Differential Phase Measurements Research Articles

Complex exponential reconstruction algorithm accelerated by cascadic multigrid method

When laser beam propagates through the turbulent atmosphere, there are branch points in wavefront, which are caused by deep turbulence or long propagation distance. Conventional least-square reconstruction algorithms cannot restore the discontinuous wavefront, which severely limits correction performance of an adaptive optics system. If the incoming wavefront contains a branch cut, there is <inline-formula><tex-math id="M1">\begin{document}$ {\rm{2}}n{\text{π}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20182137_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20182137_M1.png"/></alternatives></inline-formula> difference between the measured phase difference and the principle phase difference, which is the reason why conventional least-square reconstruction algorithms cannot reconstruct wavefront with branch points. The complex exponential reconstructor is developed to restore the discontinuous wavefront with phase difference replaced by complex exponents. However, thousands of iterations are required by the complex exponential reconstructor before converging to an acceptable solution. In order to speed up the iterative calculation, the cascadic multigrid method (CMG) is introduced in the process of wavefront reconstruction. The proposed method can be used to restore discontinuous wavefront with lower residual error similar to those reconstructed by the direct iteration. The number of float point multiplications required by the CMG method is nearly 2 orders of magnitude lower than that required by the direct iteration. The acceleration of the CMG method increases with the number of subapertures increasing. The performance of CMG method to recover continuous wavefront is also investigated and compared with conventional wavefront reconstruction algorithm based on successive over-relaxation. It is shown that the CMG method has good capability for wavefront reconstruction with high precision and low computation cost no matter whether it is applied to discontinuous or continuous wavefront. Furthermore, the CMG method is used in the adaptive optics for correcting the turbulence aberration. The direct slope wavefront reconstruction algorithm based on the assumption that the measured slope and the control voltage satisfy the linear relationship cannot restore the wavefront with branch points. As a result, the adaptive optics system with the CMG method doubles the correction quality evaluated by the Strehl ratio compared with that with the direct slope wavefront reconstruction algorithm.

Inline measurement of modal phase differences for the characterization of intermodal cross-phase modulation

We present an inline measurement technique for the phase difference between two transverse fiber modes. This technique proves to be well suited for direct measurement of an all-optically changed phase difference between two transverse modes of picosecond probe pulses, induced via intermodal cross-phase modulation by co-propagating picosecond control pulses. We achieved unprecedented agreement with the corresponding analytical description for time-independent changes of the phase difference as well as for time-dependent changes on an intra-pulse timescale. The simple and accurate predictability combined with the ability to measure modal phase differences inline poses a key step towards full all-optical control over transverse modes in fibers. This may lead the way to a variety of novel functionalities for all-fiber applications, like a spatial degree of freedom in fiber-sensing technology by using transverse fiber modes or all-optical spatial and temporal pulse shaping inside a fiber.

Measurement Method for Resistive Current Components of Metal Oxide Surge Arrester in Service

As an important power system protection device, the condition of metal oxide surge arresters (MOSAs) in service could be monitored, and online monitoring might be considered in a few critical installations. In this paper, a new resistive components measurement method termed as the remote nonsimultaneous resistive current measurement method (RNS) for MOSAs online condition monitoring is proposed. The RNS remotely and nonsimultaneously measures all types of resistive current parameters of MOSAs by employing the remote nonsimultaneous phase difference measurement method and noninteger harmonic analysis algorithm. The simulation and application results indicate that the proposed method accurately measures various parameters of MOSAs under complicated field circumstances.

Fast and Accurate THz Permittivity Measurement Using a Self-Heterodyne Technique and Multitone Signal With Nonuniform Intervals

A permittivity measurement system operating in the terahertz waveband around 300 GHz achieves fast measurement by using a self-heterodyne technique to measure phase differences. Errors are reduced because a multitone technique with nonuniform frequency intervals enables us to apply a phase-unwrapping method to the self-heterodyne system. For multitone signal generation, just single-frequency oscillators and local oscillator leakage from a modulator are used. The system achieves a measurement time of 0.03 ms at one point, which is 1/200 compared to a conventional system using a vector network analyzer. With the same measurement time, the maximum measurement error can be reduced to less than half compared to the conventional two-tone self-heterodyne system.

QUALITY ASSESSMENT OF AN EXTENDED INTERFEROMETRIC RADAR DATA PROCESSING APPROACH

Abstract. Radar data acquisition is a reliable technology to provide base data for topographical mapping. Its flexibility and weather independency makes radar data more attractive in comparison with traditional airborne data acquisition. This advantage emplaces radar data acquisition as an alternative method for many applications including Large Scale Topographical Mapping (LSTM). LSTM i.e. larger or equal than 1 : 10.000 map scale is one of the prominent priority tasks to be finished in an accelerated way especially in third world countries such as Indonesia. The available TerraSAR-X Add on Digital Elevation Model X (TanDEM-X) Intermediate Digital Elevation Model (IDEM) from German Aerospace Center (DLR) as one useful global scientific data set however still complies with High Resolution Terrain Information (HRTI) Level 3 only. The accuracy of the end product of pairwise bi-static TanDEM-X data can be improved by some potential measures such as incorporation of Ground Control Points (GCPs) within the interferometric data processing. It is expected that the corresponding end product can fulfil HRTI Level 4 specification. From this point, we focus on the step of phase difference measurements in radar interferometry to generate elevation model with least square adjustment approach using three main parameters i.e. height reference, absolute phase offset and baseline. Those three parameters are considered to be essential within the Digital Surface Model (DSM) generation process. Therefore it is necessary to find the optimal solution within aforementioned adjustment model. In this paper we use an linearized model, as discussed in section 2.4, to process the bi-static TanDEM-X datasets and investigate how this improves the accuracy of the generated DSM. As interferometric radar data processing relies on accurate GCP data we use Indonesian Geospatial Reference System (SRGI) for our investigations. Also, we use baseline and phase offset information from TanDEM-X metadata. Subsequently, the DSM generated using Sentinel Application Platform (SNAP) desktop, is the main product used for LSTM. This product has to be assessed using check points derived from conventional airborne data acquisition using RCD-30 metric camera and the accuracy is compared with the accuracy of the IDEM. Summarized, this paper aims on an improvement of the DSM generation by adjusting main parameters through our linearized model.

Study on the Detection Method of Ultrasonic Hydrogen Concentration

In this paper, the ultrasonic phase difference detection method is proposed aiming at the problem existing in hydrogen detection technology. The method is based on the significant difference between the sound speed of hydrogen and other gases. Using the double channel design, the ultrasonic speed difference is transformed into the phase difference. The measured phase difference is used to reflect the change of gas concentration, and the measurement accuracy is improved. Digital temperature sensor is used to compensate the environment temperature, and the working temperature range of the sensor is enlarged. The experimental results show that the relative error of this measurement method is less than 2%, which meets the requirements of relevant national standards, and realizes the fast, high accuracy, low power consumption, low cost detection, and has high theoretical significance and application value.

A Method for the Measurement of Digitizers’ Absolute Phase Error

A lot of engineering applications, from telecommunications to power systems, require accurate measurement of phase angles. Some of them, like synchrophasor measurement and calibration of instrument transformers with digital output, in order to reach high phase measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this paper a method for the measurement of digitizers’ absolute phase errors is proposed. It adopts a sinewave and two square waves, that are the digitizer sample clock and a phase reference signal. Combining the measurements of the relative phase differences between the adopted signals it is possible to accurately evaluate the absolute phase error of a digitizer.

Локальная навигационная система для автоматического причаливания судна

This paper shows that it is necessary to solve the problem of accurate ship positioning to provide automatic ship berthing. It is impossible to solve this problem using global positioning systems since they do not provide the proper precision. The principles and methods of development of a local navigation system are discussed. The system operation is based on measurement of the distance between the antennas of radio equipment installed on a ship and at the quay. Microwave propagation analysis is used for distance measurements. It is followed by a homodyne procession of microwave signals and the phase difference measurements on low-frequency signals. The block diagram of the rangefinder and its operation principles are described. The main equations that determine functioning of the system are given. The procedure of the range finding by measuring the phase difference between signals is analyzed; some limitations of the method are shown. Some aspects of system operation concerning selection of its operating frequencies are discussed. It is shown that using the proposed block diagram gives possibility to create an effective local navigation system to provide automatic ship berthing.

Self-calibration of lensless holographic endoscope using programmable guide stars.

Coherent fiber bundle (CFB)-based endoscopes enable optical keyhole access in applications such as biophotonics. In conjunction with objective lenses, CFBs allow imaging of intensity patterns. In contrast, digital optical phase conjugation enables lensless holographic endoscopes for the generation of pixelation-free arbitrary light patterns. For real-world applications, however, this requires a non-invasive in situ calibration of the complex optical transfer function of the CFB with only single-sided access. We show that after an initial calibration in a forward direction, a differential phase measurement of the back-reflected light allows for tracking and compensating of bending-induced phase distortions. Furthermore, we present a novel in situ calibration procedure based on a programmable guide star, which requires access to only one side of the fiber.

Phase Difference Measurement Method Based on Progressive Phase Shift

This paper proposes a method for phase difference measurement based on the principle of progressive phase shift (PPS). A phase difference measurement system based on PPS and implemented in the FPGA chip is proposed and tested. In the realized system, a fully programmable delay line (PDL) is constructed, which provides accurate and stable delay, benefitting from the feed-back structure of the control module. The control module calibrates the delay according to process, voltage and temperature (PVT) variations. Furthermore, a modified method based on double PPS is incorporated to improve the resolution. The obtained resolution is 25 ps. Moreover, to improve the resolution, the proposed method is implemented on the 20 nm Xilinx Kintex Ultrascale platform, and test results indicate that the obtained measurement error and clock synchronization error is within the range of ±5 ps.

Calibrating SuperDARN Interferometers Using Meteor Backscatter

AbstractAccurate geolocation of ionospheric backscatter measured by the Super Dual Auroral Radar Network (SuperDARN) high‐frequency radars is critical for the integrity of polar ionospheric convection maps, which involve combining SuperDARN line‐of‐sight velocity measurements originating from multiple locations. Geolocation requires estimation of the propagation paths of the high‐frequency radio signal to and from the scattering volume. The SuperDARN radars comprise both a main and interferometer antenna array to allow the estimation of the elevation angle of arrival of the returning signal, and hence its most likely propagation path. However, over the history of operation of SuperDARN (>20 years) elevation angle data have not been routinely used owing to problems with the calibration of phase difference measurements. Instead, virtual height models have been used to estimate the most likely propagation paths, and these are often of limited accuracy. Here we present a method for calibrating SuperDARN interferometer measurements using backscatter from meteor trails measured in the near field‐of‐view of the SuperDARN radars. We present estimates of calibration factors for the SuperDARN radar in Saskatoon, Canada, at different temporal resolutions: 3 months, 10 days, and 1 day. The calibration factor varies over the 9‐year interval studied, such that employing a single value for the whole interval would lead to significant errors in elevation angle measurements at times. The higher‐resolution results show the ability of the technique to determine the calibration factor routinely at a high time resolution.

Research on high‐precision passive localization based on phase difference changing rate

SummaryPassive localization method has a wider applicable prospect as a rising localization resort with well flexibility. The acquisition of phase difference changing rate is a very practical problem in passive localization for the way how to get the phase difference, and a better error precision directly affects the accuracy of the localization. Firstly, based on the analysis of the positioning principle of phase difference changing rate, it studies the characteristics of phase difference changing rate and proposes a novel resolving phase ambiguity algorithm based on a double baselines system cosine theorem (DBSCT), which can eliminate the phase difference ambiguity efficiently. Secondly, it studies two typical methods to extract the high‐precision phase difference changing rate from the unambiguity phase difference, namely, difference algorithm and Kalman algorithm. Finally, it compares the Kalman algorithm with the difference algorithm through computer simulation. Simulation results show that the Kalman algorithm can efficiently smoothen the phase difference data and suppress the measurement noise to achieve a high positioning accuracy. Simulation results also show that with a certain phase difference measurement accuracy, the phase difference rate accuracy extracted by the Kalman algorithm is higher than that we require. Therefore, we can appropriately relax the phase difference measurement accuracy requirements to achieve the same positioning accuracy. So, it has a great application value.

Photonics-Based Dual-Band Radar for Landslides Monitoring in Presence of Multiple Scatterers

In this paper, a dual-band photonics-based radar system used for precise displacement measures in a multitarget scenario is described. The radar was designed for monitoring applications to prevent both structural failures of buildings and landslides. The radar system exploits the technique of stepped frequency continuous wave signal modulation and the displacement of the targets is evaluated through differential phase measurements. In this work, encouraged by the results already achieved in the single-target scenario, we present an investigation extended to the case of multiple targets. We aim to evaluate the accuracy of the displacement estimation both from a simulated and experimental point of view, and to understand how multiple targets impact on the final estimate of displacements. Simulation results demonstrate that it is possible to achieve a typical accuracy of less than 0.2 mm for distances up to 400 m. These results are confirmed by preliminary experimental outcomes, which take into account different operative conditions with multiple targets. Finally, concluding remarks and perspectives draw the agenda for our future investigations.

Distributed Expectation-Maximization Algorithm for Speaker Localization in Reverberant Environments

Localization of acoustic sources has attracted a considerable amount of research attention in recent years. A major obstacle to achieving high localization accuracy is the presence of reverberation, the influence of which obviously increases with the number of active speakers in the room. Human hearing is capable of localizing acoustic sources even in extreme conditions. In this study, we propose to combine a method based on human hearing mechanisms and a modified incremental distributed expectation-maximization (IDEM) algorithm. Rather than using phase difference measurements that are modeled by a mixture of complex-valued Gaussians, as proposed in the original IDEM framework, we propose to use time difference of arrival measurements in multiple subbands and model them by a mixture of real-valued truncated Gaussians. Moreover, we propose to first filter the measurements in order to reduce the effect of the multipath conditions. The proposed method is evaluated using both simulated data and real-life recordings.

Differential Phase Measurement Accuracy of a Monobit Receiver

Differential phase measurements using two receiver channels are used to calculate the angle of arrival of a target signal. A monobit receiver architecture is a desirable receiver type due to its low hardware complexity, sampling rate, and power efficiency. The application motivating this paper benefits from the use of automatic gain control circuitry and sensitivity offered by the monobit architecture. However, the one-bit sampling of the input signal introduces undesirable non-linear effects. This paper analyzes the effects of a monobit receiver architecture on the differential phase accuracy. Simulated results are compared to measurement data collected from prototype monobit receiver hardware. The measured data had good agreement with the simulated results. At a high-input signal-to-noise ratio of 30 dB, the differential phase measurement sigma was approximately 0.66° for input phase shifts of 0°, 45°, and 90°. While the differential phase measurement accuracy is less than predicted by the Cramer–Rao lower bound, it is sufficient for the low cost, power, and size constrained sensor application motivating this paper.

Improvement of measurement accuracy in birefringence phase difference measurement using phase-stepping method

Improvement of measurement accuracy in birefringence phase difference measurement using phase-stepping method

Estimation of Crack Mouth Opening Displacement in Concrete Using Optical Fiber Sensors

Concrete is a multi-phase composite material and used widely in construction industry because of high compressive strength and low cost. Its limited tensile strength makes it prone to cracking. Important parameters like characteristic length, fracture energy Gf critical crack width WC are used to understand cracks in concrete. The crack width is estimated either as crack mouth opening displacement (CMOD/COD) or as crack tip opening displacement (CTOD). Several optical and non-optical methods can provide information about crack presence but do not provide information on crack opening and crack width which are important from considerations of durability. To this end we present our research results in three point bend tests on pre-notched concrete samples (M-20 composition) using (a) Intensity based plastic optic fiber (POF) using phase difference measurement method (b) Fiber Bragg grating (FBG) method. The CMOD estimation and relative sensitivity of these methods will be presented.

A Urinary Bladder Volume Measurement Circuit Using a Simplified Very Small Phase Difference Measurement Circuit

SUMMARYIn order to implement the measurement and the evaluation of analog signals in high accuracy, to detect not only amplitude level but also phase information is necessary. For example, measurement of very small phase difference is desired in fields such as electric power and organism‐related. Particularly, in organism‐related field, impedance measurement is important and it is used to measure the urinary bladder volume, the respiratory volume, and so on. For these purposes, portable and real‐time measurement devices with small sized is suitable. In this paper, we propose the urinary bladder volume measurement circuit using a simplified very small phase difference measurement circuit. This circuit is able to infer the changes of urinary bladder volume by measuring bioimpedance and phase difference of urinary bladder noninvasively with four‐terminal method.

A Novel Method Based on Hilbert Transform for Signal Processing of Coriolis Mass Flowmeter

The signal phase differences of Coriolis sensor and the mass flow are proportional. To improve the measurement accuracy of flow signal processing for Coriolis mass flowmeter, a novel method based on Hilbert Transform algorithm was proposed. The main method is as follows, two signals enhanced by LZ-filter with noise-canceling were considered as Hilbert Transform, then, the phase difference of the two filtered signals was calculated by a triangle characteristic of sin function. Synchronously, the instantaneous frequency was estimated by the structure of the analytical signal. Finally, the mass flow value was obtained by calculating the phase difference. The simulation experiments and Digital Signal Processing system (DSP) verification testing demonstrate that the new signal processing method, which is the LZ algorithm, has better characteristics of real-time and high-precision than the others. The experimental results show that the accuracy of phase difference measurement is 0.02% and the tracking accuracy of frequency is better than 0.07%.

Pressure passivity of cerebral mitochondrial metabolism is associated with poor outcome following perinatal hypoxic ischemic brain injury

Hypoxic ischemic encephalopathy (HIE) leads to significant morbidity and mortality. Impaired autoregulation after hypoxia-ischaemia has been suggested to contribute further to injury. Thalamic lactate/N-Acetylasperate (Lac/NAA) peak area ratio of > 0.3 on proton (1H) magnetic resonance spectroscopy (MRS) is associated with poor neurodevelopment outcome following HIE. Cytochrome-c-oxidase (CCO) plays a central role in mitochondrial oxidative metabolism and ATP synthesis. Using a novel broadband NIRS system, we investigated the impact of pressure passivity of cerebral metabolism (CCO), oxygenation (haemoglobin difference (HbD)) and cerebral blood volume (total haemoglobin (HbT)) in 23 term infants following HIE during therapeutic hypothermia (HT). Sixty-minute epochs of data from each infant were studied using wavelet analysis at a mean age of 48 h. Wavelet semblance (a measure of phase difference) was calculated to compare reactivity between mean arterial blood pressure (MABP) with oxCCO, HbD and HbT. OxCCO-MABP semblance correlated with thalamic Lac/NAA (r = 0.48, p = 0.02). OxCCO-MABP semblance also differed between groups of infants with mild to moderate and severe injury measured using brain MRI score (p = 0.04), thalamic Lac/NAA (p = 0.04) and neurodevelopmental outcome at one year (p = 0.04). Pressure passive changes in cerebral metabolism were associated with injury severity indicated by thalamic Lac/NAA, MRI scores and neurodevelopmental assessment at one year of age.