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Abstract
The results of two survey methods, geological photointerpretation and historical photogrammetry, are compared in order to evaluate the temporal evolution of a unstable slope located in the Tuscan-Emilian Apennines (Italy). Historical aerial photos of the area, derived from photogrammetric surveys conducted in 1954 (scale 1:60000), in 1971 (scale 1:20000), and in 1976 (scale 1:17000) were available. A photogrammetric flight was further conducted in 2000, at a scale of 1:4400, with a traditional GPS ground survey support. First, the results of photographic analysis with the photointerpretation method are presented: the landslides are described from a geological point of view, showing its temporal evolution. To quantitatively assess the landslide movements, Digital Terrain Models were generated by means of an analytical plotter and a digital photogrammetric workstation, with semi-automatic and automatic procedures. To generate these products, it was necessary to solve problems related to a lack of data concerning the aerial cameras used for the historical flights (internal orientation) and the difficulty identifying control points on the photos in order to define the external orientation. An unconventional photogrammetric methodology, based on identification of homologous points in zones considered outside the landslide area, has been there developed and tested to insert the various surveys into a single reference system.
Highlights
The historical aerial photos are of fundamental importance for qualitative analysis of the territory, but for a quantitative assessment as well
The historical aerial photos are of fundamental importance for qualitative analysis of Mailing address: Dr Antonio Zanutta, Dipartimento di Ingegneria delle Strutture, dei Trasporti, delle Acque, del Rilevamento, del Territorio (DISTART), Università degli Studi di Bologna, Viale Risorgimento 2, 40136
Appropriate comparison of photogrammetric surveys of a zone realised in different years allows identification of geometric changes occurring during the time interval in question
Summary
The territory (traditionally conducted by photointerpretation of stereoscopic models), but for a quantitative assessment as well. Appropriate comparison of photogrammetric surveys of a zone realised in different years allows identification of geometric changes occurring during the time interval in question (differential photogrammetry, Anzidei et al, 2000; Baldi et al, 2002, 2005) This technique has many fields of application: for example, the study of changes in urban areas, farming activities and evolution of coastlines (Dolan et al, 1980; Overton and Fisher, 1996), checking glaciers (Kääb and Funk, 1999) and monitoring unstable slopes (Kääb, 2000). Applicability of the two methods obviously depends on the availability of aerial photos of the territory, covering a sufficiently long time span In this regard, it should be remembered that the first Italian national scale photogrammetric coverage, with classic pseudo-vertical photos (23×23 cm), was conducted in 19541955 by the Istituto Geografico Militare (IGM). A quantitative analysis of the landslide movements was performed comparing multitemporal DTMs produced with an analytical plotter (DIGICART 40, Officine Galileo), and a digital photogrammetric workstation (Helava System)
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