Damien Closson

Space-borne radar interferometric mapping of precursory deformations of a dyke collapse, Dead Sea area, Jordan

Satellite radar interferometry provides a technique to monitor a zone involving active salt tectonic phenomena. We detected movements in the Dead Sea area between 1993 and 1999. These preceded the catastrophic collapse (22 March 2000) of a newly built 12 km dyke belonging to the industrial salt evaporation ponds of the Arab Potash Company. Eighteen other dykes are present and still operational in this area of complex seismotectonic and hydrogeological settings. We used differential Synthetic Aperture Radar (SAR) interferometry (DInSAR) to investigate precursory deformations. Analysis of data shows that the collapsed area and its surroundings were in active subsidence at least 7 years before the event (maximum 44 mm in slant range from 16 December 1995 to 11 October 1997). This case emphasizes DInSAR as a tool suitable to identify deformations in such sensitive areas. It should be used at the stage of pre-feasibility studies of major projects and later in their stability monitoring, when required conditions of application are met.

Anticipating and managing engineering problems in the complex karst environment

Karst environments are characterized by distinctive landforms and a peculiar hydrologic behavior dominated by subsurface drainage. Karst systems can be extremely complex, heterogeneous, and unpredictable due to the wide range of geological and hydrological controlling factors. The great variability results in serious problems for engineers, and in difficulties to characterize the karstified rock masses, and in designing the engineering works to be performed. The design and development of engineering projects in karst environments require specific approaches aimed at minimizing the detrimental effects of hazardous processes and environmental problems. Further, karst aquifers (that provide approximately 20–25 % of the world’s drinking water) are extremely vulnerable to pollution, due to the direct connection between the surface and the subsurface drainage, the rapidity of the water flow in conduit networks, and the very low depuration capability. Sinkholes are the main source of engineering problems in karst environments, and may cause severe damage in any human structure. The strategies and solutions that may be applied to mitigate sinkhole problems are highly variable and largely depend on the kind of engineering structure, the karst setting, and the typology and size of the sinkholes. A sound geological model, properly considering the peculiarities of karst and its interactions with the human environment, is essential for the design of cost-effective and successful risk reduction programs. Due to the unique direct interaction between surface and subsurface environments, and the frequent ground instability problems related to underground karstification, management of karst environments is a very delicate matter. Disregarding such circumstances in land-use planning and development inevitably results in severe problems with high economic impacts. Karst environments require specific investigation methods in order to properly manage and safeguard the sensitive geo-ecosystems and natural resources associated with them.

Robust Techniques for Coherent Change Detection Using Cosmo-Skymed SAR Images

The satellite-borne SAR (Synthetic Aperture Radar) is a quite promising tool for high-resolution geo-surface measurement. Recently, there has been a great interest in Coherent Change Detection (CCD), where the coherence between two SAR images is evaluated and analyzed to detect surface changes. The sample coherence threshold may be used to distinguish between the changed and unchanged regions in the scene. Using COSMO-SkyMed (CSK) images, we show that for changed areas, the coherence is low but not completely lost. This situation, which is caused by the presence of bias in the coherence estimate, considerably degrades the performance of the sample threshold method. To overcome this problem, robust detection in inhomogeneous data must be considered. In this work, we propose the application and improvement of three techniques: Mean Level Detector (MLD), Ordered Statistic (OS) and Censored Mean Level Detector (CMLD), all applied to coherence in order to detect surface changes. The probabilities of detection and false alarm are estimated experimentally using high-resolution CSK images. We show that the proposed method, CMLD with incorporation of guard cells (GC) in the range direction, is robust and allows for nearly 4% higher detection probability in case of low false alarm probability.

Facing Engineering Problems in the Fragile Karst Environment

This contribution, as an introduction to the main topic of the session “Engineering problems in karst”, aims at providing some guidelines about how to deal with engineering problems in karst environments: these include, but are not limited to, pollution, different types of geological hazards (sinkholes and subsidence, flash floods, etc.), and the related geotechnical constraints. Eventually, the assessment of human impacts on karst landscapes, with specific regard to the disturbance induced by man’s activities, is discussed, pointing out to the problems in managing water resources in karst, and providing some guidelines for possible developments in this fragile environment.

Detecting potential human activities using coherent change detection

This paper describes detection and interpretation of temporal changes in an area of interest using coherent change detection in repeat-pass Synthetic Aperture Radar imagery, with the main goal of detecting subtle scene changes such as potential human activities. Possibilities of introducing knowledge sources in order to improve the final result are also presented.

InSAR Phase Filtering via Joint Subspace Projection Method: Application in Change Detection

A new approach is presented to estimate the synthetic aperture radar (SAR) interferometric phase via the joint subspace projection. In this letter, a new formulation is proposed to transform the cost function minimization problem into the problem of finding the roots of a second-order polynomial whose coefficients are evaluated via the joint noise subspace. The proposed method enjoys a substantially reduced computational complexity and improves the estimation of the interferometric phase. Results obtained using real SAR data show the effectiveness of the proposed method. In the change detection application, the method offers much better separation between the changed and unchanged coherence pixels than existing filters.

Improving Ccd Performance by the Use of Local Fringe Frequencies

Coherent Change Detection (CCD) using multi-temporal Synthetic Aperture Radar (SAR) is one of the most important applications of remote sensing technology. With the advent of high- resolution SAR images, CCD has received a lot of attention. In CCD, the interferometric coherence between two SAR images is evaluated and analyzed to detect surface changes. Unfortunately, the sample coherence estimator is biased, especially for low-coherence values. The consequence of this bias is the apparition of highly coherent pixels inside the changed area. Within this context, the detection performance will considerably degrade, particularly when using high resolution SAR data. In this paper, we propose a new CCD method based on cleaning of coherence inside changed areas, which is characterized by high Local Fringe Frequencies (LFF) values, followed by a space-averaged coherence method. According to the proposed method, the results obtained with Cosmo-SkyMed (CSK) SAR data show an enhancement of change detection performance of about 6% while preserving subtle changes.

Earthen Dike Leakage at the Dead Sea

The Dead Sea is a terminal lake located in the biggest pull-apart basins punctuating the Jordan-Dead Sea Transform. It is the lowest place on Earth (428 m bsl, 2014). The coastal areas are crossed by complex faulted zones and are characterized by highly karstic and fractured rock formations genetically connected with faults. Climate conditions range from semi-arid to arid. The potential evaporation rate is about 2500 mm/year. The riparian states withdraw large percentages of their fresh water from the Jordan River, the main tributary of the Dead Sea. A downward trajectory of the lake level was first noticed in the 1960s. Then, it has been dropping at an increasing rate: from about 60 cm/year in the 1970s up to 1.5 m/year in the 2010s. The magnitude of the shoreline withdrawal can reach several kilometers. Most of the new empty spaces have been progressively used by two mineral companies to build up salt evaporation ponds. From the early 1980s, sinkholes, subsidence and later landslides have appeared at an increasing rate all along the coast. In the 1990s, ground collapses started impeding the industrial development of the Arab Potash Company. Since then, security engineers are fighting bitterly against the multi-facetted salt karst issues to preserve their dikes. Here, sinkholes and subsidence leading to dikes leakage have a significant economic impact. The degradation of the Dead Sea coast is worsening and an early warning system to help avoiding further losses as much as possible should be set up rapidly.

Salt Tectonics of the Lisan Diapir Revealed by Synthetic Aperture Radar Images

1.1 General setting In the Oligocene, the Africa-Arabia plate broke up separating Arabia and Sinai as individual plate and sub-plate. Since then, the Arabian plate moves northward along the Jordan Dead Sea Transform (JDST) fault more rapidly than the Sinai sub-plate. This left-lateral strike slip movement (Figure 1) had displaced Early Miocene dykes across the fault zone up to 100 km (Quennell, 1958; Freund et al., 1970; Garfunkel et al., 1981) and had resulted in the development of rhomb-shaped grabens such as the Dead Sea pull-apart basin along the main fault (Figure 1, inset). The Dead Sea Basin is the largest pull-apart along the JDST fault. It is about 150 km x 15 km. Repeated structural subsidence resulted in the accumulation of sedimentary rocks as much as 10 km thick (Garfunkel and Ben Avraham, 1996). Inside the basin, two sets of faults, both oriented roughly N-S, can be recognized (Figure 1, inset). The first set is the extension of the northern and southern segments of the JDST fault, forming the pull-apart basin (Ben Avraham, 1997; Garfunkel, 1997). These faults are accommodating most of the horizontal motion of the JDST fault. The second set is constituted by the transverse faults, oriented NNW-SSE, that cross obliquely the basin at interval of 20-30 km. Between these faults, the basin infill is slightly back-tilted toward the south with no large deformations (Gardosh et al., 1997; Ben Avraham, 1997; Al Zoubi and ten Brink, 2001). Strong deformations are known only near the diapirs formed by the salt of the Sedom Formation (2 km thick). The Sedom formation formed from the late Miocene to the Pliocene (5.3 2.5 Ma). It is composed of 75% rocksalt which arrived via marine ingression from the Mediterranean and Red Seas. This flooding has ceased, however, with a rise of intrusive rock in the Araba and Jezreel valleys (Figure 1). The rocksalt is interbeded with anhydrite and gypsum, reddish dolomite, silt, sand and clay. Since the early Miocene, the center of sedimentary deposition existed where the Lisan area (Figure 1, inset) is currently located. During the Pliocene excessive accumulation of sediment caused a diapiric upward movement of accumulated lower-density sediment to begin, thus forming several salt

Estimation of crop extent using multi-temporal PALSAR data

The aim of the approach proposed in this paper is to determine a potential crop extent prior to the crop season, by determining regions that might change in time vs. those that surely do not change. We use multi-annual PALSAR-1 data since in dry conditions, L-band HH/HV data have a potential of distinguishing between bare soil and other classes. In addition, a more accurate map can be reached with multi-temporal data than using a single date. We work on HH and HV data sets separately and analyze the two outputs using ground-truth information. In a final phase, we combine these two outputs and compare the result with the ground-truth too, to test the usefulness of fusing the HH/HV information. This approach is the first step in our three-step procedure for estimation of cultivated area in small plot agriculture in Malawi. Validation results show that the proposed approach is promising.