Optical Correlation Research Articles

Evolution of the off-fault deformation of strike-slip faults in a sand-box experiment

Surface deformation associated with strike-slip faults can be distributed in space, with deformation located either along the primary fault strand or around it and referred to as off-fault deformation (OFD). Fault displacement hazard evaluation require to identify and estimate surface slip rates along active fault strands. We calculate the horizontal and vertical displacement of the analogue models surfaces with optical image correlation and photogrammetry, to investigate the OFD’s development with increasing cumulative deformation. The criterion uses the gradient of the horizontal displacement norm perpendicular to the basal fault. Below 0.005 (noise level), there is no deformation, up to 0.03, it is off-fault-deformation, above 0.03, it is on-fault. We confirm previous observations made on analogue models that the surface deformation starts with a broad diffuse deformation, then produces fault strands alternating with relay zones that may be abandoned and reactivated. OFD is located first between Riedels, then between synthetic shears, and finally takes place in the relay zones. We also show that the OFD initially accommodates 100% of the applied slip (no faults), then decreases abruptly during the Riedels stage down to 20 to 30% to finally remain stable for the rest of the experiment. The abandonment and reactivation of the relay zones has the consequence of maintaining the OFD ratio on a stable value. Our experiments show that, like the OFD ratio, the width of the fault zone decreases with cumulative displacement to reach a stable value. Consequently, the OFD is correlated with this fault zone width and its geometric complexities. The ratios of OFD observed in this study are also consistent with measurements of OFD made on seven natural faults that exhibit different cumulative displacements. Hence our models suggest that strike-slip faults will never reach a continuous, linear geometry, and will always maintain a minimum amount of OFD.

Brillouin Optical Correlation Domain Analysis With Over 2.5 Million Resolution Points Based on Raman Amplification and Injection Locking

We propose and experimentally demonstrate a long-range Brillouin optical correlation domain analysis (BOCDA) system based on distributed Raman amplification and injection-locking to reach over 2.6 million resolving points. The optimization of key parameters in the Raman amplification, time domain data processing, differential measurement scheme, and injection-locking are applied to achieve a spatial resolution of 2 cm over a 50 km sensing fiber. Our result corresponds to at least twice improvement compared to former records, and the best one among distributed Brillouin sensors in terms of the number of resolving points.

Brillouin optical correlation domain analysis at MHz sampling rates using lock-in-free orthogonally polarized probe sidebands

Brillouin optical correlation domain analysis at MHz sampling rates using lock-in-free orthogonally polarized probe sidebands

Chaos and synchronization within soliton molecules

We experimentally demonstrate the synchronization of regularly vibrating soliton molecules by means of an injected modulated signal. Such synchronization is analyzed in real time through the sensitive balanced optical correlation technique. We also unveil the existence of chaotic intra-molecular vibrations, to which we successfully apply a similar control strategy. These findings strengthen the hypothesis of internal dynamics of soliton molecules essentially ruled by a reduced number of degrees of freedom, allowing applicative prospects.

Mixed-mode fracture of compacted tailing soils. II: Crack properties from full-field displacement fields

This paper deals with the acquisition of the crack evolution and propagation behaviors of the compacted tailing soils from full-field displacement fields by incorporating two-dimensional optical technique-digital image correlation (2D DIC). Meanwhile, the fracture properties, such as mode I+II fracture toughness were also measured and compared to the results obtained in Part I. Cracking properties, such as strain energy rate, cracking initiation angle, and size of critical distance were investigated from the perspective of full-field displacement field and compared to the classic fracture mechanics. It is more intuitive to recognize the mixed mode fracture properties of the compacted tailing soils under asymmetric loading conditions by using optical techniques in full-field displacement fields. This work largely enriched the database of the fracturing properties of compacted tailings soils.

Rapid Remeasure of Dense Civilian Networks as a Game‐Changer Tool for Surface Deformation Monitoring: The Case Study of the Mw 6.4 2020 Petrinja Earthquake, Croatia

AbstractThe Mw 6.4 right‐lateral Petrinja earthquake (2020, Croatia) is one of the largest continental earthquakes of central Europe for decades. The slip pattern of such events is usually difficult to retrieve with terrestrial geodesy due to limited monitoring means. This study takes advantage of a unique data set of dense measurements of coseismic displacement in the epicentral area, obtained by repeated measurements of benchmark networks designed for civilian purposes, and supplemented by far‐field continuous GNSS measurements. Elastic modeling of these data shows two coseismic slip patches that extend over a 15 × 10 km rupture plane, locally reaching the surface, and that a right‐lateral sub‐parallel secondary fault in the central part of the rupture likely accommodated part of the coseismic deformation. This study demonstrates that rapid re‐measurement of pre‐existing civilian networks offers unique coseismic constrains in the near‐field where InSAR or optical image correlation may decorrelate.

Ganglion cell complex thickness with spectral domain optical coherence tomography and correlations in a normative pediatric South Asian cohort.

Spectral domain optical coherence tomography (SD-OCT) was used to assess the perifoveal Ganglion cell complex (GCC) thickness in healthy Pakistani children. 174 eyes of 87 healthy children (3 to 16 years) were included after a thorough eye examination. Significant refractive error was excluded (>± 5 DS), glaucoma, ocular pathology, intraocular surgery, trauma, and systemic ailments. The perifoveal GCC analysis was done by Optopol Revo 80® high resolution SD-OCT. The average age was 11.1 ± 3.12 years. The average GCC thickness globally was 120.01 ± 76.74 μm, superiorly; 117.51 ± 8.77 μm, superonasally; 120.47 ± 8.78 μm, superotemporally, 103.83 ± 8.25 μm, inferiorly; 117.41 ± 8.71 μm, inferonasally 120.57 ± 8.88 μm, and inferotemporally; 107.15 ± 7.69 μm. The average GCC thickness was positively correlated with axial length (p=.02) and the GCC thickness in all sectors was significantly higher amongst males as compared to females (p < .05). Our study provides normative data for the macular GCC thickness in healthy children of our population. GCC thickness estimation is an important diagnostic parameter in glaucoma and optic neuropathies. Establishing a normative database for our pediatric population would help immensely in the diagnosis and monitoring of optic nerve disorders. RESEARCH HIGHLIGHTS: Spectral domain optical coherence tomography guided measurement of the ganglion cell complex thickness of the Pakistani pediatric population has not been done before. Our study provides normative data for the macular ganglion cell complex in healthy children of our population and studies its correlations with age, gender, intraocular pressure, axial length, refractive status, and corneal thickness. This will guide us in optic nerve and neurological disease diagnosis and monitoring.

Effect of matrix modification on the durability of cementitious composites reinforced with aligned Ensete fibre

Researchers are looking for new eco-friendly products to preserve non-renewable and non-biodegradable resources.Fibres obtained from natural sources offer indisputable advantages over synthetic reinforcement materials, including low density, low cost, abundance, comparable strength, non-toxicity and minimum environmental impact.However, when using natural fibres in a pure Portland cement matrix, the mechanical strength is significantly reduced due to the alkalinity of the cement. To date, there has been no study on the durability and mitigation of Ensete ventricosum (Ev) fibres in cementitious matrices. Therefore, in this study, the effects of partial replacement of Portland cement with different supplementary cementitious materials (SCM) including metakaolin (MK), fly ash (FA) and scoria (SC) were investigated. The composites, varying in matrix composition and reinforced by aligned Ev fibres, were subjected to 0 and 25 wet-dry cycles before being tested in a four-point bending configuration. A detailed investigation of the cracking behaviour was carried out using optical Digital Image Correlation techniques. The microstructure of the Ev fibres was next examined using scanning electron microscopy. The flexure tests showed that after 25 wet/dry cycles, Ev fibre reinforced composites with 100% Portland cement matrix had completely lost their ductility and strength while ternary matrices of 70% FA and 10% MK exhibited minimal degradation, demonstrating that partial replacement of Portland cement by SCMs can reduce the degradation of natural fibres in cement-based composites.

Off‐Fault Deformation in Regions of Complex Fault Geometries: The 2013, Mw7.7, Baluchistan Rupture (Pakistan)

AbstractObservations of recent earthquake surface ruptures show that ground deformations include a localized component occurring on faults, and an off‐fault component affecting the surrounding medium. This second component is also referred to as off‐fault deformation (OFD). The localized component generally occurs on complex networks of faults that connect at depth onto a unique fault plane, whereas OFD consists of distributed fracturing and diffuse deformation of the bulk volume, and occurs over scales of hundreds of meters to kilometers around the faults. High‐resolution optical image correlation presents a unique potential to characterize the complexity of the surface displacements, including on‐fault displacements and OFDs. In this study, we used sub‐pixel correlation of 0.5‐m resolution optical images to measure the surface displacement field with a &lt;20 cm accuracy for a 30‐km long section of the 2013 Mw7.7 Baluchistan, Pakistan, rupture. Our results document significant variability in the fault displacements, associated with large proportions of OFD in regions of fault geometrical complexity. Conversely, in regions where the fault geometry is simple, surface deformation is entirely accommodated by the primary faults with 0% OFD. When combining the localized deformation on faults with the OFD, we show that the total surface displacement budget is constant along the strike of the rupture, despite strong variations observed in the rupture geometry. Based on this analysis, we propose an idealized scenario of earthquake surface deformation as a function of the rupture geometrical variations.

Measurement of viscoelastic constants and Poisson’s ratio of carbon fiber reinforced composites using in-situ imaging

Dynamic Mechanical Analysis (DMA) is conducted to measure the viscoelastic nature of a material. The commercial DMA equipment calculates the complex modulus ( E*) by assuming a constant Poisson’s ratio. In this work, a method is developed for the simultaneous measurement of Poisson’s ratio and complex modulus ( E*) for carbon fiber (CF) reinforced Acrylonitrile Butadiene Styrene (ABS) composites using in-situ optical measurements and digital image correlation. The computation of E* includes shear deflection and relaxes the assumption of constant Poisson’s ratio to obtain accurate values. DMA was conducted on 3D printed CF-ABS composite specimens with oscillating displacement of 10 µm and static load of 1 N at 1 Hz loading frequency. The results in this work reveal that CF-ABS composite does not have a constant Poisson’s ratio over temperature. Additionally, applying the Poisson’s ratio correction results in higher values for the complex modulus. This work is beneficial for composites where the shear deflection component should not be neglected, and where variation of Poisson’s ratio with respect to temperature is important.

Polarization Calibration of a Microwave Polarimeter with Near-Infrared Up-Conversion for Optical Correlation and Detection.

This paper presents a polarization calibration method applied to a microwave polarimeter demonstrator based on a near-infrared (NIR) frequency up-conversion stage that allows both optical correlation and signal detection at a wavelength of 1550 nm. The instrument was designed to measure the polarization of cosmic microwave background (CMB) radiation from the sky, obtaining the Stokes parameters of the incoming signal simultaneously, in a frequency range from 10 to 20 GHz. A linearly polarized input signal with a variable polarization angle is used as excitation in the polarimeter calibration setup mounted in the laboratory. The polarimeter systematic errors can be corrected with the proposed calibration procedure, achieving high levels of polarization efficiency (low polarization percentage errors) and low polarization angle errors. The calibration method is based on the fitting of polarization errors by means of sinusoidal functions composed of additive or multiplicative terms. The accuracy of the fitting increases with the number of terms in such a way that the typical error levels required in low-frequency CMB experiments can be achieved with only a few terms in the fitting functions. On the other hand, assuming that the calibration signal is known with the required accuracy, additional terms can be calculated to reach the error levels needed in ultrasensitive B-mode polarization CMB experiments.

Plaque composition on ultra-high-resolution coronary computed tomography angiography with optical coherence tomography correlation.

A 68-year-old man presented to our chest pain unit with angina and a low pre-test probability for coronary artery disease (CAD). Troponin levels were normal, and echocardiography showed an intact left ventricular function. Coronary computed tomography angiography (CCTA) was performed using a first-generation dual-source photon-counting detector computed tomography (PCD-CT, NAEOTOM Alpha®, Siemens Healthineers) in a novel ultra-high resolution (UHR) mode. Data were reconstructed at 0.6 and 0.2 mm to reflect the typical appearance on standard and PCD-CT scanners (Panels A/D and B/E, respectively). The RCX presented with a mixed plaque and moderate-to-severe stenosis, right coronary artery (RCA) with a soft plaque and moderate-to-severe stenosis (Panels A and B), and LAD with a mostly a calcified plaque and mild stenosis (Figure 1D). UHR reconstructions revealed a fibrous cap on the calcified plaque (Panel E). Subsequent invasive coronary angiography including optical coherence tomography (OCT) confirmed a significant stenosis in the RCA [Panel C, fibrous plaque with micro-calcifications (arrowhead)] and left circumflex coronary artery (LCX) (mostly fibrotic components). Both were successfully treated with drug-eluting stents [thrombolysis in myocardial infarction (TIMI) coronary grade flow 3 (TIMI 3)]. Further, OCT confirmed the mild stenosis of the LAD caused by lesion with a fibrous cap over the calcification (Panel F).

Deep HDR Deghosting by Motion-Attention Fusion Network.

Multi-exposure image fusion (MEF) methods for high dynamic range (HDR) imaging suffer from ghosting artifacts when dealing with moving objects in dynamic scenes. The state-of-the-art methods use optical flow to align low dynamic range (LDR) images before merging, introducing distortion into the aligned LDR images from inaccurate motion estimation due to large motion and occlusion. In place of pre-alignment, attention-based methods calculate the correlation between the reference LDR image and non-reference LDR images, thus excluding misaligned regions in LDR images. Nevertheless, they also exclude the saturated details at the same time. Taking advantage of both the alignment and attention-based methods, we propose an efficient Deep HDR Deghosting Fusion Network (DDFNet) guided by optical flow and image correlation attentions. Specifically, the DDFNet estimates the optical flow of the LDR images by a motion estimation module and encodes that optical flow as a flow feature. Additionally, it extracts correlation features between the reference LDR and other non-reference LDR images. The optical flow and correlation features are employed to adaptably combine information from LDR inputs in an attention-based fusion module. Following the merging of features, a decoder composed of Dense Networks reconstructs the HDR image without ghosting. Experimental results indicate that the proposed DDFNet achieves state-of-the-art image fusion performance on different public datasets.

The Geodetic Centroid (gCent) Catalog: Global Earthquake Monitoring with Satellite Imaging Geodesy

ABSTRACT Remote sensing geodetic observations (Interferometric Synthetic Aperture Radar [InSAR] and optical correlation [“pixel tracking”]) serve an increasingly diverse and important role in earthquake monitoring and response. This study introduces the Geodetic Centroid (gCent) catalog—an earthquake catalog derived solely from space-based geodetic observations—and analysis of 74 earthquakes (Mw 4.3–7.4) imaged from 1 August 2019 to 01 February 2022. For gCent, we use InSAR and optical correlation observations derived from the Sentinel-1 satellites and various publicly available optical satellites to systematically image all global earthquakes Mw 5.5 or larger and shallower than 25 km, Mw 7.0 or larger at any depth, and other high-impact earthquakes or seismic events of special interest. We invert surface displacements from successfully imaged earthquakes for the location, orientation, and dimensions of a single slipping fault patch that describes the centroid characteristics of the earthquake. These centroid models, in turn, are compiled into a catalog and used in U.S. Geological Survey/Advanced National Seismic System (ANSS) operational earthquake response products such as ShakeMaps and finite-fault models. We provide a comparison of the gCent catalog to the ANSS Comprehensive Catalog and Global Centroid Moment Tensor (Global CMT) catalog to compare reported locations, depths, and magnitudes. We find that global earthquake catalogs not only generally provide reasonably comparable locations (within 10 km on average), but also they systematically overestimate depth that may have implications for earthquake shaking predictions based solely on earthquake origin information. Geodetic magnitudes are comparable to seismically inferred magnitudes, indicating that gCent models are unlikely to be systematically biased by the presence of postseismic deformation. We additionally highlight limitations of the gCent catalog induced by both the limitations of remote sensing imaging of earthquakes and our imposition of a simplified earthquake source description that does not include spatially distributed slip.

Hardware optical correlation method for dynamic detection of micrometer gaps with sub-nanometer resolution.

Surface plasmon lithography breaks through the diffraction limit with surface plasmon effect and achieves high-resolution imaging below sub-wavelengths. The dynamic detection and control of the working distance between the mask and the substrate is particularly important for the quality of the lithography samples. In this paper, the mask-substrate gap sensing mechanism is analyzed, and a mask-substrate gap absolute distance measurement model is established based on the principle of white light interference. We design a Fizeau interferometer demodulation system based on a hardware optical correlation method, and focus on analyzing the influence of the sub-nanometer surface profile of the optical wedge on the resolution. Finally, we propose a data processing method for extracting the dynamic gap value by SSA (singular spectrum analysis). The experimental results show that the system shows high performance with a gap detection range of 3.0∼6.0 µm, the stability of ±0.12 nm, and the resolution of better than 0.30 nm.

Recent Progress in Long-Range Brillouin Optical Correlation Domain Analysis.

Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security, etc. The long-range high-spatial-resolution Brillouin optical correlation domain analysis (BOCDA) has extensive development and application prospects. In this paper, long-range BOCDAs are introduced and summarized. Several creative methods underpinning measurement range enlargement, including the interval enhancement of the adjacent correlation peak (CP), improvements in the signal-to-noise ratio, and the concurrent interrogation of multiple CPs, are discussed and experimentally verified, respectively. The main drawbacks in the present BOCDA schemes and avenues for future research and development have also been prospected.

Research and application advances in rehabilitation assessment of stroke.

Stroke has a high incidence and disability rate, and rehabilitation is an effective means to reduce the disability rate of patients. To systematize rehabilitation assessment, which is the foundation for rehabilitation therapy, we summarize the assessment methods commonly used in research and clinical applications, including the various types of stroke rehabilitation scales and their applicability, and related biomedical detection technologies, including surface electromyography (sEMG), motion analysis systems, transcranial magnetic stimulation (TMS), magnetic resonance imaging (MRI), and combinations of different techniques. We also introduce some assessment techniques that are still in the experimental phase, such as the prospective application of artificial intelligence (AI) with optical correlation tomography (OCT) in stroke rehabilitation. This review provides a useful bibliography for the assessment of not only the severity of stroke injury, but also the therapeutic effects of stroke rehabilitation, and establishes a solid base for the future development of stroke rehabilitation skills.

Optical Dielectric Constant and Electronegativity Difference in A&lt;i&gt;&lt;sup&gt;N&lt;/sup&gt;&lt;/i&gt;B&lt;sup&gt;8-&lt;/sup&gt;&lt;i&gt;&lt;sup&gt;N&lt;/sup&gt;&lt;/i&gt; Type Binary Compounds

An empirical relation that correlates the optical dielectric constant and the electronegativity difference in ANB8-N type binary compounds is presented. The relation uses only one numerical constant common to all I-VII, II-VI and III-V compounds. The simplicity of the relation provides a clue to understand the role of the charge transfer from one atom to another in the origin of the optical dielectric constant. It is also shown that the optical dielectric constant correlates better with the Pauling ionicity scale than with the Phillips ionicity scale. The possible physical background of the found relation is discussed based on the results obtained.

3-D displacement profiles obtained from optical image correlation of the Hebgen Lake area

3-D displacement profiles obtained from optical image correlation of the Hebgen Lake area

Broadband intermodal fiber interferometer for sensor application: fundamentals and simulator.

An intermodal fiber interferometer using the light from an incoherent broadband source has been considered analytically and implemented as a laboratory device. It was shown that this optical scheme could be used to measure external perturbations that cause a change in the optical length of a multimode fiber. The use of an optical spectrum analyzer and correlation functions approach in extracting the utility signal made it possible to achieve a linear response to the measured external perturbation and effective fading mitigation. A pair of integral coefficients was introduced: the contrast coefficient for characterization of the coherency of the operation regime, and the fading coefficient for estimating the signal stability against non-signal parasitic influences. Analytical expressions for the utility signal parameters were derived in dependence on the parameters of the light source, multimode fiber, and optical spectrum analyzer. The relationships among fiber length, width of the light source spectrum, and frequency resolution of the optical spectrum analyzer were stated for the optimum regime of interferometer operation. The simulation of the external perturbations performed at the elaborated device proved the applicability of the proposed scheme as a sensor of various physical quantities.