## 7 Conclusions  
The aim of this work was to verify the efficacy and sensitivity of the DIC technique for landslide displacement measurements. For that purpose, the kinematic behavior of the 3 December 2013 Montescaglioso landslide was investigated, using different remotely sensed imagery and different data processing software.  
The measured displacement values, achieved with all the available processed datasets (e.g., LANDSAT 8 OLI-TIRS, high-resolution airborne optical ortho-photos, DTMs and COSMO-SkyMed SAR imagery), range between a few meters (2-3 m) in the NW sector of the landslide body and up to 20-21 m in its central portion, consistent with the results attained by other authors, both in terms of displacement magnitude and direction [38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76].  
A detailed study in areas not involved in the landslide movement was performed to estimate the environmental-instrumental background noise in terms of pixel and meters values, and comparisons of the results obtained from the different datasets and software were performed.  
The maximum achieved accuracy values for the pixels and displacements are on the order of 0.1 pixels and 0.1 m, respectively. The different datasets show different sub-pixel accuracies (8/10 of a pixel referred to the DTM results, 1/10 of a pixel for the ortho-photos and between 1/10 and 2/10 of a pixel for the CSK absolute and temporal amplitude SAR imagery), as well as different reliability windows, thereby demonstrating the importance of the dataset characteristics on the final results of the analyses.  
Specifically, the LANDSAT 8 OLI-TIRS results indicate that the radiometric and geometric resolutions of the images have different impacts. The LANDSAT 8 OLI-TIRS images are characterized by one of the best sub-pixel accuracies (1/10 of a pixel) because of their high radiometric accuracy; however, because of the low nominal geometric resolution (i.e., 15 m), the achieved background noise value is on the order of 1.4 m.  
The Montescaglioso landslide is a case in which the availability of different datasets and the irregular patterns of ground deformation have provided ideal conditions for successfully testing the sub-pixel image correlation technique and demonstrating the potential use of this technique as an investigation/monitoring tool for landslides.  
The results achieved shed light on the potential of the herein proposed DIC approach for landslide monitoring, because of its capabilities to be applied at different spatial and temporal scale, to a variety of landslides. Furthermore, the rapidly increasing geometric, radiometric and temporal resolution of optical sensors could reduce most of the present limitations of such a methodology (e.g., limited displacement accuracy and low data sampling rate), especially if combined with the growing data processing capabilities of high performance computing.  
Conceptualization, P.C. and P.M.; methodology, P.C. and P.M.; validation, P.C. and P.M.; formal analysis, P.C.; investigation, P.C.; data curation, P.C., P.M and F.B.; writing-original draft preparation, P.C.; writing-review and editing, P.C., P.M. and F.B.; visualization, P.C., P.M.; supervision, P.M. and F.B.  
The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.  
The authors would like to thank the Italian Space Agency (ASI) for providing the COSMO-SkyMed SAR images, and local authorities for the DTMs and aerial optical orthophotos used in this study.  
The authors declare no conflict of interest.