GOCE SGG filtering with FIR, IIR and wavelet MRA

<p>GOCE Satellite Gravity Gradiometry (SGG) data have been widely used in gravity field research in order to provide improved representations of the gravity field spectrum either in the form of Global Geopotential Models (GGMs) or grids at satellite altitude. One of the key points in utilizing SGG observations is their proper filtering, in order to remove noise and long-wavelength correlated error, while the signals in the GOCE measurement bandwidth (MBW) should be preserved. Due to the gradiometer’s design, the GOCE satellite can achieve high accuracy and stable measurements in the MBW of 0.005 Hz to 0.1 Hz. The gravity gradient in MBW are at an equivalent accuracy level, while   are of lower accuracy. Outside of the MBW, systematic errors, colored noise, and noise with sharp peaks are observed, especially in the frequencies lower than 0.005 Hz. With that in mind, the present work focuses on the investigation of various filtering options ranging from Finite Impulse Response (FIR) filters, Infinite Impulse Response (IIR) filters, and filtering based on Wavelets. The latter are employed given their inherent characteristic of being localized both in frequency and space, meaning that the signal can be decomposed at different levels, thus allowing multi-resolution approximation (MRA). The analysis is performed with one month of GOCE SGG data in order to conclude on the method that provides the overall best results. SGG observations are reduced to a GGM in order to account for the long- and medium-wavelengths of the gravity field spectrum. Then, various filter orders are investigated for the FIR and IIR filters, while selective reconstruction is employed for the WL-MRA. Evaluation of the results is performed in terms of the smoothness of the filtered fields and the Power Spectral Density (PSD) functions of the entire GOCE tensor.</p>

Abnormal Fano Profile in Graphene-Wrapped Dielectric Particle Dimer

We give a theoretical study on the near field enhancement and far field spectrum of an adjacent graphene-wrapped sphere dimer with different radii. The Fano profile is found in the near field enhancement spectrum of such a symmetry-broken dimer system, which is, however, hidden in the far field spectrum. We demonstrate that this kind of Fano profile is rising from the coupling of dimer’s plasmon hybridization modes by analyzing the dipole moments of each sphere. Moreover, different orientation of incident wave polarization will lead to the different plasmon hybridization coupling, thus giving rise to a different Fano profile. By changing the Fermi energy level, we could achieve tunable Fano profile in near field enhancement.

Fractional prediction of ground temperature based on soil field spectrum

Ground temperature is an important physical indicator reflecting the natural ecological environment of the Earth's surface. Soil spectrum is a comprehensive reflection of soil properties, but there are few studies on the prediction of ground temperature based on soil field spectrum using fractional calculus. In this paper, the fractional derivative is used to study the correlation between soil spectrum and ground temperature from zeroth order to second order, and the characteristic wavelength bands are extracted. Simulations show that the fractional approach can amplify the difference of the soil field spectral signal. The wavelength bands for the 0.01 significance test begin with 0.6th order, while the 1.3th order sees 33 wavelength bands. Coefficients of determination of 0.7, 0.8, 0.9, 1.3, 1.4, 1.5, 1.6, and 1.7-order are all greater than 0.66, indicating that the established model of linear stepwise multiple regression gives a better prediction.

Analysis of occurrence of guided disorders in selected railway equipment — impact of load on measurement results

The parameter of interfering signals, determining the type of coupling, is the disturbing frequency. For frequencies less than 30 MHz, main impact comes by conducted emissions. The article presents an analysis of the occurrence of disturbances and the impact of the load of the selected railway equipment’s on the measurement result of the conducted disturbances. Keywords: electromagnetic field, spectrum, interference, induction and capacitive coupling

Effects of multi-scale and regular grid geometries on decaying turbulence

The influence of a multi-scale fractal based geometry on the decay of turbulence is investigated by comparing the turbulence produced by a square fractal element grid to that produced by two regular grids with similar physical properties. Comparison of the grid wakes at constant grid Reynolds number, $Re_{M}$, identifies that in the far field both regular grids produce comparable or higher turbulence intensities and local Reynolds numbers, $Re_{\unicode[STIX]{x1D706}}$, than the square fractal element grid. This result is illustrative of a limitation of multi-scale geometries to produce the oft-quoted high levels of turbulence intensity and $Re_{\unicode[STIX]{x1D706}}$. In the far field, the spectra are approximately collapsed at all scales for all three grids at a given $Re_{\unicode[STIX]{x1D706}}$. When a non-equilibrium near field spectrum with $\langle uv\rangle \neq 0$ is compared to a far field spectrum at the same $Re_{\unicode[STIX]{x1D706}}$ but with $\langle uv\rangle \approx 0$, it is shown that their shapes are markedly different and that the non-equilibrium spectrum has a steeper slope, giving the appearance of being nearer $k^{-5/3}$, although there is no theoretical expectation of an inertial range at such locations in the flow. However, when a non-equilibrium spectrum with $\langle uv\rangle \approx 0$ is compared to a far field spectrum at the same $Re_{\unicode[STIX]{x1D706}}$, they are once again collapsed. This is shown to be related to non-zero Reynolds shear stress at scales that penetrate the scaling range for the present experiment, and hence the influence of shear is not limited to the largest scales. These results demonstrate the importance of local properties of the flow on the turbulence spectra at given locations in the inherently inhomogeneous flow found in the non-equilibrium region downstream of grids. In particular, how the presence of local shear stress can fundamentally change the shape of the spectra at scales that can be mistakenly interpreted as an inertial range.