Table I. Main characteristics of aerial photos utilised for production of multi-temporal map of landslides in instudy area. Fig. la-d. Multitemporal aerial photos details concerning landslide bodies (Municipality of Vergato, Bologna, Tuscan-Emilian Apennines, Italy; 6=44°17'25’N, w=11°07'16’E): a) 1954; b) 1971; c) 1976; d) 2000. This work examines the instability phenom- ena affecting the slope on the right bank of the Reno River, below the Vergato-Piandisetta road in the vicinity of Ca di Malta and Ca del Bosco (Bologna). This slope is composed of terrains pertaining to the Scaly Clay Complex: their poor mechanical properties make it one of the most unstable geological complexes in the en- tire Apennine territory. ~“ The multi-temporal landslide map was pro- duced by means of careful photo-interpretive examination of all the available aerial photos, Fig. 2. Distribution of old or very old landslide bodies identified in 1954 aerial photos, classifiable as slip and slip-flow, with elements of activity. Fig. 3. Three-dimensional perspective view of southern portion of slope under study, obtained by projecting the 2000 digital orthophoto onto the corresponding 2x2 m DTM (heigh exaltation: 30%). The image represents a vector/raster result which has metric characteristics, coming from photogrammetric restitution. The border of the Ca di Malta landslide is indicated with a yellow line; red lines show local roads. These photos show the Ca del Bosco land- slide reactivated at its top, with the formation of a few slip-flows, the most evident of which is the one formed from the right side of the scarp at 290 m high near a few farm annexes of Ca di Sotto homes. The alimentation area of this land- slide is characterised by a sharp depression, bounded by a main scarp of about 20 m and by a series of secondary scarps and tiers. The de- posit is channelled in the medium-high section of the old 1971 flow, which is topographically depressed and concave, filling it with more than 10 m of sediment (estimated thickness). The Se ses See ESE Pron eae wae saree Mee Lastly, the landslides occurring between 1976 and 2000 were essentially a total or partial reactivations of previous Ca del Bosco and Ca di Table II. Characteristics of available photogrammet- ric surveys and theoretical assessment of level error, as- suming Ope = Standard Deviation (SD) in measurement of horizontal parallax =+10 “4m and, for pre-2000 sur- veys, 0-=SD of focal length of camera =+10 wm. Val- ues expressed in meters. Table IV. Characteristics of images acquired with photogrammetric scanner. Fig. 4. Comparison between the reference DTM (DIGICART 2x2 m) and DTM automatically generated with Helava system; colour classified differences are shown overlapped the shaded relief model. Antonio Zanutta, Paolo Baldi, Gabriele Bitelli, Mauro Cardinali and Alberto Carrara Fig. 5. High differences obtained from 1976 and 1954 surveys. Differences (in meters) superimposed on 1976 ortho-photo are indicated by different colours. Fig. 6. High differences between the 8x8 m DTMs obtained from 2000 and 1976 surveys. Differences (in me- ters) superimposed on 2000 orthophoto are indicated by different colours. Qualitative and quantitative photogrammetric techniques for multi-temporal landslide analysis Fig. 7. Statistic of differences between 2000 and 1976 DTMs. Antonio Zanutta, Paolo Baldi, Gabriele Bitelli, Mauro Cardinali and Alberto Carrara
