MULTI-TEMPORAL AND MULTI-SENSOR GLACIER MONITORING

Glaciers are subject to drastic mass loss in the last decades and their importance as an environmental and hydrological resource requires regular monitoring. Geomatics techniques are the ideal tool to survey these complex and remote areas, with different remote sensing platforms and sensors to choose from depending on the scale and accuracy to be monitored. In this case study, the Broulè glacier (Valpelline, Aosta Valley, Italy) was monitored for several years using a DJI Phantom 4 RTK UAV, an airborne PhaseOne camera, and a very high-resolution images Pléiades satellite stereo pair to estimate the glacier's melting and to investigate the possibility of carrying out monitoring campaigns limiting in-situ surveys. A comparison of the 3D models and cartographic products obtained from the different sensors made it possible to estimate the accuracies achievable and check them on rocky areas around the glacier considered to be invariant over time. Although the orography of the area and the poor accessibility did not allow a balanced distribution of Ground Control Points (GCPs) and Check Points (CPs), the RMSE in the photogrammetric models was a few centimetres. An altimetric comparison between the photogrammetric DSMs allowed us to estimate the error at -1.6 m, which is strongly influenced by the altimetry of the terrain. Therefore, although it is impossible to rely solely on satellite imagery for a centimetric survey, it seems possible to continue the multi-temporal monitoring over the years using remote sensing (aerial and satellite) with a previous good cartographic base supported by good field campaigns.