Imaging of Buried Archaeological Materials: The Reflection Properties of Archaeological Wood   总被引：1，自引：0，他引：1  

Stephanie H.L. Arnott  Justin K. Dix  Angus I. Best  David J. Gregory 《Marine Geophysical Researches》2005,26(2-4):135-144

Effective marine archaeological site management demands detailed information on not only the spatial distribution of artefacts but also the degradation state of the materials present. Although sonar methods have frequently been used in an attempt to detect buried wooden shipwrecks they are currently unable to indicate their degradation state. To assess the sensitivity of acoustic measurements to changes in the degradation state of such material, and hence the potential for sonars to quantify degradation, laboratory measurements of compressional wave velocity, as well as bulk density for oak and pine samples, in varying states of decay, were undertaken. These data enabled the calculation of theoretical reflection coefficients for such materials buried in various marine sediments. As wood degrades, the reflection coefficients become more negative, resulting in the hypothesis that the more degraded wood becomes, the easier it should be to detect. Typical reflection coefficients of the order of −0.43 and −0.52 for the most degraded oak and pine samples in sand are predicted. Conversely, for wood exposed to seawater the predicted reflection coefficients are large and positive for undegraded material (0.35 for oak, 0.18 for pine) and decrease to zero or slightly below for the most degraded samples. This indicates that exposed timbers, when heavily degraded, can be acoustically transparent and so undetectable by acoustic methods. Corroboration of these experimental results was provided through comparison with high resolution seismic reflection data that has been acquired over two shipwrecks.  相似文献   

ASPI experiment: measurements of fields and waves on board the INTERBALL-1 spacecraft     

S. Klimov  S. Romanov  E. Amata  J. Blecki  J. Büchner  J. Juchniewicz  J. Rustenbach  P. Triska  L. J. C. Woolliscroft  S. Savin  Yu. Afanas’yev  U. de Angelis  U. Auster  G. Bellucci  A. Best  F. Farnik  V. Formisano  P. Gough  R. Grard  V. Grushin  G. Haerendel  V. Ivchenko  V. Korepanov  H. Lehmann  B. Nikutowski  M. Nozdrachev  S. Orsini  M. Parrot  A. Petrukovich  J. L. Rauch  K. Sauer  A. Skalsky  J. Slominski  J. G. Trotignon  J. Vojta  R. Wronowski 《Annales Geophysicae》1997,15(5):514-527

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and searchcoil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.  相似文献   

Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks     

Angus I. Best  Mark S. Sams 《Geophysical Prospecting》1997,45(2):327-344

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Radiative Exchange in an Urban Street Canyon   总被引：1，自引：4，他引：1  

Ian N. Harman  Martin J. Best  Stephen E. Belcher 《Boundary-Layer Meteorology》2004,110(2):301-316

The influence of building geometry on the radiation terms ofthe surface energy balance is a principal reason for surfacetemperature differences between rural and urban areas.Methods exist to calculate the radiation balance in an urban area,but their validity across the range of urban geometries andmaterials has not been carefully considered.Here the exchange of diffuse radiation in an urban street canyon isinvestigated using a method incorporating all reflections of radiation.This exact solution is compared to two commonly used approximationsthat retain either no reflections, or just one reflection of radiation.The area-averaged net radiative flux density from the facets of the canyondecreases in magnitude monotonically as the canyon aspect ratio increases.The two approximate solutions possess unphysical differences from thismonotonic decrease for high canyon aspect ratios or low materialemissivities/high material albedos.The errors of the two approximate solutions are small for near blackbodymaterials and small canyon aspect ratios but can be an order ofmagnitude for intermediate material properties and deep street canyons.Urban street canyon models need to consider at least one reflectionof radiation and multiple reflections are desirable for full applicability.  相似文献   

Sedimentology and kinematics of a large, retrogressive growth-fault system in Upper Carboniferous deltaic sediments, western Ireland   总被引：2，自引：0，他引：2  

P. B. Wignall  J. L. Best 《Sedimentology》2004,51(6):1343-1358

Growth faulting is a common feature of many deltaic environments and is vital in determining local sediment dispersal and accumulation, and hence in controlling the resultant sedimentary facies distribution and architecture. Growth faults occur on a range of scales, from a few centimetres to hundreds of metres, with the largest growth faults frequently being under‐represented in outcrops that are often smaller than the scale of feature under investigation. This paper presents data from the exceptionally large outcrops of the Cliffs of Moher, western Ireland, where a growth‐fault complex affects strata up to 60 m in thickness and extends laterally for ≈ 3 km. Study of this Namurian (Upper Carboniferous) growth‐fault system enables the relationship between growth faulting and sedimentation to be detailed and permits reconstruction of the kinematic history of faulting. Growth faulting was initiated with the onset of sandstone deposition on a succession of silty mudstones that overlie a thin, marine shale. The decollement horizon developed at the top of the marine shale contact for the first nine faults, by which time aggradation in the hangingwall exceeded 60 m in thickness. After this time, failure planes developed at higher stratigraphic levels and were associated with smaller scale faults. The fault complex shows a dominantly landward retrogressive movement, in which only one fault was largely active at any one time. There is no evidence of compressional features at the base of the growth faults, thus suggesting open‐ended slides, and the faults display both disintegrative and non‐disintegrative structure. Thin‐bedded, distal mouth bar facies dominate the hangingwall stratigraphy and, in the final stages of growth‐fault movement, erosion of the crests of rollover structures resulted in the highest strata being restricted to the proximity of the fault. These upper erosion surfaces on the fault scarp developed erosive chutes that were cut parallel to flow and are downlapped by the distal hangingwall strata of younger growth faults.  相似文献   

Physics of Rocks for Hydrocarbon Exploration: Introduction     

Angus Best 《Geophysical Prospecting》2014,62(6):1203-1204

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XIII Upper Cainozoic     

R.J. Allen  J.G. Best  J.E. Coaldrake  T.H. Connah  H.G.S. Cribb  D. Hill 《Australian Journal of Earth Sciences》2013,60(1-2):387-423

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The alluvial architecture of a suspended sediment dominated meandering river: the Río Bermejo,Argentina          下载免费PDF全文

Gregory H. Sambrook Smith  James L. Best  Jessica Z. Leroy  Oscar Orfeo 《Sedimentology》2016,63(5):1187-1208

The alluvial architecture of fine‐grained (silt‐bed) meandering rivers remains poorly understood in comparison to the extensive study given to sand‐bed and gravel‐bed channels. This paucity of knowledge stems, in part, from the difficulty of studying such modern rivers and deriving analogue information from which to inform facies models for ancient sediments. This paper employs a new technique, the parametric echosounder, to quantify the subsurface structure of the Río Bermejo, Argentina, which is a predominantly silt‐bed river with a large suspended sediment load. These results show that the parametric echosounder can provide high‐resolution (decimetre) subsurface imaging from fine‐grained rivers that is equivalent to the more commonly used ground‐penetrating radar that has been shown to work well in coarser‐grained rivers. Analysis of the data reveals that the alluvial architecture of the Río Bermejo is characterized by large‐scale inclined heterolithic stratification generated by point‐bar evolution, and associated large‐scale scour surfaces that result from channel migration. The small‐scale and medium‐scale structure of the sedimentary architecture is generated by vertical accretion deposits, bed sets associated with small bars, dunes and climbing ripples and the cut and fill from small cross‐bar channels. This style of alluvial architecture is very different from other modern fine‐grained rivers reported in the literature that emphasize the presence of oblique accretion. The Río Bermejo differs from these other rivers because it is much more active, with very high rates of bank erosion and channel migration. Modern examples of this type of highly active fine‐grained river have been reported rarely in the literature, although ancient examples are more prevalent and show similarities with the alluvial architecture of the Río Bermejo, which thus represents a useful analogue for their identification and interpretation. Although the full spectrum of the sedimentology of fine‐grained rivers has yet to be revealed, meandering rivers dominated by lateral or oblique accretion probably represent end members of such channels, with the specific style of sedimentation being controlled by grain size and sediment load characteristics.  相似文献   

Investigation of the impact of anthropogenic heat flux within an urban land surface model and PILPS-urban     

M. J. Best  C. S. B. Grimmond 《Theoretical and Applied Climatology》2016,126(1-2):51-60

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Organochlorine residues in whales landed at Durban,South Africa     

John Henry  Peter B Best 《Marine pollution bulletin》1983,14(6):223-227

The levels of DDT and its metabolites found in the blubber of 29 minke, 6 fin and 1 sei whale landed at the Durban whaling station in 1974 were on average much lower than those found in baleen whales from the North Atlantic, but of the same order as those measured from the Antarctic and North Pacific. In 12 sperm whales examined at Durban the levels of DDT and its metabolites in the blubber were substantially lower than in any other locality so far examined, including the Antarctic, but this may partly reflect the comparative youth of the animals sampled. Low levels of Dieldrin were found in some minke whales only. No PCB could be detected in any of the whales examined.  相似文献