GPYSA7 0016-8033 Abstract Web of Science Google Scholar McMechan, 2007, Topographic corrections to slowness measurements in parsimonious migration of land data: Geophysics, 72, no. 2, S77–S80, doi: 10.1190/1.2431328. Gray, 2009, Direct downward continuation from topography using explicit wavefield extrapolation: Geophysics, 74, no. 6, S105–S112, doi: 10.1190/1.3263914. Bagaini, 2006, Straight-rays redatuming: A fast and robust alternative to wave-equation-based datuming: Geophysics, 71, no. 3, U37–U46, doi: 10.1190/1.2196032. Verschuur, 2006, An integrated method for resolving the seismic complex near-surface problem: Geophysical Prospecting, 54, 739–750, doi: 10.1111/j.
Numerical tests demonstrate that our anisotropic multicomponent GB-PSDM can accurately image subsurface structures under complex topography conditions. Using the crosscorrelation imaging condition and combining with the 2D anisotropic ray-tracing algorithm, we develop two 2D anisotropic multicomponent Gaussian-beam prestack depth migration (GB-PSDM) methods, i.e., using the slant stack and nonslant stack, for irregular topography. The Green’s function is calculated with a Gaussian beam summation emitted from the receiver point at the irregular surface. The other scheme does not perform the local slant stack. One is based on the local slant stack as in classic GBM, in which the PP- and PS-wave seismic records within the local region are directly decomposed into local plane-wave components from irregular topography. We use Gaussian beams to calculate the wavefield from irregular topography, and we use two schemes to derive the down-continued recorded wavefields. We have extended the GBM method to work for 2D anisotropic multicomponent migration under complex surface conditions. It retains the dynamic features of the wavefield and overcomes the multivalued traveltimes and caustic problems of Kirchhoff migration. Gaussian-beam migration (GBM) is an accurate and flexible depth migration technique, which is adaptable for imaging complex surface areas.
Redundant calibration absorbs some of the decoherence effect however, reducing its impact compared to if the visibilities were perfectly calibrated.Elastic-wave migration in anisotropic media is a vital challenge, particularly for areas with irregular topography. We also investigate the possibility of signal loss due to decoherence effects when non-redundant visibilities are averaged together, finding that the decoherence is worst when bright point sources pass through the beam, and that its magnitude varies significantly between baseline groups and types of primary beam variation. The temporal structure modulates the cosmological 21 cm power spectrum, but only at the level of a few per cent in our simulations. In comparison, only a low level of additional spectral structure is induced. For all of these types, we find that additional temporal structure is induced in the gain solutions, particularly when bright point sources pass through the beam. We use simulations to study several generic types of primary beam variation, including differences in the width of the main lobe, the angular and frequency structure of the sidelobes, and the beam ellipticity and orientation. In this paper, we seek to build an understanding of how differences in the primary beam response between antennas affect redundantly calibrated interferometric visibilities and their resulting frequency (delay-space) power spectra. In reality, there are many reasons why baselines will not be exactly identical, giving rise to a host of effects that spoil the redundancy of the array and induce spurious structure in the calibration solutions if not accounted for. Since identical baselines should see an identical sky signal, this provides a way of finding a relative gain/bandpass calibration without needing an explicit sky model. Radio interferometer arrays such as HERA consist of many close-packed dishes arranged in a regular pattern, giving rise to a large number of ‘redundant’ baselines with the same length and orientation.
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