PSI Technique Research Articles

Reliability assessment of land subsidence monitoring results using PSI technique in Ho Chi Minh City, Vietnam

ABSTRACT Groundwater exploitation, soft ground, and urban development are the main causes of land subsidence in Vietnam. This study focuses on identifying, zoning, monitoring, and evaluating land subsidence using PSI technique with IBI method applied to Ho Chi Minh City. The results show diverse land subsidence trends from 2014 to 2021 with different levels in varying locations 98,278 km2 had subsided by over 10 cm, 214,593 km2 had subsided by 5 to 10 cm, and 1.377,897 km2 had subsided by less than 5 cm. Notably, certain areas have higher subsidence funnel centres. To ensure accuracy when using PSI techniques, both natural and human-induced factors must be considered during data collection, which influences the actual subsidence rate. Though difficult, this technique provides reliable insights into this complex phenomenon, e.g. in the geodetic precise levelling method to detect millimetre-level deformations in urban areas. The average PS density in urban areas is between 0,5% and 2,5% of the original number of pixels. The positioning accuracy of a PS is within 1 m in all three directions if a large number of SAR scenes are used. Therefore, the results have been documented with 1 mm precision.

Early experience of wafer-free Le Fort I osteotomy with patient-specific implants in cleft lip and palate patients

The use of virtual surgical planning and patient-specific saw and drill guides combined with customized osteosynthesis is becoming a gold standard in orthognathic surgery. The aim of this study is to report preliminary results of the use of virtual surgical planning and the wafer-free PSI technique in cleft patients. Patient-specific saw and drill guides combined with milled patient-specific 3D titanium alloy implants were used in reposition and fixation in Le Fort I osteotomy of 12 cleft patients. Surgical information was retrieved from hospital records. Pre- and post-operative lateral cephalograms were analyzed. In 10 of 12 cases, the implants fitted as planned to predesigned drill holes and bone contours with high precision. In one patient, the mobilization of the maxilla was too demanding for virtually planned advancement, and the implants could not be used. In another patient, PSI fitting was impaired due to an insufficient mobilization of maxilla and tension on PSI fixation with screws. After the surgery, the mean advancement of the anterior maxilla (point A) of all patients was 5.8mm horizontally (range 2.7-10.1) and -3.1mm vertically (range -9.2 to 3.4). Skeletal relationships of the maxilla and mandible could be corrected successfully in all patients except for the one whose PSI could not be used. Virtual surgical planning combined with PSI is a possible useful clinical adjunct for the correction of maxillary hypoplasia in cleft patients. Large maxillary advancements and scarring may be cause problems for desired advancement and for the use of implants.

How feasible is creating a natural disaster information management open-access repository (NDIM-OAR) in Iran?

Although creating sustainable information systems is highly important to facilitate information flow in natural disaster information management (NDIM), only a few LIS studies have focused on evaluating the feasibility of related technological solutions. An open access repository (OAR) for NDIM has been assessed by Technical, Economic, Legal, Operational, Scheduling, Cultural, and Behavioral (TELOS-CB) dimensions, using the PSI technique. Five NDIM stakeholder groups participated including governmental, public, and research institutions, NGOs (non-governmental organizations), and LIS specialists. The results indicate that the NDIM-OAR is technically more feasible, while the cultural dimension has been considered the most challenging. NGOs have the largest scoring range and governmental stakeholders have the most coherent scoring. Despite of the wide range and seemingly excessive sensitivity of NDM information in Iran, more in-depth, interpretive, cross-disciplinary studies are required reaching a comprehensive decision for an NDIM-OAR. The research is among the first multi-disaster, multi-stakeholder feasibility analyses in LIS.

Polarimetric Persistent Scatterer Interferometry for Ground Deformation Monitoring with VV-VH Sentinel-1 Data

With the launch of the Sentinel-1 satellites, it becomes easy to obtain long time-series dual-pol (i.e., VV and VH channels) SAR images over most areas of the world. By combining the information from both VV and VH channels, the polarimetric persistent scatterer interferometry (PolPSI) techniques is supposed to achieve better ground deformation monitoring results than conventional PSI techniques (using only VV channel) with Sentinel-1 data. According to the quality metric used for polarimetric optimizations, the most commonly used PolPSI techniques can be categorized into three main categories. They are PolPSI-ADI (amplitude dispersion index as the phase quality metric), PolPSI-COH (coherence as the phase quality metric), and PolPSI-AOS (taking adaptive optimization strategies). Different categories of PolPSI techniques are suitable for different study areas and with different performances. However, the study that simultaneously applies all the three types of PolPSI techniques on Sentinel-1 PolSAR images is rare. Moreover, there has been little discussion about different characteristics of the three types of PolPSI techniques and how to use them with Sentinel-1 data. To this end, in this study, three data sets in China have been used to evaluate the three types of PolPSI techniques’ performances. Based on results obtained, the different characteristics of PolPSI techniques have been discussed. The results show that all three PolPSI techniques can improve the phase quality of interferograms. Thus, more qualified pixels can be used for ground deformation estimation by PolPSI methods with respect to the PSI technique. Specifically, this pixel density improvement is 50%, 12%, and 348% for the PolPSI-ADI, PolPSI-COH, and POlPSI-AOS, respectively. PolPSI-ADI is the most efficient method, and it is the first choice for the area with abundant deterministic scatterers (e.g., urban areas). Benefitting from its adaptive optimization strategy, PolPSI-AOS has the best performances at the price of highest computation cost, which is suitable for rural area applications. On the other hand, limited by the medium resolution of Sentinel-1 PolSAR images, PolPSI-COH’s improvement with respect to conventional PSI is relatively insignificant.

Spinal decompression with patient-specific guides

BACKGROUND CONTEXTPatient-specific instruments (PSI) have been well established in spine surgery for pedicle screw placement. However, its utility in spinal decompression surgery is yet to be investigated. PURPOSEThe purpose of this study was to investigate the feasibility and utility of PSI in spinal decompression surgery compared with conventional freehand (FH) technique for both expert and novice surgeons. STUDY DESIGNHuman cadaver study. METHODSThirty-two midline decompressions were performed on 4 fresh-frozen human cadavers. An expert spine surgeon and an orthopedic resident (novice) each performed 8 FH and 8 PSI-guided decompressions. Surgical time for each decompression method was measured. Postoperative decompression area, cranial decompression extent in relation to the intervertebral disc, and lateral recess bony overhang were measured on postoperative CT-scans. In the PSI-group, the decompression area and osteotomy accuracy were evaluated. RESULTSThe surgical time was similar in both techniques, with 07:25 min (PSI) versus 06:53 min (FH) for the expert surgeon and 12:36 min (PSI) vs. 11:54 (FH) for the novice surgeon. The postoperative cranial decompression extent and the lateral recess bony overhang did not differ between both techniques and surgeons. Further, the postoperative decompression area was significantly larger with the PSI than with the FH for the novice surgeon (477 vs. 305 mm2; p=.01), but no significant difference was found between both techniques for the expert surgeon. The execution of the decompression differed from the preoperative plan in the decompression area by 5%, and the osteotomy planes had an accuracy of 1–3 mm. CONCLUSIONPSI-guided decompression is feasible and accurate with similar procedure time to the standard FH technique in a cadaver model, which warrants further investigation in vivo. In comparison to the FH technique, a more extensive decompression was achieved with PSI in the novice surgeon's hands in this study. CLINICAL SIGNIFICANCEThe PSI-guided spinal decompression technique may be a useful alternative to FH decompression in certain situations. A special potential of the PSI technique could lie in the technical aid for novice surgeons and in situations with unconventional anatomy or pathologies such as deformity or tumor. This study serves as a starting point toward PSI-guided spinal decompression, but further in vivo investigations are necessary.

Monitoring deformations of Istanbul metro line stations through Sentinel-1 and levelling observations

Turkey, as a developing country, is designing and performing massive construction projects around Istanbul. Beginning from the 1960s, rapid urbanization has been taking place due to industrialization, which brings an increase in the population. Yet, construction projects have been accelerated especially during the last decade, and many new projects are scheduled to be completed in a short time. Ground-based observations are generally carried out to monitor the deformations within construction sites, especially through geometric levelling, and GNSS techniques. However, in most cases, these monitoring measurements are only scheduled within the period of the construction process, and ensuing deformations are usually not considered. In addition to these techniques, the space-based interferometric technique can also be used to define the line of sight surface displacements with high accuracy, using the phase difference between image result for synthetic aperture radar images. In particular, Persistent Scatter Interferometry is one of the interferometric methods that are capable of defining the two-dimensional (vertical and horizontal) deformation for the desired epoch with a high temporal resolution. Thus it can be used as a complementary method for monitoring ground deformations, where the measurement is made by ground-based observations. In this study, the deforming areas related to underground metro construction are investigated through significant displacements between 2015 and 2018 of Sentinel-1 space-borne SAR data using the PSI technique. These results are validated by comparison with available levelling data corresponding to the new metro line.

Detection of surface deformation in opak fault Yogyakarta using quasi persistent scatter interferometry synthetic aperture radar

The Opak Fault is an active fault located in Yogyakarta. As an active fault, it leads to natural disasters, one of them being the Yogyakarta earthquake in 2006. Since then, Opak Fault surface deformation has not reoccured; hence measurement to detect this movement is essential. A widely used method in surface deformation measurement is Persistent Scatter Interferometry Synthetic Aperture Radar. A refined version of the PSI technique, the QPSI method, allows identifying and estimating targets undergoing movement through the reflectivity and amplitude stability of SAR waves. This study analyzed multi temporal Sentinel-1 Ascending and Descending data to analyze the Quasi-PSI performance in detecting surface deformation surrounding the Opak Fault. Results showed subsidence of the Opak Fault with a displacement accumulation up to -50mm throughout a period of 6 years. A majority of the surface deformation occurring in the area of interest lies at the border between Bantul Graben and the highlands of Gunung Kidul. Some of the surface displacements implied the presence of ongoing slope activity. In the area with a velocity displacement of -7 to -10 mm/year, a cumulative displacement greater than -50 mm was found. Furthermore, areas with a -2.5 to -5.5 mm/year velocity displayed a cumulative displacement ranging from -30 mm to – 40 mm. Surface deformation in the study area expressed an adequate result with a few sparse zones. Nonetheless, results from the ascending and descending modes present dissimilarity between results from several locations.

Determination of deformations by using the PSI technique at a common dump site of three different open-pit marble mines in Turkey

Determination of deformations by using the PSI technique at a common dump site of three different open-pit marble mines in Turkey

Land subsidence mapping and monitoring using modified persistent scatterer interferometric synthetic aperture radar in Jharia Coalfield, India

Subsidence has been adversely affecting Jharia Coalfield (JCF) for the last few decades. This study attempts to show the feasibility of the modified Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique with C-band SAR data to investigate the slow surface deformation caused by coal mine fire and underground mining activities in JCF. Also, a multi-temporal analysis of SAR images of ENVISAT ASAR has been carried out for monitoring and mapping of temporal land subsidence of the area under study. The modified PSI technique has proven its ability to detect land subsidence over the vegetated and rural areas. It also resolves low spatial density of permanent scatterers by considering partially correlated scatterers as permanent scatterers (PSs) and extracting information from these PSs. The study has been concentrated towards detecting continuous slow rate subsidence of five major sites of JCF. The maximum rate of slow deformation among all sites is recorded as 29 mm/year with a cumulative subsidence value of 90 mm. Field validation of subsidence results obtained through PS-InSAR is correlated with the previously published report and the master plan of JCF, showing subsidence locations. Conclusively, the adopted methodology is practically feasible for detection, monitoring and mapping of slow deformation using C-band SAR data in coal mine area.

Determination of the Long-Term Ground Surface Displacements Using a PSI Technique—Case Study on Wrocław (Poland)

Wrocław is a major city located in the southwestern part of Poland in an aseismic tectonic fault zone. Slow, long-term, vertical displacements have been observed there from the 1930s based on the levelling network measurements with the use of a precise levelling method. Due to the high cost of classic surveys, these were performed at intervals of several decades and the most recent measurement of ground surface displacement was performed in 1999. The main aim of this study is to determine the ground surface displacements on the area of Wrocław in the 1995–2019 period, the spatio-temporal analysis of deformations and the identification of the potential factors causing these deformations. To determine the ground movements, an advanced PSI technique and data from ERS-2, Envisat, and Sentinel-1 sensors were used. Application of SAR technology for the first time in this area, provided new knowledge about the process of deformation in short time intervals over the entire area of the city. The results verify the hypothesis on the linearity of displacements obtained from historical geodetic observations. The obtained results show that the displacements, which continue to occur in the area of Wrocław have a cyclic character with 4–5 year long period of subsidence and 2–3 year long periods of stabilization or uplift. The displacement trends indicate that the area of the city gradually subsides in relation to the reference area located on the Fore-Sudetic Block.

Evaluation of polarimetric capabilities of dual polarized Sentinel-1 and TerraSAR-X data to improve the PSInSAR algorithm using amplitude dispersion index optimization

Polarimetric data is an additional source of information in PSI technique to improve its performance in land subsidence estimation. The combination of polarimetric data and radar interferometry can lead to an increase in coherence and the number of PS pixels. In this paper, we evaluated and compared the dual polarized Sentinel-1A (S1A) and TerraSAR-X (TSX) data to improve the PSInSAR algorithm. The improvement of this research is based on minimizing Amplitude Dispersion Index (ADI) by finding the optimum scattering mechanism to increase the number of PSC and PS pixels. The proposed method was tested using a dataset of 40 dual-pol SAR data (VV/VH) acquired by S1A and 20 dual-pol SAR data (HH/VV) acquired by TSX. The results revealed that using the TSX data, the number of PS pixels increased about 3 times in ESPO method than using the conventional channels, e.g., HH, and VV. This increase in S1A data was about 1.7 times in ESPO method. In addition, we investigated the efficiency of the three polarimetric optimization methods i.e. ESPO, BGSM, and Best for the dual polarized S1A and TSX data. Results showed that the PS density increased about 1.9 times in BGSM and about 1.5 times in Best method in TSX data. However, in S1A data, PS density increased about 1.1 times in BGSM. The Best method was not successful in increasing the PS density using the S1A data. Also, the effectiveness of the method was evaluated in urban and non-urban regions. The experimental results showed that the method was successful in significantly increasing the number of final PS pixels in both regions.

Single-Source Multiaxis Cold-Atom Interferometer in a Centimeter-Scale Cell

Using the technique of point source atom interferometry, we characterize the sensitivity of a multi-axis gyroscope based on free-space Raman interrogation of a single source of cold atoms in a glass vacuum cell. The instrument simultaneously measures the acceleration in the direction of the Raman laser beams and the component of the rotation vector in the plane perpendicular to that direction. We characterize the sensitivities for the magnitude and direction of the rotation vector measurement, which are 0.033 $^{\circ}/\mathrm{s}$ and 0.27 $^{\circ}$ with one second averaging time, respectively. The sensitivity could be improved by increasing the Raman interrogation time, allowing the cold-atom cloud to expand further, correcting the fluctuations in the initial cloud shape, and reducing sources of technical noise. The unique ability of the PSI technique to measure the rotation vector in a plane may permit applications of atom interferometry such as tracking the precession of a rotation vector and gyrocompassing.

A Case Study on Offshore Platform Deformation Monitoring by using InSAR

The Interferometric Synthetic Aperture Radar (InSAR) technique is well established technique for onshore applications such as landslide, mining, volcano, urban and dam deformation monitoring. However, the ability of the InSAR technique for the offshore application particularly on the oil platform deformation monitoring is still a pending question. Therefore, a study needs to be conducted in order to assess the feasibility of the InSAR technique for monitoring the deformation of offshore platform. In this study, an advanced InSAR technique called Stanford Method of Persistent Scatterer (StaMPS) was utilized to process a stack of TerraSAR-X data. A mask has been developed as an additional module in the StaMPS to remove the noise on the ocean and relax the assigned condition imposed on the processing parameters. The results show that the number of persistent scatterer (PS) points on the offshore platform increased from 15 to 22 points and a smoother pattern of the velocity estimation could be seen when masking was applied to identify the deformation. Furthermore, some limitations and possible solutions of the PSI technique on the offshore platform application are summarized in this paper to guide future users on this application.

Ciphertext-Only Attack on Phase-Shifting Interferometery-Based Encryption

The phase-shifting interferometry-based (PSI-based) encryption is one of most typical optical encryption systems. In this paper, we demonstrate a new approach to ciphertext-only attack (COA) on PSI-based encryption, revealing that there is serious security risk in PSI-based encryption. With the proposed COA approach, an opponent can crack the ciphertexts directly without use of the keys of the system. This demonstration, as far as our best knowledge, shows the PSI technique is vulnerable to COA for the first time. A series of attack results are shown to demonstrate the feasibility and robustness of the attack method. Our study reveals a critical security issue that should be taken in to account when designing an optical information security system.

Short term comparison of functional recovery after Total Knee Replacement with standard technique or PSI technique, using gait analysis

Short term comparison of functional recovery after Total Knee Replacement with standard technique or PSI technique, using gait analysis

Numerical Study of Wall Ventilation in a Transonic Wind Tunnel

Transonic wind tunnels (TWT) are sophisticated tools for the investigations of flows with Mach numbers of order one. The most characteristic feature of a facility such as this is, for sure, the openings in the walls of the test section. The openings in the walls permit the proper relief effect, and this, on the other hand, makes possible the experimentation at the transonic range. The results to be presented in this paper correspond to an analysis of the flow in the test section of a TWT containing a NACA 0012 airfoil. Both numerical and experimental investigations were conducted. For the numerical investigation, a threedimensional, finite-difference code, based on the diagonalalgorithm, was employed, whereas for the experimentation, the classical static-pressure taps as well as the pressure sensitive paint (PSP) techniques were used. The classical static-pressure tap method is indicated as PSI technique. The pressure distributions were investigated for Mach numbers in the range of 0.6 – 0.8 and angles of attack from 0° up to 8°. The relief effect due to the slots, which provides for avoiding choking effects, is clearly demonstrated when one compares the flow along both solid and perforated walls. In the first part of this research report, the main focus will be on the numerical results. Notwithstanding this, and for comparison purposes, some experimental results will be called upon here, together with some literature data.

Combined use of space-borne SAR interferometric techniques and ground-based measurements on a 0.3 km2 subsidence phenomenon

The built-up area of the village Hilsprich (Lorraine, France) is affected by a subsidence phenomenon localized over a few hundred square metres, causing damage to buildings. In this study, differential SAR interferometry (DInSAR) was used to:•estimate the boundaries of the subsidence in order to optimize ground-based monitoring networks (levelling and geophysical measurements)•estimate the maximum deformation and highlight the evolution of the phenomenon (previously unknown due to insufficient historical ground-based data).The study was based both on L-band ALOS/PALSAR SAR data and C-band Envisat/ASAR data. The interest in PALSAR data lies in its better performance for InSAR with respect to C-band data on the affected non-urban areas (such as fields and farmlands) where, in addition, conventional techniques such as topographical survey information were limited, and had often not been carried out before the first damage was observed. Conventional DInSAR based on PALSAR data processing for the 2008–2010 period identified the boundary of the subsidence area and estimated its maximum magnitude. The PSI technique in the ASAR archive gave information regarding the beginning of the subsidence. The precision of the DInSAR results was consistent with the topographical data (in locations where this information was known) and therefore favours the SAR interferometric techniques in this context. Combined with the knowledge of the regional geological and structural setting, together with results from ground-based electrosounding, the results of the study established a basis for an increased understanding of the subsidence phenomenon, which was revealed to affect an elliptical bowl-shaped area due to salt dissolution.

Persistent Scatterers Interferometry detects and measures ground subsidence in Lisbon

Results from the application of Persistent Scatterers Interferometry in Lisbon Metropolitan Area revealed two previously unknown subsiding urban areas: one (Laranjeiras) is located in the center of Lisbon; another (Vialonga) is to be found toward the North, in an industrial region crossed by Lisbon's main highway and railway lines. The two subsiding sectors are bordered by sharp velocity gradients, and the subsidence pattern appears partially delimited by mapped geologic faults. Surface geology and urbanization alone are unable to explain the phenomena. In the Vialonga area, the historical record of water pore pressure shows a clear decline of the levels (up to 65 m in 27 years), providing evidence of over-exploitation of groundwater resources. Limited information from wells drilled inside and outside the subsidence area points to a spatial correlation between the subsidence and the water pressure levels, and suggests that faults could be acting as hydraulic barriers in the aquifer system. The surface subsidence detected is probably caused by compaction of a clay-rich Oligocene-aged aquitard, led by over-exploitation of adjacent aquifers. The same Oligocene aquitard layer is present in the Laranjeiras area, immediately bellow a multi-layered sand–clay–limestone Miocene aquifer, but further work is needed to diagnose the possibility of over-exploitation of groundwater here. In this work we were able to independently confirm the PSI results, by comparing autonomous PSI results processed for the same geographical areas, and by comparing PSI with leveling and continuous GPS derived subsidence velocities, whose close match provided further ground validation of the space-borne PSI technique.

Measurement of surface figure of plane optical surfaces with polarization phase-shifting Fizeau interferometer

A Fizeau interferometer based set up for measurement of surface forms of plane optical surfaces has been discussed. Phase shifting interferometry has been applied using polarization phase shifter. A linearly polarized (632.8 nm) He–Ne laser has been used as the source. Light reflected from the object and the reference/master surfaces are made circularly polarized in opposite senses by means of two properly oriented quarter wave retardation plates placed at appropriate positions, one inside and other outside the interference cavity of the interferometer, and phase shifts are introduced between the object and the reference/master waves by varying angular orientation of a polarizer/analyzer. Final result is made free from any residual wave-front aberrations introduced by the (intra-cavity) wave plate by subtracting phase values obtained by PSI technique between a high optical quality master surface and the reference surface from that obtained for the test object surface with respect to the same reference surface for each point of the interference field. Results are shown for a plane surface. Advantages of the technique presented are linearity and high accuracy in phase stepping, no perturbation of the interference cavity during the phase shifting and possibility of real time or dynamic interferometry.

Residual stresses in Co-based laser claddings investigated by lab X-rays and synchrotron diffraction techniques

It is a well known fact that cracking related problems may occur during the laser cladding deposition process. In particular for the improvement of thick coatings it is of prime interest to know how processing parameters affect the residual stress state. The residual strains developed in Co-based thick clad layers were investigated by laboratory Cu-K alpha and Synchrotron X-rays. On the surface the strain tensor is determined by the Sin(2)psi technique. Strain mapping performed by synchrotron radiation shows that tensile stresses dominate the upper region but may change into compressive towards the inner part of the coating. The effect of laser overlap is discussed and a mechanism for stress concentration is proposed.