Satellite Techniques: New Perspectives for the Monitoring of Dams

Transcription

1 Satellite Techniques: New Perspectives for the Monitoring of Dams 190 Marco Corsetti, Michele Manunta, Maria Marsella, Silvia Scifoni, Alberico Sonnessa, and Chandrakanta Ojha Abstract Dam deformation detection, analysis, and monitoring represent a growing issue for a large part of commercial companies and research groups at national and international levels. Although dam failures are usually sudden, in the majority of cases it is possible to predict when structural damage conditions might become serious. Keywords Earth dams Differential interferometric synthetic aperture radar (DInSAR) Monitoring of subsidence Nowadays, the development of innovative methodologies for the static and dynamic structural modeling allows to sharply improve the capability of predicting collapses, thus preventing and reducing the associated risks. With respect to this issue, several geomatics techniques can be profitably exploited for the implementation of analytical and mathematical models, by benefiting from the availability of dense and precise local deformation measurements provided by both satellite and ground sensors with high temporal and spatial coverage. During the last twenty years, the rapid development of space technologies has allowed the detection of ground displacements from satellite observations with high accuracy and wide spatial coverage. Space technologies, thanks to their effectiveness to monitor the whole infrastructure with no need to install localized control points, allow us to integrate and improve the monitoring capabilities provided by ground-based methods. The availability of spatially dense deformation measurements is of crucial importance for M. Corsetti (&) M. Marsella S. Scifoni A. Sonnessa C. Ojha DICEA, Civil Engineering Faculty, Rome, Italy marco.corsetti@uniroma1.it M. Manunta C. Ojha IREA-CNR, Istituto per il Rilevamento Elettromagnetico dell Ambiente (IREA), Consiglio Nazionale delle Ricerche (CNR), Napoli, Italy structural modeling because it allows us to overcome the drawbacks of traditional monitoring systems, which provide high accuracy measurements only on a limited number of points. The aim of this work is to show the results of a case study relevant to the monitoring of a dam. In particular, we show how satellite measurements can be profitably exploited and effectively integrated in order to improve the current monitoring systems and increase the safety of dams. The paper deals with the DInSAR (Differential Interferometric Synthetic Aperture Radar) technique to monitor the behavior of Genzano di Lucania dam. The results of this work are very promising and open new perspectives for static analysis of large dam behaviour as well as of large infrastructures Introduction Reliable methods of design and careful controls, in construction stages, are basic assumptions for civil engineering works. Even more, in case of dams involving high risk for human beings and downstream properties, a constant check during operational stages is of primary relevance to preserve safety. Usually, structural movements are one of the major indicators of dam behaviour and nowadays measures can be obtained with the required frequency by means of electronic G. Lollino et al. (eds.), Engineering Geology for Society and Territory Volume 5, DOI: / _190, Springer International Publishing Switzerland

2 990 M. Corsetti et al. devices. However, due to the dimension of the structure and to adverse environmental conditions, usual equipments are limited to a limited number of points, not always enough for monitoring purpose or modelling aim. New Ground-Based techniques overcomes these drawbacks, allowing a whole and continuous control of structural movement through satellite or terrestrial sensor stations, without any need to access the structure (Di Pasquale et al. 2013; Nico et al. 2013). The SAR interferometry technology will be used to monitor a large earth dam. The structure of the paper is the following. The basic principles of SAR interferometry are presented in Sect The characteristics of dams used in this paper are summarized in Sect The first results obtained by SAR interferometry are presented in Sect Finally, a few conclusions are drawn in Sect SBAS-DInSAR technique and dataset In order to retrieve the deformation measurements, i.e., mean displacement velocitymaps and associated time series, relevant to the Genzano di Lucania dam, weapplied the advanced DInSAR technique referred to as Small BAseline Subset(SBAS) algorithm (Berardino et al. 2002; Bonano et al. 2012; Calò et al. 2014; Lanari et al. 2004). In particular, for our purposes we benefited from themulti-sensor full-resolution SBAS approach (Bonano et al. 2012). Such a technique, by jointlyprocessing data acquired by geometrically compatible SAR sensors, as in the caseof ERS-1/2 and ENVISAT acquisitions, allows us to generate very long deformationtime series, spanning almost 20 years, with an accuracy of about 5 mm (Calò et al. 2014).The key point of the multi-sensor SBAS technique is the selection criteria of thesar data pairs used for generating the interferograms. In order to mitigate thenoise (i.e., the decorrelation phenomena) affecting the interferograms, and tomaximize the reliable measure points, only SAR data pairs characterized by smallspatial and temporal separation (baseline) between the satellite orbits are processed(berardino et al. 2002). Moreover, no cross interferogram between images acquired by differentsar sensors is generated, and only ERS-ERS and ENVISAT-ENVISAT interferometricpairs are selected DInSAR dataset In this work, we applied the multi-sensor SBAS technique to a SAR dataset of77 ERS-1/2 and ENVISAT scenes, acquired from descending orbits between 1992and 2006 over the Murgie area (Southern Italy). The dataset is characterized by aspatial resolution of about 10 m and a revisit time of 35 days. For the SBASDInSARprocessing, 200 ERS/ERS and ENVISAT/ENVISAT interferogramshave been selected and generated, characterized by maximum spatial and temporalbaselines of about 400 m and 1500 days, respectively. In addition, precise satelliteorbital information obtained by the Delft Institute for Earth-oriented Space Research(DEOS), and topographic information retrieved from the Digital ElevationModel (DEM) with a 3-arc-second spacing (approximately 90 m 90 m) producedby the Shuttle Radar Topography Mission (SRTM) in February of 2000have been used for the correct co-registration of the SAR images with respect to acommon grid (Sansosti et al. 2006) and for the interferogram generation Monitored Dam Earth Dam The Genzano dam is situated on the eastern side of the common with the same name, in the upper valley of the Bradano river (Potenza). The reservoir is obtained stopping the waters of the Fiumarella river (an affluent of the Bradano river) with a zoned earth dam with a central vertical core (Figs and 190.2). The dam, built in the period , is still subject to vertical deformation due to the consolidation of a cohesive thick (300 m) foundation layer. Currently the dam is monitored with an array of piezometers, inclinometers and sensors of pressure. Furthermore, he position of a set of marks is measured by topographic techniques Results In this section we present the results provided by the DIn- SAR technique. The results obtained from the SBAS-DIn- SAR analysis have been reported in a GIS environment (Fig ), where it was possible to analyze both the velocity maps of annual average, both the time series concerning the movements observed on the dam of Genzano in The annual average speeds of displacement are available on the crest of dam and on the upstream slope (covered with rip-rap material). On the downstream slope, there are not coherent points, that can be observed with SAR technique. The time series of deformation (Fig ), extended for about 15 years, show some failure in the dam increasing during the time. The maximum speed is on the

3 190 Satellite Techniques: New Perspectives for the Monitoring of Dams 991 Fig The Genzano dam Fig A cross section of earth dam (Ente per lo Sviluppo dell Irrigazione e la Trasformazione Fondiaria in Puglia e Lucania 1985) crest dam, nearly constant and equal to 1.55 cm/year, as a result of the consolidation process following from to the application of the load connected to the construction of the dam. The maximum values of about 25 cm can be found along the crest, the minimum, almost exhausted, at toe of embankment. A comparison of satellite measurements with conventional (assestimetric and geometric leveling measurements) and numerical model (Corsetti et al. 2012), confirm the reliability of the SAR technique (Fig ) Conclusions The basic principles of Synthetic Aperture Radar (SAR) interferometry have presented with emphasis on the application to the measuring of dam displacements. The utilization of SAR data allow us an overview of the structure and the chance to describe the behavior of dam even in previous periods (until 1992) in which the traditional measures of topographic control of movement weren t established yet.

4 992 M. Corsetti et al. Fig ERS-ENVISAT displacement time series References Fig Crest displacements: satellite versus conventional measurements and numerical model The applicability of this method, when it comes to the control of large dams, is subject to the real presence of a number of coherent control points in the area that we want to investigate. In case of territories which doesn t have a certain number of coherent points, because of the presence of vegetation, invaded area or snow cover etc., it is possible to install some artificial reflectors that act like radar targets. Berardino P, Fornaro G, Lanari R, Sansosti E (2002) A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms. IEEE Trans Geosci Remote Sens 40(11): Bonano M, Manunta M, Marsella M, Lanari R (2012) Long term ERS/ ENVISAT deformation time-series generation at full spatial resolution via the extended SBAS technique. Int J Remote Sens 33 (15): doi: / Calò FF, Ardizzone F, Castaldo R, Lollino P, Tizzani P, Guzzetti F, Manunta M (2014) Enhanced landslide investigations through advanced DInSAR techniques: the Ivancich case study, Assisi, Italy. Remote Sens Environ 142: doi: /j.rse Corsetti M, Marsella M, Paoliani P, Bonano M, Manunta M (2012) Monitoraggio di una diga in terra con la tecnica radar satellitare, L ACQUA, p 31 40, ISSN: Di Pasquale A, Corsetti M, Guccione P, Lugli A, Nicoletti M, Nico G, Zonno M (2013) Ground-based radar interferometry as a supporting tool I natural and man-made disasters. In: Proceedings of the 33rd annual EARSeL symposium, Matera, Italy, 3 6 June 2013 Ente per lo Sviluppo dell Irrigazione e la Trasformazione Fondiaria in Puglia e Lucania (1985) Lavori per la costruzione di una diga in terra sulla Fiumarella di Genzano (perizia di variante e suppletiva) sezione tipo al 500, Direzione generale per le dighe e le infrastrutture idriche ed elettriche (M.I.T.), dicembre 1985

5 190 Satellite Techniques: New Perspectives for the Monitoring of Dams 993 Lanari R, Mora O, Manunta M, Mallorqui J, Berardino P, Sansosti E (2004) A small baseline approach for investigating deformations on full resolution differential SAR interferograms. IEEE Trans Geosci Remote Sens 42: Massonnet D, Feigl KL (1998) Radar interferometry and its applications to changes in the Earth s surface. Rev Geophys 36: Nico G, Corsetti M, Di Pasquale A, Donnarumma D, Dotti L. Fiorentino L, Nicoletti M (2013) On the monitoring of dams by means of ground-based radar interferometry. In: Proceedings of the 9th ICOLD European Club Symposium, Venice, Italy, April 2013 Sansosti E, Berardino P, Manunta M, Serafino F, Fornaro G (2006) Geometrical SAR image registration. IEEE Trans Geosci Remote Sens 44(10): doi: /tgrs