Polarization analysis of multi-component seismic data is used in both exploration seismology and earthquake seismology. In
single-station polarization processing, it is generally assumed that any noise present in the window of analysis is incoherent,
i.e., does not correlate between components. This assumption is often violated in practice because several overlapping seismic
events may be present in the data. The additional arrival(s) to that of interest can be viewed as coherent noise. This paper
quantifies the error because of coherent noise interference. We first give a general theoretical analysis of the problem.
A simple mathematical wavelet is then used to obtain a closed-form solution to the principal direction estimated for a transient
incident signal superposed with a time-shifted, unequal amplitude version of itself, arriving at an arbitrary angle to the
first wavelet. The effects of relative amplitude, arrival angle, and the time delay of the two wavelets on directional estimates
are investigated. Even for small differences in angle of arrival, there may be significant error (>10°) in the azimuth estimate. 相似文献
Self-organizing map (SOM) is used to simulate summer daily precipitation over the Yangtze–Huaihe river basin in Eastern China, including future projections. SOM shows good behaviors in terms of probability distribution of daily rainfall and spatial distribution of rainfall indices, as well as consistency of multi-model simulations. Under RCP4.5 Scenario, daily rainfall at most sites (63%) is projected to shift towards larger values. For the early 21st century (2016–2035), precipitation in the central basin increases, yet decreases occur over the middle reaches of the Yangtze River as well as a part of its southeast area. For the late 21st century (2081–2100), the mean precipitation and extreme indices experience an overall increase except for a few southeast stations. The total precipitation in the lower reaches of the Yangtze River and in its south area is projected to increase from 7% at 1.5 °C global warming to 11% at 2 °C, while the intensity enhancement is more significant in southern and western sites of the domain. A clustering allows to regroup all SOM nodes into four distinct regimes. Such regional synoptic regimes show remarkable stability for future climate. The overall intensification of precipitation in future climate is linked to the occurrence-frequency rise of a wet regime which brings longitudinally closer the South Asia High (eastward extended) and the Western Pacific Subtropical High (westward extended), as well as the reduction of a dry pattern which makes the two atmospheric centers of action move away from each other. 相似文献