Surveillance of landslide risk areas with ground-based interferometric SAR for Civil Protection in Emilia Romagna (Italy).

Following a 2009-2010 winter season characterized by rainfall rates exceeding 30 years averages, the Agency for Civil Protection of Emilia Romagna Region (Italy) decided to intensify surveillance of several landslide risk areas after the recommendation of the Risk Committee. Among other measures, a GB-InSAR application campaign was kicked off on several slopes hosting buildings, roads and lifeline, that had experienced landslide reactivation in the past years or during the season. Owing to a close collaboration between Universities and operative offices of Emilia Romagna Region, seven slopes were monitored for 8 to 15 days each from March to May 2010. Despite the dense vegetation cover and the low displacement rate which characterize these landslides, GB-InSAR surveying allowed to recognize the general displacement field of the slopes and to identify areas with higher displacement rate. In most sites movements were practically null, proving the substantial dormancy of the monitored phenomena. However, in some test sites velocity reached up to some ten mm/day, such as for instance in the Renzuno landslide and in the Romanoro-Cerreto landslide, that are the examples brought in this paper. Maximum cumulated LoS displacement was about 150 mm in 15 days in Renzuno and about 26 mm in 7 days in Romanoro-Cerreto. In both cases, the spatial distribution of active zones proved to be consistent with field evidences, while velocity changes were quite directly correlated with rainfall pattern during the survey period. The experience was also successful on developing a suitable strategy for data processing, based on temporal under sapling of SAR acquisitions, that is able to minimize the noise generated by low-quality signal in vegetated areas, thus enhancing the confidence on quantitative estimates of displacement rates.