DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE

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1 JOURNAL OF APPLIED ENGINEERING SCIENCES Article Number: 124_VOL. 1(16), issue 1_2013, pp ISSN ISSN-L (Print) / e-issn: DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE SARACIN Aurel, Tehnical University of Civil Engineering Bucharest, Faculty of Geodesy, saracinaurel@yahoo.com A B S T R A C T This article brings to the attention of specialists in terrestrial measurements, using radar interferometry for tracking movements and deformations land and buildings, using systems already on the market surveying instruments. Received: January 20, 2013 Accepted: March 10, 2013 Revised: March 31, 2013 Available online: May 31, 2013 Keywords: sensor module, linear rail, scenario, real-time monitoring INTRODUCTION Increasingly be required to perform fast and accurate measurements, low-cost, sometimes in difficult environmental conditions and terrain. Using electromagnetic waves and processing of data can lead to achieving these desiderata and more, radar interferometry can collect real-time lowest shape changes of monitored object. MATERIALS AND METHODS An ground radar interferometry system (Ground-Based Synthetic Aperture Radar (GB-SAR)) is an active sensor for information acquisition, based on the emission and reflection of microwaves to and from the object being examined (fig.1) [10]. Fig.1. Harmonic waves form There are three techniques [2], according to the figures below (fig. 2-4): Fig.2. Stepped Frequency Continuous Wave (SF-CW)

2 SARACIN A.: DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE Fig.3. Synthetic Aperture Radar Technique (SAR) Fig.4. Technique interferometry (InSAR) Such radar works by transmitting short pulses of electromagnetic energy that will be reflected by the land surface and the object examined: 1. GB-SAR concept 2R t = (1) c Fig.5. Real Aperture Radar (RAR) Fig.6. Synthetic Aperture Radar (SAR)

3 JOURNAL OF APPLIED ENGINEERING SCIENCES Article Number: 124_VOL. 1(16), issue 1_2013, pp ISSN ISSN-L (Print) / e-issn: c τ c R = 2 2 B λ ϕ = (2) 2 L Displacement sensor on a track approximately parallel positioned with the scenario to be monitored and to acquisition some radar images from slightly different angles (fig.7). Fig.7. Principle takeover radar images Interferometry technique is based on measuring the difference in path by comparing components of phase at two radar images, results as master and slave (fig.8) [4]. Fig.8. Referral displacement d λ = Φ 4 π M S (3) Influence of weather conditions and ambiguities: Φ ( ) (4) M S = Φ R + Φ atm + Φ n + Φ noise

4 SARACIN A.: DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE Determining the actual displacement d (fig.9) [1]: d R = d p (5) h Fig.9. Actual displacement GB-InSAR system consists of four main components (fig.10, 11, 12 and 13): - Sensor module that contains the proper radar and antennas. - Alignment of scan, consisting of a 2-3 meters of linear rail and motor used to move parallel the sensor module to the observed scene for getting more radar images of the same scene from slightly different positions, using SAR technique. - Control unit, PC with software to control the radar system. - Power supply, containing two 12 volt car batteries connected in series, and external power supplies for the safety of your PC. Fig.10. All components of GB-InSAR system Fig.11. Sensor module and linear rail Fig.12. PV panel as power supplies Fig.13. Mobile system

5 JOURNAL OF APPLIED ENGINEERING SCIENCES Article Number: 124_VOL. 1(16), issue 1_2013, pp ISSN ISSN-L (Print) / e-issn: In Europe, this technique is developed and promoted by the Politechnic di Milano, "Scuola di Ingegneria dei Sistemi" (IDS) by IBIS systems designed for various types of applications. IBIS technology revolutionizes the traditional approach of measuring the movement and deformation of land and structures, both in the slow movement (static) and vibration measurements (dynamic). Among its innovative features include: remote monitoring of movements in very inaccessible areas to investigate scenario at a distance of up to 4 km; monitoring some areas of 1-2 km square order while other sensors measure the displacement of selected points at a time, IBIS measures the simultaneous movement of the whole scenario, in real time; sub-millimeter accuracy of measurement: 1/10 mm, in normal circumstances, up to 1/100 mm in special situations; operation at any time, in any weather conditions: day, night, fog and rain; autonomous operation: the system can work continuous monitoring or running without human intervention. Real-time feedback for movement allows its use as early warning risk; dynamic measurement: IBIS allows continuous monitoring of slow movements and deformations, but can also measure the vibrations of structures (resonant frequencies, vibration modes), up to 100 Hz. 2. IBIS terrestrial radar system types 2.1. IBIS-M (M-exploitation of surface mine) IBIS-M system was developed for the mining industry, which allows monitoring of slopes in long-term, providing an early warning system of landslides and forecasting future operating. This not only increases the safety of surface mining, but also increases productivity by allowing a better assessment of the volume of ore mined (fig.14) [9]. IBIS-M360 is an integrated monitoring system based on multiple fixed and / or mobile units, controlled by interface using a single advanced software to provide a complete 360 degree coverage of slopes a career in real time, rendering engineers an overview of the entire career pits, providing comprehensive information about potential areas of instability. IBIS-M360 is based to a long-range, high resolution and fast scanning capabilities, was adapted to the specific requirements of the user, therefore, is ideal for all types of operations in open pits (fig.15) [9]. Fig.14. IBIS-M in mining Fig.15. IBIS-M360 system

6 SARACIN A.: DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE 2.2. IBIS-L (L from land) [8] IBIS-L system was designed for monitoring the 2D displacements of the land, such as landslides, slopes, volcanoes and glaciers, and large structures, for example dams. It can cover several square kilometers at a distance until 4 km, without being necessary the access in monitored area without manually installing reflectors. It can operate a continuous monitoring with real-time feedback of displacements or its use as a risk warning device (fig.16) [3], [5] IBIS-S (S for structure) [8] IBIS-S system is designed to monitor displacement and deformation structures such as bridges, towers and buildings in dynamic conditions (measurements of vibration) and static (slow displacement in time) (fig.17) [6]. Fig.16. IBIS-L system Fig.17. IBIS-S system 3. Software required IBIS-M and IBIS-L is provided with Guardian software package that is specifically designed for monitoring. Guardian offers automatic radar data processing in real-time, view maps of displacement with multiple options for analysis (extraction time series for displacement, speed, settlements, etc.), and the ability to create multiple scenarios warning of danger, defining the criteria used for alarm monitoring (fig.18). Fig.18. Guardian software window

7 JOURNAL OF APPLIED ENGINEERING SCIENCES Article Number: 124_VOL. 1(16), issue 1_2013, pp ISSN ISSN-L (Print) / e-issn: Guardian IBIS uses automatic atmospheric correction algorithms to provide accurate and reliable displacement maps that are fully geo-referenced on a digital terrain model. Ability to manage long-term projects with large data sets makes Guardian software to be appropriate for long-term follow movements, geotechnical and geological analysis that can be useful for the authorities in case of landslide risk. IBIS-S system can work with specially developed software IBISDV who process raw files generated during sessions of measurements. The software has a complete set of features for evaluating static and dynamic overall structural movements. Static information that can be obtained is the image in the power spectrum monitored scenario to select the monitored points and displacement time history of investigated points belonging to monitor structures (bridges, dams, landslides, etc.) [7]. Can retrieve and process data together with IBIS-S, data from dynamic sensors installed on the monitored structure to identify the resonance frequencies of the structure. This information may lead to a complete monitoring system of efforts and viability status in a structure (fig.19). Fig.19. Monitoring efforts in a structure RESULTS Advantages over traditional techniques: remote sensor at a distance of 1 km, accuracy of the displacement up to 1/100 mm simultaneous mapping (for hundreds or thousands of points) of real-time deformation, quick installation and operation, static and dynamic monitoring, sampling vibration of structures with frequencies up to 100 Hz, work day and night, in all weather conditions, provide direct displacements, which are not derived from other components of the movements [8]. Monitoring applications:

8 SARACIN A.: DISPLACEMENT AND DEFORMATION MEASUREMENT USING GROUND RADAR INTERFEROMETRY TECHNIQUE Static: structural load tests, structural displacement and danger of collapse, cultural Heritage. Dynamic: measuring the resonance frequency of the structures, modal analysis of structural forms, real-time monitoring of deformation structures. CONCLUSIONS Determining with sub-millimeter accuracy ( mm) of displacements and deformations. Possibility to observe at large distances up to 4 km of the monitored objectivs, considering the rough terrain sometimes or very difficult availability monitored surface structures. The objectiv can be monitored continuously at predetermined intervals both day and night. An important disadvantage is the very large volume of necessary equipment ( kg) and high energy use ( W). It is necessary to realize a stable platform whith concrete fasteners in the same position at each stage of observations, for the systems IBIS-L and IBIS-M. A good georeferencing is very useful when many points are needed to observe with ground radar interferometry systems. REFERENCES 1. ALBA, M., BERNARDINI, G., GIUSSANI, A., RICCI, P. P., RONCORONI F., SCAIONI, M., VALGOI, P.and ZHANG, K., Measurement of dam deformations by terrestrial interferometric techniques. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVII, Part B1, pp BERNARDINI, G., PASQUALE, G. D., GALLINO, N., and GENTILE, C. (2007). Microwave interferometer for ambient vibration measurement on civil engineering structures: 2. Application to fullscale bridges. In Proc. Experimental Vibration Analysis for Civil Engineering Structures (EVACES'07). 3. LUZI, G., MONSERRAT, O., CROSETTO, M., COPONS, R.and ALTIMIR, J., Ground-Based SAR Interferometry applied to landslides monitoring in mountainous areas. Proceedings of the International Conference Mountain Risks, Florence. 4. SIMONS, M. and ROSEN, P., Interferometric Synthetic Aperture Radar Geodesy, Treatise on Geophysics, Schubert, G. (ed.), Volume 3- Geodesy, Elsevier Press, pp , BURGMANN, R.; ROSEN, P. and FIELDING, E., Synthetic Aperture Radar Interferometry to measure Earth's surface topography and its deformation, Ann.~Rev.~Earth Planet.~Sci., 2000, 28, MADSEN, S. N. and ZEBKER, H. A., Synthetic Aperture Radar Interferometry: Principles and Applications, Manual of Remote Sensing, Artech House, 1999, BERARDINO, P., FORNARO, G., LANARI, R. and SANSOSTI, E., (2002) A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms. IEEE Transactions on Geoscience and Remote Sensing 40: *** viewed at 09/01/ *** viewed at 15/12/ *** viewed at 14/12/2012.