Removal Of Coherent Noise Research Articles

Interpretation and use of coherence in multi-channel measurements

The coherence function can be a powerful tool when analyzing data from multi-channel measurements. Often, coherence is used to describe the amount of incoherent noise in an output signal, though more generally the coherence between two signals is a representation of the linearity of the relationship between the signals as a function of frequency. Such degradation in the coherence then can be understood to not only be caused by potential incoherent noise, but also by moving sensors or a changing acoustic environment. Aside from its use as a diagnostic tool, coherence can also be used to condition measured data. For example, a sensor can be placed on a source of unwanted sound, and the portion of the desired signal coherent with the sensor's output (the "coherent output power") can be removed. In this paper, methods for coherent noise removal and signal enhancement are presented in both the frequency and time domains. Example measurements are used to demonstrate the effectiveness of the techniques for situations where separating noise sources is otherwise difficult.

Seismic Coherent Noise Removal With Residual Network and Synthetic Seismic Samples

Seismic Coherent Noise Removal With Residual Network and Synthetic Seismic Samples

Multiple and Coherent Noise Removal from X-Profile 2D Seismic Data of Southern Iraq Using Normal Move Out-Frequency Wavenumber Technique

Multiple eliminations (de-multiple) are one of seismic processing steps to remove their effects and delineate the correct primary refractors. Using normal move out to flatten primaries is the way to eliminate multiples through transforming these data to frequency-wavenumber domain. The flatten primaries are aligned with zero axis of the frequency-wavenumber domain and any other reflection types (multiples and random noise) are distributed elsewhere. Dip-filter is applied to pass the aligned data and reject others will separate primaries from multiple after transforming the data back from frequency-wavenumber domain to time-distance domain. For that, a suggested name for this technique as normal move out- frequency-wavenumber domain method for multiple eliminations. The method is tested on a fake reflection event to authorize their validity, and applied to a real field X-profile 2D seismic data from southern Iraq. The results ensure the possibility of internal multiple types existing in the deep reflection data in Iraq and have to remove. So that the interpretation for the true reflectors be valid. The final processed stacked seismic data using normal move out- frequency-wavenumber domain technique shows good, clear, and sharp reflectors in comparison with the conventional normal move out stack data. Open-source Madagascar reproducible package is used for processing all steps of this study and the package is very efficient, accurate, and easy to implement normal move out, frequency-wavenumber domain, Dip-filter programs. The aim of the current study is to separate internal multiples and noise from the real 2D seismic data.

Multiple and Coherent Noise Removal from X-Profile 2D Seismic Data of Southern Iraq Using Common Depth Point Muting Procedures and Depending on Madagascar Open-Source Package

This article describes how to predict different types of multiple reflections in pre-track seismic data. The characteristics of multiple reflections can be expressed as a combination of the characteristics of primary reflections. Multiple velocities always come in lower magnitude than the primaries, this is the base for separating them during Normal Move Out correction. The muting procedure is applied in Time-Velocity analysis domain. Semblance plot is used to diagnose multiples availability and judgment for muting dimensions. This processing procedure is used to eliminate internal multiples from real 2D seismic data from southern Iraq in two stages. The first is conventional Normal Move Out correction and velocity auto picking and stacking, and the second stage is muting. Many Common Depth Point gathers are tested to select the proper muting dimension, later on; the auto pick for the muted semblance is done for the whole 2D seismic data. The following step is to stack the Normal Move Out corrected data. Differences are calculated between the two stages of the process which greatly help to determine the eliminated multiple locations within the sedimentary secession. This will reduce the risk of interpreting these sequences as primary reflectors spatially within deep thin layers. Madagascar open source package is used in these processing steps. Madagascar open source package is very efficient, accurate, and easy to correct any part of the Python code used in the two stages of processing.

Single-shot wavelength-multiplexed phase microscopy under Gabor regime in a regular microscope embodiment

Phase imaging microscopy under Gabor regime has been recently reported as an extremely simple, low cost and compact way to update a standard bright-field microscope with coherent sensing capabilities. By inserting coherent illumination in the microscope embodiment and producing a small defocus distance of the sample at the input plane, the digital sensor records an in-line Gabor hologram of the target sample, which is then numerically post-processed to finally achieve the sample’s quantitative phase information. However, the retrieved phase distribution is affected by the two well-known drawbacks when dealing with Gabor’s regime, that is, coherent noise and twin image disturbances. Here, we present a single-shot technique based on wavelength multiplexing for mitigating these two effects. A multi-illumination laser source (including 3 diode lasers) illuminates the sample and a color digital sensor (conventional RGB color camera) is used to record the wavelength-multiplexed Gabor hologram in a single exposure. The technique is completed by presenting a novel algorithm based on a modified Gerchberg–Saxton kernel to finally retrieve an enhanced quantitative phase image of the sample, enhanced in terms of coherent noise removal and twin image minimization. Experimental validations are performed in a regular Olympus BX-60 upright microscope using a 20X 0.46NA objective lens and considering static (resolution test targets) and dynamic (living spermatozoa) phase samples.

Experimental optimization of lensless digital holographic microscopy with rotating diffuser-based coherent noise reduction.

Laser-based lensless digital holographic microscopy (LDHM) is often spoiled by considerable coherent noise factor. We propose a novel LDHM method with significantly limited coherent artifacts, e.g., speckle noise and parasitic interference fringes. It is achieved by incorporating a rotating diffuser, which introduces partial spatial coherence and preserves high temporal coherence of laser light, crucial for credible in-line hologram reconstruction. We present the first implementation of the classical rotating diffuser concept in LDHM, significantly increasing the signal-to-noise ratio while preserving the straightforwardness and compactness of the LDHM imaging device. Prior to the introduction of the rotating diffusor, we performed LDHM experimental hardware optimization employing 4 light sources, 4 cameras, and 3 different optical magnifications (camera-sample distances). It was guided by the quantitative assessment of numerical amplitude/phase reconstruction of test targets, conducted upon standard deviation calculation (noise factor quantification), and resolution evaluation (information throughput quantification). Optimized rotating diffuser LDHM (RD-LDHM) method was successfully corroborated in technical test target imaging and examination of challenging biomedical sample (60 µm thick mouse brain tissue slice). Physical minimization of coherent noise (up to 50%) was positively verified, while preserving optimal spatial resolution of phase and amplitude imaging. Coherent noise removal, ensured by proposed RD-LDHM method, is especially important in biomedical inference, as speckles can falsely imitate valid biological features. Combining this favorable outcome with large field-of-view imaging can promote the use of reported RD-LDHM technique in high-throughput stain-free biomedical screening.

Seismic Coherent Noise Removal of Source Array in the NSST Domain

The technique of the source array based on the vibroseis can provide the strong energy of a seismic wave field, which better meets the need for seismic exploration. The seismic coherent noise reduces the signal-to-noise ratio (SNR) of the source array seismic data and affects the seismic data processing. The traditional coherent noise removal methods often cause some damage to the effective signal while suppressing coherent noise or cannot suppress the interference wave effectively at all. Based on the multi-scale and multi-direction properties of the non-subsampled Shearlet transform (NSST) and its simple mathematical structure, the seismic coherent noise removal method of source array in NSST domain is proposed. The method is applied to both the synthetic seismic data and the filed seismic data. After processing with this method, the coherent noise of the seismic data is greatly removed and the effective signal information is greatly protected. The analysis of the results demonstrates the effectiveness and practicability of the proposed method on coherent noise attenuation.

High-Resolution Snow Depth on Arctic Sea Ice From Low-Altitude Airborne Microwave Radar Data

We present new high-resolution snow depth data on Arctic sea ice derived from airborne microwave radar measurements from the IceBird campaigns of the Alfred Wegener Institute (AWI) together with a new retrieval method using signal peakiness based on an intercomparison exercise of colocated data at different altitudes. We aim to demonstrate the capabilities and potential improvements of radar data, which were acquired at a lower altitude (200 ft) and slower speed (110 kn) and had a smaller radar footprint size (2-m diameter) than previous airborne snow radar data. So far, AWI Snow Radar data have been derived using a 2–18-GHz ultrawideband frequency-modulated continuous-wave (FMCW) radar in 2017–2019. Our results show that our method in combination with thorough calibration through coherent noise removal and system response deconvolution significantly improves the quality of the radar-derived snow depth data. The validation against a 2-D grid of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> snow depth measurements on level landfast first-year ice indicates a mean bias of only 0.86 cm between radar and ground truth. Comparison between the radar-derived snow depth estimates from different altitudes shows good consistency. We conclude that the AWI Snow Radar aboard the IceBird campaigns is able to measure the snow depth on Arctic sea ice accurately at higher spatial resolution than but consistent with the existing airborne snow radar data of NASA Operation IceBridge. Together with the simultaneous measurements of the total ice thickness and surface freeboard, the IceBird campaign data will be able to describe the whole sea-ice column on regional scales.

Spectral structure-oriented filtering of seismic data with self-adaptive paths

We have developed an algorithm to perform structure-oriented filtering (SOF) in 3D seismic data by learning the data structure in the frequency domain. The method, called spectral SOF (SSOF), allows us to enhance the signal structures in the [Formula: see text]-[Formula: see text]-[Formula: see text] domain by running a 1D edge-preserving filter along curvilinear self-adaptive trajectories that connect points of similar characteristics. These self-adaptive paths are given by the eigenvectors of the smoothed structure tensor, which are easily computed using closed-form expressions. SSOF relies on a few parameters that are easily tuned and on simple 1D convolutions for tensor calculation and smoothing. It is able to process a 3D data volume with a 2D strategy using basic 1D edge-preserving filters. In contrast to other SOF techniques, such as anisotropic diffusion, anisotropic smoothing, and plane-wave prediction, SSOF does not require any iterative process to reach the denoised result. We determine the performance of SSOF using three public domain field data sets, which are subsets of the well-known Waipuku, Penobscot, and Teapot surveys. We use the Waipuku subset to indicate the signal preservation of the method in good-quality data when mostly background random noise is present. Then, we use the Penobscot subset to illustrate random noise and footprint signature attenuation, as well as to show how faults and fractures are improved. Finally, we analyze the Teapot stacked and depth-migrated subsets to show random and coherent noise removal, leading to an improvement of the volume structural details and overall lateral continuity. The results indicate that random noise, footprints, and other artifacts can be successfully suppressed, enhancing the delineation of geologic structures and seismic horizons and preserving the original signal bandwidth.

Using Data‐Regrouping Methods to Attenuate Shot‐to‐Shot Coherent Interference Noise in Marine Seismic Data

AbstractsUnwanted interference noise often causes problems during seismic reflection data acquisition and processing. In this paper we present two novel data‐regrouping methods that enable improved shot‐to‐shot coherent interference noise attenuation in marine seismic data. The two approaches are based on line mixing and/or shot skipping: (1) for a 3‐D marine seismic reflection data acquisition which is typically carried out by shooting closely spaced parallel lines, we propose to mix the shot gathers from two adjacent sail lines to break up shot‐to‐shot coherent noise. This approach takes advantage of the fact that adjacent sail lines are usually acquired with a significant time interval, resulting in different types of noise; (2) for a 2‐D/3‐D acquisition, we propose an algorithm to skip and reorder the original shots to decrease the continuity of the shot‐to‐shot coherent noise. This approach could also supply more aperture data for the first or last shot from both sides, which is beneficial for the coherent noise removal at the edge area. After regrouping the original data, the coherent noise can then be further randomized or isolated by sorting and transforming to other domains, typically the common p‐shot domain where a random noise attenuation tool could be applied to identify and attenuate such noise. Field data examples confirm the effectiveness of the methods.

A Seismic Shift in Scalable Acquisition Demands New Processing: Fiber-Optic Seismic Signal Retrieval in Urban Areas with Unsupervised Learning for Coherent Noise Removal

With the development of fiber-optic seismic acquisition systems, dense seismic monitoring of the near surface in urban areas is quickly becoming much easier than ever before. We provide a case study illustrating the use of data from a new type of deployment, a fiber-optic array in existing telecommunications conduits underneath the Stanford University campus in California. We perform cross correlations of strain-rate measurements of the ambient wavefield to extract signals that mimic the response of the array to virtual active seismic sources at any receiver location. Now that we can so easily use our telecommunications infrastructure for continuous, dense, urban seismic acquisition, data collected in such a manner will go to waste unless we significantly automate ambient noise processing. We analyze 37 days of ambient noise; introduce an exploratory data analysis tool that clusters a week of noise to help us quickly find coherent, repeating noises that inhibit reliable extraction of useful signals; and design filters to remove nearby car recordings from the next 30 days of noise. We review a metric to quantify convergence of the cross correlations and use that metric extended throughout the array to support filtering out recordings of cars near the array.

Application of FK Filtering for Coherent Noise Removal in High Frequency Shallow Marine Data

The use of seismic reflection to study earth subsurface is commonly troubled by the presence of the coherent noise in the seismic data. This unwanted signal were generated by various sources and therefore had their own noise characteristic. The acquisition of the shallow marine seismic survey were done using a sparker source to obtain a high frequency seismic data. This however results in a stronger noise level in the recorded data. The application of FK filter were used to eliminate this unwanted noise using the data obtained from the Malacca Strait and Terengganu Bay. The result obtained prove to be successful in reducing the coherent noise while preserving the frequency content of the seismic data.

Comment on: “Survey design for coal-scale 3D-PS seismic reflection” (S. Strong and S. Hearn, Geophysics, 81, no. 6, P57–P70)

PreviousNext No AccessGEOPHYSICSVolume 82, Issue 3Comment on: “Survey design for coal-scale 3D-PS seismic reflection” (S. Strong and S. Hearn, Geophysics, 81, no. 6, P57–P70)Authors: Gijs VermeerGijs Vermeer3DSymSam — Geophysical Advice, Voorschoten, The Netherlands. E-mail: .Search for more papers by this authorEmail the author at [email protected]https://doi.org/10.1190/geo2016-0709.1 SectionsAboutFull TextPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail REFERENCESStrong, S., and S. Hearn, 2016, Survey design for coal-scale 3D-PS seismic reflection: Geophysics, 81, no. 6, P57–P70, doi: 10.1190/geo2015-0560.1.AbstractWeb of ScienceGoogle ScholarVermeer, G. J. O., 2012, 3D seismic survey design, 2nd ed.: SEG.AbstractGoogle ScholarWe thank Gijs Vermeer for expanding on this topic, and we appreciate the additional insight provided.In the following, we restate important concepts from the paper and provide additional clarification on specific points.Our methodology recognizes that practical survey design will invariably involve compromises between geophysical and economic considerations. We believe that plots of fold, offset, and azimuth provide a useful visual indication of the effect of relaxing ideal design parameters. Vermeer correctly observes that such plots are based on discrete shot-receiver pairs. It is true that in raw form, these plots can be complex and misleading.One way to improve the validity of this type of presentation is to allow for the smoothing effects of limited bandwidth. In our paper, we have followed the spatial filtering approach of Cary and Lawton (2003). This yields distributions that are generally simpler and arguably more meaningful. Of course, it is important to also recognize the dependence of such plots on assumed earth parameters (e.g., P- and S-velocities), particularly in the case of PS modeling. We typically examine a series of plots covering a reasonable range of earth parameters.We also agree that there is an element of subjectivity in assessing such distributions. However, other factors being equal, we consider that an “even” distribution of fold, azimuth, and offset is more desirable than an “uneven” distribution. The final designs considered for our survey produced distributions (Figures 11, 12, and 13) that were compromises away from the ideal (e.g., Figure 8) but that were considered “acceptable” in terms of the variability in fold, offset, and azimuth.The specific 3D-PS survey considered here was funded by a research grant, with in-kind contractor support.The spacings used were accepted as being larger than ideal. Nevertheless, this is quite applicable to coal-industry seismic reflection in which we are often forced to use larger spacings than ideal. Our PS surveys are often done as an extension of a P survey, and parameters may be biased by the demands of the primary exercise.Unfortunately, receiver spacings are not always designed from first principles, being commonly influenced by client experience and budgets. However, a useful guide for bin sizes, and hence receiver intervals, is provided by the expected resolution limits.For the 3D survey described in the paper, we have used the equations provided by Chen and Schuster (1999) to deduce a nominal resolution of order 10–15 m at the target depth. We have used this as a guide for designing the receiver interval.We agree with Vermeer that when compromises need to be made, finer inline spacing is generally more important than crossline. This is especially true in the shallow coal environment and, as pointed out, tends to allow for better coherent-noise removal and improved spatial imaging. Our production P and PS surveys generally do use spacings that are finer in the inline direction and sparser in the crossline direction. For the particular survey discussed in the paper, one of the primary goals was to investigate the influence of azimuthal variation on the seismic data. The reduced crossline spacings used were aimed at improving azimuthal distributions in the raw data.Despite the design constraints, this survey provided a data set that enabled the overall project goals to be achieved.Again, we thank Vermeer for his insightful contribution to this topic. REFERENCES Cary, P. W., and D. C. Lawton, 2003, Bandlimited design and stacking of P-P and P-S surveys: 73rd Annual International Meeting, SEG, Expanded Abstracts, 842–845. AbstractGoogle Scholar Chen, J., and G. T. Schuster, 1999, Resolution limits of migrated images: Geophysics, 64, 1046–1053, doi: 10.1190/1.1444612.GPYSA70016-8033 AbstractWeb of ScienceGoogle ScholarFiguresReferencesRelatedDetails Volume 82Issue 3May 2017Pages: 1MJ-Z23ISSN (print):0016-8033 ISSN (online):1942-2156 publication data© 2017 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryReceived: 28 Dec 2016Accepted: 02 Feb 2017Published Online: 21 Mar 2017Published in print: 01 May 2017 CITATION INFORMATION Gijs Vermeer, (2017), "Comment on: “Survey design for coal-scale 3D-PS seismic reflection” (S. Strong and S. Hearn, Geophysics, 81, no. 6, P57–P70)," GEOPHYSICS 82: X1-X3. https://doi.org/10.1190/geo2016-0709.1 Plain-Language Summary PDF Download Metrics Loading ...

Extended viewing angle holographic display system with tilted SLMs in a circular configuration

This paper presents an extended viewing angle holographic display for reconstruction of real world objects in which the capture and display systems are decoupled. This is achieved by employing multiple tilted spatial light modulators (SLMs) arranged in a circular configuration. In order to prove the proper reconstruction and visual perception of holographic images the Wigner distribution function is employed. We describe both the capture system using a single static camera with a rotating object and a holographic display utilizing six tilted SLMs. The experimental results based on the reconstruction of computer generated and real world scenes are presented. The coherent noise removal procedure is described and implemented. The experiments prove the possibility to view images reconstructed in the display binocularly and with good quality.

Evaluation of 3C microelectromechanical system data on a 2D line: Direct comparison with conventional vertical-component geophone arrays and PS-wave analysis

A 2D vibroseis line was acquired in the Vienna Basin (Austria) for the purpose of comparing the data of digital multicomponent single sensors based on microelectromechanical system (MEMS) sensors alongside conventional vertical-component geophone arrays. For efficient removal of coherent noise during processing, all source points were recorded in single-sweep mode, i.e., no vertical stacking was performed in the field. On this densely sampled data set, several noise-reduction techniques, such as digital array forming, frequency-wavenumber (f-k) filtering in shot and receiver domains, and polarization filters, proved to be valuable in reducing source-generated noise. The results showed that, with the use of single-sweep recording and polarization filter techniques, it is possible to produce seismic sections for a single-receiver three-component (3C) MEMS line that are comparable to a conventional geophone array line in signal-to-noise ratio. However, the higher number of single geophones and hence the stronger attenuation of random noise in the conventional array resulted in an advantage for the analog geophone data set. The second goal for this survey was to evaluate additional information contained in the horizontal components of the MEMS data. The multicomponent data allowed for the processing of mode-converted shear-wave data, performed for the first time in the Vienna Basin. Azimuthal anisotropy related to horizontal stresses was observed in the Neogene section of the shear-wave data set. A PP-PS event correlation allowed the identification of major shallow horizons. Interpretation of the final sections confirmed that the PS data are useful to distinguish between gas reservoirs and high-porosity water sands, which can cause similar P-wave amplitude variation with offset (AVO) effects.

Application of multichannel Wiener filters to the suppression of ambient seismic noise in passive seismic arrays

We are concerned with the detection and location of small seismic events, such as can be encountered in monitoring hydro-fracturing with surface sensors. Ambient seismic noise is the main problem in detection of weak seismic phases from these events, particularly as the sites of interest are often within or near producing fields. Band-pass filtering and stacking are the most widely used techniques for enhancing the signal-to-noise ratio (SNR) in passive seismic experiments, but they are of limited value when noise and signal share the same frequency band. Seismic arrays can be used to reduce the unwanted noise (e.g., traffic noise, pumping noise, scattering ground roll) by delay-and-sum techniques (also called beamforming) or by frequency-wavenumber filtering. Beamforming maximizes the array response for the assumed direction and slowness of the signal. Whereas in some situations it can be highly effective, and the azimuth and slowness of the signal can be determined by a grid search approach, it is vulnerable to contamination by side-lobe energy, particularly for broadband signals and noise (Rost and Thomas, 2002). Frequency-wavenumber filtering can be very effective but requires regularly spaced arrays and implicitly assumes plane-wave propagation. Both methods perform poorly when the waveform changes significantly between stations of the array, as might be caused, for example, by differences in site response. In this article, we present a multichannel Wiener filtering technique, which allows the removal of coherent noise from three-component 2D arrays without making a priori assumptions about the mode of propagation (e.g., no plane-wave assumption is required for the noise field). We test the effectiveness of this filter with two case studies. In the first case, we add synthetic signals of varying strengths to actual noise data recorded with a hexagonal array during hydro-fracturing within a producing oil field in Wyoming, USA. Using this test, we are able to provide estimates of the smallest event detectable with the filtered data, and compare the results with conventional techniques, such as stacking. The second test case is a dense, small-aperture 2D seismic array of 95 stations placed within an area of 130 m x 56 m on a landslide deposit in the Northern Apennines, Italy. Numerous microearthquakes have been recorded with this array, whose faint P-phases serve as an ideal data set for testing filtering techniques.

Structural setting of the Bay of Naples (Italy) seismic reflection data: implications for Campanian volcanism

This paper focuses on the recent tectonic evolution of the Bay of Naples with the aim of exploring the connection between local tectonics and volcanism. We reprocessed the seismic reflection dataset acquired in the area in the late 1973. The new processing was highly successful in obtaining a decisive strong reduction of random noise, removal of coherent noise and reduction of spatial aliasing. Classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns. The results show that the faults affecting the Bay of Naples exhibit prevailing NE structural strikes, with the exception of the Pozzuoli Caldera where NW patterns are also common. Many faults are subvertical and show seismic evidence of volcanic activity along them. A main alignment of conjugate NE–SW faults, named here as “Magnaghi–Sebeto line”, intersects several submarine volcanic banks and separates the bay into two sectors, characterized by important geological, geophysical and petrochemical differences. The structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the NW–SE fault system, along which, in the Campanian–Lucanian Apennine chain, great vertical displacements occur.

High-resolution coherent noise removal

In shallow hard water-bottom areas seismic data can be contaminated with linear refracted noise that may totally obscure signal amplitudes at medium and far offsets. Such noise is often highly aliased and resistant to removal via conventional approaches such as FK filtering or linear slant-stack. These can fail to remove the noise sufficiently for an accurate interpretation of amplitudes at far offsets, and have a tendency to smear signal amplitudes at all offsets.

Tomographic estimation of seismic velocity on an interactive workstation

Tomographic estimation of seismic velocity from directly transmitted arrivals in offset VSP or crosshole data requires the following processing operations: (a) statics estimation and corrections; (b) stacking to enhance arrivals of interest and to remove coherent noise; (c) deconvolution and time picking; (d) iteration between tomographic inversion of picked source-receiver delay times and ray tracing. Velocity tomography with reflection data may also require migration to estimate the position of reflectors for picking two-way travel times. A workstation based software system has been developed which permits interactive tomographic velocity estimation from shallow crosshole and offset VSP data. The flexibility gained by performing velocity tomography interactively has many advantages, such as easy comparisons of intermediate results and the ability to update filtering sequences to accommodate the results of interactive analyses of signal and noise characteristics. We illustrate this for shallow crosshole velocity tomography with examples of (a) interactive tau-p filtering for arrival enhancement and coherent noise removal; (b) the dependence of tomogram resolution on raypath coverage; (c) interactive smoothing to compensate for resolution artifacts related to incomplete tomographic raypath coverage. The use of interactive smoothing to cater for different types of geological prior information in tomography is discussed.

Comments on "The Removal of Coherent Noise from Short Digitized Records" (includes Author reply) [Letters to the editor

Comments on "The Removal of Coherent Noise from Short Digitized Records" (includes Author reply) [Letters to the editor