Patigno landslide monitoring by the integration of multi-temporal observations

The morphological variations of unstable areas can be computed using different methodologies that allow performing repeated surveys over time: aerial digital photogrammetry, aerial and terrestrial laser scanning, Synthetic Aperture Radar (SAR) satellites, terrestrial data, and GNSS observations in addition to the classical topographic applications.

In this work, the displacements of the Patigno landslide, a deep-seated gravitational slope deformation located in the Northern Apennine (Tuscany, Italy), are evaluated using archival aerial photogrammetry, continuous GNSS observations and multi-temporal SAR satellite data. In particular, the aerial photogrammetric surveys carried out in 1975 (scale 1:13000), 1987 (scale 1:13000), 2004 (scale 1:30000), 2010 (scale 1:10000), and 2013 (scale 1:30000) were analysed. These images have been processed using Socet Set software, in order to estimate the movements of several ground points on the study area. After the extraction of the photogrammetric models, the common reference system was verified by measuring checkpoints in the multi-temporal series located outside the deformation area, choosing well defined artificial points (mainly corners of buildings). Starting from the stereoscopic models, 5 automatic DEMs were extracted with 5 m grid step on the area that included the landslide and its surroundings: from the DEMs it was possible to obtain the corresponding orthophotos; thanks to the good visibility over the whole landslide area in the 1975 model, a DTM was obtained adapting the contour level to the real terrain morphology by means of stereoscopic devices. On the photogrammetric models, the approaches based on the measurements of homologous points in the multi-temporal dataset was adopted: 165 natural points were identified and measured in stereoscopy on each model (mainly corners of buildings); from the comparison of the 3D coordinates, displacement vectors in the four periods 1975-1987, 1987-2004, 2004-2010 and 2010-2013 were obtained. Due to the vegetation cover, the points were measured almost exclusively in the built-up areas of the Patigno, Noce and Val di Termine villages and, to a limited extent, on isolated buildings.

The interferometric data acquired by the Sentinel-1A/B satellites from 22-March-2015 to 18-May-2019, and the GNSS data acquired by a continuous station located in the central sector of the landslide (2004/01/01- 2018/12/31) were also analyzed. The GNSS data have been processed with GAMIT/GLOBK and RTKLib software.

The results obtained with the three different techniques will be presented along with the estimation of the spatial and temporal evolution of the landslide movement. The area where the continuous GNSS station is located moves with a velocity of about 3 cm/yr, along the direction of maximum slope, in accordance with the displacement rates measured with the photogrammetric and SAR data analysis.