Detection of Terrain Morphologic Features Using GPS, TLS, and Land Surveys: "Tana della Volpe" Blind Valley Case Study

Abstract

The aim of this article is to review the potentiality and reliability of the integrated usage of GPS, Terrestrial Laser Scanner (TLS), and Total Station Survey (TSS) measurements in the geomorphologic studies. Test surveys based on these techniques were done in the area of "Tana della Volpe" blind valley and the adjacent "Monticino" quarry, near Brisighella, Ravenna, Northern Apennines, Italy. Such sites are characterised by peculiar geomorphologic attributes such as the presence of slope, karst and anthropic forms. We surveyed about 18,000 GPS points and about 42,200,000 TLS points in a total of 22 scans. The processing of the survey's whole data set produced three distinct arrays of three-dimensional (3-D) coordinates complemented by orthometric heights. Moreover, an integrated multi-step procedure was implemented based on the following premises: 1) the removal of points not referred to the bare earth surface 2) the combination of three coordinate sets into a single one referred to the whole study; 3) the generation of a bare earth digital model; 4) the elaboration of a unified contour map. The resulting high correspondence between the observed forms and the 3-D models was used to realise a detailed thematic geomorphologic map by means of which it is now possible to locate and highlight the forms observed in the field. In particular by means of TLS measurements we found a maximum difference in the spatial attitude of the observed discontinuities of 5.6° and some interesting coincidences in the evaluation of the joint roughness of several centimeters.