Lidar Data (lidar + data)

Distribution by Scientific Domains


Selected Abstracts


Instability investigation of cantilevered seacliffs

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008
Adam P. Young
Abstract Wave action is a fundamental mechanism in seacliff erosion, whereby wave undercutting creates an unstable cantilevered seacliff profile and can lead to large catastrophic cliff failures, thus threatening coastal infrastructure. This study investigated the instability of two such failures that occurred in Solana Beach, California, by combining terrestrial LIDAR scanning, cantilever beam theory and finite element analysis. Each landslide was detected by evaluating the surface change between subsequent high resolution digital terrain models derived from terrestrial LIDAR data. The dimensions of failed cantilever masses were determined using the surface change measurements and then incorporated into failure stress analysis. Superimposing stress distributions computed from elastic cantilever beam theory and finite element modeling provided a method to back-calculate the maximum developed tensile and shear stresses along each failure plane. The results of the stress superposition revealed that the bending stresses caused by the cantilevered load contributed the majority of stress leading to collapse. Both shear and tensile failure modes were investigated as potential cliff failure mechanisms by using a comparison of the back-calculated failure stresses to material strengths found in laboratory testing. Based on the results of this research, the tensile strength of the cliff material was exceeded at both locations, thus causing the cliffs to collapse in tension. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Analysis of soil moisture patterns in forested and suburban catchments in Baltimore, Maryland, using high-resolution photogrammetric and LIDAR digital elevation datasets

HYDROLOGICAL PROCESSES, Issue 2 2006
D. E. Tenenbaum
Abstract Field observations of near-surface soil moisture, collected over several seasons in a watershed in suburban Maryland, are compared with values of the topographic soil moisture index generated using digital elevation models (DEMs) at a range of grid cell sizes from photogrammetric and light detection and ranging (LIDAR) data sources. A companion set of near-surface soil moisture observations, DEMs and topographic index values are also presented for a nearby forested catchment. The degree to which topographic index values are an effective indicator of near-surface soil moisture conditions varies in the two environments. The urbanizing environment requires topographic index values from a DEM with a much finer grid cell resolution than the LIDAR data can provide, and the relationship is stronger in wetter conditions. In the forested environment, the DEM resolution required is considerably lower and adequately supported by the photogrammetric data, and the relationship is strong under all moisture conditions. These results provide some insights into the length scales of near-surface hydrological processes in the urbanizing environment, and the resolution of terrain data required to model those processes. Copyright © 2006 John Wiley & Sons, Ltd. [source]


EVALUATION OF LIGHT DETECTION AND RANGING (LIDAR) FOR MEASURING RIVER CORRIDOR TOPOGRAPHY,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2002
Zachary H. Bowen
ABSTRACT: LIDAR is relatively new in the commercial market for remote sensing of topography and it is difficult to find objective reporting on the accuracy of LIDAR measurements in an applied context. Accuracy specifications for LIDAR data in published evaluations range from 1 to 2 m root mean square error (RMSEx,y) and 15 to 20 cm RMSEz. Most of these estimates are based on measurements over relatively flat, homogeneous terrain. This study evaluated the accuracy of one LIDAR data set over a range of terrain types in a western river corridor. Elevation errors based on measurements over all terrain types were larger (RMSEz equals 43 cm) than values typically reported. This result is largely attributable to horizontal positioning limitations (1 to 2 m RMSEx,y) in areas with variable terrain and large topographic relief. Cross-sectional profiles indicated algorithms that were effective for removing vegetation in relatively flat terrain were less effective near the active channel where dense vegetation was found in a narrow band along a low terrace. LIDAR provides relatively accurate data at densities (50,000 to 100,000 points per km2) not feasible with other survey technologies. Other options for projects requiring higher accuracy include low-altitude aerial photography and intensive ground surveying. [source]


Empirical prediction of debris-flow mobility and deposition on fans

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2010
Christian Scheidl
Abstract A new method to predict the runout of debris flows is presented. A data base of documented sediment-transporting events in torrent catchments of Austria, Switzerland and northern Italy has been compiled, using common classification techniques. With this data we test an empirical approach between planimetric deposition area and event volume, and compare it with results from other studies. We introduce a new empirical relation to determine the mobility coefficient as a function of geomorphologic catchment parameters. The mobility coefficient is thought to reflect some of the flow properties during the depositional part of the debris-flow event. The empirical equations are implemented in a geographical information system (GIS) based simulation program and combined with a simple flow routing algorithm, to determine the potential runout area covered by debris-flow deposits. For a given volume and starting point of the deposits, a Monte-Carlo technique is used to produce flow paths that simulate the spreading effect of a debris flow. The runout zone is delineated by confining the simulated potential spreading area in the down slope direction with the empirically determined planimetric deposition area. The debris-flow volume is then distributed over the predicted area according to the calculated outflow probability of each cell. The simulation uses the ARC-Objects environment of ESRI© and is adapted to run with high resolution (2·5,m × 2·5,m) digital elevation models, generated for example from LiDAR data. The simulation program called TopRunDF is tested with debris-flow events of 1987 and 2005 in Switzerland. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Sensitivity of post-hurricane beach and dune recovery to event frequency

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2009
Chris Houser
Abstract The recovery of Santa Rosa Island in northwest Florida is characterized following Hurricane Katrina (September 2005), which was preceded by Hurricanes Ivan (2004) and Dennis (2005). Beach and dune recovery were quantified to the east and west of Pensacola Beach through a comparison of LiDAR data collected immediately following Hurricane Katrina and in July 2006 after almost a year of recovery. East of Pensacola Beach (the Santa Rosa Unit), the shoreline retreated by an average of 64 m during the 2004,2005 hurricane season and recovered by an average of 19 m. To the west of Pensacola Beach (the Fort Pickens Unit), the shoreline retreated by an average of 30 m, and while no significant shoreface recovery was observed, the presence of vegetation on low-profile dunes promoted backshore accretion. It is found that beachface recovery in the Santa Rosa Unit and backshore accretion in the Fort Pickens Unit occurred at the widest sections of the island where the pre-storm profile volume had been relatively large and overwash penetration was at a minimum. The narrow sections of the island (between cuspate headlands) had a smaller profile volume before the storms, leading to greater overwash penetration and in some cases island breaching in both sections, which limited the volume of sediment available for shoreface recovery. The alongshore variation in recovery is not only related to the island width, but also the offshore bathymetry, height of the pre-storm dunes and the overwash penetration. If sufficient time is allowed for the return of vegetation and the recovery of the dunes, the variations in storm impact observed during Hurricane Ivan will be reinforced during subsequent storms. In this respect, the level of impact during subsequent storms and the ability of the island to recover will depend on the frequency of storm events. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Unstructured grid generation using LiDAR data for urban flood inundation modelling

HYDROLOGICAL PROCESSES, Issue 11 2010
Ryota Tsubaki
Abstract Inundation disasters, caused by sudden water level rise or rapid flow, occur frequently in various parts of the world. Such catastrophes strike not only in thinly populated flood plains or farmland but also in highly populated villages or urban areas. Inundation of the populated areas causes severe damage to the economy, injury, and loss of life; therefore, a proper management scheme for the disaster has to be developed. To predict and manage such adversity, an understanding of the dynamic processes of inundation flow is necessary because risk estimation is performed based on inundation flow information. In this study, we developed a comprehensive method to conduct detailed inundation flow simulations for a populated area with quite complex topographical features using LiDAR (Light Detection and Ranging) data. Detailed geospatial information including the location and shape of each building was extracted from the LiDAR data and used for the grid generation. The developed approach can distinguish buildings from vegetation and treat them differently in the flow model. With this method, a fine unstructured grid can be generated representing the complicated urban land features precisely without exhausting labour for data preparation. The accuracy of the generated grid with different grid spacing and grid type is discussed and the optimal range of grid spacing for direct representation of urban topography is investigated. The developed method is applied to the estimation of inundation flows, which occurred in the basin of the Shin-minato River. A detailed inundation flow structure is represented by the flow model, and the flow characteristics with respect to topographic features are discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source]


Characterization of diverse plant communities in Aspen Parkland rangeland using LiDAR data

APPLIED VEGETATION SCIENCE, Issue 3 2007
Jason G. Su
Moss (1983) Abstract Question: How effective is high-resolution airborne LiDAR technology for quantifying biophysical characteristics of multiple community types within diverse rangeland environments? Location: Native Aspen Parkland vegetation in central Alberta, Canada. Methods: Vegetation within 117 reference plots stratified across eight types, including forest, shrubland, upland grassland and lowland meadow communities, were assessed in 2001 for the height, cover and density of vegetation within various strata (herb, shrub and tree layers). Actual ground data were subsequently compared against modelled values for each community type and strata derived from the analysis of airborne LiDAR data obtained in 2000. Results: LiDAR data were effective for quantifying vegetation height, cover and density of the overstory within closed- and open Populus forest communities. However, LiDAR measurements typically underestimated the height and cover of shrublands, as well as most of the herbaceous communities. Analysis of LiDAR intensity data indicated reflectance generally decreased as LiDAR sampling points moved upwards from the ground to the vegetation canopy. Conclusions: While LiDAR technology is useful for characterizing deciduous forest properties, the quantification of understory vegetation characteristics, as well as those of individual shrublands and grasslands, was more limiting. Further refinements in analysis methods are necessary to increase the reliability of characterizing these communities. [source]


A non-linear and non-Gaussian state-space model for censored air pollution data

ENVIRONMETRICS, Issue 2 2005
Craig J. Johns
Abstract Lidar technology is used to quantify airborne particulate matter less than 10,,m in diameter (PM10). These spatio-temporal lidar data on PM10 are subject to censoring due to detection limits. A non-linear and non-Gaussian state-space model is modified to accommodate data subject to detection limits and outline strategies for Markov-chain Monte Carlo estimation and filtering. The methods are applied to spatio-temporal lidar measurements of dust particle concentrations. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Interactions of multiple disturbances in shaping boreal forest dynamics: a spatially explicit analysis using multi-temporal lidar data and high-resolution imagery

JOURNAL OF ECOLOGY, Issue 3 2010
Udayalakshmi Vepakomma
Summary 1.,Mixed-wood boreal forests are often considered to undergo directional succession from shade-intolerant to shade-tolerant species. It is thus expected that overstorey gaps should lead to the recruitment of shade-tolerant conifers into the canopy in all stand development stages and that the recruitment of shade-intolerant hardwoods would be minimal except in the largest gaps. 2.,We analysed short-term gap dynamics over a large 6-km2 spatial area of mixed-wood boreal forest across a gradient of stands in different developmental stages with different times of origin since fire (expressed as stand ,age') that were affected differentially by the last spruce budworm (SBW) outbreak. Structural measurements of the canopy from lidar data were combined with spectral classification of broad species groups to characterize the gap disturbance regime and to evaluate the effect of gap openings on forest dynamics. 3.,Estimated annual gap opening rates increased from 0.16% for 84-year-old stands to 0.88% for 248-year-old stands. Trees on gap peripheries in all stands were more vulnerable to mortality than interior canopy trees. 4.,Due to recovery from the last SBW outbreak 16 years previously, gap closure rates were higher than opening rates, ranging from 0.44% to 2.05% annually, but did not show any relationship with stand age. There was, however, a continuing legacy of the last SBW outbreak in old-conifer stands in terms of a continued high mortality of conifers. In all stands, the majority of the openings were filled from below, although a smaller but significant proportion filled from lateral growth of gap edge trees. 5.,Synthesis. The forest response to moderate- to small-scale disturbances in old-growth boreal forest counters the earlier assumption that the transition from one forest state to the next is slow and directional with time since the last fire. Overall, a small 6% increase in hardwoods was observed over 5 years, largely due to regeneration in-filling of hardwoods in gaps instead of successional transition to more shade-tolerant conifers. Gaps are vital for hardwood maintenance while transition to softwoods can occur without perceived gap-formation as overstorey trees die, releasing understorey trees. [source]


Scaling turbulent atmospheric stratification.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008
I: Turbulence, waves
Abstract In this first of a three-part series, we argue that the dynamics of turbulence in a stratified atmosphere should depend on the buoyancy over a wide range of vertical scales and on energy flux over a wide range of horizontal scales; it should be scaling, but anisotropic, not isotropic. We compare the leading statistical theories of atmospheric stratification which are conveniently distinguished by the elliptical dimension Ds which quantifies their degree of spatial stratification. This includes the mainstream isotropic 2-D (large scales), isotropic 3-D (small scales) theory but also the more recent linear gravity wave theories (Ds = 7/3) and the classical fractionally integrated flux (FIF) 23/9-D unified scaling model. In the latter, the horizontal wind has a k,5/3 spectrum as a function of horizontal wavenumber determined by the energy flux and a k,11/5 energy spectrum as a function of vertical wavenumber determined by the buoyancy force variance flux. In this model, the physically important notion of scale is determined by the turbulent dynamics, it is not given a priori (i.e. the by usual Euclidean distance). The 23/9-D FIF model is the most physically and empirically satisfying, being based on turbulent (spectral) fluxes. The FIF model as originally proposed by Schertzer and Lovejoy is actually a vast family of scaling models broadly compatible with turbulent phenomenology and with the classical turbulent laws of Kolmogorov, Corrsin and Obukov. However, until now it has mostly been developed on the basis of structures localized in space,time. In this paper, we show how to construct extreme FIF models with wave-like structures which are localized in space but unlocalized in space,time, as well as a continuous family of intermediate models which are akin to Lumley,Shur models in which some part of the localized turbulent energy ,leaks' into unlocalized waves. The key point is that the FIF requires two propagators (space,time Green's functions) which can be somewhat different. The first determines the space,time structure of the cascade of fluxes; this must be localized in space,time in order to satisfy the usual turbulence phenomenology. In contrast, the second propagator relates the turbulent fluxes to the observables; although the spatial part of the propagator is localized as before, in space,time it can be unlocalized. (It is still localized in space, now in wave packets.) We display numerical simulations which demonstrate the requisite (anisotropic, multifractal) statistical properties as well as wave-like phenomenologies. In parts II and III we will examine the empirical evidence for the spatial and temporal parts, respectively, of the model using state-of-the-art lidar data of aerosol backscatter ratios (which we use as a surrogate for passive scalar concentration). Copyright © 2008 Royal Meteorological Society [source]


Scaling turbulent atmospheric stratification.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008
II: Spatial stratification, intermittency from lidar data
Abstract We critically re-examine existing empirical studies of vertical and horizontal statistics of the horizontal wind and find that the balance of evidence is in favour of the Kolmogorov kx,5/3 scaling in the horizontal, Bolgiano-Obukov scaling kz,11/5 in the vertical corresponding to a Ds = 23/9 stratified atmosphere in (x, y, z) space. This interpretation is particularly compelling once one recognizes that the 23/9-D turbulence can lead to long-range biases in aircraft trajectories and hence to spurious statistical exponents in wind, temperature and other statistics reported in the literature. Indeed, we show quantitatively that one is easily able to reinterpret the major aircraft-based campaigns (GASP, MOZAIC) in terms of the model. In part I, we have seen that this model is compatible with ,turbulence waves' which can be close to classical linear gravity waves in spite of their very different nonlinear mechanism. We then use state-of-the-art lidar data of atmospheric aerosols (considered as passive tracers) in order to obtain direct estimates of the effective (,elliptical') dimension of the spatial part: Ds = 23/9 = 2.55 ± 0.02. This result essentially rules out the standard 3-D or 2-D isotropic theories or the anisotropic quasi-linear gravity wave theories which have Ds = 3, 2, 7/3 respectively. In this paper we focus on the multifractal (intermittency) statistics showing that there is a very small but apparently real variation in the value of Ds, ranging for the weak and intense structures so that Ds ranges from roughly 2.53 to 2.57. We also show that the passive scalars are well approximated by universal multifractals; we estimate the exponents to be ,h = 1.82 ± 0.05, ,v = 1.83 ± 0.04, C1h = 0.037 ± 0.0061 and C1v = 0.059 ± 0.007 (h for horizontal, v for vertical). Copyright © 2008 Royal Meteorological Society [source]


Scaling turbulent atmospheric stratification.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008
III: Space, time stratification of passive scalars from lidar data
Abstract In this third and final part of the series, we concentrate on the temporal behaviour of atmospheric passive scalars. We first recall that,although the full (x, y, z, t) turbulent processes respect an anisotropic scale invariance,that due to advection,the generator will generally not be a diagonal matrix. This implies that the scaling of (1-D) temporal series will generally involve three exponents in real space: 1/3, 1/2, 3/5, for spectra ,, = 5/3, 2, 11/5, with the first and last corresponding to domination by advection (horizontal and vertical respectively), and the second to pure temporal development (no advection). We survey the literature and find that almost all the empirical ,, values are indeed in the range 5/3 to 2. We then use meteorological analyses to argue that, although pure temporal development is unlikely to be dominant for time-scales less than the eddy turnover time of the largest structures (about 2 weeks), an intermittent vertical velocity could quite easily explain the occasionally observed ,, , 2 spectra. We then use state-of-the-art vertically pointing lidar data of backscatter ratios from both aerosols and cirrus clouds yielding several (z, t) vertical space,time cross-sections with resolution of 3.75 m in the vertical, 0.5,30 s in time and spanning 3,4 orders of magnitude in temporal scale. We first test the predictions of the anisotropic, multifractal extension of the Corrsin-Obukhov law in the vertical and in time, separately finding that the cirrus and aerosol backscatters both followed the theoretical (anisotropic) scalings accurately; three of the six cases show dominance by the horizontal wind, the others by the vertical wind. In order to test the theory in arbitrary directions in this (z, t) space, and in order to get more complete information about the underlying physical scale, we develop and apply a new Anisotropic Scaling Analysis Technique (ASAT) which is based on a nonlinear space,time coordinate transformation. This transforms the original differential scaling into standard self-similar scaling; there remains only a ,trivial' anisotropy. This method is used in real space on 2-D structure functions. It is applied to both the new (z, t) data as well as the (x, z) data discussed in part II. Using ASAT, we verify the theory to within about 10% over more than three orders of magnitude of space,time scales in arbitrary directions in (x, z) and (z, t) spaces. By considering the high- (and low-) order structure functions, we verify the theory for both weak and strong structures; as predicted, their average anisotropies are apparently the same. Putting together the results for (x, z) and (z, t), and assuming that there is no overall stratification in the horizontal (x, y) plane, we find that the overall (x, y, z, t) space is found to have an effective ,elliptical dimension' characterizing the overall space,time stratification equal to Deff, st = 3.21 ± 0.05. Copyright © 2008 Royal Meteorological Society [source]


Evaluation of a large-eddy model simulation of a mixed-phase altocumulus cloud using microwave radiometer, lidar and Doppler radar data

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 618 2006
J. H. Marsham
Abstract Using the Met Office large-eddy model (LEM) we simulate a mixed-phase altocumulus cloud that was observed from Chilbolton in southern England by a 94 GHz Doppler radar, a 905 nm lidar, a dual-wavelength microwave radiometer and also by four radiosondes. It is important to test and evaluate such simulations with observations, since there are significant differences between results from different cloud-resolving models for ice clouds. Simulating the Doppler radar and lidar data within the LEM allows us to compare observed and modelled quantities directly, and allows us to explore the relationships between observed and unobserved variables. For general-circulation models, which currently tend to give poor representations of mixed-phase clouds, the case shows the importance of using: (i) separate prognostic ice and liquid water, (ii) a vertical resolution that captures the thin layers of liquid water, and (iii) an accurate representation the subgrid vertical velocities that allow liquid water to form. It is shown that large-scale ascents and descents are significant for this case, and so the horizontally averaged LEM profiles are relaxed towards observed profiles to account for these. The LEM simulation then gives a reasonable cloud, with an ice-water path approximately two thirds of that observed, with liquid water at the cloud top, as observed. However, the liquid-water cells that form in the updraughts at cloud top in the LEM have liquid-water paths (LWPs) up to half those observed, and there are too few cells, giving a mean LWP five to ten times smaller than observed. In reality, ice nucleation and fallout may deplete ice-nuclei concentrations at the cloud top, allowing more liquid water to form there, but this process is not represented in the model. Decreasing the heterogeneous nucleation rate in the LEM increased the LWP, which supports this hypothesis. The LEM captures the increase in the standard deviation in Doppler velocities (and so vertical winds) with height, but values are 1.5 to 4 times smaller than observed (although values are larger in an unforced model run, this only increases the modelled LWP by a factor of approximately two). The LEM data show that, for values larger than approximately 12 cm s,1, the standard deviation in Doppler velocities provides an almost unbiased estimate of the standard deviation in vertical winds, but provides an overestimate for smaller values. Time-smoothing the observed Doppler velocities and modelled mass-squared-weighted fallspeeds shows that observed fallspeeds are approximately two-thirds of the modelled values. Decreasing the modelled fallspeeds to those observed increases the modelled IWC, giving an IWP 1.6 times that observed. Copyright © 2006 Royal Meteorological Society [source]


Light detection and ranging (lidar) in the Witham Valley, Lincolnshire: an assessment of new remote sensing techniques

ARCHAEOLOGICAL PROSPECTION, Issue 4 2006
Simon Crutchley
Abstract Airborne light detection and ranging (lidar) allows the identification and accurate recording of upstanding features on the ground to sub-metre accuracy. The technique has previously been tested in areas of known high monument density such as the Stonehenge World Heritage Site with exciting results, but it is also proving useful in less spectacular areas. This paper will look at some recent work carried out by the Aerial Survey Team at English Heritage concentrating on an area in the Witham Valley, east of Lincoln in the east of England. The area has recently been covered by an archaeological aerial survey project as part of the National Mapping Programme; examining the lidar data for the same area has revealed some interesting results. Lidar clearly has potential for recording certain site types and especially in highlighting relationships between sites in the broader landscape, but there are limitations with the standard off the shelf data due to issues of spatial resolution. The study also makes clear the importance of not using lidar data alone, but ensuring that it is part of an examination of all readily available sources. Copyright © 2006 English Heritage. NMR. [source]