# Past, Present and Future Monitoring at the Vallcebre Landslide (Eastern Pyrenees, Spain)
## 4 Summary and Conclusions
In order to 'automatically' filter some systematic errors, during the monitoring operation (acquisition and data handling) it is convenient to be very'systematic' (to follow exactly the same field and processing procedures). Contrary to structural monitoring, when working with natural materials like soils and rock, we have to accept natural variability. To address this variability, it is better to apply continuous techniques, both in the time and spatial domains, i.e., the two axes presented in Figure 28. It must be highlighted that the tentative classification of the different techniques in the figure (time frequency/spatial resolution) corresponds to the Valleebre landslide implementation as reflected in this paper; other setups could be adopted at Valleebre and other sites. The actual installation depends not only on the site, but also on the level of risk and the available budget. The systems that were operated continuously relies on automatic acquisition. We learned that 'automatic' does not means 'free of maintenance'. On the contrary, the continuous systems need continuous surveillance and maintenance [2]. Another recommendation for long-term monitoring networks is that, when feasible, it is better to avoid points or benchmarks that may exhibit their own movements (large boulders, light poles, trees, concrete pillars, old stone walls and so on). The discreet marking of points diminishes natural disturbance and vandalism. Finally yet importantly, it is mandatory to include within the network several fixed points in stable areas around the landslide for verification purposes. Over the years, some improvements in the electrical supply (solar panels) and data transmission (remote download) have been introduced in the Valleebre setup. Currently, wire extensometer and the piezometer readings can be downloaded from a remote location by means of the mobile phone network. All the works described in this paper are capable of qualifying the Valleebre landslide as a real-scale \"in situ\" lab or observatory. The relatively slow rate of motion and the sustained long-term mobility make it suitable for the testing and validation of several new systems within the frameworks of European and National Projects. In the near future, we plan to install an experimental array of distributed fiber optics [27] in order to assess its field performance. The projected array includes around 600 m of FO buried in a trench besides a country road, roughly along the 1000 m contour line shown in Figure 27. This area is subjected to shear displacements produced by the landslide lateral limits and the transition from the middle to the lower unit. The wire extensometer and the GPS control points present in the zone will permit the cross-calibration of the FO array results and performance. Basic research on the performance of the different instruments and methods that have been applied in the Valleebre landslide should help to choose a monitoring strategy in new sites. In making such choices, we must bear in mind that the monitoring must address some fundamental geotechnical questions [28; 29]. Instruments and methods that help to answer these questions should be selected. As [PERSON] stated, \"If there is no question, there should be no instrumentation\". Geological investigation and methodology, J.A.G., J.M. and J.C.; Radar monitoring concept and processing, M.C. and O.M. ; data analysis and validation, J.A.G. and J.M. ; supervision and search for funding, J.C. and J.M. ; writing, J.A.G. All authors have read and agreed to the published version of the manuscript. The three decades work summarized here has been funded mainly by EC and Spanish Research Projects.