea Level Rise. Hence, we propose the CEM methodology to cope with computing shoreline position as the interface between the land and the water at a previously chosen vertical datum. Furthermore, CEM evolution during the studied period may be used to quantify the coastal landscape changes. In any case an accurate CEM is needed, both for newly-made CEMs and for historical CEMs mostly compiled from historical photogrammetric flights. A new approach to historical CEM 3D geo-referencing is proposed along this work to avoid the costly and time-consuming necessity of ground control points. The proposed methodology was tested for geo-referencing a historical grid format CEM, comprising a little coastal area of Almeria (South Spain), obtained by digital stereo-photogrammetry from a B&W photogrammetric flight taken in 1977 at an approximated scale of 1:18000. The reference CEM was the 10 m grid-spacing digital elevation model produced by the Andalusia Regional Government (Spain) coming from a 1: 20000 scale W&B photogrammetric flight made in 2001. The results obtained from this work may be deemed as very promising, showing a high efficiency for historical CEM 3D geo-referencing when it was compared to traditional methods such as photogrammetric absolute orientation based on surveyed ground control points and self-calibrating bundle adjustment techniques. This preliminary approach could be used as a previous course matching to be subsequently refined by 3D robust surface matching.