## 1 Introduction  
The purpose of local monitoring is to closely model displacements, evolution and deformations of civil engineering structures and local natural phenomena, such as landslides; in this paper, we will focus on landslides, but the proposed methodology and results can be extended to many other applications of local monitoring. A landslide is a serious geologic hazard defined as the movement of a mass of rock, debris, or earth down a slope [1]. In Italy, landslides kill or injure people almost every year. A recently published Italian catalogue covers a 68-years window, from 1941 to 2010, and lists 3139 landslide events that have resulted in deaths, missing persons, and injured people [2]. Globally, these geologic hazards are causing destructions that can be estimated to billions of dollars every year. Due to this, and because of the high number of human casualties, an accurate and continuous monitoring of areas prone to landslides is desired. Landslides monitoring is a multi-disciplinary approach which leads to the estimation of the slope movement and the design and planning of safety measures. Landslides can move slowly (millimeter or centimeter per year) over an extended period of time. Then, for various reasons, they can disastrously accelerate and collapse. Their monitoring must allow an accurate modeling of the phenomenon both in space and in time; moreover the latency of the results should be as small as possible. In the past, landslides were monitored only by geotechnical instruments such as accelerometers and displacement transducers. In the last fifty years, techniques that integrated geodetic and geotechnical measurements have been developed and extensively applied, with satisfactory results: more details are given in [3; 4]. One of the best examples is the case of Meirato landslide (Italy), where total stations, together with other geodetic instruments, were used with success [5]. Moreover, in the last twenty years, a new technique emerged as an alternative to traditional approaches: landslides monitoring by Global Navigation Satellite System (GNSS) technology [6; 7]. Typically, the relative static processing is applied. It exploits data from (at least) two GNSS receivers, simultaneously tracking the same satellites. One receiver is the reference station, the other is called the rover. By double differencing the carrier phase observations, the baseline between the reference and the rover is estimated. In local monitoring, one or more reference receivers are installed in stable locations outside the landslide and several rovers, whose positions are estimated and monitored in time, are installed on the landslide. An early study on this technique was conducted in 2000 by Gili et al. [8]. Their research was focused on the landslide of Vallcebre (Spain) and they compared the results of single frequency GNSS receivers with the results from photogrammetry and geodetic measurements. It was found out that the precision of GNSS is anywhere between 12 and 16 mm in the horizontal plane and 18-24 mm in elevation. With the availability of dual frequency receivers, the results improved and horizontal precisions better than 1 cm were constantly observed [9; 10; 11]. In [12; 13], a procedure to process regional permanent networks is described, implemented, and tested. The procedure allows to completely automate all the process: the quality check of the data, their processing and the network adjustment, the quality check of the results and the analysis of the time series of the estimated coordinates. Such an approach, clearly adapted to the specific application, can be set up also for local permanent networks and can provide an automated monitoring of the displacements in quasi-real-time, for example, by hourly sessions.