Time‐domain estimation of MT Impedance tensor

Geophysics ◽  
1994 ◽  
Vol 59 (5) ◽  
pp. 712-721 ◽  
Author(s):  
Umberto Spagnolini
Keyword(s):  
Time Domain ◽  
Bayes Estimation ◽  
Impedance Tensor ◽  
Data Sets ◽  
Least Mean Square ◽  
Step Size ◽  
Juan De Fuca ◽  
The Time Domain ◽  
Reference Processing ◽  
Frequency Domain Techniques

The spectral analysis of magnetotelluric (MT) data for impedance tensor estimation requires the stationarity of measured magnetic (H) and electric (E) fields. However, it is well known that noise biases timedomain tensor estimates obtained via an iterative search by a descent algorithm to determine the least‐mean‐square residual between measured and estimated E data obtained from H data. To limit the noise that slows down, or even prevents convergence, the steepest descent step size is based upon the statistics of the residual (Bayes’ estimation). With respect to uncorrelated noise, the time‐domain technique is more robust than frequency‐domain techniques. Furthermore, the technique requires only short‐time stationarity. The time‐domain technique is applied to data sets (Lincoln Line sites) from the EMSLAB Juan de Fuca project (Electromagnetic Sounding of the Lithosphere and Asthenosphere Beneath the Juan de Fuca Plate), as well as to data from a southern Italian site. The results of EMSLAB data analysis are comparable to those obtained by robust remote reference processing where larger data sets were used.

A Numerical Method for Representing Retardation Functions With Complex Exponentials

2017 ◽  
Author(s):  
Fushun Liu ◽  
Lei Jin ◽  
Jiefeng Chen ◽  
Wei Li
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Added Mass ◽  
Memory Effects ◽  
Floating Structure ◽  
Frequency Dependent ◽  
Laplace Domain ◽  
The Time Domain ◽  
Frequency Domain Techniques

Numerical time- or frequency-domain techniques can be used to analyze motion responses of a floating structure in waves. Time-domain simulations of a linear transient or nonlinear system usually involve a convolution terms and are computationally demanding, and frequency-domain models are usually limited to steady-state responses. Recent research efforts have focused on improving model efficiency by approximating and replacing the convolution term in the time domain simulation. Contrary to existed techniques, this paper will utilize and extend a more novel method to the frequency response estimation of floating structures. This approach represents the convolution terms, which are associated with fluid memory effects, with a series of poles and corresponding residues in Laplace domain, based on the estimated frequency-dependent added mass and damping of the structure. The advantage of this approach is that the frequency-dependent motion equations in the time domain can then be transformed into Laplace domain without requiring Laplace-domain expressions of the added mass and damping. Two examples are employed to investigate the approach: The first is an analytical added mass and damping, which satisfies all the properties of convolution terms in time and frequency domains simultaneously. This demonstrates the accuracy of the new form of the retardation functions; secondly, a numerical six degrees of freedom model is employed to study its application to estimate the response of a floating structure. The key conclusions are: (1) the proposed pole-residue form can be used to consider the fluid memory effects; and (2) responses are in good agreement with traditional frequency-domain techniques.

scholarly journals Simulation of Low Inertia Power Systems Based on Shifted Frequency Analysis

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1860
Author(s):  
Jan Dinkelbach ◽  
Ghassen Nakti ◽  
Markus Mirz ◽  
Antonello Monti
Keyword(s):  
Power Systems ◽  
Power System ◽  
Frequency Analysis ◽  
Time Domain ◽  
Step Size ◽  
Modeling Approaches ◽  
Dynamic Phasors ◽  
Instantaneous Values ◽  
The Time Domain ◽  
Synchronous Generation

New types of power system transients with lower time constants are emerging due to the replacement of synchronous generation with converter interfaced generation and are challenging the modeling approaches conventionally applied in power system simulation. Quasi-stationary simulations are based on classical phasor models, whereas EMT simulations calculate the instantaneous values of models in the time domain. In addition to these conventional modeling approaches, this paper investigates simulation based on dynamic phasor models, as has been proposed by the Shifted Frequency Analysis. The simulation accuracy of the three modeling approaches was analyzed for characteristic transients from the electromagnetic to the electromechanical phenomena range, including converter control as well as low inertia transients. The analysis was carried out for systems with converter interfaced and synchronous generation whilst considering the simulation step size as a crucial influence parameter. The results show that simulations based on dynamic phasors allow for larger step sizes than simulations that calculate the instantaneous values in the time domain. This can facilitate the simulation of more complex component models and larger grid sizes. In addition, with dynamic phasors, more accurate simulation results were obtained than with classical phasors, in particular—but not exclusively—in a low inertia case. Overall, the presented work demonstrates that dynamic phasors can enable fast and accurate simulations during the transition to low inertia power systems.

Obtaining multi-loop pursuit-control pilot models from computer simulation

2008 ◽  
Vol 222 (2) ◽  
pp. 189-199 ◽  
Author(s):  
R A Hess
Keyword(s):  
Computer Simulation ◽  
Time Domain ◽  
Flight Control ◽  
Linear Models ◽  
Degree Of Freedom ◽  
Pilot Model ◽  
Pursuit Control ◽  
The Time Domain ◽  
Frequency Domain Techniques ◽  
Six Degree Of Freedom

A method for generating simplified pursuit-control pilot models for computer simulation of multi-axis flight control tasks has been developed. The method involves a sequential loop closure synthesis procedure for creating the pilot model and includes handling qualities estimation. The original model formulation previously reported in the literature used frequency-domain techniques, primarily Bode diagrams to select model gains. The present research demonstrates how similar results can be obtained in the time-domain. This latter approach is particularly useful when complex, non-linear aircraft models are being used. The time-domain approach is exercised in a six-degree of freedom rotorcraft control simulation and in a six-degree of freedom tailless fighter simulation, both involving linear models.

DCT-BASED VARIABLE STEP SIZE GRIFFITHS' LMS ALGORITHM FOR RANDOM NOISE CANCELLATION IN ECGs

2012 ◽  
Vol 12 (05) ◽  
pp. 1250025
Author(s):  
VEENA N. HEGDE ◽  
RAVISHANKAR DEEKSHIT ◽  
P. S. SATYANARAYANA
Keyword(s):  
Random Noise ◽  
Noise Cancellation ◽  
Lms Algorithm ◽  
Frequency Resolution ◽  
Variable Step Size ◽  
Least Mean Square ◽  
Step Size ◽  
Low Leakage ◽  
Variable Step ◽  
The Time Domain

This paper presents a new random noise cancellation technique for cancelling muscle artifact effects from ECG using ALE in the transformed domain. For this a transform domain variable step size griffith least mean square (TVGLMS) algorithm is proposed. The technique is based on the adaptation of the gradient of the error surface. The method frees both the step size and the gradient from observation noise and reduces the gradient mis-adjustment error. The sluggishness introduced due to the averaging of the gradient in the time domain is overcome by the transformed domain approach. The proposed algorithm uses a discrete cosine transform (DCT)-based signal decomposition due to its improved frequency resolution compared to a discrete Fourier transform (DFT). Furthermore, as the data used symmetrical, DCT usage results in low leakage (bias and variance). The performance of the proposed method has been tested on ECG signals combined with WGN, extracted from MIT database, and compared with several existing techniques like LMS, NLMS, and VGLMS.

SEISMIC DATA COMPRESSION METHODS

Geophysics ◽  
1974 ◽  
Vol 39 (4) ◽  
pp. 499-525 ◽  
Author(s):  
Lawrence C. Wood
Keyword(s):  
Time Domain ◽  
Seismic Data ◽  
Walsh Transform ◽  
Data Sets ◽  
Convergence Properties ◽  
Long Distance ◽  
Visual Degradation ◽  
Band Pass ◽  
The Time Domain ◽  
Seismic Data Compression

This paper discusses two ways of compressing seismic data prior to long‐distance transmission for display. A Walsh transform technique and an analogous time‐domain method eliminate redundant seismic information allowing data sets to be compressed with little visual degradation. The basic approach consists of using an average 3-bit code to describe data in such a way as to minimize information loss; the method also uses the Walsh transform to achieve further compaction through sequency bandlimiting. A second technique is entirely a time‐domain operation and does not use transforms. The Walsh method, however, produces larger compression ratios than the time technique before serious image degradation occurs. Both schemes have six basic parts: bandlimiting, quantization, encoding, decoding, interpolation, and band‐pass filtering; they differ only in band limiting and interpolation. Band limiting sequencies in the Walsh domain is very similar to, but not the same as, alias filtering and resampling in time. Reducing Walsh bandwidths by some power of two has a time‐domain implementation consisting of an averaging procedure with subsequent resampling, while the inverse Walsh transform step can be viewed as a means of interpolating in the time domain. The convergence properties of three Rademacher derived transforms—Hadamard, Paley, and Walsh—are studied with regard to exploration seismic data. Hadamard energy has been found to be uniformly distributed over its entire spectrum, whereas Walsh and Paley transforms concentrate about 80 percent of the total energy into a major lobe occupying about 15 percent of the total bandwidth (2 msec sampling). Smaller minor lobes containing the remaining 20 percent are discarded while bandlimiting. The major lobe energy suffices for many seismic applications such as VA/VD plot displays. Optimum quantization and encoding of major lobe energy results in an overall 28:1 compression factor for 12 bit data sampled every 2 msec. Analogous time domain compression, on the other hand, only achieves a 16:1 reduction because of the power of two restriction imposed by the resampling and averaging process.

RANDOM NOISE CANCELLATION IN BIOMEDICAL SIGNALS USING VARIABLE STEP SIZE GRIFFITH LMS ADAPTIVE LINE ENHANCER

2012 ◽  
Vol 12 (04) ◽  
pp. 1240020 ◽  
Author(s):  
VEENA N. HEGDE ◽  
RAVISHANKAR DEEKSHIT ◽  
P. S. SATYANARAYANA
Keyword(s):  
Time Domain ◽  
Random Noise ◽  
Noise Cancellation ◽  
Variable Step Size ◽  
Mean Square ◽  
Least Mean Square ◽  
Step Size ◽  
Adaptive Line Enhancer ◽  
Variable Step ◽  
Observation Noise

This paper presents a new method of random noise cancellation for removing artefacts from biomedical signals using an adaptive line enhancer (ALE). The ALE is implemented using proposed time domain variable step size Griffith least mean square (VSGLMS) algorithm. The technique is based on the adaptation of the gradient of the error surface. The method makes both the step size and the gradient free from observation noise and reduces the gradient mis-adjustment error. Here, both the gradient and the scale factor for the step size are free from the input noise effects, which makes the algorithm robust to both stationary and non-stationary observation noise. Further the additional computational load involved for this is marginal. The VSGLMS adaptive filter technique for ALE is tested on noise cancellation of two types of bio-medical signals — separation of electro cardiogram (ECG) signal from a background of electro myogram (EMG) and heart sound signal (HSS) from lung sound signal (LSS). Application of VSGLAM–ALE for the separation of HSS from LSS and ECG from EMG has been demonstrated using synthetic White Gaussian noise (WGN). It is found that VSGLMS–ALE can separate the desired signals like ECG or HSS at an input SNR of -5 dB to 27 dB. The performance of VSGLMS is compared with state-of-the-art least mean square LMS–ALE and normalised LMS–ALE. The results of PSDs, time domain waveforms, and mean square error (MSE) have proven that VSGLMS performs better than advanced techniques.

Apodisation in the time domain

1992 ◽  
Vol 2 (4) ◽  
pp. 615-620
Author(s):  
G. W. Series
Keyword(s):  
Time Domain ◽  
The Time Domain

JOINT INTERPRETATION OF AIRBORNE ELECTROMAGNETIC DATA IN THE TIME DOMAIN AND FREQUENCY DOMAIN

2018 ◽  
Vol 12 (7-8) ◽  
pp. 76-83
Author(s):  
E. V. KARSHAKOV ◽  
J. MOILANEN
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Time Domain ◽  
Frequency Interval ◽  
Single Spectrum ◽  
Simultaneous Inversion ◽  
Homogeneous Half Space ◽  
Time Domain Data ◽  
The Time Domain

Тhe advantage of combine processing of frequency domain and time domain data provided by the EQUATOR system is discussed. The heliborne complex has a towed transmitter, and, raised above it on the same cable a towed receiver. The excitation signal contains both pulsed and harmonic components. In fact, there are two independent transmitters operate in the system: one of them is a normal pulsed domain transmitter, with a half-sinusoidal pulse and a small "cut" on the falling edge, and the other one is a classical frequency domain transmitter at several specially selected frequencies. The received signal is first processed to a direct Fourier transform with high Q-factor detection at all significant frequencies. After that, in the spectral region, operations of converting the spectra of two sounding signals to a single spectrum of an ideal transmitter are performed. Than we do an inverse Fourier transform and return to the time domain. The detection of spectral components is done at a frequency band of several Hz, the receiver has the ability to perfectly suppress all sorts of extra-band noise. The detection bandwidth is several dozen times less the frequency interval between the harmonics, it turns out thatto achieve the same measurement quality of ground response without using out-of-band suppression you need several dozen times higher moment of airborne transmitting system. The data obtained from the model of a homogeneous half-space, a two-layered model, and a model of a horizontally layered medium is considered. A time-domain data makes it easier to detect a conductor in a relative insulator at greater depths. The data in the frequency domain gives more detailed information about subsurface. These conclusions are illustrated by the example of processing the survey data of the Republic of Rwanda in 2017. The simultaneous inversion of data in frequency domain and time domain can significantly improve the quality of interpretation.

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