Cross-correlation Principle Research Articles

Modal group refractive index measurement of few-mode fibers based on time-domain cross-correlation

We propose a measurement method based on the time-domain cross-correlation technique, combined with the cut-back method, enabling the measurement of group refractive indices (n g ) in few-mode fibers (FMF). A Mach–Zehnder interferometric system, equipped with high-precision and extensive range delay devices, is established. The system records off-axis holograms of spatial reference light at various delays interfering with the emitted light from the fiber under test. The interference energy is extracted from these holograms, and a time-domain mode energy curve is developed utilizing the principle of cross correlation. Optimal holograms at each of the curve peaks are used to reconstruct the modal field distribution, effectively separating and accurately identifying each mode within the FMF. By integrating the cut-back method, the n g corresponding to each mode is calculated based on the changes in group delay before and after fiber cutting. The n g of modes in the two-mode fibers was measured and the differential group delay calculated from the measurement agrees with the manufacturer’s specifications. The measured n g of a standard single-mode fiber aligns with the manufacturer’s specifications. Furthermore, the n g of the higher-order modes in four-mode fibers were measured by exciting them at different angles and validating the wave optics theory that the n g of the fiber modes is independent of the excitation angle. This method can simultaneously measure the n g of several modes in a fiber, providing support for the development and application of FMFs.

Identification of Microbial Strains via 2D Cross-Correlation of LC-MS Data.

Mass spectrometry is commonly used in the identification of species present in microbial samples, but the high similarity in the peptide composition between strains of a single species has made analysis at the subspecies level challenging. Prior research in this area has employed methods such as Principal Component Analysis (PCA), the k-Nearest Neighbors' (kNN) algorithm, and Pearson correlation. Previously, 1D cross-correlation of mass spectra has been shown to be useful in the classification of small molecule compounds as well as in the identification of peptide sequences via the SEQUEST algorithm and its variants. While direct application of cross-correlation to mass spectral data has been shown to aid in the identification of many other types of compounds, this type of analysis has not been demonstrated in the literature for the purpose of LC-MS based identification of microbial strains. A method of identifying microbial strains is presented here that applies the principle of 2D cross-correlation to LC-MS data. For a set of N = 30 yeast isolate samples representing 5 yeast strains (K-97, S-33, T-58, US-05, WB-06), high-resolution LC-MS-Orbitrap data were collected. Reference spectra were then generated for each strain from the combined data of each sample of that strain. Sample strains were then predicted by computing the 2D cross-correlation of each sample against the reference spectra, followed by application of correction factors measuring the asymmetry of the 2D correlation functions.

Nonlinear edge enhancement imaging based on Laguerre-Gaussian superimposed vortex filters.

Nonlinear reconstruction, which is based on the principle of cross correlation, is a commonly employed reconstruction technique in incoherent correlated digital holography systems. However, the modulation of phase masks in these systems is suppressed during the reconstruction process, resulting in an inability to express the characteristics of the phase masks. Consequently, achieving edge enhancement within these systems is constrained. We propose a nonlinear reconstruction method utilizing Laguerre-Gaussian superimposed vortex filters, which modulates the spectrum of the target during the reconstruction process. Experimental results demonstrate that this method performs well in reconstructing image edges for various phase-masked incoherent imaging systems and effectively suppresses noise. Additionally, this method enables directional edge enhancement.

Flow velocity computation using a single ERT sensor

Flow velocity is an important parameter in the multi-phase flow detection field. Electrical resistance tomography (ERT) is an advanced and non-invasive measuring technique for velocity estimation that has received considerable interest in the past decade. The process involves using two adjacent ERT sensors to collect measurements in a cross-sectional pipe, and the application of the cross-correlation (CC) principle for computing flow velocity. Currently, however, inaccurate assumptions, uncertain parameters, and noisy data greatly limit ERT efficiency and accuracy in practice. A new flow velocity computation method is presented that uses a single ERT sensor to replace two adjacent ERT sensors. According to the measurements of the single sensor and the corresponding ERT images, two key variables are computed that tightly align with the flow velocity. The proposed method overcomes the limitations of existing flow computation methods to some extents. Moreover, it can compute flow velocities in not only solid-liquid but also gas-liquid two-phase flows. Finally, experiments are conducted to validate the proposed method, and demonstrate its accuracy and reliability over existing methods.

A π-Phase-Shifted Fiber Bragg Grating Partial Discharge Sensor toward Power Transformers

Partial discharge (PD) ultrasonic detection is an early sign of the insolation defects of power transformers. The early diagnosis of PD requires the high sensitivity and reliability of ultrasonic sensing systems. For this purpose, a reformative PD ultrasonic sensing system based on phase-shifted FBG (PS-FBG) was demonstrated. By using PS-FBG as the ultrasonic sensing unit, the ultrasonic sensing system improved the response to the ultrasonic signal and overcame the electromagnetic noise. To compensate for the influence of temperature change on the ultrasonic sensing system, an automatic wavelength scanning demodulating method was carried out. The wavelength spanning strategy was optimized based on the principle of cross-correlation, in order to quicken the spanning. A PD detection test in the transformer oil was conducted, and the result shows that PS-FBG was 17.5 times more sensitive than PZT. Because of the better ultrasonic response, the proposed system was able to achieve the early diagnosis of insolation faults in a power transformer.

High-Sensitivity Fiber-Optic Low-Frequency Acoustic Detector Based on Cross-Correlation Demodulation

Fiber-optic acoustic sensors based on Fabry-Perot (F-P) interference structure have advantages of compact structure, high sensitivity, convenience to manufacture and immunity to electromagnetic interference. To simplify the demodulation system of the fiber-optic F-P sensor and reduce the demodulation cost, a low-frequency acoustic detector based on the principle of optical cross-correlation (OCC) demodulation is proposed. A fiber-optic F-P interference sensor based on the phenylene sulfide (PPS) diaphragm is used as a low-frequency acoustic detection unit. The OCC demodulation system of the F-P acoustic sensors mainly includes a superluminescent diode (SLED), a flat glass wafer and single-mode fibers. The flat glass wafer is used as the static correlation reference cavity of the PPS diaphragm-based F-P acoustic sensor. The experimental results show that the detector is responsive to low-frequency acoustic waves from below 20 Hz to 250 Hz. For the acoustic waves with a frequency of 20 Hz, the minimum detection limit (MDL) of sound pressure is 0.65 mPa. The detector has the potential for low-cost and high-sensitivity acoustic detection for applications such as infrasonic detection and photoacoustic gas detection.

Leakage Signal Analysis of Urban Gas Pipeline Based on Improved Variational Mode Decomposition

Aiming at problems of multipoint leakage source detection and low positioning accuracy in urban gas pipelines, a multipoint leak location method base on improved variational mode decomposition (VMD) was proposed. By improving the VMD decomposition of the original leakage signal, the parameters of the VMD were optimized to reduce the influence of noise and weak correlation signals on the leak location. Then the multi-point leakage location model of pipeline was established, and the sensitive modal component Intrinsic mode function (IMF) with the most leakage information was selected by multiscale entropy. According to the characteristics of the blind source separation method, the relevant time delays of the simultaneous leakage of multiple points on the pipeline and the frequency of the signal are extracted. Finally, The location of the leak source is determined according to the principle of cross-correlation. The experimental results show that compared with the direct cross-correlation method and the VMD-based method, the proposed multipoint leak diagnosis method has less error, the minimum relative error is 1.61%, and the positioning accuracy is higher.

Cross‐correlation codeless processing of BOC modulated signals

Encrypted global navigation satellite system signals (GNSS) can be tracked using codeless techniques that do not require the knowledge of the spreading code used for signal generation. These techniques can also be applied to binary offset carrier (BOC) modulated signals whose unknown code sequence can be removed through squaring. In this study, an alternative codeless approach based on the cross-correlation principle is considered. Cross-correlation codeless processing is commonly used for tracking signal components on different frequencies, such as the global positioning system (GPS) L1 and L2 P(Y) signals, and it is adapted here to BOC modulations broadcast on a single frequency. A cross-correlation codeless framework is proposed where the BOC signal is split into two data streams that are cross-multiplied to remove the unknown code sequence. Two architectures, open-loop and closed-loop processing, are proposed and analysed. The codeless cross-correlation function is introduced and open-loop processing is used to reconstruct it from the received samples. Closed-loop processing based on cross-correlation phase lock loop (PLL) and delay lock loop (DLL) are used to estimate the signal parameters. The proposed cross-correlation framework is thoroughly analysed theoretically, through simulations and using real data. The analysis shows the effectiveness of the cross-correlation framework.

Signal processing and identification on the surface of Pinus massoniana Lamb. glulam using acoustic emission and improvement complete ensemble empirical mode decomposition with adaptive noise

A signal processing method to analyze and investigate acoustic emission (AE) signal characteristics on the surface of anisotropic Pinus massoniana Lamb. glulam material is introduced. The classical pencil lead break (PLB) method is used to simulate the AE source and research the AE signal characteristics of the specimen along the direction of both parallel and perpendicular to the grain. An effective noise-reduction method, which combines improvement complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) and wavelet packet (WP) analysis, is proposed to denoise the original AE signal in the specimen and calculate the propagation rates of the AE signal in two directions based on the principle of cross-correlation. Moreover, the energy attenuation characteristics of the AE signal in the process of propagation are also evaluated. The experimental results indicate that the proposed approach can effectively reduce the noise of the AE signal in glulam, and it can be seen that the frequency of the AE signal is mainly concentrated at 40 kHz from the spectrum diagrams of the signal. Meanwhile, the propagation rate of the AE signal along the grain direction is approximately twice that of the perpendicular to grain, while the law of the energy attenuation is just the opposite, and provides an effective theoretical basis for the research of the influence of the adhesive layer inside the glulam on the characteristics of AE signal.

Underwater distance measurement using frequency comb laser.

In this paper, we theoretically and experimentally analyze the frequency-comb interferometry at 518 nm in the underwater environment, which we use to measure the underwater distance with high accuracy and precision. In the time domain, we analyze the principle of pulse cross correlation. The interferograms can be obtained in the vicinity of N∙lpp, where N is an integer and lpp is the pulse-to-pulse length. Due to the strong dispersion of water, the pulse can be broadened as the distance increases. The distance can be measured via the peak position of the interferograms. The experimental results show a difference within 100 μm at 8 m range, compared with the reference values. In the frequency domain, we analyze the principle of dispersive interferometry. The spectrograms can be observed near the location of N∙lpp, due to the low resolution of the optical spectrum analyzer. Because of the strong dispersion of water, the modulation frequency of the spectrogram is not constant. A balanced wavelength will exist with the widest fringe, at which the group optical path difference between the reference and measurement arm is equal to N∙lpp. The position of the widest fringe can be used to measure the distance. Compared with the reference values, the experimental results indicate a difference within 100 μm at 8 m range.

Research on Accuracy of Normal Moveout in Reflection Seismic Exploration by Cross Correlation Method

In this paper, we took the time-distance curve equation and the Normal Moveout (NMO) principle as breakthrough point. According to the forward seismic simulation model and the cross-correlation principle in signal processing, we have convincingly studied the accuracy of NMO in simulation experiment. Firstly, the time-distance curve equation of single-layer reflection and the characteristics of cross-correlation are simply analysed. Then, we build the seismic forward model by Tesseral software, and accurate results are obtained after the simulation experiment is carried out. Finally, we get the conclusion by analysing and summarizing these results. The conclusion shows that the method effectively demonstrates the feasibility of the cross-correlation method in testing the accuracy of NMO, and provides a new idea for analysing the accuracy of velocity picking, even the accuracy of the underground model during petroleum exploration.

Acoustic emission signal source localization on plywood surface with cross-correlation method

The high-speed data acquisition equipment which is based on NI and LabVIEW software was used to establish the acoustic emission (AE) signal collection platform, and adopted wavelet analysis method to extract the weak of AE signal waveform from noise, aiming at the localization of AE source on plywood surface. The signal cross-correlation analysis method is used to determine the time difference between the AE signals and the different sensors,so that further calculates the average propagation speed of AE signal on the plywood surface. A kind of AE signal source localization method which is based on the cross-correlation method was proposed according to the principle of geometric positioning, and verified by means of the testing experiment which selected the lead break to simulate AE source. This paper has shown that wavelet analysis can effectively extract AE signal waveform, and the localization method based on cross-correlation principle can precisely calibrate the position of AE signal source.

Studying the Relationship between Financial Structure and Amount of Investment in Anzali Free Zone

The purpose of this study is to investigate the relationship between financial structure and amount of investment in the Anzali Free Zone. The intention of financial structure of an economic is institutional mechanisms for financing. Bank and capital market are the most important financing institutions in any economy. The research is conducted with the aim of applied research and used cross–correlation principle. The participants of the present study were 200 participants including staff and executives and investors in the Anzali Free Zone, which were selected only 130 participants with respect to the Morgan tables. Moreover, the results showed that there is a significant correlation coefficients and the relationship of the main hypothesis was also strong and straight. In addition, the result revealed that financial structure of bank–based was unsuccessful at attracting investment in the Anzali Free Zone. DOI: 10.5901/mjss.2015.v6n5p360

Analysis of the synchronization error measurement via non-collinear cross-correlation

AbstractThe method for measuring synchronization error of ultra-short pulses was introduced based on the principle of non-collinear cross-correlation. The analytical expression for the measurement was deduced according to the cross-correlation signal. The influences of angular error on the measurement were analyzed by simulated experiments. The incident angle and the angular error tolerance were both required to be considered and determined for the synchronization error measurement of ultra-short pulses. The results provide a theoretical basis for the measurement and control of the synchronization error in the coherent beam combination, plasma parameter diagnosis, etc.

Measurement of bubble velocity using Capacitively Coupled Contactless Conductivity Detection (C4D) technique

The feasibility of applying Capacitively Coupled Contactless Conductivity Detection (C4D) technique to measurement of bubble velocity in gas–liquid two-phase flow in millimeter-scale pipe is investigated. And, a new method, which combines the C4D technique and the principle of cross-correlation velocity measurement, is proposed for the measurement of bubble velocity. This research includes two parts. First, based on the principle of C4D, a new five-electrode C4D sensor is developed. Then, with two conductivity signals obtained by the C4D sensor, the velocity measurement of bubble is implemented according to the principle of cross-correlation. The research results indicate that the C4D technique is highly effective and anticipates a broad potential in the field of two-phase flow. Experimental results show that the five-electrode C4D sensor is suitable for measuring the velocity of single bubbles with a relative error of less than 5%.

Spatially-Adaptive Advection Radar Technique for Precipitation Mosaic Nowcasting

A new numerical nowcasting technique to predict the radar reflectivity field at very short term, up to few hours, is presented. The method is based on the spatial segmentation of the reflectivity field and estimated advection field to produce radar reflectivity forecasts and, for this reason, is named Spatially-adaptive Precipitation Advective Radar Estimator (SPARE). A large data set coming from the Italian radar network mosaic (spatial domain size of about 1200 1200 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) is used to test the overall performance of SPARE against the simplest method of radar map temporal persistence. An original approach to estimate the radar field motion, based on the phase cross-correlation principle, is formulated in this paper. Results are given either in terms of skill scores of predicted radar maps or in terms of predicted uncertainty. The latter provides a new methodology to evaluate the expected performance of SPARE predictions.

A Fast and Efficient Time-Delay Estimation Algorithm for Sound Localization

Time-delay estimation is an important research topic of sound localization. According to the specificity of time-delay in sound localization, a fast and efficient time-delay estimation algorithm is proposed based on the principle of fast linear cross correlation. Relative to the original time-delay estimation algorithm based on fast linear cross correlation, the proposed algorithm has enormous advantages in the time complexity and space complexity. The computing speed is twice faster than the original time-delay estimation algorithm, while the size of the memory space used is half of the original time-delay estimation algorithm.

Improve matching results for structure from motion problems

In this paper we propose a method to improve feature point matching results for structure from motion problems, which includes techniques for promoting the correspondence quality using epipolar geometry, fast decision from relative positions of matches and local geometry constraints. We start with feature points extracted from each image and initial set of matches obtained by cross correlation and relaxation principle, then several strategies exploited to detect outliers. Our method is performed before projective reconstruction phase and only two views of scene are needed. Experiments have been carried out and the results demonstrate the efficiency of proposed strategies.

A dynamic view of cellular processes by in vivo fluorescence auto- and cross-correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) is becoming increasingly popular as a technique that aims at complementing live cell images with biophysical information. This article provides both a short overview over recent intracellular FCS applications and a practical guide for investigators, who are seeking to integrate FCS into live cell imaging to obtain information on particle mobility, local concentrations, and molecular interactions. A brief introduction to the principles of FCS is provided, particularly emphasizing practical aspects such as the choice of appropriate dyes and positioning of the measurement volume in the sample. Possibilities and limitations in extracting parameters from autocorrelation curves are discussed, and attention is drawn to potential artifacts, such as photobleaching and probe aggregation. The principle of dual-color cross-correlation is reviewed along with considerations for proper setup and adjustment. Practical implications of nonideal conditions including incomplete focus overlap and spectral cross-talk are considered. Recent examples of both auto- and cross-correlation applications demonstrate the potential of FCS for cell biology.

Reading the structure of brains

It is a fashionable philosophical tenet to consider Darwinian evolution as a process which incorporates knowledge into brains. We ask ourselves: can this knowledge about the world be recognised in the structure of brains? The present article gives a partial answer to this. Mechanisms of information handling and storage may well be related to the impressive major cortices of the vertebrate brain, the cerebral and the cerebellar cortices. The structure of the first fits the idea of an associative memory while the second strongly suggests computation of movement in terms of velocities. In some insect brains the mechanisms of visual perception can be related to detailed neuroanatomical structure, and one such network incorporates knowledge about the optics of a camera-type eye. Another one provides the wiring that would be expected in a set of velocity detectors using the principle of cross-correlation of neighbouring inputs.Knowledge acquired during a lifetime is also laid down in brains but the search for the ‘engram’ in the structure of brains has not yet been very successful.