Conventional space-borne InSAR for landslide investigations: examples from the northern Apennines (Italy)
Paolo Farina(1) , Alessandro Corsini(2)
, and Florian Marks(1)
University of Firenze,
V. La Pira 4,
(2) University of Modena and Reggio Emilia, Largo S. Eufemia 19, I-41100, Modena, Italy
In the last years space-borne SAR interferometry (InSAR) has been intensely applied for the retrieval of the ground deformation field induced by slope instabilities. The technique, providing an accurate measurement of ground displacements without the necessity of positioning any targets on the ground and without any physical contact with the slope, seems suitable and very appealing for the assessment of the temporal evolution of slow landslides (up to few centimeters per year). Unfortunately, the acquisition parameters of the current satellite SAR missions, in terms of temporal coverage, incidence angle and wavelength employed combined with the great diversity of mass movements often hamper the quality of the InSAR results. In particular, the large variability of landslide types and failure geometries, material involved, land cover, deformation rates and style of activity makes difficult to acquire with continuity reliable ground displacement measurements on active landslides. The paper presents some of the results obtained by the authors in northern Italy within different research projects, aimed at testing the potentiality of application of C-band and L-band space-borne interferometry for landslide investigations. The work shows how some of the InSAR limits can be overcome by processing SAR data acquired in different wavelengths. In fact, the use of L-band SAR data, with a wavelength larger than the C-band one generally considered for ground motion measurements, reduces some of the limitations of differential SAR interferometry, in particular signal decorrelation induced by vegetation cover and “rapid” displacements. SAR data acquired by the C-band ERS1-ERS2 and Envisat satellites over the northern Apennines (Italy) have been interferometrically processed together with L-band J-ERS SAR data and combined with in-situ information to reconstruct the movement pattern during the ‘90s of large slow-moving landslides involving quite large settlements. The selected test-sites, located in the sector of the northern Apennines between the Emilia-Romagna an Liguria regions, are complex phenomena and, in the majority of cases, are associated with multiple rotational or rotational-translational sliding at the head and earth slides or flows in the body of the landslide. They are characterized by displacement rates ranging from few mm/y during dormancy periods, up to few m/y corresponding to periods of intense rainfall. Because during the prolonged dormancy periods their accumulation zones, characterised by a gentle topography, have in many cases been chosen as favourable location for settling villages, these mass movements usually cause severe damage to infrastructures and buildings, influencing the socio-economic conditions of the villages. The obtained results were quite satisfactory, probably thanks to the presence of urban fabric over the monitored landslides which favours the preservation of the interferometric coherence.