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31.
Ramesh Sivanpillai X. Ben Wu R. Srinivasan Charles T. Smith Michael G. Messina 《GeoJournal》2008,71(4):211-220
Comparing satellite data derived map products are affected by differences in data characteristics, image acquisition dates,
processing techniques, and classification schemes used for assigning pixels to a thematic class. By comparing two forest maps
generated from Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Very High Resolution Radiometer (AVHRR) images acquired
on the same day, and processed using identical classification scheme and methods these differences were minimized. The ETM+
derived map had higher classification accuracy values and more precise area estimates than the AVHRR derived map. In the ETM+
derived map, 87 of the 599 verification data were misclassified, whereas in the AVHRR derived map, 155 of the 469 verification
data were misclassified. Detailed error analyses by land cover class revealed that a land use based definition of forest accounted
for 74% (64 out of 87) and 57% (89 out of 155) of the classification errors in ETM+ and AVHRR derived maps, respectively. 相似文献
32.
F. Shuttleworth
J. Wardley Smith
《Marine pollution bulletin》1971,2(12):191-19233.
G. R. Cooper G. Petrie A. D. N. Smith M. Sowton K. B. Atkinson 《The Photogrammetric Record》1969,6(33):239-258
The International Society for Photogrammetry held the Xlth International Congress at Lausanne during July 1968. The authors review the activities of five of the seven I.S.P. Commissions. 相似文献
34.
The historical development of analytical aerial triangulation block adjustment is mentioned by way of introduction. The advantages of separating the plan and height adjustments are given and the observation equations of a typical adjustment section are analysed to show that this convenient practice is justified in normal circumstances. The principles of a direct solution of the normal equations suitable for a moderate-sized computer, are explained and developed in detail for the height adjustment. The advantages of tie-strips in the height adjustment are demonstrated and the difficulties which then arise are discussed. An approximate method which overcomes these difficulties is developed. Details of the computer programmes used are given in Appendix B. 相似文献
35.
Experiments were conducted in an oscillatory water tunnel to investigate what effects temporal inertia has on the resistance of a granular medium. The flow law governing stationary porous media flow is reasonably well accepted and understood but the effects of unsteady flow have commonly been neglected. The present research was designed to assess the magnitude of the acceleration effects on media of uniformly packed spheres of equal diameter and on one sample of randomly placed stone.Oscillatory flow tests were made in a large oscillatory flume tunnel with periods varying from 3 to 12 seconds. The influence of properties of the medium (grain size and porosity) were tested by using spheres with two different diameters and packing each size sphere in different geometric arrangements. Tests made on a stone sample provided a qualitative assessment of the effects of more random material properties.For the experiments described in this paper, the Forchheimer unsteady-stationary flow law described the oscillatory measurements well when velocities and energy losses were maximum. Empirical coefficients determined from steady-stationary flow were generally found to apply to the unsteady flow, however some evidence of dependency on the period of oscillation was noted. 相似文献
36.
An inexpensive Pull-Up Shallow Water Seismometer (PUSS) has been designed and built to conduct long range seismic refraction experiments in the North Sea and the continental shelf around Britain, with the particular goal of studying the crustal and lithospheric structure under the epeirogenic basin of the North Sea. Signals from a gimbal-mounted 3-component geophone and a hydrophone are frequency modulated and mixed with clock and flutter correction signals before being recorded on a standard speed cassette tape recorder, with one hour of recording time. A 100 hour programmable timer allows the interval between the time of reset of the clock and each shot window of optional 5 or 10 min duration, to be preselected. The PUSS is launched and recovered using a pull-up technique originally developed for current meters. The replay system is also described.In May 1976 sea trials of 5 PUSSes were conducted along a 200 km refraction line in the North Sea. The encouraging performance of the equipment resulted in the decision to build a further 10 units and to proceed with a 400 km refraction line planned for the summer of 1977. 相似文献
37.
Estuary/ocean exchange and tidal mixing in a Gulf of Maine Estuary: A Lagrangian modeling study 总被引:2,自引:0,他引:2
Ata Bilgili Jeffrey A. Proehl Daniel R. Lynch Keston W. Smith M. Robinson Swift 《Estuarine, Coastal and Shelf Science》2005,65(4):607-624
A Lagrangian particle method embedded within a 2-D finite element code, is used to study the transport and ocean–estuary exchange processes in the well-mixed Great Bay Estuarine System in New Hampshire, USA. The 2-D finite element model, driven by residual, semi-diurnal and diurnal tidal constituents, includes the effects of wetting and drying of estuarine mud flats through the use of a porous medium transport module. The particle method includes tidal advection, plus a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. Our approach involves instantaneous, massive [O(500,000)] particle releases that enable the quantification of ocean–estuary and inter-bay exchanges in a Markovian framework. The effects of the release time, spring–neap cycle, riverine discharge and diffusion strength on the intra-estuary and estuary–ocean exchange are also investigated.The results show a rather dynamic interaction between the ocean and the estuary with a fraction of the exiting particles being caught up in the Gulf of Maine Coastal Current and swept away. Three somewhat different estimates of estuarine residence time are calculated to provide complementary views of estuary flushing. Maps of residence time versus release location uncover a strong spatial dependency of residence time within the estuary that has very important ramifications for local water quality. Simulations with and without the turbulent random walk show that the combined effect of advective shear and turbulent diffusion is very effective at spreading particles throughout the estuary relatively quickly, even at low (1 m2/s) diffusivity. The results presented here show that a first-order Markov Chain approach has applicability and a high potential for improving our understanding of the mixing processes in estuaries. 相似文献
38.
Data collected in three Californian estuaries indicate that hypersaline conditions exist during the dry summers typical of a Mediterranean climate. The generalised seasonal and longitudinal hydrographic structures are described and explained. It is argued that this seasonal hypersalinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residence times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of concern are the trends to increase pollutant loading in the same systems that are experiencing an increase in residence times owing to freshwater extraction in the watershed. 相似文献
39.
40.
The results of the two- and three-dimensional magnetic inversions performed on data located between 20°–24° N on the Mid-Atlantic Ridge indicate the crustal magnetization has decayed exponentially for the last 10 Ma, and that this decay has been fairly symmetric about the ridge axis. After removal of the mean temporal decay, the residual field is characterized by more positive magnetizations at the second-order discontinuities, regardless of initial magnetization direction. A model that involves the preferential emplacement of serpentinized lithologies near the discontinuities is proposed to explain this correlation. The temporal detrending method also indicates that several ridge-parallel depressions located on the flanks of the ridge axis are regions of more positive magnetizations. These bathymetric depressions may mark the locations of detachment faulting that occurred during amagmatic periods of extension. The general symmetry of the crustal magnetization about the ridge axis does not support the occurrence of continuous detachment faulting proposed to correspond to the inner and outer corners of ridge axis discontinuities. 相似文献