A new method for analysing nonlinear and non-stationary data has been developed. The key part of the method is the empirical mode decomposition method with which any complicated data set can be dec...

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The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis

A new Ensemble Empirical Mode Decomposition (EEMD) is presented. This new approach consists of sifting an ensemble of white noise-added signal (data) and treats the mean as the final true result. Finite, not infinitesimal, amplitude white noise is necessary to force the ensemble to exhaust all possible solutions in the sifting process, thus making the different scale signals to collate in the proper intrinsic mode functions (IMF) dictated by the dyadic filter banks. As EEMD is a time–space analysis method, the added white noise is averaged out with sufficient number of trials; the only persistent part that survives the averaging process is the component of the signal (original data), which is then treated as the true and more physical meaningful answer. The effect of the added white noise is to provide a uniform reference frame in the time–frequency space; therefore, the added noise collates the portion of the signal of comparable scale in one IMF. With this ensemble mean, one can separate scales naturall...

/pdf/ensemble-empirical-mode-decomposition-a-noise-assisted-data-4htvj7tcuy.pdf

Ensemble empirical mode decomposition: a noise-assisted data analysis method

During the late 1990s, Huang introduced the algorithm called Empirical Mode Decomposition, which is widely used today to recursively decompose a signal into different modes of unknown but separate spectral bands. EMD is known for limitations like sensitivity to noise and sampling. These limitations could only partially be addressed by more mathematical attempts to this decomposition problem, like synchrosqueezing, empirical wavelets or recursive variational decomposition. Here, we propose an entirely non-recursive variational mode decomposition model, where the modes are extracted concurrently. The model looks for an ensemble of modes and their respective center frequencies, such that the modes collectively reproduce the input signal, while each being smooth after demodulation into baseband. In Fourier domain, this corresponds to a narrow-band prior. We show important relations to Wiener filter denoising. Indeed, the proposed method is a generalization of the classic Wiener filter into multiple, adaptive bands. Our model provides a solution to the decomposition problem that is theoretically well founded and still easy to understand. The variational model is efficiently optimized using an alternating direction method of multipliers approach. Preliminary results show attractive performance with respect to existing mode decomposition models. In particular, our proposed model is much more robust to sampling and noise. Finally, we show promising practical decomposition results on a series of artificial and real data.

Variational Mode Decomposition

One of the most ubiquitous and long-lasting recent changes to the surface of our planet is the accumulation and fragmentation of plastics. Within just a few decades since mass production of plastic...

/pdf/accumulation-and-fragmentation-of-plastic-debris-in-global-2ayi1pcd8z.pdf

Accumulation and fragmentation of plastic debris in global environments.

Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

We examine a group of wave-like cloud patterns that occurred along the coast of Texas on a National Oceanic and Atmospheric Administration satellite advanced very high resolution radiometer IR images taken on January 22, 1999. These wave-like cloud patterns were interpreted to be signatures of a coastal lee wave packet on the basis of simultaneous field observations and theories developed by Zheng et al. [1998a]. The wave packet contains 13 waves with crest lines generally parallel to the coastline. The lengths of leading wave crest lines are longer than 500 km. The average wavelength is 9.5 km, ranging from 6.2 to 14.7 km. The width of the horizontal distribution band of the wave packet is as wide as 113 km. This case represents the most energetic coastal lee wave packet that has ever been reported.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JC000019

Analysis of coastal lee waves along the coast of Texas observed in advanced very high resolution radiometer images

[1] TOPEX/POSEIDON altimeter data from October 1992 to June 2002 are used to calculate the energy flux of M2 internal tides along the margin of Northwestern Pacific. This arc borderline of the Pacific Basin is characterized by sharp changes in bottom topography, which constitute good boundary conditions for internal tidal energy concentration. We extract baroclinic tides, that yield energy transmission, from temporarily coherent internal tide signals in the altimeter data. We use the field measurements of current velocities in the South China Sea (SCS) to test the method. The results show that satellite-derived M2 tide components agree with the field data very well. Computation results indicate that the maximum energy flux of M2 internal tides, 3 kW m−1, appears in the Ryukyu Trench. The total energy flux of M2 internal tides along the margin of Northwestern Pacific is about 15GW.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2003GL018008

Estimates of M2 internal tide energy fluxes along the margin of Northwestern Pacific using TOPEX/POSEIDON altimeter data

Causes of geometric distortion in space shuttle imagery of targets on the Earth's surface are analysed. A mathematical model formulating the geometric distortion caused by the incidence angle and the local azimuth angle are derived, and the corresponding image processing scheme for orthorectification is developed. The method is used for rectifying two sequential space shuttle photographs of continental shelf waters off the coast of south-west Africa taken by the space shuttle Atlantis during mission STS-36 in March 1990. The results indicate that mismatches between coastline images in unrectified photographs and a standard map have been almost eliminated in the rectified photographs, and the two photographs also match each other very well. Application of the spatial Fourier transform to oceanic internal wave packet signals at a selected test site yields directional wavenumber spectra, from which components of the wave field, the dominant wavelength, and propagation directions are determined. Comp...

Digital orthorectification of space shuttle coastal ocean photographs

Dynamics of the slope water off New England and its influence on the Gulf Stream as inferred from satellite IR data

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JC014437

Quanan Zheng

Papers

Analysis of coastal lee waves along the coast of Texas observed in advanced very high resolution radiometer images

Estimates of M2 internal tide energy fluxes along the margin of Northwestern Pacific using TOPEX/POSEIDON altimeter data

Digital orthorectification of space shuttle coastal ocean photographs

Dynamics of the slope water off New England and its influence on the Gulf Stream as inferred from satellite IR data

Fission of Shoaling Internal Waves on the Northeastern Shelf of the South China Sea