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21.
Derek D. Lichti Jacky Chow Herv Lahamy 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(3):317-326
One of the important systematic error parameters identified in terrestrial laser scanners is the collimation axis error, which models the non-orthogonality between two instrumental axes. The quality of this parameter determined by self-calibration, as measured by its estimated precision and its correlation with the tertiary rotation angle κ of the scanner exterior orientation, is strongly dependent on instrument architecture. While the quality is generally very high for panoramic-type scanners, it is comparably poor for hybrid-style instruments. Two methods for improving the quality of the collimation axis error in hybrid instrument self-calibration are proposed herein: (1) the inclusion of independent observations of the tertiary rotation angle κ; and (2) the use of a new collimation axis error model. Five real datasets were captured with two different hybrid-style scanners to test each method’s efficacy. While the first method achieves the desired outcome of complete decoupling of the collimation axis error from κ, it is shown that the high correlation is simply transferred to other model variables. The second method achieves partial parameter de-correlation to acceptable levels. Importantly, it does so without any adverse, secondary correlations and is therefore the method recommended for future use. Finally, systematic error model identification has been greatly aided in previous studies by graphical analyses of self-calibration residuals. This paper presents results showing the architecture dependence of this technique, revealing its limitations for hybrid scanners. 相似文献
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This paper reports results from field experiments and hydrological modelling on the dynamics of runoff generation in highly convergent parts of the landscape in a logged and burnt eucalypt forest in south‐eastern Victoria, Australia. Large‐scale rainfall simulation experiments were conducted to explore runoff generating mechanisms from harvested areas, and to assess the effectiveness of standard water quality protective measures, here a disturbed filter strip, in preventing accession of sediment to near‐stream areas. We then examined the likely effects of varying antecedent moisture conditions on surface and subsurface runoff generating mechanisms. Very small volumes of surface runoff were generated only at very high rainfall intensity rates that exceeded a 100 year recurrence interval event during the simulated experiments. There was little or no identifiable impact of either compaction from logging operations or fire‐induced hydrophobicity on surface infiltration or generation of surface runoff. Measured soil hydraulic properties and soil depths explained the paucity of surface runoff, and the dominance of subsurface storm flow as the prime runoff generating mechanism. Deep lateral subsurface flow was observed from the cut‐face of a fire access track and into a streamhead downslope of the experimental plots. Water balance modelling using Topog_Dynamic indicated the conditions under which saturated overland flow in this environment could be generated are rare, but that care should be taken in siting of roads and tracks in lower parts of convergent landscapes. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
23.
The Maliac Ocean: the origin of the Tethyan Hellenic ophiolites 总被引：1，自引：0，他引：1
Jacky Ferriere Peter O. Baumgartner Frank Chanier 《International Journal of Earth Sciences》2016,105(7):1941-1963
24.
Assessing the impact of land use change on hydrology by ensemble modelling (LUCHEM) II: Ensemble combinations and predictions 总被引：1，自引：0，他引：1
Neil R. Viney H. Bormann L. Breuer A. Bronstert B.F.W. Croke H. Frede T. Gräff L. Hubrechts J.A. Huisman A.J. Jakeman G.W. Kite J. Lanini G. Leavesley D.P. Lettenmaier G. Lindström J. Seibert M. Sivapalan P. Willems 《Advances in water resources》2009
This paper reports on a project to compare predictions from a range of catchment models applied to a mesoscale river basin in central Germany and to assess various ensemble predictions of catchment streamflow. The models encompass a large range in inherent complexity and input requirements. In approximate order of decreasing complexity, they are DHSVM, MIKE-SHE, TOPLATS, WASIM-ETH, SWAT, PRMS, SLURP, HBV, LASCAM and IHACRES. The models are calibrated twice using different sets of input data. The two predictions from each model are then combined by simple averaging to produce a single-model ensemble. The 10 resulting single-model ensembles are combined in various ways to produce multi-model ensemble predictions. Both the single-model ensembles and the multi-model ensembles are shown to give predictions that are generally superior to those of their respective constituent models, both during a 7-year calibration period and a 9-year validation period. This occurs despite a considerable disparity in performance of the individual models. Even the weakest of models is shown to contribute useful information to the ensembles they are part of. The best model combination methods are a trimmed mean (constructed using the central four or six predictions each day) and a weighted mean ensemble (with weights calculated from calibration performance) that places relatively large weights on the better performing models. Conditional ensembles, in which separate model weights are used in different system states (e.g. summer and winter, high and low flows) generally yield little improvement over the weighted mean ensemble. However a conditional ensemble that discriminates between rising and receding flows shows moderate improvement. An analysis of ensemble predictions shows that the best ensembles are not necessarily those containing the best individual models. Conversely, it appears that some models that predict well individually do not necessarily combine well with other models in multi-model ensembles. The reasons behind these observations may relate to the effects of the weighting schemes, non-stationarity of the climate series and possible cross-correlations between models. 相似文献
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Bedload transport data from planebed and step‐pool reach types are used to determine grain size transport thresholds for selected upland streams in southeast Australia. Morphological differences between the reach types allow the effects of frictional losses from bedforms, microtopography and bed packing to be incorporated into the dimensionless critical shear stress value. Local sediment transport data are also included in a regime model and applied to mountain streams, to investigate whether empirical data improve the delineation of reach types on the basis of dimensionless discharge per unit width (q*) and dimensionless bedload transport (qb*). Instrumented planebed and step‐pool sites are not competent to transport surface median grains (D50s) at bankfull discharge (Qbf). Application of a locally parametrized entrainment equation to the full range of reach types in the study area indicates that the majority of cascades, cascade‐pools, step‐pools and planebeds are also not competent at Qbf and require a 10 year recurrence interval flood to mobilize their D50s. Consequently, the hydraulic parameters of the regime diagram, which assume equilibrium conditions at bankfull, are ill suited to these streams and provide a poor basis of channel delineation. Modifying the diagram to better reflect the dominant transported bedload size (equivalent to the D16 of surface sediment) made only slight improvements to reach delineation and had greatest effect on the morphologies with smaller surface grain sizes such as forced pool‐riffles and planebeds. Likewise, the Corey shape factor was incorporated into the regime diagram as an objective method for adjusting a base dimensionless critical shear stress (τ*c50b) to account for lithologically controlled grain shape on bed packing and entrainment. However, it too provided only minor adjustments to reach type delineation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
27.
Sediment transport,redistribution and storage on logged forest hillslopes in south‐eastern Australia
Post‐logging changes in catchment sediment yield have traditionally been attributed to increases in hillslope erosion and delivery rates as a result of forest harvesting activities. Linking hillslope erosion to catchment yield in forestry environments remains difficult, however, primarily because of the scarcity of data on the nature of hillslope sediment storage and delivery processes. A large rainfall simulator (350 m2) was used to apply rainstorms to a logged hillslope containing a snig track (skid trail) and a general logging or harvesting area (GHA) on 10 forest compartments in south‐eastern Australia. The experiments confirmed that the compacted, disturbed surfaces, such as roads and tracks, are the dominant sources of sediment in forestry areas. Sediment transport rates were limited by available sediment supply on both the snig track and the GHA, introducing important implications for the modelling of these surfaces using sediment transport capacity theories. Sediment delivery from the snig track to the adjacent GHA, via a cross‐bank (drainage diversion), was strongly influenced by the percentage fine fraction in the eroded sediment. Preferential deposition of coarse aggregates was measured at erosion control structures and on the adjacent GHA. Over 50% of fine‐grained material were deposited on the hillslope over a relatively short, flow path length of <5 m, highlighting the effectiveness of runoff diversion as a practice in reducing sediment flux. The transfer of water and sediment from disturbed to less disturbed parts of the landscape, and the associated potential for sediment storage, needs to be considered as part of any catchment impact assessment. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
28.
Geoffrey J. Syme V. Ratna Reddy Paul Pavelic Barry Croke Ram Ranjan 《Hydrogeology Journal》2012,20(5):985-993
The issue of scale is examined in the context of a watershed development policy (WSD) in India. WSD policy goals, by improving the natural resource base, aim to improve the livelihoods of rural communities through increased sustainable production. It has generally been practiced at a micro-level of less than 500?ha, as this was seen to be a scale that would encourage participative management. There has been some concern that this land area may be too small and may lead to less than optimal hydrological, economic and equity outcomes. As a result there has been a move to create guidelines for meso-scale WSD of above 5,000?ha in an endeavour to improve outcomes. A multidisciplinary team was assembled to evaluate the proposed meso-scale approach. In developing an adequate methodology for the evaluation it soon became clear that scale in itself was not the only determinant of success. The effect of geographical scale (or level) on WSD is determined by the variation in other drivers that will influence WSD success such as hydrological conditions, land use and available institutional structures. How this should be interpreted at different levels in the light of interactions between biophysical and socio-economic scales is discussed. 相似文献
29.
The term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies. However, considerable confusion remains regarding its definition and quantification, especially as it relates to fluvial systems. This confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately. Extreme flood events provide a useful framework to assess variability in connectivity, particularly the connection between channels and floodplains. The catastrophic flood of January 2011 in the Lockyer valley, southeast Queensland, Australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes. High resolution aerial photographs and multi‐temporal LiDAR digital elevation models (DEMs), coupled with hydrological modeling, are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls. Longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel–floodplain connectivity. The major control on connectivity was significant non‐linear changes in channel capacity due to the presence of notable macrochannels which contained a > 3000 average recurrence interval (ARI) event at mid‐catchment locations. The spatial pattern of hydrological connectivity was not straight‐forward in spite of bankfull discharges for selected reaches exceeding 5600 m3 s–1. Data indicate that the main channel boundary was the dominant source of sediment while the floodplains, where inundated, were the dominant sinks. Spatial variability in channel–floodplain hydrological connectivity leads to dis‐connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains. Consideration of such variability for even the most extreme flood events, highlights the need to carefully consider non‐linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative ‘connectivity index’. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
Jacky Croke John D. Jansen Kathryn Amos Timothy J. Pietsch 《Quaternary Science Reviews》2011,30(13-14):1681-1695
This study reports the nature and timing of Quaternary fluvial activity in the Fitzroy River basin, which drains a diverse 143,000 km2 area in northeastern Queensland, before discharging into the Great Barrier Reef Marine Park. The catchment consists of an extensive array of channel and floodplain types that we show have undergone large-scale fluvial adjustment in-channel planform, geometry and sinuosity. Optically stimulated luminescence (OSL) dating of quartz sediments from fifteen (3–18 m) floodplain cores throughout the basin indicates several discrete phases of active bedload activity: at ～105–85 ka in Marine Isotope Stage (MIS) 5, at ～50–40 ka (MIS 3), and at ～30–10 ka (MIS 3/2). The overall timing of late Quaternary fluvial activity correlates well with previous accounts from across Australia with rivers being primarily active during interstadials. Fluvial activity, however, does not appear to have been synchronous throughout the basin’s major sub-catchments. Fluvial activity throughout MIS 2 (i.e. across the Last Glacial Maximum) in the meandering channels of the Fitzroy correlates well with regional data in tropical northeastern Queensland, and casts new light on the river response to reduced rainfall and vegetation cover suggested by regional palaeoclimate indicators. Moreover, the absence of a strong Holocene signal is at odds with previous accounts from elsewhere throughout Australia. The latitudinal position of the Fitzroy across the Tropic of Capricorn places this catchment at a key location for elucidating the main hydrological drivers of Quaternary fluvial activity in northeastern Australia, and especially for determining tropical moisture sources feeding into the headwaters of Cooper Creek, a major river system of the continental interior. 相似文献