Persistent Scatterer Interferometry Data Research Articles

ARTIFICIAL NEURAL NETWORK FOR PREDICTION OF LAND SUBSIDENCE IN MUDSLIDES REGION THROUGH INSAR AND RAIN DATA

Abstract. Mudslides are powerful and fast-moving mass movements that pose significant risks to human lives, infrastructure, and natural environments. They are commonly triggered by intense rainfall and their impact is particularly severe in mountainous regions. Synthetic Aperture Radar (SAR) technology can be used to calculate the subsidence of the territory over time by means of a temporal series of SAR images through the Persistent Scatterer Interferometry (PSI) technique. In some research Interferometric SAR (InSAR PSI) data were used to train Long Short-Term Memory (LSTM) based Artificial Neural Network (ANN) to provide movements forecasting. This paper proposes a new LSTM based ANN to forecast future territory movements considering both the past InSAR PSI data, the rain forecasting of the next acquisition and the past cumulative amount of rain since the movements of mudslides are strictly dependent to the quantity of rainfall accumulated in the terrain. The results of the proposed ANN are shown in terms of Mean Square Error (MSE) and Mean Absolute error (MAE) by comparing them with a LSTM-based ANN trained with only the InSAR PSI data.

Localized Subsidence Zones in Gävle City Detected by Sentinel-1 PSI and Leveling Data

Among different sets of constraints and hazards that have to be considered in the management of cities and land use, land surface subsidence is one of the important issues that can lead to many problems, and its economic consequences cannot be ignored. In this study, the ground surface deformation of Gävle city in Sweden is investigated using the Persistent Scatterer Interferometry (PSI) technique as well as analyzing the historical leveling data. The PSI technique is used to map the location of hazard zones and their ongoing subsidence rate. Two ascending and descending Sentinel-1 datasets, collected between January 2015 and May 2020, covering the Gävle city, were processed and analyzed. In addition, a long record of a leveling dataset, covering the period from 1974 to 2019, was used to detect the rate of subsidence in some locations which were not reported before. Our PSI analysis reveals that the center of Gävle is relatively stable with minor deformation ranged between −2 ± 0.5 mm/yr to +2 ± 0.5 mm/yr in vertical and east–west components. However, the land surface toward the northeast of the city is relatively subsiding with a higher annual rate of up to −6 ± 0.46 mm/yr. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposits map was overlaid with PSI results and it shows the subsidence areas are mostly located in zones where the subsurface layer is marked by artificial fill materials. The knowledge of the spatio-temporal extents of land surface subsidence for undergoing urban areas can help to develop and establish models to mitigate hazards associated with such land settlement.

Monitoring mining-induced subsidence by integrating differential radar interferometry and persistent scatterer techniques

ABSTRACT Surface subsidence is a dominant component of the displacement vector triggered by underground mining. Over the last few decades, Differential Interferometry Synthetic Aperture Radar (DInSAR) has been used to efficiently monitor this phenomenon with great spatial and temporal coverage. More advanced multi-temporal DInSAR (MTInSAR) algorithms have been proposed to overcome some of the limitations of conventional DInSAR. However, advanced MTInSAR approaches are also not perfect in terms of measuring mining subsidence (e.g., temporal decorrelation, ambiguity, nonlinearity). For this reason, we propose a fusion of the Persistent Scatterer Interferometry (PSInSAR) and DInSAR results. By combining these complementary techniques, the atmospheric errors in PSInSAR data are reduced and larger deformation rates could have been detected more accurately (thanks to DInSAR) than by an approach solely based on PS-InSAR. This allows to measure areas with fast-moving subsidence (1 m/year) due to ongoing underground coal exploitation. Data from ascending and descending orbits of Sentinel-1A\\B were used to obtain the vertical deformation component. The resulting integrated vertical deformation map was compared with the results from levelling benchmarks. The Root Mean Square Error (RMSE) calculated based on this comparison was 22 mm. Moreover, the maximal vertical cumulative subsidence detected in the study area was 1.05 m/year.

Analysis of Damage to Buildings in Urban Centers on Unstable Slopes via TerraSAR-X PSI Data: The Case Study of El Papiol Town (Spain)

Persistent Scatterer Interferometry (PSI) data, deriving from the processing of SAR images acquired by high-resolution sensors such as TerraSAR-X, provide accurate measurements of displacements affecting structures (e.g., buildings) and linear infrastructure networks (e.g., roads, bridges, embankments, and pipelines). Such widespread displacements, when available on buildings on unstable slopes, offer new perspectives for their integration in procedures pursuing the analysis and the prediction of the physical vulnerability of exposed buildings. In this letter, both deterministic and probabilistic cause (differential settlements)—effects (damage) relationships are generated by using PSI-derived building settlements and the results of building damage surveys. The procedure is applied to El Papiol town (Spain), whose urban area has been suffering diffuse damage of different severity to buildings and roads due to extremely slow-moving landslide phenomena.

Integration of persistent scatterer interferometry and ground data for landslide monitoring: the Pianello landslide (Bovino, Southern Italy)

We present an example of integration of persistent scatterer interferometry (PSI) and in situ measurements over a landslide in the Bovino hilltop town, in Southern Italy. First, a wide-area analysis of PSI data, derived from legacy ERS and ENVISAT SAR image time series, highlighted the presence of ongoing surface displacements over the known limits of the Pianello landslide, located at the outskirts of the Bovino municipality, in the periods 1995–1999 and 2003–2008, respectively. This prompted local authorities to install borehole inclinometers on suitable locations. Ground data collected by these sensors during the following years were then compared and integrated with more recent PSI data from a series of Sentinel-1 images, acquired from March 2014 to October 2016. The integration allows sketching a consistent qualitative model of the landslide spatial and subsurface structure, leading to a coherent interpretation of remotely sensed and ground measurements. The results were possible thanks to the synergistic operation of local authorities and remote sensing specialists, and could represent an example for best practices in environmental management and protection at the regional scale.

Surface Deformation Monitoring in Coal Mine Area Based on PSI

It is difficult to get robust deformation results using conventional differential interferometric synthetic aperture radar (D-InSAR) method, due to the limitation of the phase measurement error, baseline error, and atmospheric delay in synthetic aperture radar (SAR) interferometry. Persistent scatterer interferometry (PSI) represents a powerful tool to measure mining subsidence, as it offers a synoptic view that can be repeated at different time intervals and at various scales. In many cases, PSI data are integrated with in situ monitoring instrumentation, since the joint use of satellite and ground-based data facilitates the geological interpretation of mining subsidence and allows a better understanding of mining subsidence geometry and kinematics. In this paper, PSI interferometry and conventional ground-based monitoring techniques have been used to characterize and to monitor Ge-Ting mining located in Shandong, China. The PSI technique used in this paper overcomes most of the limitations of conventional interferometric approaches by identifying, within the area of interest, a set of “radar benchmarks” (PS), where very precise displacement measurements can be carried out. More than 78000 PS were identified by processing SAR images acquired from 2004 to 2009 by the ENVISAT. The PSInSAR application at a sub-regional scale detected slow ground deformations ranging from 0 to −58 cm/year and resulting from various processes (swelling/shrinkage of clay soils and water pumping). The results reveal the evolution process of “bowl” in mining subsidence and are helpful to the early warning of the mine disaster.

Monitoring the Impact of Groundwater Pumping on Infrastructure Using Geographic Information System (GIS) and Persistent Scatterer Interferometry (PSI)

Transportation infrastructure is critical for the advancement of society. Bridges are vital for an efficient transportation network. Bridges across the world undergo variable deformation/displacement due to the Earth’s dynamic processes. This displacement is caused by ground motion, which occurs from many natural and anthropogenic events. Events causing deformation include temperature fluctuation, subsidence, landslides, earthquakes, water/sea level variation, subsurface resource extraction, etc. Continual deformation may cause bridge failure, putting civilians at risk, if not managed properly. Monitoring bridge displacement, large and small, provides evidence of the state and health of the bridge. Traditionally, bridge monitoring has been executed through on-site surveys. Although this method of bridge monitoring is systematic and successful, it is not the most efficient and cost-effective. Through technological advances, satellite-based Persistent Scatterer Interferometry (PSI) and Geographic Information Systems (GIS) have provided a system for analyzing ground deformation over time. This method is applied to distinguish bridges that are more at risk than others by generating models that display the displacement at various locations along each bridge. A bridge’s health and its potential risk can be estimated upon analysis of measured displacement rates. In return, this process of monitoring bridges can be done at much faster rates; saving time, money and resources. PSI data covering Oxnard, California, revealed both bridge displacement and regional ground displacement. Although each bridge maintained different patterns of displacement, many of the bridges within the Oxnard area displayed an overall downward movement matching regional subsidence trends observed in the area. Patterns in displacement-time series plots provide evidence for two types of deformation mechanisms. Long-term downward movements correlate with the relatively large regional subsidence observed using PSI in Oxnard. Thermal dilation from seasonal temperature changes may cause short-term variabilities unique to each bridge. Overall, it may be said that linking geologic, weather, and groundwater patterns with bridge displacement has shown promise for monitoring transportation infrastructure and more importantly differentiating between regional subsidence and site-specific displacements.

Monitoring soil creep landsliding in an urban area using persistent scatterer interferometry (El Papiol, Catalonia, Spain)

Soil creep is characterised by slow displacement, with depths of a few meters and loosely defined limits. Buildings and infrastructure located on slopes affected by such landslides may suffer significant damages if their foundations are poorly dimensioned. The presence of soil creep in urban areas makes it necessary to develop landslide activity maps, derive hazard maps, and implement risk management plans. Even though both geological and geomorphological analyses can provide basic information, it is often necessary to use additional techniques to obtain information about ground displacements. This paper proposes a method to derive a soil creep activity map using a multi-approach analysis based on geological, geomorphological, and persistent scatterer interferometry (PSI) data. PSI is a satellite-based technique to estimate land displacement velocity. The work described in this paper was carried out in the town of El Papiol, in the metropolitan area of Barcelona (Spain). This is an urban area that has been heavily affected by soil creep over the past decades. The results achieved show that PSI data substantially improve the information provided by the geological and geomorphological analyses and make it possible to accurately define the landslide area and estimate its activity.

A GIS-Based Procedure for Landslide Intensity Evaluation and Specific risk Analysis Supported by Persistent Scatterers Interferometry (PSI)

The evaluation of landslide specific risk, defined as the expected degree of loss due to landslides, requires the parameterization and the combination of a number of socio-economic and geological factors, which often needs the interaction of different skills and expertise (geologists, engineers, planners, administrators, etc.). The specific risk sub-components, i.e., hazard and vulnerability of elements at risk, can be determined with different levels of detail depending on the available auxiliary data and knowledge of the territory. These risk factors are subject to short-term variations and nowadays turn out to be easily mappable and evaluable through remotely sensed data and GIS (Geographic Information System) tools. In this work, we propose a qualitative approach at municipal scale for producing a “specific risk” map, supported by recent satellite PSI (Persistent Scatterer Interferometry) data derived from SENTINEL-1 C-band images in the spanning time 2014–2017, implemented in a GIS environment. In particular, PSI measurements are useful for the updating of a landslide inventory map of the area of interest and are exploited for the zonation map of the intensity of ground movements, needed for evaluating the vulnerability over the study area. Our procedure is presented throughout the application to the Volterra basin and the output map could be useful to support the local authorities with updated basic information required for environmental knowledge and planning at municipal level. Moreover, the proposed procedure is easily managed and repeatable in other case studies, as well as exploiting different SAR sensors in L- or X-band.

PRELIMINARY INVESTIGATION OF THE LAND SUBSIDENCE PHENOMENA OCCURRING AT THE INDUSTRIAL-COMMERSIAL AREA OF ELEONAS, ATHENS, GREECE

Land subsidence is a common phenomenon occurring in several regions worldwide.The current work focus on the industrial-commersial area of Eleonas, Athens, where vertical displacements were identified by Persistent Scatterer Interferometry (PSI) analysis. The rate of deformation in the study area according to the PSI results, during the period from May 1992 to December 2000, ranged between -1.5 and -10 mm/yr. The evaluation of the geological, geotechnical and hydrogeological conditions of the area combined with the PSI data provided substantial information for the interpretation of the land subsidence phenomenon. Also, the knowledge of the land use distribution and the activities taking place in the area helped the detection of its causal factors.

Mapping groundwater level and aquifer storage variations from InSAR measurements in the Madrid aquifer, Central Spain

Groundwater resources are under stress in many regions of the world and the future water supply for many populations, particularly in the driest places on Earth, is threatened. Future climatic conditions and population growth are expected to intensify the problem. Understanding the factors that control groundwater storage variation is crucial to mitigate its adverse consequences. In this work, we apply satellite-based measurements of ground deformation over the Tertiary detritic aquifer of Madrid (TDAM), Central Spain, to infer the spatio-temporal evolution of water levels and estimate groundwater storage variations. Specifically, we use Persistent Scatterer Interferometry (PSI) data during the period 1992–2010 and piezometric time series on 19 well sites covering the period 1997–2010 to build groundwater level maps and quantify groundwater storage variations. Our results reveal that groundwater storage loss occurred in two different periods, 1992–1999 and 2005–2010 and was mainly concentrated in a region of ∼200km2. The presence of more compressible materials in that region combined with a long continuous water extraction can explain this volumetric deficit. This study illustrates how the combination of PSI and piezometric data can be used to detect small aquifers affected by groundwater storage loss helping to improve their sustainable management.

Land subsidence investigated through Persistent Scatterer Interferometry technique: the case study of Sibari Plain (Italy)

Land subsidence is defined as the lowering of ground surface that can be caused by both natural and anthropogenic factors such as the natural compaction of sediments and the groundwater over-pumping.This work aims at investigating recent subsidence in the Sibari plain located in Calabria Region (Italy) by means of SAR (Synthetic Aperture Radar) Interferometry technique. In particular, PSI (Persistent Scatterer Interferometry) data acquired by different satellite sensors and spanning the period 1992-2011 were exploited for detecting the phenomenon in the area. In this study, implementations of PSI data and the PS-Time software were used respectively to map the spatial distribution of terrain deformation rates and to analyze the temporal evolution patterns of the displacements. The results demonstrated that recent subsiding movements are mostly due to human activities, as they are only recorded in site-specific urban areas. Moreover, the detailed PS Time Series analysis highlighted that, in these areas, subsidence has positively decreased or stabilized from the second semester of the year 2010.

Mapping landslide phenomena in landlocked developing countries by means of satellite remote sensing data: the case of Dilijan (Armenia) area

ABSTRACTLandslide detection and mapping are essential issues for reducing impact of such natural disasters, and for improving the future built-up expansion and planning strategies, especially in developing countries where a reasonable land-use design is an important concern for sustainable growth and environmental management. Armenia is a landlocked country and its urban development is strongly tied to the improvement of infrastructures, which must takes into account the environmental setting and the slope instability of the area, in order to identify risks and possible damages to settlements and economic activities. The use of satellite-based Earth Observation data has advanced significantly in the last decade and has turned out to be very useful for measuring and monitoring slow-moving surface deformation phenomena with millimetric precision. In this framework, this study aims at providing a remote sensing-based Landslide Inventory Map (LIM) and a Landslide Susceptibility Map (LSM) over Dilijan (Armenia) area, performed within the Secondary Cities Urban Development in Armenia project. In particular, LIM and LSM in the study area were produced by using ground deformation measurements derived from satellite Synthetic Aperture Radar (SAR) data, acquired by ALOS and ENVISAT sensors from 2003 up to 2010, and integrated with photo-interpretation of recent optical images and morphological analysis of Digital Elevation Model (DEM). Given the extensive presence of vegetation in the area of interest, satellite SAR images were processed to produce both SqueeSAR™ and Temporary Coherent Scatterers data, which are PSI (Persistent Scatterer Interferometry) data conceived as evolution of PSInSAR™ approach and particularly suited for non-urban and rural areas characterized by low density of coherent terrain benchmarks over time. Landslide mapping produced through this work identifies the most hazardous landslide-affected and landslide-prone areas around Dilijan city, and can be used for further estimating environmental risks for urban infrastructure development in the area.

Investigating uplift in Lesina Marina (Southern Italy) with the aid of persistent scatterer SAR interferometry and in situ measurements

We apply persistent scatterer interferometry (PSI) techniques to synthetic aperture radar (SAR) data from ERS and ENVISAT satellites on the Lesina Marina area, a coastal tourist village in Apulia, Southern Italy, where the excavation of a canal exposed grey micro- and meso-crystalline gypsum which is now showing a high density of cavities and sinkholes due to gravitational collapse processes. We observe PS objects undergoing displacements, along the sensor line of sight, forming the same relatively smooth pattern in all the processed data stacks. Vertical displacement rates, derived through integration of ascending and descending geometries, reach about 4 mm/year on locations adjacent to the canal, gently decreasing towards the western end of the built-up area . High-precision leveling measurements, performed in 1999 and 2010, reveal a substantial agreement with the ENVISAT PSI data, taking into account a small bias due to the choice of the leveling reference point. The dataset, thus validated, suggests the presence of an uplift phenomenon going on steadily for the entire timespan covered by the SAR observations (1992–2009). These observations, supported by petrographic data and in situ investigations, seem only in part compatible with a residual diapirism, and hint instead to more complex processes, such as a combination of diapirism and the hydration of the residual anhydrite in the core of the gypsum mass. These results confirm the importance of the integration between in situ, geologic and geophysical, remotely sensed investigations, as the latter often represent an essential tool to infer whether a given phenomenon, which can be hypothesized by the former, is presently under development.

Exploitation of the full potential of PSI data for subsidence monitoring

Abstract. Persistent Scatterer Interferometry (PSI) is a remote sensing technique used to measure and monitor land deformation from a stack of interferometric SAR images. The main products that can be derived using the PSI technique are the deformation maps and the time series of deformation. In this paper, an approach to apply the PSI technique to a stack of Sentinel-1 images is described. Moreover, the problems encountered during the processing are detailed and an explanation of how they were dealt with is provided. Finally, Sentinel-1 deformation maps and time series obtained over the metropolitan area of Mexico DF are shown.

Building Deformation Assessment by Means of Persistent Scatterer Interferometry Analysis on a Landslide-Affected Area: The Volterra (Italy) Case Study

In recent years, space-borne InSAR (interferometric synthetic aperture radar) techniques have shown their capabilities to provide precise measurements of Earth surface displacements for monitoring natural processes. Landslides threaten human lives and structures, especially in urbanized areas, where the density of elements at risk sensitive to ground movements is high. The methodology described in this paper aims at detecting terrain motions and building deformations at the local scale, by means of satellite radar data combined with in situ validation campaigns. The proposed approach consists of deriving maximum settlement directions of the investigated buildings from displacement data revealed by radar measurements and then in the cross-comparison of these values with background geological data, constructive features and on-field evidence. This validation permits better understanding whether or not the detected movements correspond to visible and effective damages to buildings. The method has been applied to the southwestern sector of Volterra (Tuscany region, Italy), which is a landslide-affected and partially urbanized area, through the use of COSMO-SkyMed satellite images as input data. Moreover, we discuss issues and possible misinterpretations when dealing with PSI (Persistent Scatterer Interferometry) data referring to single manufactures and the consequent difficulty of attributing the motion rate to ground displacements, rather than to structural failures.

A Procedure to Map Subsidence at the Regional Scale Using the Persistent Scatterer Interferometry (PSI) Technique

In this paper, we present a procedure to map subsidence at the regional scale by means of persistent scatterer interferometry (PSI). Subsidence analysis is usually restricted to plain areas and where the presence of this phenomenon is already known. The proposed procedure allows a fast identification of subsidences in large and hilly-mountainous areas. The test area is the Tuscany region, in Central Italy, where several areas are affected by natural and anthropogenic subsidence and where PSI data acquired by the Envisat satellite are available both in ascending and descending orbit. The procedure consists of the definition of the vertical and horizontal components of the deformation measured by satellite at first, then of the calculation of the “real” displacement direction, so that mainly vertical deformations can be individuated and mapped.

Natural and Anthropogenic Geohazards in Greater London Observed from Geological and ERS-1/2 and ENVISAT Persistent Scatterers Ground Motion Data: Results from the EC FP7-SPACE PanGeo Project

We combine geological data and ground motion estimates from satellite ERS-1/2 and ENVISAT persistent scatterer interferometry (PSI) to delineate areas of observed natural and anthropogenic geohazards in the administrative area of Greater London (United Kingdom). This analysis was performed within the framework of the EC FP7-SPACE PanGeo project, and by conforming to the interpretation and geohazard mapping methodology extensively described in the Production Manual (cf. http://www.pangeoproject.eu ). We discuss the results of the generation of the PanGeo digital geohazard mapping product for Greater London, and analyse the potential of PSI, geological data and the PanGeo methodology to identify areas of observed geohazards. Based on the analysis of PSI ground motion data sets for the years 1992–2000 and 2002–2010 and geology field campaigns, we identify 25 geohazard polygons, covering a total of ~650 km2. These include not only natural processes such as compaction of deposits on the River Thames flood plain and slope instability, but also anthropogenic instability due to groundwater management and changes in the Chalk aquifer, recent engineering works such as those for the Jubilee Line Extension project and electricity tunnelling in proximity to the River Thames, and the presence of made ground. In many instances, natural and anthropogenic observed geohazards overlap, therefore indicating interaction of different processes over the same areas. In terms of ground area covered, the dominant geohazard is anthropogenic land subsidence caused by groundwater abstraction for a total of ~300 km2, followed by natural compression of River Thames sediments over ~105 km2. Observed ground motions along the satellite line-of-sight are as high as +29.5 and −25.3 mm/year, and indicate a combination of land surface processes comprising ground subsidence and uplift, as well as downslope movements. Across the areas of observed geohazards, urban land cover types from the Copernicus (formerly GMES) EEA European Urban Atlas, e.g., continuous and discontinuous urban fabric and industrial units, show the highest average velocities away from the satellite sensor, and the smallest standard deviations (~0.7–1.0 mm/year). More rural land cover types such as agricultural, semi-natural and green areas reveal the highest spatial variability (up to ~4.4 mm/year), thus suggesting greater heterogeneity of observed motion rates within these land cover types. Areas of observed motion in the PSI data for which a geological interpretation cannot be found with sufficient degree of certainty are also identified, and their possible causes discussed. Although present in Greater London, some geohazard types such as shrink–swell clays and ground dissolution are not highlighted by the interpretation of PSI annual motion rates. Reasons for absence of evidence of the latter in the PSI data are discussed, together with difficulties related to the identification of good radar scatterers in landsliding areas.

An Approach to Persistent Scatterer Interferometry

This paper describes a new approach to Persistent Scatterer Interferometry (PSI) data processing and analysis, which is implemented in the PSI chain of the Geomatics (PSIG) Division of CTTC. This approach includes three main processing blocks. In the first one, a set of correctly unwrapped and temporally ordered phases are derived, which are computed on Persistent Scatterers (PSs) that cover homogeneously the area of interest. The key element of this block is given by the so-called Cousin PSs (CPSs), which are PSs characterized by a moderate spatial phase variation that ensures a correct phase unwrapping. This block makes use of flexible tools to check the consistency of phase unwrapping and guarantee a uniform CPS coverage. In the second block, the above phases are used to estimate the atmospheric phase screen. The third block is used to derive the PS deformation velocity and time series. Its key tool is a new 2+1D phase unwrapping algorithm. The procedure offers different tools to globally control the quality of the processing steps. The PSIG procedure has been successfully tested over urban, rural and vegetated areas using X-band PSI data. Its performance is illustrated using 28 TerraSAR-X StripMap images over the metropolitan area of Barcelona.

Multi-Temporal Evaluation of Landslide Movements and Impacts on Buildings in San Fratello (Italy) By Means of C-Band and X-Band PSI Data

This work provides a multi-temporal and spatial investigation of landslide effects in the San Fratello area (Messina province within the Sicily region, Italy), by means of C-band and X-band Persistent Scatterer Interferometry (PSI) data, integrated with in situ field checks and a crack pattern survey. The Sicily region is extensively affected by hydrogeological hazards since several landslides regularly involved local areas across time. In particular, intense and catastrophic landslide phenomena have recently occurred in the San Fratello area; the last event took place in February 2010, causing large economic damage. Thus, the need for an accurate ground motions and impacts mapping and monitoring turns out to be significantly effective, in order to better identify active unstable areas and to help proper risk-mitigation measures planning. The combined use of historical and recent C-band satellites and current X-band Synthetic Aperture Radar sensors of a new generation permits spatially and temporally detection of landslide-induced motions on a local scale and to properly provide a complete multi-temporal evaluation of their effects on the area of interest. PSI ground motion rates are cross-compared with local failures and damage of involved buildings, recently recognized by in situ observations. As a result, the analysis of landslide-induced movements over almost 20 years and the validation of radar data with manufactured crack patterns, permits one to finally achieve a complete and reliable assessment in the San Fratello test site.