Catastrophic flooding edited by L. Mayer and D. Nash,Allen and Unwin,London, 1987. ISBN 0-04-551142-x     

Adrian McDonald 《地球表面变化过程与地形》1990,15(1):99-100

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Attenuation of marine seismic interference noise employing a customized U-Net     

Jing Sun  Sigmund Slang  Thomas Elboth  Thomas Larsen Greiner  Steven McDonald  Leiv-J. Gelius 《Geophysical Prospecting》2020,68(3):845-871

Marine seismic interference noise occurs when energy from nearby marine seismic source vessels is recorded during a seismic survey. Such noise tends to be well preserved over large distances and causes coherent artefacts in the recorded data. Over the years, the industry has developed various denoising techniques for seismic interference removal, but although well performing, they are still time-consuming in use. Machine-learning-based processing represents an alternative approach, which may significantly improve the computational efficiency. In the case of conventional images, autoencoders are frequently employed for denoising purposes. However, due to the special characteristics of seismic data as well as the noise, autoencoders failed in the case of marine seismic interference noise. We, therefore, propose the use of a customized U-Net design with element-wise summation as part of the skip-connection blocks to handle the vanishing gradient problem and to ensure information fusion between high- and low-level features. To secure a realistic study, only seismic field data were employed, including 25,000 training examples. The customized U-Net was found to perform well, leaving only minor residuals, except for the case when seismic interference noise comes from the side. We further demonstrate that such noise can be treated by slightly increasing the depth of our network. Although our customized U-Net does not outperform a standard commercial algorithm in quality, it can (after proper training) read and process one single shot gather in approximately 0.02 s. This is significantly faster than any existing industry denoising algorithm. In addition, the proposed network processes shot gathers in a sequential order, which is an advantage compared with industry algorithms that typically require a multi-shot input to break the coherency of the noise.  相似文献   

Spatiotemporal development of physical,chemical, and biological characteristics of stormwater plumes in Santa Monica Bay,California (USA)     

Alina A. Corcoran  Kristen M. Reifel  Burton H. Jones  Rebecca F. Shipe 《Journal of Sea Research》2010,63(2):129-142

This study characterized stormwater plume development and associated phytoplankton dynamics in a coastal marine ecosystem through shipboard monitoring. We focused on plumes within Santa Monica Bay, California (USA), a coastal system that is subject to rapid pulses of untreated runoff from the urbanized watershed of Los Angeles during the winter rainy season. The physical, chemical, and biological signatures of stormwater plumes were tracked over time after each of 4 precipitation events ranging in magnitude from 1.5 cm to 9 cm. Low salinity surface plumes persisted in Santa Monica Bay for at least 2 to 5 days over spatial scales of up to 15 km. This is consistent with a 6-day residence time for surface water plume parcels, which was estimated from a drifter trajectory in the bay. Shipboard sampling and salinity measurements in the surf zone showed that plumes often persisted even longer nearshore. Plume waters were generally characterized by higher concentrations of dissolved nitrogen, colored dissolved organic matter, and higher light attenuation than non-plume waters. The magnitude of the effect of stormwater runoff on phytoplankton dynamics was dependent on the size of each storm and subsequent residence time of runoff within the bay. Rain events led to increases in primary productivity, phytoplankton biomass, and specifically, increases in diatom biomass, as measured by concentrations of biogenic silica.  相似文献   

Longitude by Dava Sobel     

John McDonald 《GPS Solutions》1998,2(1):67-68

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Fluorescence spectra of Titan tholins: in-situ detection of astrobiologically interesting areas on Titan's surface     

Robert Hodyss  Gene McDonald  Mark A. Smith  J.L. Beauchamp 《Icarus》2004,171(2):525-530

We report the three-dimensional fluorescence spectra of Titan tholins in water and acetonitrile, and separate some of the fluorescent components of tholins using two-dimensional thin layer chromatography. In acetonitrile, tholins exhibit a broad fluorescence with a maximum at 471 nm, and an excitation maximum at 410 nm. The fluorescence spectrum of a water extraction displays a more complicated spectrum with multiple peaks. TLC results indicate the presence of at least three distinct fluorescent species. In addition, we obtained the two-dimensional fluorescence spectrum of tholins in water ice at 77 K, close to the surface temperature of Titan. The fluorescence of tholins in a 77 K ice matrix is red-shifted in comparison to a water solution, and undergoes a further red-shift when the water solution is heated prior to freezing. These results suggest that a simple fluorescence probe could be used on the surface of Titan to identify sites where tholins have been mixed with water, and possibly reveal information about the extent of heating the tholin-water mixture has undergone. This would be useful for a future mission with the goal of examining the organic chemistry of Titan.  相似文献   

Comment on “Origin of a late Eocene to pre‐Miocene buried crater and breccia lens at Fohn‐1, North Bonaparte Basin,Timor Sea: A probable extraterrestrial connection” by J. D. Gorter and A. Y. Glikson     

Wolf U. Reimold  Christian Koeberl  Cedric Wright  Iain McDonald 《Meteoritics & planetary science》2001,36(5):747-749

Abstract— Gorter and Glikson (2000) proposed that the Fohn‐1 structure in the Timor Sea north of Australia probably is an impact structure. Examination of their evidence reveals that it is almost impossible to confirm any of their conclusions, as the authors do not provide sufficient detail of their experimental methods. Problems with the presentation of both seismic and geochemical data cast further doubt on their conclusions. Absence of evidence for shock metamorphism and non‐chondritic siderophile element patterns in the few samples analysed make it likely that Fohn‐1 is neither a probable, nor even a possible, impact structure.  相似文献   

A Digital System for the Acquisition and Processing of Geoacoustic Data     

Eugene Herrin  John A. McDonald 《Geophysical Journal International》1971,26(1-4):13-20

Summary In the autumn of 1969 we accepted delivery of three TC-200 digital data acquisition systems from Teledyne Geotech. These systems can record up to 16 channels of long period, digital data with a specified sampling rate (currently 1 per second) on magnetic tape in an 'IBM compatible' format. Identifying headers are automatically written at the beginning of each file on tape and Universal Time is written each minute. The actual dynamic range of the receding system is about 66 dB, but an operating range of 120 dB is automatically assured by the use of binary, gain-ranging amplifiers. The systems have been tested and are now operating satisfactorily at Blacknest Laboratory near Reading in England, at the University of Alaska and at a field site east of Dallas, Texas.  相似文献   

The Structure of Atmospheric Turbulence and its Application to the Design of Pipe Arrays   总被引：1，自引：0，他引：1  

John A. McDonald  E. J. Douze  Eugene Herrin 《Geophysical Journal International》1971,26(1-4):99-109

Summary Turbulent boundary layers at the surface of the Earth limit the detection of infrasonic waves with periods greater than 1 s. Pipe arrays designed to improve the signal-to-noise ratios of infrasonic waves usually assume that the background noise due to this turbulent boundary layer is incoherent between the array inlets. The power at various points on a surface was measured; coherences between these points were determined and they were found to be significant in the period range 1–100 s. Such coherent noise must be considered when pipe arrays are designed.  相似文献   

Artificial Ground-Water Recharge Investigations in Northeastern Illinois     

C. K. McDonald  R. T. Sasman 《Ground water》1967,5(2):26-30

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Analyzing Slug Tests in Wells Screened Across the Watertable: A Field Assessment     

Stanford  Kristen L.  McElwee  Carl D. 《Natural Resources Research》2000,9(2):111-124

The slug test is the most widely used technique for the in situ estimation of hydraulic conductivityin confined and unconfined formations. Currently, there are no generally accepted methods in thegroundwater literature for the analysis of response data from slug tests performed in wells screenedacross the watertable. A field study was undertaken in an attempt to develop a set of practicalguidelines for tests conducted in such wells. Three wells, screened within unconsolidated materialexhibiting a range of hydraulic conductivities (.05–30.0 m/day), were installed to depths of up to9 m (30 ft) in Kansas River alluvium that ranges in thickness from 15 m to 21 m (50 ft to 70 ft)near Lawrence, Kansas. Intensive well-development efforts removed any drilling debris that couldinterfere with well-formation hydraulics. Once the wells were developed properly, a series of slugtests was performed at each well. The tests were designed to assess the role of the unsaturatedzone and the appropriateness of assuming a fixed hydraulic head upper boundary. The results ofthis investigation can be summarized as follows: (1) the sufficiency of well development shouldbe based on repeat slug tests and not the clarity of pumped water; (2) the effective screen radiusfor best model analysis should be based on a mass balance and not nominal screen dimensions;(3) the watertable can be represented as a constant head boundary and flow in the unsaturatedzone can be ignored in most situations; (4) conventional techniques for the analysis of slug-testdata seem to be reasonable for slug tests conducted in wells screened across the watertable, whenused with the appropriate effective screen radius and normalized head range; and (5) fluctuationsin the watertable elevation through time can be exploited to obtain some insight into the natureof vertical variation in hydraulic conductivity at a well. The results of this investigation indicatethat multiple slug tests should be performed at wells screened across the watertable in order toreliably assess the sufficiency of well development and the appropriateness of conventional theory.  相似文献