scholarly journals The Compass Error Comparison of an Onboard Standard Gyrocompass, Fiber-Optic Gyrocompass (FOG) and Satellite Compass

Sensors ◽  
2019 ◽  
Vol 19 (8) ◽  
pp. 1942 ◽  
Author(s):  
Krzysztof Jaskólski ◽  
Andrzej Felski ◽  
Paweł Piskur
Keyword(s):  
Fourier Transform ◽  
Control System ◽  
Frequency Domain ◽  
Spectrum Analysis ◽  
Input Signal ◽  
Fiber Optic ◽  
Finite Impulse Response ◽  
Low Frequency ◽  
Ship Control ◽  
The Fourier Transform

The aim of the presented research was to analyze the accuracy indications of three types of compass systems for the purposes of meeting warship modernization requirements. The authors of this paper have made an attempt to compare the accuracy of an onboard standard gyrocompass, a fiber-optic gyrocompass (FOG) and a satellite compass in real shipping circumstances. The research was carried out in the Gulf of Gdansk area, during the preparation of hydrographic surveys on stable courses. Three heading recordings have been taken into consideration. The helmsman’s operation and vessel inertia were analyzed and removed according to a spectrum analysis. Transient characteristics and the spectrum analysis (based on the Fourier transform theory and headings descriptions in the frequency domain) are presented. Data, processed using a band-stop finite impulse response (FIR) filter to reduce low-frequency heading distortions, are presented for further analyses. The statistics of errors of the compasses investigated, as well as the spectrum of these errors, are also presented. Based on accuracy measurements, the possibility of using the most accurate heading data as the input signal to the automatic ship control system was considered.

The Spectra of Filters

2021 ◽  
pp. 204-268
Author(s):  
Victor Lazzarini
Keyword(s):  
Fourier Transform ◽  
Impulse Response ◽  
Discrete Time ◽  
Filter Design ◽  
Finite Impulse Response ◽  
Infinite Impulse Response ◽  
Main Body ◽  
Analysis Tool ◽  
The Fourier Transform ◽  
Definition Of

This chapter now turns to the discussion of filters, which extend the notion of spectrum beyond signals into the processes themselves. A gentle introduction to the concept of delaying signals, aided by yet another variant of the Fourier transform, the discrete-time Fourier transform, allows the operation of filters to be dissected. Another analysis tool, in the form of the z-transform, is brought to the fore as a complex-valued version of the discrete-time Fourier transform. A study of the characteristics of filters, introducing the notion of zeros and poles, as well as finite impulse response (FIR) and infinite impulse response (IIR) forms, composes the main body of the text. This is complemented by a discussion of filter design and applications, including ideas related to time-varying filters. The chapter conclusion expands once more the definition of spectrum.

Resonant behavior and frequency preferences of thalamic neurons

1994 ◽  
Vol 71 (2) ◽  
pp. 575-582 ◽  
Author(s):  
E. Puil ◽  
H. Meiri ◽  
Y. Yarom
Keyword(s):  
Fourier Transform ◽  
Frequency Response ◽  
Low Frequency ◽  
Wide Band ◽  
Inward Rectifier ◽  
Membrane Potentials ◽  
Resting Potential ◽  
Voltage Response ◽  
Current Input ◽  
The Fourier Transform

1. We studied the voltage responses of thalamocortical neurons to a periodic current input of variable frequency, in slices of mediodorsal thalamus (guinea pig). The ratio of the Fourier transform of the voltage response to the Fourier transform of the oscillatory current input was used to calculate the frequency response of the neurons at different resting and imposed membrane potentials. 2. Most neurons displayed a resonant hump in the frequency response curve. A narrow band of low-frequency (2-4 Hz) resonance occurred near the resting level [-66 +/- 8 mV (SD)] and at imposed membrane potentials in a range of -60 to -80 mV. An additional wide band (12-26 Hz) of peak resonant frequencies was observed at depolarized levels. 3. The low-frequency resonance was insensitive to tetrodotoxin (TTX) application in concentrations (0.5-1 microM) that blocked a depolarization activated inward rectifier and Na(+)-dependent action potentials. TTX, however, eliminated the wide-band resonant hump centered at 12-26 Hz that we observed at depolarized membrane potentials. 4. Application of Ni2+ (0.5-1 mM) reversibly blocked all slow spikes and greatly reduced the low-frequency resonant humps, without changing the resting potential. Octanol in concentrations of 50 microM had similar effects. 5. Application of Cs+ (3-5 mM), a blocker of the hyperpolarization activated inward rectifier, produced a 5- to 10-mV depolarization and completely blocked the rectification. Cs+ did not alter the low-frequency resonant hump or its dependence on membrane voltage.(ABSTRACT TRUNCATED AT 250 WORDS)

A PUBLIC MESH WATERMARKING ALGORITHM BASED ON ADDITION PROPERTY OF FOURIER TRANSFORM

2006 ◽  
Vol 06 (01) ◽  
pp. 35-43 ◽  
Author(s):  
LI LI ◽  
ZHIGENG PAN ◽  
DAVID ZHANG
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Spatial Domain ◽  
Experimental Results ◽  
Original Image ◽  
The Fourier Transform

This paper presents a public mesh watermarking algorithm whereby the resultant watermarked image minus the original image is the watermark information. According to the addition property of the Fourier transform, a change of spatial domain will cause a change in the frequency domain. The watermark information is then scaled down and embedded in one part of the x-coordinate of the original mesh. Finally, the x-coordinate of the test mesh is amplified before extraction. Experimental results prove that our algorithm is resistant to a variety of attacks without the need for any preprocessing.

THEORETICAL TRANSFORMS OF THE GRAVITY ANOMALIES OF TWO IDEALIZED BODIES

Geophysics ◽  
1978 ◽  
Vol 43 (3) ◽  
pp. 631-633 ◽  
Author(s):  
Robert D. Regan ◽  
William J. Hinze
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Vertical Line ◽  
The Fourier Transform ◽  
Line Elements ◽  
Distribution Of Magnetization

Odegard and Berg (1965) have shown that the interpretational process can be simplified for several idealized bodies by utilizing the Fourier transform of the resultant theoretical gravity anomalies. Additional studies relating similar conclusions for other idealized bodies have been reported by Gladkii (1963), Roy (1967), Sharma et al (1970), Davis (1971), Eby (1972), and Saha (1975), and a summary of the spatial and frequency domain equations is given in Regan and Hinze (1976, Table 1); however, the transforms of the three‐dimensional prism and vertical line elements, often utilized in interpretation, have not been previously examined in this manner. Although Bhattacharyya and Chen (1977) have developed and utilized the transform of the 3-D prism in their method for determining the distribution of magnetization in a localized region, it is still of value to present the interpretive advantages of the transform equation itself.

scholarly journals How can the Fourier Transform be Used in Radio Astronomy to Perform Spectral Analysis of Pulsars

2021 ◽  
Vol 10 (2) ◽  
Author(s):  
Pranesh Kumar ◽  
Arthur Western
Keyword(s):  
Spectral Analysis ◽  
Fourier Transform ◽  
Discrete Fourier Transform ◽  
Low Frequency ◽  
Radio Frequency Interference ◽  
Radio Waves ◽  
Folding Algorithm ◽  
Radio Signals ◽  
Multiple Characteristics ◽  
The Fourier Transform

The analysis of pulsars is a complicated procedure due to the influence of background radio waves. Special radio telescopes designed to detect pulsar signals have to employ many techniques to reconstruct interstellar signals and determine if they originated from a pulsating radio source. The Discrete Fourier Transform on its own has allowed astronomers to perform basic spectral analysis of potential pulsar signals. However, Radio Frequency Interference (RFI) makes the process of detecting and analyzing pulsars extremely difficult. This has forced astronomers to be creative in identifying and determining the specific characteristics of these unique rotating neutron stars. Astrophysicists have utilized algorithms such as the Fast Fourier Transform (FFT) to predict the spin period and harmonic frequencies of pulsars. However, FFT-based searches cannot be utilized alone because low-frequency pulsar signals go undetected in the presence of background radio noise. Astrophysicists must stack up pulses using the Fast Folding Algorithm (FFA) and utilize the coherent dedispersion technique to improve FFT sensitivity. The following research paper will discuss how the Discrete Fourier Transform is a useful technique for detecting radio signals and determining the pulsar frequency. It will also discuss how dedispersion and the pulsar frequency are critical for predicting multiple characteristics of pulsars and correcting the influence of the Interstellar Medium (ISM).

The Remaining Cases Where m = 2 and B = 3 or B = 4

2016 ◽  
Author(s):  
Isroil A. Ikromov ◽  
Detlef Müller
Keyword(s):  
Fourier Transform ◽  
Domain Decomposition ◽  
Frequency Domain ◽  
Fourier Integral ◽  
Basic Approach ◽  
Small Letter ◽  
The Fourier Transform ◽  
Frequency Domain Decomposition

This chapter discusses the remaining cases for l = 1. With the same basic approach as in Chapter 5, the chapter again performs an additional dyadic frequency domain decomposition related to the distance to a certain Airy cone. This is needed in order to control the integration with respect to the variable x₁ in the Fourier integral defining the Fourier transform of the complex measures ν‎subscript Greek small letter delta superscript Greek small letter lamda. It first applies a suitable translation in the x₁-coordinate before performing a more refined analysis of the phase Φ‎superscript Music sharp sign. The chapter then treats the case where λ‎ρ‎(̃‎δ‎) ≲ 1 and hereafter deals with the case where λ‎ρ‎(̃‎δ‎) ≲ 1 and B = 4. Finally, the chapter turns to the case where B = 3.

scholarly journals Magnetic storm free ULF analysis in relation with earthquakes in Taiwan

2012 ◽  
Vol 12 (5) ◽  
pp. 1747-1754 ◽  
Author(s):  
S. Wen ◽  
C.-H. Chen ◽  
H.-Y. Yen ◽  
T.-K. Yeh ◽  
J.-Y. Liu ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Cross Correlation ◽  
Low Frequency ◽  
Magnetic Anomalies ◽  
Magnetic Storms ◽  
Frequency Range ◽  
Geomagnetic Data ◽  
Before And After ◽  
The Cross ◽  
The Fourier Transform

Abstract. Despite early optimism, pre-earthquake anomalous phenomena can be determined by using enhanced amplitude at the ultra-low-frequency range from geomagnetic data via the Fourier transform. In reality, accuracy of the enhanced amplitude in relation to earthquakes (deduced from time-varied geomagnetic data) would be damaged by magnetic storms and/or other unwanted influences resulting from solar activity and/or variations in the ionosphere, respectively. We substitute values of the cross correlation between amplitudes, summarized from the earthquake-related (0.1–0.01 Hz) and the comparable (0.01–0.001 Hz) frequency bands, for isolated amplitude enhancements as indexes of determination associated with seismo-magnetic anomalies to mitigate disturbance caused by magnetic storms. A station located about 300 km away from the others is also taken into account to further examine whether changes of the cross correlation values are caused by seismo-magnetic anomalies limited within local regions or not. Analytical results show that the values suddenly decrease near epicenters a few days before and after 67% (= 6/9) of earthquakes (M > = 5) in Taiwan between September 2010 and March 2011. Seismo-magnetic signals determined by using the values of cross correlation methods partially improve results yielded from the Fourier transform alone and provide advantageous information of earthquake locations.

scholarly journals Multiscale Asymptotic Analysis and Parallel Algorithm of Parabolic Equation in Composite Materials

2014 ◽  
Vol 2014 ◽  
pp. 1-12
Author(s):  
Xin Wang ◽  
Xi-liang Duan ◽  
Yang Gao
Keyword(s):  
Fourier Transform ◽  
Parabolic Equation ◽  
Asymptotic Analysis ◽  
Frequency Domain ◽  
Expansion Method ◽  
Convergence Result ◽  
Oscillating Coefficients ◽  
Multiscale Fem ◽  
Periodic Configuration ◽  
The Fourier Transform

An efficient parallel multiscale numerical algorithm is proposed for a parabolic equation with rapidly oscillating coefficients representing heat conduction in composite material with periodic configuration. Instead of following the classical multiscale asymptotic expansion method, the Fourier transform in time is first applied to obtain a set of complex-valued elliptic problems in frequency domain. The multiscale asymptotic analysis is presented and multiscale asymptotic solutions are obtained in frequency domain which can be solved in parallel essentially without data communications. The inverse Fourier transform will then recover the approximate solution in time domain. Convergence result is established. Finally, a novel parallel multiscale FEM algorithm is proposed and some numerical examples are reported.

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