Interferometry Method Research Articles

Subsurface Imaging Using Interferometry of Distributed Acoustic Sensing Ambient Noise Measurement along a Dark Fiber Line: A Case Study in Downtown Reno, Nevada

ABSTRACT Distributed acoustic sensing (DAS) technology is an emerging field of seismic sensing that enables recording ambient noise seismic data along the entire length of a fiber-optic cable at meter-scale resolution. Such a dense spatial resolution of recordings over long distances has not been possible using traditional methods because of limited hardware resources and logistical concerns in an urban environment. The low spatial resolution of traditional passive seismic acquisition techniques has limited the accuracy of the previously generated velocity profiles in many important urban regions, including the Reno-area basin, to the top 100 m of the underlying subsurface. Applying the method of seismic interferometry to ambient noise strain rate data obtained from a dark-fiber cable allows for generating noise cross correlations, which can be used to infer shallow and deep subsurface properties and basin geometry. We gathered DAS ambient noise seismic data for this study using a 12 km portion of a dark-fiber line in Reno, Nevada. We used gathered data to generate and invert dispersion curves to estimate the near-surface shear-wave velocity structure. Comparing the generated velocity profiles with previous regional studies shows good agreement in determining the average depth to bedrock and velocity variations in the analyzed domain. A synthetic experiment is also performed to verify the proposed framework further and better understand the effect of the infrastructural cover along the cable. The results obtained from this research provide insight into the application of DAS using dark-fiber lines in subsurface characterization in urban environments. It also discusses the potential effects of the conduit that covers such permanent fiber installations on the produced inversion results.

Application of holography method for the restoration of the Williams series near the crack tip

The article describes the processing of the results of a series of experiments performed by the interference-optical method of holographic interferometry (holographic photoelasticity) aimed at computing the amplitude coefficients of the M. Williams series constituting the stress and displacement fields at the crack tip for several cracked configurations. The main objective of this study is the experimental and computational determination of the coefficients of the M. Williams series for the stress, strain and displacement fields associated with the crack tip in an isotropic linearly elastic medium taking into account regular (non-singular) terms in the multiparameter Williams series. These coefficients are named generalized stress intensity factors. The method of holographic interferometry is shown to be a convenient and efficacious tool for reconstructing the stress field near the tip of the crack, because during the experiment it is possible to obtain two families of interference fringe patterns: absolute retardation fringes (isodromics) for vertical and horizontal polarizations. Experimental outcomes were thoroughly processed using the developed digital application allowing us to accumulate the isodromics orders and coordinates of points belonging to absolute retardations. In this work, absolute retardation fringes in a plate with a central horizontal crack and a crack inclined at different angles are obtained. For each type of experimental sample, the coefficients of the Williams series were calculated taking into account non-singular terms (in the representation of M. Williams, fifteen terms were preserved). A procedure for linearization of nonlinear algebraic equations following from the relations of Favre’s law is proposed. By solving the obtained overdeterministic system of linear algebraic equations, the generalized stress intensity factors (coefficients of the M. Williams series) are estimated. Conjointly, the finite element analysis of the specimens with same geometry was effectuated. The experimentally determined values of the Williams series are compared with the results of the finite element calculation of the stress-strain state performed in the SIMULIA Abaqus software.The results of the numerical and experimental studies were found to be quite consistent. It is lucidly shown that it is imperative to keep the higher order terms in the Williams series expansions for the fields associated with the crack tip.

Research and Verification of a Novel Interferometry Method by Joint Processing of Downlink Pseudo-Noise Ranging and DOR Signals for Deep Space Exploration

Research and Verification of a Novel Interferometry Method by Joint Processing of Downlink Pseudo-Noise Ranging and DOR Signals for Deep Space Exploration

MEASUREMENT OF TRANSPORTED GAS CONSUMPTION: ANALYSIS OF MEASUREMENT METHODS

One of the key aspects in the development of the economy of the Republic of Azerbaijan is the export of natural gas to foreign countries. The relevance of the issue of measuring consumption increases over time with the expansion of gasification operations in the country and the growth of gas exports to the international market. Therefore, there is a demand for the development of new projects for the improvement of the used metering systems in accordance with modern standards, their reconstruction with more efficient methods, and the discovery and application of new measuring devices and methods. During such reconstruction activities, the main focus is naturally on creating optimal and cost-effective information measurement systems. The measurement process is a precision-demanding operation, and various nuances affect the reliability of the result. Metrology is the scientific discipline that implements measurement processes. The key stage for its accuracy is the proper organization of the measurement device and methods in accordance with the characteristics of these devices. Additionally, the expertise of the personnel involved in the measurement process significantly influences the reliability of the measurement result. Failure to adhere to these processes negatively impacts the reliability of the result. In Azerbaijan, the widely used method of consumption measurement is the orifice metering method (ISO 5167-1), but this method has both advantages and disadvantages for large-diameter flow meters. These include a limited range of measured flow velocities, fouling and contamination of the diaphragm edge during operation, the complexity and high labor intensity of regular technical maintenance, high costs of spare parts, and the construction and installation of measuring devices. These problems lead to inaccuracies in gas consumption measurement, causing time and material losses during the process. Improving the accuracy of gas measurement in Azerbaijan can significantly increase financial gains. Therefore, alongside traditional methods, there is an interest in developing new methods for measuring volume flow with high accuracy and user convenience, as well as lower initial and operating costs. One of the promising areas for the development of modern flow measurement technology is the use of optoelectronics. Among them, the most significant interest lies in the use of Laser Doppler interferometry methods. These methods have been proven to be the most effective for studying physically dispersed environments (such as gas and liquid). The advantages of Laser Doppler anemometry, based on these methods, such as high accuracy and speed, a wide measurement range, resistance to noise, the possibility of simulated calibration, controllability of characteristics, and non-changeability according to the surrounding environment, make them highly favorable. The high accuracy of flow meters based on Laser Doppler anemometry allows them to be used both as working tools and as metrological support means for the verification of flow meters. Keywords: Gas consumption measurement, Measurement systems, Measurement methods, Orifice metering method, Laser Doppler.

SAL vibration estimation and compensation based on triangular interferometric signals.

Synthetic aperture Ladar (SAL) is an extension of synthetic aperture technology in the optical frequency band. Owing to the short wavelength of lasers, the system has high-resolution, high-data-rate, and refined imaging capabilities, which has potential in high-resolution observation fields such as ground observation and space target observation. However, the short wavelength of lasers also makes SAL severely sensitive to vibrations even on the micron order which cause azimuth defocusing and range cell migration. To address this problem, we establish a de-chirp signal model under vibration environment, and propose a vibration error estimation and compensation method using triangular interferometric signals. According to the symmetrical characteristics of triangular frequency modulated continuous wave (T-FMCW) and the time-frequency information introduced by the azimuthal vibration phase, we use a two-stage interferometry method to estimate instantaneous frequency introduced by the vibration errors that cause range cell migration. For the scenarios without obvious range cell migration, we use a one-stage interferometry method to estimate the instantaneous frequency. Subsequently, we establish a vibration compensation filter using the estimated instantaneous frequency to compensate for the vibration errors. We use two experiments to verify the effectiveness and superiority of the proposed method. The results show that the proposed method effectively eliminates range cell migration and azimuthal phase errors introduced by vibration errors, producing SAL imaging results with higher resolution than the conventional spectral correlation method.

Development of Band-Limitless Demodulation Method for Sinusoidal Phase Modulation Interferometry (Evaluation of Noise Floors, Maximum Measurement Speeds and Resolutions)

Development of Band-Limitless Demodulation Method for Sinusoidal Phase Modulation Interferometry (Evaluation of Noise Floors, Maximum Measurement Speeds and Resolutions)

Primena tehnika vizuelizacije strujanja za određivanje sile otpora projektila

The paper provides an overview of flow visualization methods. From the many ways of classifying flow visualization methods, the chosen method of classification is in accordance with the experimental procedure. Flow visualization methods that involve the addition of foreign material are the simplest, from the point of view of the required material and the experimental setup, in which one tracer and an adequate light source are most often applied, except for layers sensitive to pressure and shear stress. Their application is wide and most methods from this category can be modified very easily depending on the case. Visualization methods that involve addition of energy to the fluid flow use strong sources of electromagnetic radiation, most often lasers, to excite the molecules in the fluid stream, producing an adequate quantum-mechanical effect that enables visualization. Optical methods of flow visualization are based on changes in the refractive index of light caused by the presence of a fluid in motion in the test section, in addition, the principle of superposition of light waves is used in interferometry methods. Optical methods are mainly used in areas of supersonic flow and shock wave studies, but they are also present in exhaust gas propagation studies. As computational fluid dynamics is a separate subject, the physical laws on which CFD is based on are presented, as well as an example of flow visualization, which is an integral part of most calculations performed using this method. In addition to the classification and description of flow visualization methods, the paper provides an explanation of a approximate calculation procedure based on the use of one of the optical methods, Schlieren photography, in order to calculate the resistance force during supersonic projectile flow, as well as a comparison of results based on empirical data.

Comparative analysis of MT-InSAR algorithms supported by GNSS data and corner reflectors: Assessing performance and accuracy

This paper presents a comparative analysis of Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) algorithms in a corner reflector located in Lisbon, Portugal. The reflector was monitored using daily observations from the Global Navigation Satellite System (GNSS) technique with submillimeter precision. The study focuses on comparing the performance and accuracy of different MT-InSAR approaches i) the Persistent Scatterer Interferometry (PSI) method using the open-source software StaMPS, ii) the PSI method using the commercial software SARPROZ, iii) the Quasi-PS method implemented with the SARPROZ software, as well as iv) a hybrid method Persistent scatterer – Distributed Scatterer (PS-DS) obtained from the European Ground Motion Service (EGMS) with SqueeSAR algorithm. The study period assumed was from October 2017 to January 2019, by considering the same initial information (ascending orbit Sentinel images). Statistical analysis of the time series was also performed, and the density of points in the vicinity was evaluated. To provide a comprehensive evaluation of accuracy, the uncertainties associated with both the GNSS and InSAR techniques were assessed. The findings of this comparative analysis offer valuable insights into the strengths and limitations of various MT-InSAR algorithms by using a more precise technique as a benchmark. The results improve the understanding of deformation monitoring in geodetic applications and highlight the potential for enhanced accuracy in such assessments.

Along-Track Displacement of Mw 7.8 and 7.6 Kahramanmaraş Earthquakes from Sentinel-1 Offset Tracking and Burst Overlap Interferometry

On 6th February, a pair of significant earthquakes with magnitudes of 7.8 and 7.6 struck Kahramanmaraş, Turkey. The Earthquake InSAR Data Provider (EIDP) promptly produced interferograms and offset tracking results within 3 hours of acquiring Sentinel-1 satellite data. However, it was challenging to unwrap the interferograms correctly due to high displacement gradient near the rupture. Hence, early displacement fields were derived from Pixel Offset Tracking (POT) method both in range and azimuth direction with low resolution depending on pixel sizes of Sentinel-1. We used the Burst Overlap Interferometry (BOI) method to extract the accurate along-track displacement and unwrapped the BOI interferogram using Azimuth Offset Tracking (AOT) data as a guide. Combining the unwrapped BOI interferogram and the AOT data, we derive a high-quality along-track displacement field that illuminates the entire earthquake rupture over 300 km and exhibits ±4 m displacement in the along-track direction.

Modular supersonic nozzle for the stable laser-driven electron acceleration.

The sharp density down-ramp injection (shock injection) mechanism produces the quasi-monoenergetic electron beam with a bunch duration of tens of femtoseconds via laser wakefield acceleration. The stability of the accelerated electron beam strongly depends on the stability of the laser beam and the shock structure produced by the supersonic gas nozzle. In this paper, we report the study of a newly designed modular supersonic nozzle with a flexible stilling chamber and a converging-diverging structure. The performance of the nozzle is studied both numerically and experimentally with the computational fluid dynamics simulation and the Mach-Zehnder interferometry method. The simulation results and the experimental measurements are well consistent, and both prove the effectiveness of the stilling chamber in stabilizing the gas flow.

РЕЗУЛЬТАТЫ МОНИТОРИНГА ДЕФОРМАЦИОННЫХ ПРОЦЕССОВ МЕТОДАМИ ВЫСОКОТОЧНОЙ ГЕОДЕЗИИ И РАДАРНОЙ ИНТЕРФЕРОМЕТРИИ НА ГЕОДИНАМИЧЕСКОМ ПОЛИГОНЕ ЗАПОЛЯРНОГО НЕФТЕГАЗОКОНДЕНСАТНОГО МЕСТОРОЖДЕНИЯ

To obtain information on the presence and magnitude of deformation processes during the development of the Polar oil and gas condensate field, an integrated method of surveying and geodetic works was applied, including: 4 high-precision geodetic satellite observations at all points of the field's observation network to determine global rock movements expressed by changes in the coordinates of points of the geodynamic polygon; 4 high-precision leveling of a local section of a geodynamic polygon to determine vertical movements of rocks in the area of a geo-dynamically active zone; 4 application of the radar interferometry method of stable reflectors to the oil and gas production region with a large number of man-made objects. In this paper, a comparative analysis of the anthropogenic impact of field development (based on accumulated maps of reservoir pressure selection and drop) on modern deformations of the Earth's surface (based on the results of satellite observations and radar inter-ferometry) is performed.

Studying sinkholes of the earth’s surface involving radar satellite interferometry in terms of Zhezkazgan field, Kazakhstan

Purpose is to assess the potential of radar satellite interferometry (SAR interferometry) to analyze and forecast earth’s surface displacements. Methods. The study involves the analysis of previous instrumental observations, such as high-precision levelling and seismic monitoring. The observations using global navigation satellite systems (GNSS) were carried out; satellite images were processed applying a method of sequential interferometry of persistent radar signal scatters (PS). Findings. The research results have proved similarity between the data obtained with the help of ground instrumental methods and the data received using satellite interferometry. Two types of the earth’s surface sinkholes were identified: sinkholes with smooth subsidence and hidden deformations that are not accompanied by the preliminary deformational or seismic signs. Smooth subsidence is controlled and predicted successfully with the help of the SAR interferometry methods. An algorithm has been represented to predict linear displacement trends at different time intervals involving a finite element method. Originality is in a complex approach of the research performance covering the following: comparative analysis of different monitoring methods, studying different sinkhole types, identifying limitations of the available methods, and proposing new approaches for more accurate and objective analysis of the earth’s surface deformation within the field. Practical implications. The research results are of practical value for rock mechanic specialists and mining operators. They can use the data to monitor and control earth’s surface caving as well as provide staff safety and preserve ground infrastructure where it is possible.

Problem of Measuring Absorption Using Time-Resolved Photothermal Common-Path Interferometry under Conditions of Developed Heat Diffusion

We present a study of the problem of measuring ultra-low absorption in quartz materials using the time-resolved photothermal common-path interferometry (TPCI) method, which we proposed and elaborated, with allowance for developed heat diffusion in the samples. This task is related to the implementation of one of the ways of increasing the sensitivity of measurements, namely, increasing the energy of the heating pulse by increasing its duration. Analytical formulas for the time dependence of the power of the time-varying component of the probe radiation are obtained in the Gaussian approximation for the laser beams. A correction factor that takes into account the heat diffusion effect is calculated theoretically and used during calibration. The rate at which the power of the time-varying component decreases when the sample is cooled after the end of the heating pulse is calculated. When measuring in crystalline quartz, quartz glass, and also in air, the calculated rate coincided with the experimental one, which is additional evidence for the reliability of the calculations of the correction factor for calibrating the measurements. When the duration of the heating pulse is increased to 5 ms, the calculated sensitivity of the scheme for measuring absorption in quartz glasses is 2 × 10−9 cm−1.

Axial shift mapping: a self-referencing test for measuring the axial figure of near-cylindrical surfaces

Lateral shearing self-referencing interferometry methods shift the surface under test between measurements to separate its topography from that of the reference surface. However, rigid body errors occur during shifting, creating an ambiguity in the quadratic term of the extracted surfaces. We present axial shift mapping, a lateral shearing self-referencing interferometry method for cylinders, in which the quadratic ambiguity is resolved by measuring the rigid body errors using known artifact mirrors residing in the interferometer’s field of view. First, one-dimensional lines of a flat mirror are measured with 2.8 nm RMS difference compared to a three flat test. Then, axial shift mapping is extended to cylindrical surfaces using a computer generated hologram. We find that axial shift mapping results in full surface extraction of cylindrical optics, along the axial direction, with a repeatability of 4.4 nm RMS. We also find that the reference surface extracted through axial shift mapping is within 4.5 nm RMS of the transmitted wavefront error of the computer generated hologram substrate, which was expected to be the largest contribution of reference wavefront error.

Co-seismic Ground Deformation Monitoring on Brebes-Segment of Baribis-Kendeng Fault Zone Based on Sentinel-1 Data

Co-seismic deformation is a sudden change in the earth’s surface in a fault zone. Therefore, with modern satellite imagery, it is possible to investigate. Synthetic Aperture Radar (SAR) data from Mission Sentinel-1 is one example of satellite imagery that can be used to identify deformation. We employ the interferometry method by utilizing the Interferometric synthetic aperture radar Scientific Computing Environment (ISCE) and another InSAR software to monitor the co-seismic ground deformation in the form of line-of-sight (LOS) displacement. This research focused on the Brebes Segment of the Baribis-Kendeng Fault Zone and applied the interferometry method for the March 22, 2015, Balapulang earthquake (M4.7) and December 11, 2020, Brebes earthquake (M4.2). The earthquake event choice is based on the shallow depth of the hypocenter, which represents the earthquake originating from the fault in the crustal, not the megathrust subduction. The results show that despite the earthquake occurring under the thick quaternary sediment of the north shore of Java Island, the deformation caused by the co-seismic is still emerging to the surface. The LOS displacement was detected within the range of 6 cm from the ascending and descending track of the satellite sensors. Furthermore, this result may provide new information on the Baribis-Kendeng Fault zone, specifically the Brebes Segment.

Comparison of Millimeter Radio Interferometry Methods for Fast Processes with and Without Frequency Conversion

Comparison of Millimeter Radio Interferometry Methods for Fast Processes with and Without Frequency Conversion

Complex analysis of earthquake deformations using SAR images: Examples from Croatia and Greece

This study presents an assessment of the displacements of the Earth’s crust generated by two earthquakes: one in Croatia on 29th December 2020 and one in Greece on 3rd March 2021. The main data source is SAR satellite images from Sentinel-1A and B (ascending and descending orbits) in the form of images of the amplitude and phase signals. The data is processed via SNAP software package. The results are obtained applying the differential radar interferometry method (DInSAR). The Line of Sight (LoS) displacements are converted into vertical displacements and compared with modeled deformations of the Earth’s surface using rectangle finite source model proposed by Okada.

Estimation of the sensitivity of optical measurements using a holographic interferometer

Various interferometers used for high-precision spectroscopic measurements are considered, and the choice of a holographic interferometer based on the spatial-spectral method of holographic interferometry is justified, with the help of which the movements of the phase center of a coherent light flux in a wide dynamic range are measured in real time and measurement information is recorded digitally. On the basis of mathematical relations proposed by the authors in previous publications and based on the results of experimental studies, the sensitivity of a holographic interferometer to spatial displacements of phase centers (focus points) of light streams – point light sources forming a holographic interferogram is numerically estimated. The dependence of the level of the normalized intensity of the luminous flux in the central region of the holographic interferogram on the movement of the actual point light source along the normal to the plane of the Fourier hologram is established. Based on the results of mathematical modeling, it is shown that the sensitivity of the holographic interferometer to the movements of a real point light source along the normal to the plane of the Fourier hologram depends on the parameters of the optical scheme of the holographic interferometer when exposing the hologram and during measurements. At the same time, the sensitivity of the holographic interferometer to the indicated displacements of a real point light source can only be evaluated experimentally. It is proposed to increase the sensitivity of the holographic interferometer by using a thin collecting lens in its optical scheme. For the first time, a mathematical relation was obtained and investigated for the gain coefficient of the light flux phase with a spherical wavefront, which makes it possible to numerically estimate the increase in sensitivity of a holographic interferometer implementing the spatial-spectral method of holographic interferometry with known parameters of a thin collecting lens in an optical scheme. It is shown that the sensitivity of a holographic interferometer to the movements of an imaginary point light source along the normal to the plane of the Fourier hologram is 2.86 times greater than its sensitivity to the same movements of a real point light source. It is established that the sensitivity of a holographic interferometer with a volumetric Fourier hologram and a thin collecting lens in its design can be increased by at least an order of magnitude compared to the sensitivity of known optical interferometers. The results of assessing the sensitivity of a holographic interferometer implementing the spatial-spectral method of holographic interferometry to the movements of point sources of real and imaginary light fluxes, as well as the obtained ratio for the gain of the light flux phase gain by a thin collecting lens will be useful for high-precision measurements of linear and angular displacements of objects, as well as for the construction of photonic device designs. Based on the results of the study, an experimental sample of an acousto-electric converter was developed and manufactured on the basis of a holographic interferometer, which has high sensitivity in wide dynamic and frequency ranges and is intended for use in acoustic location of unmanned aerial vehicles.

Mapping and Pre- and Post-Failure Analyses of the April 2019 Kantutani Landslide in La Paz, Bolivia, Using Synthetic Aperture Radar Data

Urban landslides have brought challenges to developing countries undergoing urbanization. Rapid approaches to assess ground deformation are required when facing the challenge of insufficient geological survey methods. Additionally, it is indeed a challenge to map landslide-affected areas, especially precipitation-induced landslides, through optical remote sensing methods. This study applied SAR change detection methods to map the slope failure event of the San Jorge Kantutani landfill site in La Paz, Bolivia, which occurred in April 2019, and Multi-Temporal Synthetic Aperture Radar Interferometry (MTInSAR) methods to assess pre- and post-failure ground stability related to this event. We found that the amplitude information of high-resolution COSMO-SkyMed SAR imagery and its texture information can be very useful in landslide mapping, especially in situations in which optical images are not available because of complex meteorological conditions and the similar spectral characteristics between the original land cover and landslide deposits. The MTInSAR analyses found that there was already significant deformation of more than 50 mm/year along the slope direction over this site before the landslide, and such deformation could be clearly discriminated from the surrounding environment. After the landslide event and the remobilization of the landslide deposit, the slope still shows a deformation velocity of more than 30 mm/year. The SAR amplitude change detection and MTInSAR fully exploited the SAR data in landslide studies and were useful in back analyzing the occurred landslides; this could be a good method for monitoring the ground stability of La Paz or even on a national scale over the long term for reducing the catastrophic effects of geological hazards in this landslide-prone city.

A white-light interferometry method for 3D measurement of compactly spaced micro-nano structural units

Micro-nanostructures refer to technologies that operate at the nanoscale and provide materials and devices with unique mechanical, physical, and chemical properties. These structures have diverse applications in fields such as microelectronics, biotechnology, aerospace, and metamaterials. As precision machining technology advances, the demand for smaller sizes and higher accuracy of structural units has increased, leading to more compact integration. Consequently, the lossless and high-precision 3D measurement of highly integrated micro-nanostructure components has become increasingly challenging. In this study, we analyzed measurement errors in compactly spaced microstructural units using white-light scanning interferometry and proposed an algorithm to optimize this technology. By combining coherent peak-histogram processing with signal correlation analysis, we were able to improve the measurement accuracy by approximately ten times compared to current mainstream algorithms. To validate our algorithm, we performed experiments using metasurfaces with structural unit spacing at the order of sub-micrometer. The results obtained demonstrated the effectiveness of our algorithm in achieving accurate measurements.