Digital aerophotogrammetric techniques applied to research on erosion

Abstract

Aerial photographs are one of the main remote sensing products used to study erosion. However, it is not appropriate to measure linear erosional features directly on photos because of geometric distortions. Thus, this paper presents an example of the use of a more accurate technique, the digital aerophotogrammetry, which was applied to the temporal study (1962 – 2006) of ravines and gullies, in the Querosene River Basin (São Pedro municipality – São Paulo State – Southeastern Brazil). The research was carried out using a photogrammetric station constituted by a notebook, the DVP software and a mirror stereoscope for computers. In order to correct the geometry of the aerial photographs used in this research (1962: 1:25,000; 1978: 1:35,000; 1995: 1:25,000; 2006: 1:30,000), internal parameters of the cameras used in aerial surveys, coordinates from planialtimetric charts (1:10,000 scale), and a digital elevation model developed from these maps were used. The results demonstrated the great potential of digital aerophotogrammetry for the study of erosion, since this technique allows the identification and representation of the principal morphological and erosional features, including small ones, such as grooves and cattle trails. In addition, the measurement of linear erosive features from 1962 to 2006 allowed the understanding of their temporal evolution and the calculation of their growth rate. This method proved to be efficient not only for erosion study, but also for geomorphological mapping.