AIR SURVEY COMES OF AGE IN THE ORDNANCE SURVEY OF IRELAND: 1965–1986     

M. C. Walsh 《The Photogrammetric Record》1987,12(69):287-291

Since the mid-1960s, the Ordnance Survey of Ireland, whose headquarters are in Dublin, has undergone great technological change. This paper emphasises the photogrammetric aspects of that change and outlines how a sophisticated range of modern equipment is used in the supply of survey data for the Irish Republic.  相似文献   

Northern Hemisphere sea ice simulations by global climate models   总被引：1，自引：0，他引：1  

John E. Walsh  Michael S. Timlin 《Polar research》2003,22(1):75-82

The study described here is a synthesis of global climate model projections of Northern Hemisphere sea ice through the end of the 21st century. The synthesis includes an enhancement of the informational content of the projections from a set of five global atmosphere-ocean-ice models. The adjustments are based on the systematic errors in the models' present-day simulations relative to the HadISST observational data set. All models show decreases of sea ice through the 21st century when forced by the B2 scenario of greenhouse gas and aerosol concentrations. However, the differences in the present-day ice coverage simulated by the models are sufficiently large that they dominate the across-model variances of the projected ice extents. The adjustments based on the present-day biases remove much of the spread among the projections. The decreases of the adjusted ice extent by the year 2100 range from about 12% to about 46%. The percentage decreases are larger in summer than in winter; much of the Arctic Ocean is ice-free at the time of the summer ice minimum by the year 2099.  相似文献   

Across‐axis variations in petrophysical properties of the North Porcupine Basin,offshore Ireland: New insights from long‐streamer traveltime tomography     

Manel Prada  Franois Lavou  Muhammad Mudasar Saqab  Brian M. O'Reilly  Sergei Lebedev  John J. Walsh  Conrad Childs 《Basin Research》2019,31(1):59-76

The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin, SW of Ireland, in which a postrift phase of extensional faulting and reactivation of synrift faults occurred during the Mid–Late Eocene. Fault zones are known to act as either conduits or barriers for fluid flow and to contribute to overpressure. Yet, little is known about the distribution of fluids and their relation to the tectono‐stratigraphic architecture of the Porcupine Basin. One way to tackle this aspect is by assessing seismic (V_p) and petrophysical (e.g., porosity) properties of the basin stratigraphy. Here, we use for the first time in the Porcupine Basin 10‐km‐long‐streamer data to perform traveltime tomography of first arrivals and retrieve the 2D V_p structure of the postrift sequence along a ~130‐km‐long EW profile across the northern Porcupine Basin. A new V_p–density relationship is derived from the exploration wells tied to the seismic line to estimate density and bulk porosity of the Cenozoic postrift sequence from the tomographic result. The V_p model covers the shallowest 4 km of the basin and reveals a steeper vertical velocity gradient in the centre of the basin than in the flanks. This variation together with a relatively thick Neogene and Quaternary sediment accumulation in the centre of the basin suggests higher overburden pressure and compaction compared to the margins, implying fluid flow towards the edges of the basin driven by differential compaction. The V_p model also reveals two prominent subvertical low‐velocity bodies on the western margin of the basin. The tomographic model in combination with the time‐migrated seismic section shows that whereas the first anomaly spatially coincides with the western basin‐bounding fault, the second body occurs within the hangingwall of the fault, where no major faulting is observed. Porosity estimates suggest that this latter anomaly indicates pore overpressure of sandier Early–Mid Eocene units. Lithological well control together with fault displacement analysis suggests that the western basin‐bounding fault can act as a hydraulic barrier for fluids migrating from the centre of the basin towards its flanks, favouring fluid compartmentalization and overpressure of sandier units of its hangingwall.  相似文献   

Adaptive base-isolation of civil structures using variable amplification   总被引：1，自引：0，他引：1  

Kenneth K. Walsh Makola M. Abdullah 《地震工程与工程振动(英文版)》2006,5(2):223-233

Semi-active dampers are used in base-isolation to reduce the seismic response of civil engineering structures. In the present study, a new semi-active damping system using variable amplification will be investigated for adaptive baseisolation. It uses a novel variable amplification device （VAD） connected in series with a passive damper. The VAD is capable of producing multiple amplification factors, each corresponding to a different amplification state. Forces from the damper are amplified to the structure according to the current amplification state, which is selected via a semi-active control algorithm specifically tailored to the system＇s tmique damping characteristics. To demonstrate the effectiveness of the VAD-damper system for adaptive base-isolation, numerical simulations are conducted for three and seven-story base-isolated buildings subject to both far and near-field ground motions. The results indicate that the system can achieve significant reductions in response compared to the base-isolated buildings with no damper. The proposed system is also found to perform well compared to a typical semi-active damper.  相似文献   

Simulation of rock failure modes in thermal spallation drilling     

Vogler  Daniel  Walsh  Stuart D. C.  von Rohr  Philipp Rudolf  Saar  Martin O. 《Acta Geotechnica》2020,15(8):2327-2340

Acta Geotechnica - Thermal spallation drilling is a contact-less means of borehole excavation that works by exposing a rock surface to a high-temperature jet flame. In this study, we investigate...  相似文献   

Measurement of ocean wave spectra using narrow-beam HE radar   总被引：1，自引：0，他引：1  

Howell  R. Walsh  J. 《Oceanic Engineering, IEEE Journal of》1993,18(3):296-305

A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix using a singular value decomposition. As a test of this algorithm, comparisons are made between wave spectrum estimates obtained from a WAVEC buoy and a pair of 25.4-MHz ground wave radars, using data collected during the 1986 Canadian Atlantic Storms Program (CASP). Overall, the results of this experiment have been positive and have demonstrated both the basic feasibility of the inversion algorithm and the wave sensing capability of HF radar. For example, significant wave height estimates deduced by two radars differed from the buoy, in an absolute value sense, by only 0.12 m on average. When using only one radar, the mean difference of this important parameter from the buoy was a reasonable 0.33 m  相似文献   

A portable rainfall simulator for field assessment of splash and slopewash in remote locations   总被引：1，自引：0，他引：1  

Michelle A. Clarke  Rory P. D. Walsh 《地球表面变化过程与地形》2007,32(13):2052-2069

This paper describes the design, operation and performance of a field‐portable ‘drip‐type’ simulator and erosion measurement system. The system was constructed specifically for soil erosion research in the humid tropics and has been used extensively in Malaysian Borneo. The simulator is capable of producing replicable storms of up to 200 mm h^?1 intensity and 20–30 minutes duration with a drop‐size distribution close to that of natural storms of such intensity (D₅₀ of simulated rainfall is 4·15 mm at 200 mm h^?1 and 3·65 mm at 160 mm h^?1, D⁵⁰ measured during natural rainfall = 3·25 mm). The simulator is portable and simply constructed and operates without a motor or electronics, thus making it particularly useful in remote, mountainous areas. The erosion measurement system allows assessment of: (1) rainsplash detachment and net downslope transport from the erosion plot; (2) slopewash (erosion transported by overland flow); and (3) infiltration capacity and overland flow. The performance of the simulator–erosion system compared with previous systems is assessed with reference to experiments carried out in primary and regenerating tropical rainforest at Danum Valley (Malaysian Borneo). The system was found to compare favourably with previous field simulators, producing a total storm kinetic energy of 727 J m^?2 (over a 20‐minute storm event) and a kinetic energy rate of 0·61 J m^?2 s^?1, approximately half that experienced on the ground during a natural rainfall event of similar intensity, despite the shorter distance to the ground. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Catchment urbanization increases benthic microalgal biomass in streams under controlled light conditions     

Jane A. Catford  Christopher J. Walsh  John Beardall 《Aquatic Sciences - Research Across Boundaries》2007,69(4):511-522

  相似文献   

Progress in NTHMP Hazard Assessment     

Frank I. González  Vasily V. Titov  Harold O. Mofjeld  Angie J. Venturato  R. Scott Simmons  Roger Hansen  Rodney Combellick  Richard K. Eisner  Don F. Hoirup  Brian S. Yanagi  Sterling Yong  Mark Darienzo  George R. Priest  George L. Crawford  Timothy J. Walsh 《Natural Hazards》2005,35(1):89-110

The Hazard Assessment component of the U.S. National Tsunami Hazard Mitigation Program has completed 22 modeling efforts covering 113 coastal communities with an estimated population of 1.2 million residents that are at risk. Twenty-three evacuation maps have also been completed. Important improvements in organizational structure have been made with the addition of two State geotechnical agency representatives to Steering Group membership, and progress has been made on other improvements suggested by program reviewers.  相似文献   

Observational Evidence of Recent Change in the Northern High-Latitude Environment   总被引：46，自引：1，他引：45  

M. C. Serreze  J. E. Walsh  F. S. Chapin III  T. Osterkamp  M. Dyurgerov  V. Romanovsky  W. C. Oechel  J. Morison  T. Zhang  R. G. Barry 《Climatic change》2000,46(1-2):159-207

Studies from a variety of disciplines documentrecentchange in the northern high-latitude environment.Prompted by predictions of an amplified response oftheArctic to enhanced greenhouse forcing, we present asynthesis of these observations. Pronounced winter andspring warming over northern continents since about 1970ispartly compensated by cooling over the northern NorthAtlantic. Warming is also evident over the centralArcticOcean. There is a downward tendency in sea ice extent,attended by warming and increased areal extent of theArctic Ocean's Atlantic layer. Negative snow coveranomalies have dominated over both continents sincethelate 1980s and terrestrial precipitation has increasedsince 1900. Small Arctic glaciers have exhibitedgenerally negative mass balances. While permafrost haswarmed in Alaska and Russia, it has cooled in easternCanada. There is evidence of increased plant growth,attended by greater shrub abundance and northwardmigration of the tree line. Evidence also suggeststhatthe tundra has changed from a net sink to a net sourceofatmospheric carbon dioxide.Taken together, these results paint a reasonablycoherent picture of change, but their interpretationassignals of enhanced greenhouse warming is open todebate.Many of the environmental records are either short,areof uncertain quality, or provide limited spatialcoverage. The recent high-latitude warming is also nolarger than the interdecadal temperature range duringthis century. Nevertheless, the general patterns ofchange broadly agree with model predictions. Roughlyhalfof the pronounced recent rise in Northern Hemispherewinter temperatures reflects shifts in atmosphericcirculation. However, such changes are notinconsistentwith anthropogenic forcing and include generallypositive phases of the North Atlantic and ArcticOscillations and extratropical responses to theEl-NiñoSouthern Oscillation. An anthropogenic effect is alsosuggested from interpretation of the paleoclimaterecord,which indicates that the 20th century Arctic is thewarmest of the past 400 years.  相似文献