Radom model 35; 22 super shot full#
Full waveform inversion (FWI), which focuses on minimizing misfit functions, measures the difference between synthetic and observed data to get the best possible data reproduction.
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However, conventional velocity analysis and tomography methods based on the travel time associated with picked events no longer meet the demands of exploration environments (Rao & Wang 2005 Tao & Sen 2015). Providing efficient inversions of velocity distribution is of significant importance for both the accurate imaging and characterization of reservoirs (Sun et al. Aside from this, the noise resistance capability of the proposed method was tested and synthetic data evaluations of both the source-independent and multi-source inversion strategies were undertaken to assess the efficiency of the proposed method.įull waveform inversion, source-independent, multi-scale inversion, multi-source inversion 1. In particular, we realized that a weighted average of the zero-offset traces in the super gather constitutes a better choice for reference traces. In order to achieve more faithful inversion results and promote computational efficiency, multi-scale source-independent inversion and multi-source inversion strategies were also adopted. Although this new method uses the same forward-modeling and inversion schemes as conventional FWI, it differs in how it calculates the misfit function and corresponding adjoint source. As the filtered data can be expressed as a convolution of the reflection coefficient and the target source wavelet, it is straightforward to use a low to high frequency selection strategy. The source wavelets for the observed and modeled wave fields are both eliminated in the misfit function, thus offsetting any adverse effects from a directly observed or adjoint source wavelet. A Wiener filter was designed to handle observed and modeled wave fields separately, with a misfit function consisting of the filtered wave field. A low-pass Wiener filter can be computed by using information from a reference trace rather than the true source wavelet. As an alternative, we present a source-independent inversion algorithm that modifies Wiener filter calculations. This is the first photoacoustic tomography approach capable of beating the half-wavelength resolution limit with a single laser shot.Multi-scale full waveform inversion (FWI) in the time domain requires an accurate source signature estimation, which is difficult to obtain from the field data.
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This improvement was demonstrated even when using a random projection transform to reduce data by 99 %, enabling substantially faster reconstruction times. The minimum observable separation was estimated as 70 ± 10 μ m, improving on the half-wavelength resolution limit of 145 μ m. We used the array system to image wire targets at ≈ 2 − 3 cm depth in both intralipid scattering solution and water. In this paper, the ability to beat the half-wavelength diffraction limit is demonstrated using a 5 MHz ring array photoacoustic tomography system and ℓ 1-norm based reconstruction approaches. However, such approaches have yet to beat the half-wavelength resolution limit.
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Recently, ℓ 1-norm based reconstruction approaches have been used with linear array systems to improve photoacoustic resolution and demonstrate undersampled imaging when there is sufficient sparsity in some domain.