Interferometry Method Research Articles

Analyzing the geomorphometric changes of Dana County due to the Sisakhat earthquake using the Differential Synthetic Aperture Radar Interferometry (D-InSAR) method.

Analyzing the geomorphometric changes of Dana County due to the Sisakhat earthquake using the Differential Synthetic Aperture Radar Interferometry (D-InSAR) method.

3D digital holographic polarimetry of laser speckle fields formed by polycrystalline blood films: a tool for differential diagnosis of thyroid pathology

The principles and effectiveness of the method of laser polarization interferometry of dehydrated blood films (facies) for the differential diagnosis of thyroid pathology have been studied. For this purpose, a theoretical description of the processes of formation and layer-by-layer phase scanning of the polarization structure of speckle fields in the blood facies of donors and patients with nodular goiter, autoimmune thyroiditis, and papillary cancer has been developed for the first time. A statistical analysis of holographically reconstructed maps of polarization ellipticity of the singly scattered component of the speckle field was conducted. Based on this analysis, the most sensitive markers for the diagnosis and differentiation of thyroid pathology were identified. Excellent diagnostic accuracy (91%–93%) and very good differentiation accuracy (86%–89%) were achieved for nodular goiter, autoimmune thyroiditis, and papillary cancer.

Mountain Landslide Monitoring Using a DS-InSAR Method Incorporating a Spatio-Temporal Atmospheric Phase Screen Correction Model

The detection of potential rural mountain landslide displacements using time-series interferometric Synthetic Aperture Radar has been challenged by both atmospheric phase screens and decoherence noise. In this study, we propose the use of a combined distributed scatterer (DS) and the Prophet_ZTD-NEF model to rapidly map the landslide surface displacements in Diqing Tibetan Autonomous Prefecture, China. We conducted tests on 28 full-resolution SENTINEL-1A images to validate the effectiveness of our methods. The conclusions are as follows: (1) Under the same sample conditions, confidence interval estimation demonstrated higher performance in identifying SHPs compared to generalized likelihood ratio test. The density of DS points was approximately eight times and five times higher than persistent scatterer interferometry and small baseline subset methods, respectively. (2) The proposed Prophet_ZTD-NEF model considers the spatial and temporal variability properties of tropospheric delays, and the root mean square error of measured values was approximately 1.19 cm instead of 1.58 cm (PZTD-NEF). (3) The proposed Prophet_ZTD-NEF method reduced the mean standard deviation of the corrected interferograms from 1.88 to 1.62 cm and improved the accuracy of the deformation velocity solution by approximately 8.27% compared to Global Position System (GPS) measurements. Finally, we summarized the driving factors contributing to landslide instability.

A comparative study of sub-sampling methods in X-ray speckle interferometry based phase contrast imaging using synchrotron radiation source

Near-field X-ray speckle interferometry is a technique for X-ray multi-modal imaging that does not require optics and is very simple to implement. It is capable of producing absorption, phase, and scatter contrast images by utilizing random scattering media like sandpaper. The generation of these images relies on the correlation of near-field speckles, with one pattern recorded in the absence of an object and another with an object present. Our study focuses on comparing and evaluating various sub-sampling methods used in a correlation-based approach in real space. Additionally, we have analyzed the potential benefits and strengths of these sub-sampling methods in the context of X-ray speckle imaging using synchrotron radiation based X-ray source, and shown that cosine and Gaussian approximations provided superior sub-pixel delay estimations.

Infrared spectra of solid-state ethanolamine: Laboratory data in support of JWST observations

Ethanolamine (NH$_2$CH$_2$CH$_2$OH; EA) has been identified in the gas phase of the interstellar medium within molecular clouds. Although EA has not been directly observed in the molecular ice phase, a solid-state formation mechanism has been proposed. However, the current literature lacks an estimation of the infrared band strengths of EA ices, which are crucial data for quantifying potential astronomical observations and laboratory findings related to their formation or destruction via energetic processing. We conducted an experimental investigation of solid EA ice at low temperatures to ascertain its infrared band strengths, phase transition temperature, and multilayer binding energy. Since the refractive index and the density of EA ice are unknown, the commonly used laser interferometry method was not applied. Infrared band strengths were determined using three distinct methods. In addition to evaluating EA band strengths, we also tested the advantages and disadvantages of different approaches used for this purpose. The obtained lab spectrum of EA was compared with the publicly available MIRI MRS James Webb Space Telescope observations towards a low-mass protostar. We used a combination of Fourier-transform transmission infrared spectroscopy and quadrupole mass spectrometry. The phase transition temperature for EA ice falls within the range of 175 to 185 K. Among the discussed methods, the simple pressure gauge method provides a reasonable estimate of band strength. We derived a band strength value of about $1 $ cm molecule$^ $ for the NH$_2$ bending mode in the EA molecules. Additionally, temperature-programmed desorption analysis yielded a multilayer desorption energy of 0.61pm 0.01 eV. By comparing the laboratory data documented in this study with the JWST spectrum of the low-mass protostar IRAS 2A, an upper-limit for the EA ice abundances was derived. This study addresses the lack of quantitative infrared measurements of EA at low temperatures, crucial for understanding EA's astronomical and laboratory presence and formation routes. Our approach presents a simple yet effective method for determining the infrared band strengths of molecules with a reasonable level of accuracy.

Evaluating the Impact of Interferogram Networks on the Performance of Phase Linking Methods

In recent years, phase linking (PL) methods in radar time-series interferometry (TSI) have proven to be powerful tools in geodesy and remote sensing, enabling the precise monitoring of surface displacement and deformation. While these methods are typically designed to operate on a complete network of interferograms, generating such networks is often challenging in practice. For instance, in non-urban or vegetated regions, decorrelation effects lead to significant noise in long-term interferograms, which can degrade the time-series results if included. Additionally, practical issues such as gaps in satellite data, poor acquisitions, or systematic errors during interferogram generation can result in incomplete networks. Furthermore, pre-existing interferogram networks, such as those provided by systems like COMET-LiCSAR, often prioritize short temporal baselines due to the vast volume of data generated by satellites like Sentinel-1. As a result, complete interferogram networks may not always be available. Given these challenges, it is critical to understand the applicability of PL methods on these incomplete networks. This study evaluated the performance of two PL methods, eigenvalue decomposition (EVD) and eigendecomposition-based maximum-likelihood estimator of interferometric phase (EMI), under various network configurations including short temporal baselines, randomly sparsified networks, and networks where low-coherence interferograms have been removed. Using two sets of simulated data, the impact of different network structures on the accuracy and quality of the results was assessed. These patterns were then applied to real data for further comparison and analysis. The findings demonstrate that while both methods can be effectively used on short temporal baselines, their performance is highly sensitive to network sparsity and the noise introduced by low-coherence interferograms, requiring careful parameter tuning to achieve optimal results across different study areas.

1.6 µm tunable and switchable single-frequency erbium-doped fiber laser.

We present a tunable and switchable single-frequency (SF) erbium-doped fiber laser (EDFL) operating at 1.6 µm. For the first time, a multichannel Sagnac filter, a "θ" sub cavity, and a saturable absorber (SA) have been combined to achieve SF operation of single- and dual-wavelength tunability as well as single-dual-triple-wavelength switching. The laser exhibited excellent stability, with no mode-hopping over the 60-minute observation period. Furthermore, linewidths measured utilizing the short-delay self-heterodyne interferometry method are less than 300 Hz. The investigated narrow linewidth SF EDFL has the potential to extend the applications in optical communications and provide a new idea for L-band tunable lasers.

Interferometry of ionospheric E-region irregularities based on Kunming VHF radars

There is a long history of using VHF radar systems to detect ionospheric irregularities based on the theory of coherent scattering. According to previous work, there is a high occurrence of field-aligned irregularities (FAIs) in the ionospheric E-region over Kunming, China. In this paper, the VHF coherent scattering radar at Kunming is used to study the FAIs in the ionospheric E-region. Different arrangement of VHF radar antenna arrays, interferometry, and FAI echo parameter inversion methods are designed and tested. The measurement results show that the temporal and spatial characteristics of the irregularities can be obtained using these methods, as well as more refined spatial three-dimensional structure information. It is indicated that the new arrangement of the VHF radar antenna array is feasible to operate interferometry detection of E-region FAIs with the Kunming VHF radar.

Sky localization of space-based detectors with time-delay interferometry

The accurate sky localization of gravitational wave (GW) sources is an important scientific goal for space-based GW detectors. The main differences between future space-based GW detectors, such as Laser Interferometer Space Antenna (LISA), Taiji, and TianQin, include the time-changing orientation of the detector plane, the arm length, the orbital period of the spacecraft and the noise curve. Because of the effects of gravity on three spacecraft, it is impossible to maintain the equality of the arm length, so the time-delay interferometry (TDI) method is needed to cancel out the laser frequency noise for space-based GW detectors. Extending previous work based on equal-arm Michelson interferometer, we explore the impacts of different first-generation TDI combinations and detector's constellations on the sky localization for monochromatic sources. We find that the sky localization power is almost unaffected by the inclusion of the TDI Michelson (X, Y, Z) combination in the analysis. We also find that the variation in the sky localization power for different TDI combinations is entirely driven by the variation in the sensitivities of these combinations. For the six particular TDI combinations studied, the Michelson (X, Y, Z) combination is the best for source localization.

Dynamic phase measurement based on two-step phase-shifting interferometry with geometric phase grating

Abstract This paper proposes a novel dynamic 2-step phase-shifting interferometry method with a geometric phase grating and direct aberration-free object phase recovery algorithm. By exploring the amplitude-phase modulation property of the geometric phase grating, two-step phase-shifting interferograms with π / 2 phase shift can be obtained in a single shot through two kinds of spatial-multiplexing arrangements. Then the restriction on the background uniformity of the 2-step phase-shifting algorithms and the system aberration can be avoided simultaneously, based on the presented direct and fast object phase demodulation strategy with an object-free state recorded in advance, so an accurate object measurement result can be guaranteed. Accordingly, a detailed analysis of the theoretical model of error sources is conducted by taking the depolarization error of geometric phase grating and phase measurement model error into consideration, with a Least Squares Iteration optimization strategy established to further improve the measurement accuracy. Experiments on various types of phase objects, such as a photo-etched quartz substrate, the spatial light modulator, and a silicon chip, validate the effectiveness and accuracy of our method when compared with the reference phase obtained from 4-step temporal phase-shifting method. The dynamic phase measurement capability is demonstrated by exhibiting the evaporation process of alcohol droplet.

Regulation of the Phase Structure in the Crystallizing Curing System PCL–DGEBA

Qualitative and quantitative aspects of the formation of various types of phase structures, sizes and compositions were considered. For the studied polycaprolactone–epoxy resin/4,4′-diaminediphenylsulfone system, a phase diagram characterized by amorphous separation with a lower critical solution temperature was constructed and its evolution was traced with increasing conversion degree of epoxy groups. A method is proposed for determining the temperature–concentration parameters that determine the type of phase structure of composite materials, based on the optical interferometry method. All types of phase structures and features of structure formation in the phase reversal region and at its boundaries have been studied using optical and scanning electron microscopy methods. The dimensions of the structural elements were determined and their correlation with the temperature and concentration regimes of the system’s curing was established. The composition of phases in cured compositions was studied using FTIR spectroscopy, DSC and scanning electron microscopy. It is shown that by varying the temperature–concentration parameters of curing reactive thermoplastic systems, it is possible to specifically regulate the type of phase structure, phase sizes and their composition, which determine the operational properties of the material.

Simultaneous estimation of multiple order phase derivatives using deep learning method in digital holographic interferometry

For non-contact deformation testing, digital holographic interferometry is a prominent optical technique where the first and second order interference phase derivatives directly embed information about the strain and curvature distributions of a deformed object. Hence, reliable extraction of multiple order phase derivatives is of great practical significance; however, this problem is marred by several challenges such as the need of multiple differentiation operations, complex shearing operations and performance degradation due to noise. In this paper, we introduce a deep learning approach for the direct and simultaneous estimation of first and second order phase derivatives in digital holographic interferometry. Our method's performance is demonstrated via rigorous numerical simulations exhibiting wide range of additive white Gaussian noise and speckle noise. Moreover, we substantiate the practical efficacy of our proposed method for processing deformation fringes acquired via digital holographic interferometry.

Estimation of seismometer clock time offsets using Kalman Filter towards accurate seismic velocity change

SUMMARY Monitoring seismic velocity changes obtained from ambient noise correlations is widely used to understand changes in rock properties in response to earthquakes, volcanic activities and environmental changes. Since continuous seismic data have been accumulated, this method can estimate long-term changes in seismic velocity, such as crustal recovery after a major earthquake and temporal variations in seismic velocity related to long-term environmental change. Changes in seismic velocity can be estimated with a high temporal resolution by measuring the phase differences of ambient noise correlations based on a seismic interferometry method. Still, these phase differences are influenced not only by seismic wave velocity changes but also by errors in clock timing in seismometers. The clock drift occurs due to out-of-synchronization with the GPS clock and the drift of the internal clock. Therefore, to accurately monitor temporal changes in crustal structure by measuring the phase differences of noise correlations, it is crucial to evaluate the contribution of errors in clock timing to the phase differences. Recently, a method using an extended Kalman filter based on a state-space model was developed for reliable detection of temporal changes in the waveforms of ambient noise correlations, with the state-space model offering the advantage of flexible modelling of time-series data. In this study, we incorporated the time-shifts caused by clock time errors of the seismometer into the state-space model of the temporal changes in ambient noise correlations. We estimated seismic velocity changes, amplitude changes of noise correlations and clock time errors from 2010 April to 2021 September at seismic stations around the Shinmoe-dake volcano in Japan, which experienced eruptions in 2011 and 2018, respectively. Several stations exhibited clear clock time offsets, and the occurrence of clock time-shifts coincided with the dates when the data logger was turned off for seismic station maintenance or replacement of the seismometer. The proposed method provides stable estimations with respect to the signal-to-noise ratio of the waveform, and this stable estimation facilitates accurate timing of seismic recordings, enabling precise analysis of seismic phase arrival times.

Twenty-Meter Laser Strainmeter "Popova Isl."

This paper describes the design and principle of operation of a 20 m laser strainmeter of unequal-arm type created on the basis of a Michelson interferometer and frequency-stabilized helium-neon laser. The interferometry methods used allow the measurement of the displacement of an Earth's crust section on the base of the laser strainmeter with an accuracy of 30 pm in the frequency range from 0 (conventionally) to 1000 Hz. This laser strainmeter, when connected to an accurate time system providing an accuracy of 1 μs, should structurally become a part of the laser interferometric seismoacoustic observatory, consisting of spatially separated laser strainmeters installed in various regions of Russia.

Ultrasensitive detection of remote acoustic vibrations at 300 m distance by optical feedback enhancement

Sensitive detection of remote vibrations at nanometer scale owns promising potential applications such as geological exploration, architecture, and public security. Nevertheless, how to detect remote vibration information with high sensitivity and anti-disturbance has become a major challenge. Reported current non-contact measurement methods are difficult to simultaneously possess characteristics of high light intensity sensitivity, long working distance, high vibration response sensitivity, and anti-disturbance of ambient light. Here, we propose a polarization-modulated laser frequency-shifted feedback interferometry method with the above characteristics, to obtain remote vibration information. The method can directly measure non-cooperative targets without the need for any cooperative markers. In each interference cycle, the energy as low as 2.3 photons can be effectively responded to, and the vibration amplitude sensitivity at 300 m can reach 0.72 nm/Hz1/2 at 1 kHz. This approach provides a strategy for the ultrasensitive detection of remote vibration that is immune to electromagnetic interference.

Automated phase-visibility modulating interferometry

This paper presents the Phase-Visibility Modulating Interferometry (PVMI) method automated by a microcontroller and three servomotors, under inhomogeneous out-of-phase amplitude modulation (OPAM) in the On-Off Modulation (OOM) mode. PVMI is implemented in a triple-aperture common-path interferometer (TACPI), based on a 4f optical imaging system. The high mechanical stability of the TACPI and the properties of the PVMI technique make the present method immune to noise, robust, fast, and convenient for measuring complex amplitude with high resolution and accuracy. PVMI does not preprocess and post-process the experimental irradiances and does not need a phase step shifter or a carrier frequency. Therefore, a calibration is unnecessary, there are no detuning errors, and no bandwidth reduction. The great advantage of automated PVMI is explained and demonstrated experimentally for three translucent objects. The focal length estimation of a lens with a percentual deviation of 0.14 to validate the automated PVMI, and the evaluation of two arbitrary translucent objects with high resolution and accuracy.

Random Forest—Based Identification of Factors Influencing Ground Deformation Due to Mining Seismicity

The goal of this study was to develop a model describing the relationship between the ground-displacement-caused tremors induced by underground mining, and mining and geological factors using the Random Forest Regression machine learning method. The Rudna mine (Poland) was selected as the research area, which is one of the largest deep copper ore mines in the world. The SAR Interferometry methods, Differential Interferometric Synthetic Aperture Radar (DInSAR) and Small Baseline Subset (SBAS), were used in the first case to detect line-of-sight (LOS) displacements, and in the second case to detect cumulative LOS displacements caused by mining tremors. The best-prediction LOS displacement model was characterized by R2 = 0.93 and RMSE = 5 mm, which proved the high effectiveness and a high degree of explanation of the variation of the dependent variable. The identified statistically significant driving variables included duration of exploitation, the area of the exploitation field, energy, goaf area, and the average depth of field exploitation. The results of the research indicate the great potential of the proposed solutions due to the availability of data (found in the resources of each mine), and the effectiveness of the methods used.

Application of a three-laser optical digital interferometry in a thermogravitational analysis for binary and ternary mixtures

Abstract We discuss the application of the three-laser optical digital interferometry method for the determination of transport properties such as the thermodiffusion, the molecular diffusion and the Soret coefficients by the thermogravitational column technique. The primary objective of this study is to illustrate the capabilities and limitations of the method for quantifying these properties in both binary and ternary liquid mixtures from an optical viewpoint. It is concluded that the system is highly robust for the analysis of binary mixtures, with the combination of the results obtained by the three wavelengths increasing the accuracy of the measurement. The study of ternary mixtures, on the contrary, is limited to certain types of conditions. While the accuracy of a three-laser interferometer can be improved, the method may be compromised if the optical contrast factor matrices are poorly conditioned.

Ultrafast Salinity Interrogation Based on a Tapered Fiber Modal Interferometry and Time-Stretching Method

Ultrafast Salinity Interrogation Based on a Tapered Fiber Modal Interferometry and Time-Stretching Method

Nonstretching normal moveout correction via an extrapolated interferometry method

Nonstretching normal moveout correction via an extrapolated interferometry method