Accuracy assessment of georectified aerial photographs: Implications for measuring lateral channel movement in a GIS     

Michael L. Hughes  Patricia F. McDowell  W. Andrew Marcus 《Geomorphology》2006,74(1-4):1-16

Aerial photographs are commonly used to measure planform river channel change. We investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number (6–30) and type (human versus natural landscape features) of ground-control points (GCPs) and the order of the transformation polynomial (first-, second-, and third-order) affected the spatial accuracy of a typical georectified aerial photograph. Error was assessed using the root-mean-square error (RMSE) of the GCPs as well as error in 31 independent test points. The RMSE and the mean and median values of test-point errors were relatively insensitive to the number of GCPs above eight, but the upper range of test-point errors showed marked improvement (i.e., the number of extreme errors was reduced) as more GCPs were used for georectification. Using more GCPs thus improved overall georectification accuracy, but this improvement was not indicated by the RMSE, suggesting that independent test-points located in key areas of interest should be used in addition to RSME to evaluate georectification error.The order of the transformation polynomial also influenced test-point accuracy; the second-order polynomial function yielded the best result for the terrain of the study area. GCP type exerted a less consistent influence on test-point accuracy, suggesting that although hard-edged points (e.g., roof corners) are favored as GCPs, some soft-edged points (e.g., trees) may be used without adding significant error. Based upon these results, we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately ± 5 m, with 10% chance of greater error. The implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis, which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them. This study demonstrates the importance of using an independent test-point analysis in addition to the RSME to evaluate and treat locational error in channel change studies.  相似文献   

Imaging H i in the lensing galaxy 2237+0305     

D. G. Barnes  R. L. Webster  R. W. Schmidt  A. Hughes 《Monthly notices of the Royal Astronomical Society》1999,309(3):641-650

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Unbiased total electron content (UTEC), their fluctuations,and correlation with seismic activity over Japan     

Pierre-Richard Cornely  John Hughes 《Acta Geophysica》2018,66(1):51-70

Earthquakes are among the most dangerous events that occur on earth and many scientists have been investigating the underlying processes that take place before earthquakes occur. These investigations are fueling efforts towards developing both single and multiple parameter earthquake forecasting methods based on earthquake precursors. One potential earthquake precursor parameter that has received significant attention within the last few years is the ionospheric total electron content (TEC). Despite its growing popularity as an earthquake precursor, TEC has been under great scrutiny because of the underlying biases associated with the process of acquiring and processing TEC data. Future work in the field will need to demonstrate our ability to acquire TEC data with the least amount of biases possible thereby preserving the integrity of the data. This paper describes a process for removing biases using raw TEC data from the standard Rinex files obtained from any global positioning satellites system. The process is based on developing an unbiased TEC (UTEC) data and model that can be more adaptable to serving as a precursor signal for earthquake forecasting. The model was used during the days and hours leading to the earthquake off the coast of Tohoku, Japan on March 11, 2011 with interesting results. The model takes advantage of the large amount of data available from the GPS Earth Observation Network of Japan to display near real-time UTEC data as the earthquake approaches and for a period of time after the earthquake occurred.  相似文献   

Evaluation of uniaxial contact models for moat wall pounding simulations     

Patrick J. Hughes  Gilberto Mosqueda 《地震工程与结构动力学》2020,49(12):1197-1215

Moat wall pounding occurs when a base-isolated building displaces beyond the provided clearance and collides with the surrounding retaining wall, inducing very high floor accelerations and interstory drifts. Previous studies on moat wall pounding typically employ simplified models of the superstructure, with a uniaxial contact spring used to model the entire moat wall. Consequently, researchers have developed sophisticated contact models to estimate the normal-direction contact force that is generated during seismic pounding. This study examines how the choice in contact model affects the seismic response of a base-isolated building subjected to impact-inducing ground excitation. Five widely used state-of-the-art contact models are summarized and implemented into an experimentally-calibrated numerical model of a base-isolated moment frame. Results of nonlinear dynamic time history analyses are shown in detail for one ground motion, followed by a larger parametric study across 28 near-fault ground motions. This work shows that peak impact force and base acceleration are moderately sensitive to the choice in contact model, while upper floor accelerations and interstory drifts are practically not affected.  相似文献   

Revision of hopewellian trading patterns in midwestern North America based on mineralogical sourcing*     

R. E. Hughes  D. M. Moore  T. E. Berres  K. B. Farnsworth 《Geoarchaeology》1998,13(7):709-729

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Deep-water macrofaunal diversity in the Faroe-Shetland region (NE Atlantic): a margin subject to an unusual thermal regime     

Bhavani E. Narayanaswamy  Brian J. Bett  & David J. Hughes 《Marine Ecology》2010,31(1):237-246

The Faroe-Shetland Channel, situated in the NE Atlantic, encompasses a number of different sediment types (habitats) as well as being subject to an unusual thermal regime. Our main objective was to assess variations in macrofaunal generic diversity and composition along two transects to gauge the relative influence of regional hydrography and local habitat heterogeneity. We found that generic richness and diversity on a West of Shetland (WoS) transect correlated most strongly with temperature range, whilst along a North of Shetland (NoS) transect, richness and diversity correlated negatively with sedimentary variables, notably total organic carbon. Macrofaunal composition at WoS is also strongly influenced by water temperature with specific genera ( e.g. Galathowenia positively associated with the temperature eigenvectors), whereas at NoS it is a combination of temperature, silt + clay fraction and total organic carbon that has an impact on composition ( e.g. Proclea and Pseudosphyrapus , showing a negative relationship with the temperature eigenvectors). Although the temperature regime exerts a strong control on regional ecology, local habitat heterogeneity remains a significant factor.  相似文献   

Probability distributions for wave runup on beaches     

Michael G. Hughes  Adrienne S. Moseley  Tom E. Baldock 《Coastal Engineering》2010

Measured probability distributions of shoreline elevation, swash height (shoreline excursion length) and swash maxima and minima from a wide range of beach types are compared to theoretical probability distributions. The theoretical distributions are based on assumptions that the time series are weakly steady-state, ergodic and a linear sum of random variables. Despite the swash process being inherently non-linear, results indicate that these assumptions are not overly restrictive with respect to modeling exceedence statistics in the upper tail of the probability distribution. The RMS-errors for a range of exceedence level statistics (50, 10, 5, 2, and 1%) were restricted to < 10 cm (and often < 5 cm) for all of the swash variables that were investigated. The results presented here provide the basis for further refinement of coastal inundation modeling as well as stochastic-type morphodynamic modeling of beach response to waves. Further work is required, however, to relate the parameters of swash probability distributions to wave conditions further offshore.  相似文献   

The optical performance of the PILOT instrument from ground end-to-end tests     

R. Misawa  J-Ph. Bernard  Y. Longval  I. Ristorcelli  P. Ade  D. Alina  Y. André  J. Aumont  L. Bautista  P. de Bernardis  O. Boulade  F. Bousqet  M. Bouzit  V. Buttice  A. Caillat  M. Chaigneau  M. Charra  B. Crane  F. Douchin  E. Doumayrou  J. P. Dubois  C. Engel  M. Griffin  G. Foenard  S. Grabarnik  P. Hargrave  A. Hughes  R. Laureijs  B. Leriche  S. Maestre  B. Maffei  C. Marty  W. Marty  S. Masi  J. Montel  L. Montier  B. Mot  J. Narbonne  F. Pajot  E. Pérot  J. Pimentao  G. Pisano  N. Ponthieu  L. Rodriguez  G. Roudil  M. Salatino  G. Savini  O. Simonella  M. Saccoccio  J. Tauber  C. Tucker 《Experimental Astronomy》2017,43(3):211-235

The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust emission in two photometric bands centred at wavelengths 240 μm (1.2 THz) and 550 μm (545 GHz), with an angular resolution of a few arcminutes. Several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in September 2015 from Timmins, Ontario, Canada. This paper presents the results of those tests, focussing on an evaluation of the instrument’s optical performance. We quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. We present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization.  相似文献   

Engineering geology for tomorrow's cities,edited by M.G. Culshaw, H.J. Reeves, I. Jefferson and T.W. Spink. Geological Society Engineering Geology Special Publication, 22, London, 2009. No. of pages: 303. Price: £95.00. ISBN 978‐1‐86239‐290‐8 (hardback).     

Will Hughes 《Geological Journal》2013,48(1):108-109

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