An informed spatial filter for dereverberation in the spherical harmonic domain

Monthly gravitational field solutions as spherical harmonic coefficients produced by the GRACE satellite mission require post-processing to reduce the effects of shortwave-length noises and north–south stripe errors. However, the spatial smoothing and de-striping filter commonly used in the post-processing step will either reduce spatial resolution or remove short-wavelength features of geophysical signals, mainly at high latitudes. Here, by using prior covariance information that reflects the spatial and temporal features of the geophysical signals and the correlated errors derived from the synthetic model, together with the covariance matrix of the formal errors for the monthly gravity spherical harmonic coefficients, we apply the Kalman filter to separate the geophysical signal from GRACE Level-2 data and simultaneously to estimate the correlated errors. By increasing the number of observations, the iterative process is applied to update the state vector and covariance in the Kalman filter because the prior information is not accurate. Due to the inevitable truncation error, multiple gridded-gain factors method considering different temporal frequencies has been developed to recover the geophysical signal. The results show that the Kalman filter can reduce the high-frequency noises and correlated errors remarkably. When compared with the commonly used filter, no spatial filter (such as Gaussian filter) is used in the Kalman filter. Therefore, the estimated signal preserves its natural resolution, and more detailed information is retained. It shows good consistency when compared with mascon solutions in both secular trend and annual amplitude.

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Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096230 ◽

1972 ◽

Vol 30 ◽

pp. 596-597

Author(s):

David A. Ansley

Keyword(s):

Spherical Aberration ◽

Focal Length ◽

Chromatic Aberration ◽

Spatial Filter ◽

Operating Conditions ◽

Objective Lens ◽

List Type ◽

Spatial Filters ◽

Transmission Electron ◽

Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

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Optimum spatial filter for optical defocus sensing

Electrical Engineering in Japan ◽

10.1002/ecja.4400640915 ◽

1981 ◽

Vol 64 (9) ◽

pp. 113-120

Author(s):

Kohji Takemura ◽

Suteo Tsutsumi

Keyword(s):

Spatial Filter ◽

Optical Defocus

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Investigation of surface texture filtering error using spline spatial filter

Izmeritel`naya Tekhnika ◽

10.32446/0368-1025it.2018-3-27-32 ◽

2018 ◽

pp. 27-32

Author(s):

V. V. Poroshin ◽

D. G. Bogomolov ◽

V. G. Lysenko

Keyword(s):

Surface Texture ◽

Spatial Filter ◽

Texture Filtering

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The Effect of Coordinate System Rotation on Spherical Harmonic Expansions. A Numerical Method.

10.21236/ada131974 ◽

1983 ◽

Author(s):

Jacob D. Goldstein

Keyword(s):

Coordinate System ◽

Numerical Method ◽

Spherical Harmonic ◽

System Rotation

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Power Experimental Optimization of Horizontal Axis Wind Turbine

Recent Advances in Electrical & Electronic Engineering (Formerly Recent Patents on Electrical & Electronic Engineering) ◽

10.2174/2352096511666180906150812 ◽

2020 ◽

Vol 13 (3) ◽

pp. 438-443

Author(s):

Sadek Ameziane ◽

Abdesselem Chikhi ◽

Mohammed Salah Aggouner

Keyword(s):

Wind Turbine ◽

Vertical Axis ◽

Energy System ◽

Spatial Filter ◽

Complex Model ◽

Vertical Axis Wind Turbine ◽

Horizontal Axis Wind Turbine ◽

Detailed Model ◽

Continuous Current ◽

Mechanical Sensors

Background: The presented article is a contribution to the realization of a wind emulator based on a continuous-current machine. The development of this topic focuses on the modeling of a vertical axis wind turbine, a DC motor with independent excitation and its control via a chopper. Methods: To carry out this work, we have studied and designed the electronic and mechanical sensors as well as a command implemented on the dSPACE DS1103 system. Results: The main purpose of this work is related, on one hand, to the control of the motor turbine by imposing the wind profile and on the other hand generate the command of the implanted MPPT. The experimental results obtained showed the great performances which characterize this improved wind energy system. Conclusion: Finally, a wind turbine with variable speed is a system having a complex model; however, a detailed model of the interaction between the wind and the aero-turbine is useful to understand certain phenomena such as rotational sampling or the spatial filter.

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Spatial filtering of signals with spectrum overlapping

Issues of radio electronics ◽

10.21778/2218-5453-2019-12-27-33 ◽

2019 ◽

pp. 27-33

Author(s):

M. E. Shevchenko ◽

A. V. Gorovoy ◽

S. N. Solovyov

Keyword(s):

Antenna Arrays ◽

A Priori ◽

Spatial Filtering ◽

Spatial Filter ◽

Radio Sources ◽

Probability Of Error ◽

Shift Keying ◽

A Priori Uncertainty

The paper considers the spatial filtering methods of signals with spectrum overlapping under conditions of a priori uncertainty of the directions of arrival from radio sources. The estimates of the directions of signals arrival obtained by ESPRIT or MUSIC are used in order to build a spatial filter. It is shown that when using ESPRIT, unlike MUSIC, an additional calculations of filter coefficients based on estimates of the directions of signals arrival are not required, and the quadrature components of the signals are formed simultaneously with estimates of the direction of their arrival. The probability of error performances of minimum shift keying signals which were divided by spatial filtering on the basis of ESPRIT and MUSIC using seven-element circular and angular antenna arrays are given.

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