Measurement Of Surface Deformation Research Articles

Flow–structure interaction of a starting jet through a flexible circular nozzle

In the present study, the flow–structure interaction of a starting jet through a flexible nozzle is experimentally investigated, with a focus on the optimal flexibility for thrust generation. Water slug is impulsively accelerated through a cylindrical nozzle, fabricated with silicone rubber of varying flexibility. In general, the flexible nozzle modifies the vortical structure of the jet and augments the thrust of the starting jet. The measurement of nozzle surface deformation revealed that a back-and-forth wave propagation on the nozzle surface is responsible for the jet-vortex evolution augmenting the thrust generation. Combining the hydrodynamic conservation equations and the linearized shell theory, we also formulated the governing equations, dominated by two relevant dimensionless parameters: the effective acceleration time of the jet ( $\varPi _0$ ) and the effective nozzle stiffness ( $\varPi _1$ ). Asymptotic analysis of the equation showed that the dimensionless wave speed ( $\hat {c}$ ) is expressed as $\hat {c}=(\varPi _{0}^{2}\varPi _{1}/2)^{0.5}$ , and the jet momentum is maximized at $\hat {c}=\hat {c}_{crit}$ ( $\simeq 3.0$ ), the condition at which the release of elastic energy stored during nozzle contraction to the jet is synchronized with the instant of termination of jet acceleration. While $\hat {c}=\hat {c}_{crit}$ , the achievable maximum jet velocity decreases with the effective acceleration time of the jet ( $\varPi _0$ ), which is attributed to the reduced speed of the surface wave by the flow inside the nozzle.

Three‐dimensional deformation measurement of aero‐engine high‐speed rotating blade surface based on stroboscopic structure digital image correlation method

Under the working conditions of aero-engine, the three-dimensional composite deformation of the blade is caused by the centrifugal force generated by high-speed rotation and the load generated by gas scouring. Aiming at the problem of three-dimensional composite deformation on the surface of aero-engine blades under high-speed rotation, a three-dimensional deformation measurement method based on stroboscopic structure digital image correlation method is proposed, and a method for eliminating rigid body displacement induced by the trigger error of the stroboscope is proposed. First, the laser trigger-stroboscopic irradiation system is used to freeze the high-speed rotating blade under a specific phase. Then, the binocular vision system is used to collect the surface image of the rotating blade. Finally, the digital image correlation method is used to measure the surface deformation field of the high-speed rotating blade. In this paper, the experimental platform is built and the displacement field and main strain field of the blade surface under high-speed rotating state are measured. The experimental results show that the stroboscopic structure digital image correlation measurement system and method have realized displacement measurement accuracy of 2 μm and strain measurement accuracy of 100 μɛ and have realized the surface deformation measurement of the ducted turbine fan blade under the condition of 6000 rpm (CFM56-7 engine N1 speed). The results show that the method is effective and can provide a reliable measurement method for the deformation measurement of high-speed rotating blades in large engine manufacturing enterprises such as Aero Engine Corporation of China.

Structural characteristics of shallow faults in the Delaware Basin

The Delaware Basin of Texas and New Mexico is experiencing elevated levels of seismicity. There have been more than 130 earthquakes with local magnitudes of at least 3.0 recorded between 2017 and 2021, with earthquakes occurring in spatiotemporally isolated and diffuse clusters. Many of these events have been linked to oilfield operations such as hydraulic fracturing and wastewater disposal at multiple subsurface levels; however, the identification and characterization of earthquake-hosting faults have remained elusive. There are two distinct levels of faulting in the central region of the basin where most earthquakes have been measured. These fault systems include a contractional basement-rooted fault system and a shallow extensional fault system. Shallow faults trend parallel to and rotate along with, the azimuth of S HMAX, are vertically decoupled from the basement-rooted faults, accommodate dominantly dip-slip motion, and are the product of more recent processes including regional exhumation and anthropogenic influences. The shallow fault system is composed of northwest–southeast-striking, high angle, and parallel trending faults which delineate a series of elongate, narrow, and extensional graben. Although most apparent in 3D seismic reflection data, these narrow elongate graben features also are observed from interferometric synthetic aperture radar (InSAR) surface deformation measurements and can be delineated using well-located earthquakes. In contrast to the basin-compartmentalizing basement-rooted fault system, shallow faults do not display any shear movement indicators, and they have small throw displacement given their mapped length, producing an anomalous mean throw-to-length ratio of 1:1000. These characteristics indicate that these features are more segmented than can be mapped with conventional subsurface data. Much of the recent seismicity in the south-central Delaware Basin is associated with these faults and InSAR surface deformation observations find that these faults also may be slipping aseismically.

DIC-Net: Upgrade the performance of traditional DIC with Hermite dataset and convolution neural network

Digital image correlation (DIC) is a non-contact optical method that tracks the speckle pattern on specimen surface to calculate the displacement and strain by image correlation algorithm. Although the traditional DIC method can conveniently measure surface deformation, it still has many limitations: (1) the accuracy of displacement and strain calculation needs to be improved in the case of high deformation gradient; (2) under match or over-match can hardly be avoided when the filters are used to reconstruct smooth displacement or strain field, and (3) boundary effect remains unresolved in computing the deformation near the boundary of region of interest or the discontinuous area (e.g. area near crack tip or crack face). Recently, the deep learning based DIC (Deep-DIC) has revealed its attractive ability in handling above issues in traditional DIC, and impressive results have been achieved. The mean value of the absolute error (MAE) on the test set has been optimized to 0.0361 pixels using existing Deep-DIC approaches, which are accompanied by a real-time measurement speed. The network structure and training dataset are two key factors for the deep learning method. However, the current working networks have been modified from other image tasks and cannot fully adapt to the demands of the DIC tasks, and the dataset they generated still has evident flaws, limiting the method's accuracy and generalization performance which is utilized to assess performance on samples outside the training set. In this paper, we firstly proposed a new Hermite dataset that is created by using the high-order Hermite element to take account more complex deformation, then a new network architecture designed for the DIC task has been developed to extract richer deformation features. A test set of 3216 examples containing six different modes of displacement is used to compare the performance of our network with others. The proposed DIC-Net-d achieves the lowest MAE in the test set. Meanwhile, in the Star5 image sets from DIC-Challenge, the proposed DIC-Net-d achieves a spatial resolution of 17.25 pixels and a noise level of 0.0136 which outperforms existing traditional and non-traditional methods. Finally, the strain network trained by our Hermite dataset is also successful in predicting the strain field of Star6 in the DIC challenge. The experiment results show the superiority of the proposed Hermite dataset and new network with respect to other Deep-DIC methods.

Synchronous measurement of surface deformation and gradient distribution in microstructures

In the traditional microfield speckle pattern interference measurement system, due to the use of high-magnification objective lens, the working distance is small and the shearing device cannot be introduced to implement shearography measurement. Thus the distribution of the deformation gradient on a microstructure surface cannot be measured. A system for the synchronous measurement of the surface deformation and gradient distribution of a microstructure was designed. Through the combination of focusing lens, convex lens, and low-magnification objective lens, the microstructure surface was clearly magnified and the internal distance of the system was enlarged. Thus the shearing device can be introduced to realize the shearography measurement under the microfield view. The synchronous full-field measurement of the structural surface deformation and its gradient distribution was further realized by the introduction of a reference light and designing of an optical path switch. In addition, the designed system had a zoom feature, which can facilitate the measurement in variable field of view in a certain range. The feasibility of the system was verified by theoretical analysis and experiment, and the practicability was validated by testing the chip and circuit board.

Performance of acoustic emission and digital image correlation for fracture analysis in cementitious mortars under fatigue loading

Fatigue loading in brittle materials introduces damage at a micro-scale. These micro-fractures can accumulate and cause a significant reduction in material stiffness or even lead to structural failure. Deformation-based monitoring techniques can be inadequate when detecting damage at a micro-level. Hence, here is where advanced nondestructive testing (NDT) methods such as acoustic emission (AE) and digital image correlation (DIC) can play a great role. The paper aims to combine AE and DIC for advanced fatigue damage analysis on a cylindrical sample subjected to a fatigue Brazilian splitting test. The damage progress quantified from cumulative AE event count, and horizontal displacement measured with DIC showed a very good correlation. The damaged region was identified with an AE localization plot and with a DIC displacement field plot, the damaged area was well represented by both techniques. When a material goes through an irreversible change, part of the released energy will generate an elastic wave. The wave will propagate through the material and the whole phenomenon is termed an acoustic emission. By using AE sensors on the surface of the sample, these waves are captured and analyzed to better understand the source of the emission. Its high sensitivity to micro-changes makes it an ideal technique to use for fatigue damage investigation. Digital image correlation relates sequentially taken images to determine displacement and strain measurements. While DIC analyzes material evolution using surface deformation measurements, AE on the other hand is capable of monitoring damage inside the volume of material. Hence, their combination provides an efficient test setup for monitoring fatigue micro-fracture. The paper aims to combine AE and DIC for advanced fatigue damage analysis on cylindrical samples that are subjected to monotonic and fatigue Brazilian splitting tests. The analysis will use damage progress under monotonic loading as a reference to further understand fatigue fracture. Methods of AE data filtering and AE source localization are discussed and evaluated for their use in fracture analysis. The utilization of DIC to track the material stiffness evolution is investigated. In addition, the paper compares fracture process zones quantified by AE and DIC. From the experimental analysis, it was found that both methods captured the fatigue damage patterns, yet provided complementary information for damage evaluation.

Surface deformation simulation for InSAR detection using a machine learning approach on the hantangang river volcanic field: A case study on the orisan mountain

Recent developments in remote sensing research have resulted in a large amount of variability in the data provided by researchers. Synthetic aperture radar (SAR) is a tool used to measure surface deformation and assess changes in the Earth’s surface. Here, we consider the usefulness of Interferometric Synthetic Aperture Radar (InSAR) in assessing past volcanic activity as a key to learning the characteristics of the deformation around a volcano. The Hantangang River volcanic field (HRVF) is a geoheritage site in the Korean Peninsula that has interesting geological characteristics. This volcanic field has formed along 110 km of the paleochannel of the Hantangang River. Since the eruptions occurred from 0.15 to 0.51 Ma, the source is limited, which has raised interest in the assessment of volcanic landforms. The recent integration of machine learning and InSAR processing has shown promising results for many purposes, such as classifying, modeling, and detecting surface deformation. To examine the future impact based on information from the past, we utilized a synthetic interferogram with the Okada model and transferred it to a machine learning algorithm. The synthetic interferogram was formed based on Sentinel-1 C-band satellite data to simulate the deformation phases. The orbital errors, the topographical data errors, and the atmospheric effect were also simulated and added to the synthetic interferogram to enrich the learning input. A convolutional neural network (CNN) trained with the unwrapped simulated interferogram data and its performance was evaluated. Our proposed method exhibits the capability to detect volcanic activity’s deformation patterns with synthetic interferogram data. The results show that an overall accuracy of more than 80% was achieved using the CNN algorithms on the validation dataset. This study is the first to use machine learning approaches for detecting prehistorical volcanic deformation and demonstrates potential techniques for developing an approach based on satellite imagery. In addition, this study has introduced the possibility of developing a rapid detection of surface deformation using InSAR data based on a machine learning approach.

Simultaneous measurement of external and internal surface shape and deformation based on photogrammetry and stereo-DIC

Mechanical structures with cavities such as auto rim and aero-engine casing are widely used in engineering. It is of great significance for their dynamic performance evaluation if one can measure the shape and deformation of the internal and external surfaces together. However, due to the narrow interior space and self-occlusion of complex structures, the conventional stereo-DIC unit is not applicable to impose the simultaneous measurement in the outer and inner areas. This paper is therefore concerned with a systematic solution for the issue. A reflection-assisted multi-view DIC system is configured, which consists of the stereo-DIC (SDIC) unit and the reflection-assisted stereo-DIC (RSDIC) unit. The design idea and selection essential of the RSDIC unit are stated. Subsequently, a correction model for reflection imaging is detailed. Close-range photogrammetry is specially adopted to compute the 3D global points. The extrinsic parameters of each DIC unit are estimated via the rear resection so that the individual reference frame can be transformed into a common coordinate system. Five experiments, including two tests of calibration accuracy, shape and deformation measurement accuracy, and applications in an aero-engine casing prototype, prove the precision and effectiveness of the proposed method.

A surface deformation measurement algorithm for reflector antennas based on complex geometrical optics

AbstractThis paper presents a new method to reveal the relation between the surface deformation and near-field amplitude of a reflector antenna based on complex geometrical optics, which could be used as an efficient way to estimate the antenna surface verified by simulation results. The measurement process based on this method is envisaged to be realized by a single scanning of the near-field amplitude which would overcome many limitations of radio holography and phase retrieval methods such as the frequency and elevation. The largest source of error in the original deformation-amplitude equation (DAE) has been corrected by considering the Gaussian feed as a complex point source. To track the ray trajectory so that the improved DAE could be solved, an iteration method including a golden section search algorithm is designed to make the solution converge. By solving the modified DAE, simulation result shows that a more accurate solution could be obtained, and the antenna surface could be recovered to a root mean square error of under 30 microns.

Monitoring Volcanic and Tectonic Sandbox Analogue Models Using the Kinect v2 Sensor

AbstractThe measurement of surface deformation in analogue models of volcanic and tectonic processes is an area in continuous development. Properly quantifying topography change in analogue models is key for a useful comparison between experiment results and nature. The aim of this work is to evaluate the capabilities of the simple and cheap Microsoft® Kinect v2 sensor for monitoring analogue models made of granular materials. Microsoft® Kinect v2 is a video‐gaming RedGreenBlue‐Depth device combining an optical camera and an infrared distance measurement sensor. The precision of the device for model topography measurements has been quantified using 64 experiments, with variable granular materials materials and distance to the model. Additionally, we tested the capabilities of averaging several distance images to increase the precision. We have developed a specific software to facilitate the acquisition and processing of the Kinect v2 data in experiment monitoring. Our results show that measurement precision is material dependent: with clear‐colored and fine‐grained materials, a precision ∼1.0 mm for digital elevation models with a 1.6 mm pixel size can be obtained. We show that by averaging ≥5 consecutive images the distance precision can reach values as low as 0.5 mm. To show the Kinect v2 capabilities, we present monitoring results from case study experiments modeling tectonics and volcano deformation. The Kinect v2 achieves lower spatial resolutions and precision than more sophisticated techniques such as photogrammetry. However, Kinect v2 provides a cheap, straightforward and powerful tool for monitoring the topography changes in sandbox analogue models.

Landslide assessment using interferometric synthetic aperture radar in Pacitan, East Java

<span>Landslides are a common type of disaster in Indonesia, especially in steep-slope areas. The landslide process can be well understood by measuring the surface deformation. Currently, there are no practical solutions for measuring surface deformation at landslide locations other than field surveys in the Pacitan Regency. We apply LiCSBAS, to identify surface deformation in several landslide locations in a specific non-urban area with mixed topographical features. LiCSBAS is a module that utilizes data from the project of looking inside the continent from space (LiCS), using the new small baseline area subset (NSBAS) method. This study utilizes the leaf area index (LAI) to validate the ability of LiCSBAS to detect surface deformation values at landslide locations. The study succeeded in identifying surface deformations at 100 landslide locations, with deformation values ranging from 15.1 to 10.9 millimeters per year. Most of the landslide locations are closely related to volcanic rocks and volcanic sediments on slopes of 30–35°. The NSBAS method in the LiCSBAS module can reduce gaps error in the sentinel-1 image network. However, the utilization of the C-band at a pixel size of 100 meters made surface deformation only well detectable in a large open landslide area.</span>

Primary Reference Technique of the Surface Deformation Measurements of an Elastically Deformed Beam

Primary Reference Technique of the Surface Deformation Measurements of an Elastically Deformed Beam

Simultaneous Measurement of Temperature and Strain in Electronic Packages Using Multiframe Super-Resolution Infrared Thermography and Digital Image Correlation

Abstract For micro-electronic components and systems, reliability under thermomechanical stress is of critical importance. Experimental characterization of hotspots and temperature gradients, which can lead to deformation in the component, relies on accurate mapping of the surface temperature. One method of noninvasively acquiring this data is through infrared (IR) thermography. However, IR thermography is often limited by the typically low resolution of such cameras. Additionally, the unique surface finish preparations required to infer physical deformation using digital image correlation (DIC) generally interfere with the ability to measure the temperature with IR thermography, which prefers a uniform high emissivity. This work introduces a one-shot technique for the simultaneous measurement of surface temperature and deformation using multiframe super-resolution-enhanced IR imaging combined with DIC analysis. Multiframe super-resolution processing uses several subpixel shifted images, interpolating the image set to extract additional information and create a single higher-resolution image. Measurement of physical deformation is incorporated using a test sample with a black background and low-emissivity speckle features, heated in a manner that induces a nonuniform temperature field and stretched to induce physical deformation. Through processing and filtering, data from the black surface regions used for surface temperature mapping are separated from the speckle features used to track deformation with DIC. This method allows DIC to be performed on the IR images, yielding a deformation field consistent with the applied tensioning. While both the low- and super-resolution data sets can be successfully processed with DIC, super-resolution helps to reduce noise in the extracted deformation fields. As for temperature measurement, using super-resolution is shown to allow for better removal of the speckle features and reduce noise, as quantified by a lower mean deviation from the spatial moving average.

Quantitative Evaluation of Coseismic Deformations Induced by Seismogenic Faulting in Mining Exploration Area During the 2018 Xingwen and 2019 Changning Earthquakes, Sichuan, China

In the period between December 2018 and July 2019, a series of earthquakes (EQs), including the 16 December 2018 Ms 5.7 Xingwen mainshock and the 17 June 2019 Ms 6.0 Changning mainshock, struck the Changning shale gas exploration field in the southern margin of the Sichuan Basin. The Xingwen and Changning EQs both occurred on concealed faults, which led to hundreds of casualties, and affected a total of over 160 thousand people in southern Sichuan. The aftershock sequences following the Xingwen and Changning EQs were clustered in the vicinity of the Jianwu syncline and Changning anticline, respectively, and occurred mostly at depths of 3–7 km. In this study, coseismic surface deformation measurements obtained through differential interferometric synthetic aperture radar (D-InSAR) data were used to identify the faulting geometries and distributions. The coseismic deformation maps have maximum line-of-sight (LOS) displacements of ∼4.53 cm on the northwest side of the Xingwen EQ source fault and ∼7.84 cm on the southwest side of the Changning EQ source fault. The calculated static Coulomb stress changes indicated that most aftershocks occurred in increasing stress zones following the mainshock ruptures. From the InSAR deformation field, a complicated concealed seismogenic doublet fault was inferred, which predominately exhibited left-lateral strike-slip motion during the Xingwen and Changning EQs. The footwall ramp of the basement fault reactivated first, and resulted in the Xingwen EQ and concentrating stresses beneath the Changning anticline, which induced the Changning EQ half a year later. Compared with previous studies, we proposed that the fault network was lubricated by water that was injected during shale gas exploration, facilitating the occurrence of the Xingwen and Changning EQs. Such work evaluated the coseismic deformations of the Xingwen and Changning EQs, and derived the regional faulting distribution from aftershock sequences. It could provide useful information for monitoring and analyzing seismic activity around the hinge zones of folds in mining exploration areas, which contributes to effective risk assessment of disasters associated with seismic geo-environments.

Shallow Aseismic Slip in the Delaware Basin Determined by Sentinel‐1 InSAR

AbstractThe Delaware Basin, Texas is currently a hot‐spot of induced seismicity and ground deformation due to fluid extraction and injection associated with horizontal drilling techniques; however, the driving mechanism behind the seismicity and deformation remains under debate. Using vertical and east‐west horizontal surface deformation measurements derived from Sentinel‐1 interferometric synthetic aperture radar (InSAR), we show that the subsurface responds differently to oil and gas activity in the northern and southeastern portions of the basin. In the north, where there is little seismicity, deformation patterns display long‐wavelengths and equidimensional patterns. In contrast, the southeast region hosts most of the seismicity and displays spatial deformation patterns with narrow linear features that strike parallel to the maximum principal horizontal stress and to trends in seismicity, suggesting movement along normal faults. We model a linear deformation feature using edge dislocations and show that the InSAR observations can be reproduced by slip on normal faults contained within the Delaware Mountain Group (DMG), the formation that hosts local wastewater injection and the majority of earthquakes. Our model consists of three parallel, high‐angle normal faults, with two dipping toward one another in a graben structure. Slip magnitudes reach up to 25 cm and are spatially correlated with injection wells. Measured seismicity can only explain ∼2% of the fault motion predicted by our fault model, suggesting that slip leading to the deformation is predominantly aseismic. We conclude that seismic and aseismic fault motion in the southeastern Delaware Basin is likely driven by wastewater injection near critically‐stressed normal faults within the DMG.

Three Mw ≥ 4.7 Earthquakes Within the Changning (China) Shale Gas Field Ruptured Shallow Faults Intersecting With Hydraulic Fracturing Wells

AbstractFrom 2017 to 2019, three destructive earthquakes (27 January 2017 Mw 4.7, 16 December 2018 Mw 5.2, and 3 January 2019 Mw 4.8) occurred in the Changning shale gas field in the southwest Sichuan Basin, China. Previous seismological studies attributed these events to hydraulic fracturing (HF), but were unable to identify the causative seismogenic faults and their slip behaviors. Here, we use Sentinel‐1 synthetic aperture radar data to measure surface deformation triggered by the three events and conduct geodetic inversions to characterize their rupture models. The resulting coseismic interferograms show prominent surface deformation with the maximum line‐of‐sight displacements of up to 4 cm. The inversion results show that all three earthquakes mainly ruptured sedimentary formations above the shale gas bed, in the upper 3 km of the crust, with slip magnitudes ranging from 8.5 to 15 cm, and stress drops ranging from ∼1.8 to ∼3.3 MPa. Their source faults intersect with horizontal HF wells, but do not root in the crystalline basement. Combined with the reported difficulty of increasing HF operation pressures prior to the three events, we argue that they were most likely induced by direct injection of pressurized fluids into the fault zones. Crustal deformation patterns inferred from regional topography and GPS velocities highlight that the Changning field is located within a triple junction region near the southeastern margin of the Tibetan Plateau with large deformation gradients; such conditions are not only favorable to the development of critically stressed faults, but also facilitate the occurrence of at least moderate magnitude earthquakes.

A SHORT REVIEW ON PERSISTENT SCATTERER INTERFEROMETRY TECHNIQUES FOR SURFACE DEFORMATION MONITORING

Abstract. Technology advancement has urged the development of Interferometric Synthetic Aperture Radar (InSAR) to be upgraded and transformed. The main contribution of the InSAR technique is that the surface deformation changes measurements can achieve up to millimetre level precision. Environmental problems such as landslides, volcanoes, earthquakes, excessive underground water production, and other phenomena can cause the earth's surface deformation. Deformation monitoring of a surface is vital as unexpected movement, and future behaviour can be detected and predicted. InSAR time series analysis, known as Persistent Scatterer Interferometry (PSI), has become an essential tool for measuring surface deformation. Therefore, this study provides a review of the PSI techniques used to measure surface deformation changes. An overview of surface deformation and the basic principles of the four techniques that have been developed from the improvement of Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR), which is Small Baseline Subset (SBAS), Stanford Method for Persistent Scatterers (StaMPS), SqueeSAR and Quasi Persistent Scatterer (QPS) were summarised to perceive the ability of these techniques in monitoring surface deformation. This study also emphasises the effectiveness and restrictions of each developed technique and how they suit Malaysia conditions and environment. The future outlook for Malaysia in realising the PSI techniques for structural monitoring also discussed in this review. Finally, this review will lead to the implementation of appropriate techniques and better preparation for the country's structural development.

Comments on “Study of Systematic Bias in Measuring Surface Deformation With SAR Interferometry”

In a recent publication, Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) claimed (see, in particular, the Discussion and Recommendation Section in their article) that the advanced differential SAR interferometry (InSAR) algorithms for surface deformation retrieval, based on the small baseline approach, are affected by systematic biases in the generated InSAR products. Therefore, to avoid such biases, they recommended a strategy primarily focused on excluding “the short temporal baseline interferograms and using long baselines to decrease the overall phase errors.” In particular, among various techniques, Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) identified the solution presented by Manunta <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2019) as a small baseline advanced InSAR processing approach where the presence of the above-mentioned biases (referred to as a fading signal) compromises the accuracy of the retrieved InSAR deformation products. We show that the claim of Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021) is not correct (at least) for what concerns the mentioned approach discussed by Manunta <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2019). In particular, by processing the Sentinel-1 dataset relevant to the same area in Sicily (southern Italy) investigated by Ansari <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> (2021), we demonstrate that the generated InSAR products do not show any significant bias.

Phase Error Analysis and Compensation of GEO-Satellite-Based GNSS-R Deformation Retrieval

Beidou geostationary earth orbit (GEO) satellite-based global navigation satellite system reflectometry (GNSS-R) technique has been developed for measuring surface deformation in a carrier-phase-based, cost-effective, and continuous manner. However, several improper assumptions in the original system and method, such as neglecting the slight GEO satellite movement during angle determination and deeming inter-channel phase difference as time-invariant, can introduce certain errors in estimating the surface deformation. In this work, these issues were analyzed and improved for more accurate estimations. Utilizing a Wilkinson power divider, the inter-channel phase error is estimated and calibrated with direct signal in the master channel. The GEO-motion phase error is theoretically modelled and compensated for based on precise ephemeris. A compensating algorithm of GNSS-R deformation retrieval technique utilizing Beidou GEO satellites is presented, by which encouraging results are yielded from field experiments emulating long-term monitoring. On artificial targets, the retrieval root mean square (RMSE) is better than 8 mm.

Shape and deformation measurements of rough surfaces by phase-shifting digital holography

In digital holography recording as reconstruction of holograms are performed digitally by modern photonic devices to increase of optical non-contacting measurements of various kinds of surfaces including both specular and rough surfaces. In this article we discusses these features of digital holography using phase shifting techniques that has much extended its capabilities. Full Text: PDF ReferencesG. Bruning, D.R. Herriott, J.E. Gallagher, D.P. Rosenfeld, A.D. White, D.J. Brangaccio, "Digital Wavefront Measuring Interferometer for Testing Optical Surfaces and Lenses", Appl. Opt. 13, 2693 (1974). CrossRef I. Yamaguchi, T. Zhang, "Phase-shifting digital holography", Opt. Lett. 22, 1268 (1997). CrossRef F. Zhang, I. Yamaguchi, L.P. Yaroslavsky, "Algorithm for reconstruction of digital holograms with adjustable magnification", Opt. Lett. 29, 1668 (2004). CrossRef I. Yamaguchi, "Holography, speckle, and computers", Optics and Lasers in Engineering 39, 411 (2003). CrossRef I. Yamaguchi, M. Yokota, "Speckle noise suppression in measurement by phase-shifting digital holography", Opt. Eng. 48 085602 (2009). CrossRef I. Yamaguchi, J. Kato, S. Ohta, "Surface Shape Measurement by Phase-Shifting Digital Holography", Opt. Rev. 8, 85 (2001). CrossRef I. Yamaguchi, J. Kato, H. Matsuzaki, "Measurement of surface shape and deformation by phase-shifting image digital holography", Opt. Eng. 42, 1267 (2003). CrossRef F. Zhang, J.D.R. Valera, I. Yamaguchi, M. Yokota, G. Mills, "Vibration Analysis by Phase Shifting Digital Holography", Opt. Rev. 11, 5 (2004). CrossRef