A polarity correction method for marine multi-component seismic exploration

An effective polarity correction method for microseismic migration-based location

Geophysics ◽

10.1190/geo2019-0497.1 ◽

2020 ◽

Vol 85 (4) ◽

pp. KS115-KS125

Author(s):

Jincheng Xu ◽

Wei Zhang ◽

Xiaofei Chen ◽

Quanshi Guo

Keyword(s):

Signal To Noise Ratio ◽

Computational Cost ◽

Real Data ◽

Correction Method ◽

Fitting Procedure ◽

Microseismic Data ◽

The Status ◽

Event Location ◽

Microseismic Events ◽

Polarity Correction

Microseismic methods are important tools for monitoring the status and consequences of hydraulic fracturing. Because microseismic data recorded at the surface have a low signal-to-noise ratio, migration-based algorithms are widely used to determine the locations of microseismic events. However, there may be polarity changes in waveforms at different receivers due to the source mechanisms, which will cause the stacking images to not reach a maximum at the event location. One way for polarity correction is to perform the source mechanism and the source location inversions simultaneously, which, however, is computationally expensive and not good for real-time monitoring. We have developed an effective polarity correction method in the data domain for migration-based location methods called the polarity correction migration-based (PCM) method. This method uses an amplitude trend least-squares fitting procedure to determine the polarities along the receiver line with low additional computational cost. Then, the fitted waveform polarities are used to convert the signs of the amplitude values to stack them consistently. Due to curve fitting, this method is more suitable for microseismic data acquired with regular arrays than with scattered arrays. Numerical experiments of synthetic and real data sets demonstrate that the proposed PCM method can improve accuracy in the detection and location of microseismic events.

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Ortho-k lenses fitting in patients with “non-typical” corneas

The Eye ◽

10.33791/2222-4408-2020-1-22-29 ◽

2020 ◽

Vol 22 (129) ◽

pp. 22-29

Author(s):

Svetlana Kravchuk ◽

Olga Zhabina

Keyword(s):

Correction Method ◽

Diameter Ratio ◽

Corneal Curvature ◽

Individual Approach ◽

Fitting In ◽

Corneal Diameter ◽

Clinical Cases

We described two clinical cases of ortho-k lenses fitting in patients with “non-typical” corneal curvature/diameter ratio. The main goal was to acknowledge effective and safe use of this myopia correction method in patients with corneal diameter greater than 11 mm. Individual approach to each patient is the key to a successful and safe ortho-k lenses fitting.

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