Strategies for waveform processing in sparker data     

Mathieu J. Duchesne  Gilles Bellefleur  Mike Galbraith  Randy Kolesar  Rick Kuzmiski 《Marine Geophysical Researches》2007,28(2):153-164

A sparker is a marine seismic impulsive source used for high-resolution seismic surveys. Sparker sources were very popular during the late 1960s and 1970s before being supplanted by small volume airguns. However, in the last 10 years there has been renewed interest in sparker technology because (1) it can be easily deployed at relatively low costs and (2) in certain areas the use of small airguns is restricted for environmental purposes. In this study a sparker source was used to assess the seismic stratigraphy of Quaternary deposits and to image the sediment/bedrock interface. Three different inverse filtering methods were tested (i.e., spiking deconvolution, match-filtering and vertical seismic profile (VSP) deconvolution) to correct the poor shot-to-shot repeatability of the source and to compress its reverberations. Results show that the matched-filter and VSP deconvolution methods, which design and apply one operator for each shot, produced comparable results, whereas the spiking deconvolution that used the same operator on all traces failed to compress the source signature properly.  相似文献   

Response of temperate lakes to drought: a paleolimnological perspective on the landscape position concept using diatom-based reconstructions     

Courtney R. Wigdahl-Perry  Jasmine E. Saros  Jennifer Schmitz  Randy Calcote  James Rusak  Dennis Anderson  Sara Hotchkiss 《Journal of Paleolimnology》2016,55(4):339-356

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Reply to the comment by Zhang et al. on: “First finding of A-type and adakitic magmatism association in Songpan–Garze fold belt, eastern Tibetan Plateau: Implication for lithospheric delamination”     

Zhang Hong-Fei  Randy Parrish  Li Zhang  Wang-Chuan Xu  Hong-Ling Yuan  Shan Gao  Quentin G. Crowley 《Lithos》2008,103(3-4):565-568

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The Georgian Star: How William and Caroline Herschel revolutionized our understanding of the cosmos,by Michael D. Lemonick     

Randy S. Kissack 《Meteoritics & planetary science》2009,44(5):781-782

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An examination of the spring 1997 mid‐latitude east pacific sea surface temperature anomaly     

Randy G. Brown  Lee‐Lueng Fu 《大气与海洋》2013,51(4):577-599

Abstract

We seek to document and explain the lifecycle of the warm Sea Surface Temperature (SST) anomaly that intensified and weakened off the west coast of the United States to peak anomalies of 4°C during April‐June 1997. We use remotely sensed observational data and model analyses to compute an energy budget for the warm anomaly. The bulk of the anomalous warming was confined to the top 50 m of ocean and occurred during May. The immediate cause for the warming was twofold: latent heat fluxes decreased in magnitude as a result of both lower wind speeds and positive moisture anomalies, while the net radiative flux into the ocean increased as a result of lower than normal fractional cloud coverage. During June, the wind speed strengthened and became northerly, resulting in larger than normal latent and sensible heat fluxes that weakened the SST anomaly. Examination of the National Centers for Environmental Prediction (NCEP) 1000‐mb geopotential height for May shows that the Aleutian low extended far south of its usual position and was responsible for the weaker southerly winds and suppressed latent heat fluxes in the warm anomaly area. Finally, we note that the near simultaneous appearance of this warm anomaly in conjunction with warm El Niño waters off Peru makes El Niño an unlikely trigger for the northeast Pacific warm anomaly. We suggest a possible alternative scenario in which both events are remotely triggered by the intraseasonal oscillation.  相似文献   

Petrography and geochemistry of the LaPaz Icefield basaltic lunar meteorite and source crater pairing with Northwest Africa 032     

Ryan A. ZEIGLER  Randy L. KOROTEV  Bradley L. JOLLIFF  Larry A. HASKIN 《Meteoritics & planetary science》2005,40(7):1073-1101

Abstract— We report on the bulk composition and petrography of four new basaltic meteorites found in Antarctica—LAP (LaPaz Icefield) 02205, LAP 02224, LAP 02226, and LAP 02436—and compare the LAP meteorites to other lunar mare basalts. The LAP meteorites are coarse‐grained (up to 1.5 mm), subophitic low‐Ti basalts composed predominantly of pyroxene and plagioclase, with minor amounts of olivine, ilmenite, and a groundmass dominated by fayalite and cristobalite. All of our observations and results support the hypothesis that the LAP stones are mutually paired with each other. In detail, the geochemistry of LAP is unlike those of any previously studied lunar basalt except lunar meteorite NWA (Northwest Africa) 032. The similarities between LAP and NWA 032 are so strong that the two meteorites are almost certainly source crater paired and could be two different samples of a single basalt flow. Petrogenetic modeling suggests that the parent melt of LAP (and NWA 032) is generally similar to Apollo 15 low‐Ti, yellow picritic glass beads, and that the source region for LAP comes from a similar region of the lunar mantle as previously analyzed lunar basalts.  相似文献   

Geochemical heterogeneity in a small, stratigraphically complex moraine aquifer system (Ontario, Canada): interpretation of flow and recharge using multiple geochemical parameters     

Randy L. Stotler  Shaun K. Frape  Humam Taha El Mugammar  Craig Johnston  Ian Judd-Henrey  F. Edwin Harvey  Robert Drimmie  Jon Paul Jones 《Hydrogeology Journal》2011,19(1):101-115

The Waterloo Moraine is a stratigraphically complex system and is the major water supply to the cities of Kitchener and Waterloo in Ontario, Canada. Despite over 30?years of investigation, no attempt has been made to unify existing geochemical data into a single database. A composite view of the moraine geochemistry has been created using the available geochemical information, and a framework created for geochemical data synthesis of other similar flow systems. Regionally, fluid chemistry is highly heterogeneous, with large variations in both water type and total dissolved solids content. Locally, upper aquifer units are affected by nitrate and chloride from fertilizer and road salt. Typical upper-aquifer fluid chemistry is dominated by calcium, magnesium, and bicarbonate, a result of calcite and dolomite dissolution. Evidence also suggests that ion exchange and diffusion from tills and bedrock units accounts for some elevated sodium concentrations. Locally, hydraulic “windows??cross connect upper and lower aquifer units, which are typically separated by a clay till. Lower aquifer units are also affected by dedolomitization, mixing with bedrock water, and locally, upward diffusion of solutes from the bedrock aquifers. A map of areas where aquifer units are geochemically similar was constructed to highlight areas with potential hydraulic windows.  相似文献   

Radar and optical observations and physical modeling of near-Earth Asteroid 10115 (1992 SK)     

Michael W. Busch  Steven J. Ostro  Jon D. Giorgini  Randy Rose  Petr Pravec  Stephen B. Broschart 《Icarus》2006,181(1):145-155

We estimate Asteroid 1992 SK's physical properties from delay-Doppler images and Doppler-only echo spectra obtained during March 22-27, 1999, at Goldstone and from optical lightcurves obtained during February-March 1999 at Ond?ejov Observatory. The images span only about 15° of sky motion and are not strong, but they place up to twenty 40 m by 160 m pixels on the asteroid and have complete rotational phase coverage. Our analysis establishes that the radar observations are confined to subradar latitudes between −20° and −40°. The echo spectra and optical lightcurves span ∼80° of sky motion, which provides important geometric leverage on the pole direction. The lightcurves are essential for accurate estimation of the asteroid's shape and spin state. We estimate the asteroid's period to be 7.3182±0.0003 h and its pole direction to be at ecliptic longitude, latitude=(99°±5°,−3°±5°). The asteroid is about 1.4 km in maximum extent and mildly asymmetric, with an elongation of about 1.5 and relatively subdued topography. The OC radar albedo is 0.11±0.02 and the SC/OC ratio is 0.34±0.05. The current orbital solution permits accurate identification of planetary close approaches during 826-2690. We use our model to predict salient characteristics of radar images and optical lightcurves obtainable during the asteroid's March 2006 approach.  相似文献   

Comment: Late Quaternary deglacial history of the Mérida Andes,Venezuela. N. D. Stansell,M. B. Abbott,P. J. Polissar,A. P. Wolfe,M. Bezada and V. Rull (2005) Journal of Quaternary Science 20: 801–812     

William C. Mahaney  Randy W. Dirszowsky  Volli Kalm 《第四纪科学杂志》2007,22(8):817-821

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Hydrogeology,Chemical and Microbial Activity Measurement Through Deep Permafrost     

Randy L. Stotler  Shaun K. Frape  Barry M. Freifeld  Brian Holden  Tullis C. Onstott  Timo Ruskeeniemi  Eric Chan 《Ground water》2011,49(3):348-364

Little is known about hydrogeochemical conditions beneath thick permafrost, particularly in fractured crystalline rock, due to difficulty in accessing this environment. The purpose of this investigation was to develop methods to obtain physical, chemical, and microbial information about the subpermafrost environment from a surface‐drilled borehole. Using a U‐tube, gas and water samples were collected, along with temperature, pressure, and hydraulic conductivity measurements, 420 m below ground surface, within a 535 m long, angled borehole at High Lake, Nunavut, Canada, in an area with 460‐m‐thick permafrost. Piezometric head was well above the base of the permafrost, near land surface. Initial water samples were contaminated with drill fluid, with later samples <40% drill fluid. The salinity of the non‐drill fluid component was <20,000 mg/L, had a Ca/Na ratio above 1, with δ¹⁸O values ～5‰ lower than the local surface water. The fluid isotopic composition was affected by the permafrost‐formation process. Nonbacteriogenic CH₄ was present and the sample location was within methane hydrate stability field. Sampling lines froze before uncontaminated samples from the subpermafrost environment could be obtained, yet the available time to obtain water samples was extended compared to previous studies. Temperature measurements collected from a distributed temperature sensor indicated that this issue can be overcome easily in the future. The lack of methanogenic CH₄ is consistent with the high sulfate concentrations observed in cores. The combined surface‐drilled borehole/U‐tube approach can provide a large amount of physical, chemical, and microbial data from the subpermafrost environment with few, controllable, sources of contamination.  相似文献