# Review of Satellite Interferometry for Landslide Detection in Italy
## 1 Introduction
This product is extremely useful for landslide studies, since it grants millimeter accuracy and medium-to-high temporal and spatial resolution [12]. For a technical description of InSAR methodologies, we refer to [9; 13; 14]. In this document, we use \"InSAR\" to refer to every type of interferometric technique (whether it is Differential or Advanced). Some authors have already set up the scene for the application of remote sensing data for landslide studies. [PERSON] et al. [15], [PERSON] et al. [16], [PERSON] et al. [17], and [PERSON] et al. [18] are all valuable examples of review papers describing the exploitation of remote sensing data in landslide best practices. [PERSON] and [PERSON] [19] proposed a comprehensive work on the use of interferometric products for landslide studies, highlighting the advantages and limitations of the technique. InSAR has some widely recognized limiting factors such as (i) geometrical effects, (ii) snow cover, (iii) phase aliasing, and (iv) the presence of vegetation or variable land cover. Despite its drawbacks, the interferometric approach has some clear advantages: (i) great cost/benefit ratio, (ii) a wide area coverage combined with millimeter accuracy, (ii) temporal repetitiveness (up to 6 days with Sentinel-1 images), (iii) all-weather and day/night acquisitions, (iv) data coverage in inaccessible areas, and (v) the possibility of back analyzing phenomena from 1992 (the first year of acquisition of the C-band satellite ERS 1). All these characteristics led to a wide exploitation of interferometric products over the last 10 years. The diffusion of InSAR products was certainly eased by the recent launch of the Sentinel-1 constellation, which granted free access to radar images with a regular acquisition plan entirely dedicated to scientific purposes [20]. This review is neither focused on technical aspects, nor on a general presentation of the InSAR advantages and limitations. This paper is aimed to illustrate the role of satellite interferometry for landslide monitoring and mapping in Italy, highlighting current applications and future perspectives. Italy was chosen for several reasons: (i) it is one of the most landslide-prone countries in Europe [21];(ii) the country registers relevant human and economic losses related to landslide events every year [22]; (iii) as a consequence of the previous points, the request for landslide monitoring and mapping tools is very high (including InSAR data) [17]; (iv) Italy has been the testing ground for several innovative InSAR applications since early 2000; (v) many InSAR providers and InSAR-based research centers are located in Italy, which is the primary target for their research activities; (vi) InSAR is a well-established technique in Italy, being utilized with standardized procedures for many years by both scientists and end users; (vii) three Italian regions are running landslide monitoring services based on InSAR data, and a nationwide ground motion service will be implemented in the future. Therefore, Italy is one of the best sample use cases to illustrate the past and current state of the InSAR technique applied to landslide studies. This review aims to testify where and how InSAR has been profitably used to study landslides in Italy and to propose a temporal overview of InSAR-related studies over the last 20 years. Moreover, the review illustrates the most common InSAR applications for landslide studies with a focus on the evolution of the applications, following the technological advancements of the processing techniques and of the acquisition capabilities of the radar sensors.