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Light Detection (light + detection)
Kinds of Light Detection Selected AbstractsEVALUATION OF LIGHT DETECTION AND RANGING (LIDAR) FOR MEASURING RIVER CORRIDOR TOPOGRAPHY,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2002Zachary 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] Detection of a low-relief 18th-century British siege trench using LiDAR vegetation penetration capabilities at Fort Beauséjour,Fort Cumberland National Historic Site, CanadaGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2009Koreen Millard Airborne Light Detection and Ranging (LiDAR), a remote sensing data collection technique, has many applications in the field of archaeology, including aiding in the planning of field campaigns, mapping features beneath forest canopy, and providing an overview of broad, continuous features that may be indistinguishable on the ground. LiDAR was used to create a high-resolution digital elevation model (DEM) in a heavily vegetated area at Fort Beauséjour,Fort Cumberland National Historic Site, Canada. Previously undiscovered archaeological features were mapped that were related to the siege of the fort in 1755. Features that could not be distinguished on the ground or through aerial photography were identified by overlaying hillshades of the DEM created with artificial illumination from various angles. LiDAR provides accurate digital topographic models with the additional benefit of mapping vertical surfaces in accurate detail below the forest canopy. © 2009 Wiley Periodicals, Inc. [source] Fullerene Sensitized Silicon for Near- to Mid-Infrared Light DetectionADVANCED MATERIALS, Issue 5 2010Gebhard J. Matt A novel light-sensing scheme based on a silicon/fullerene-derivative heterojunction allows optoelectronic detection in the near- to mid-infrared (IR), which is fully compatible with complementary metal oxide semiconductor (CMOS) technology. Although silicon and the fullerene derivative do not absorb in the IR, a heterojunction of these materials absorbs and generates a photocurrent (PC) in the near- to mid-IR, presumably caused by an interfacial absorption mechanism. [source] Unstructured grid generation using LiDAR data for urban flood inundation modellingHYDROLOGICAL PROCESSES, Issue 11 2010Ryota 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] Light detection and ranging (lidar) in the Witham Valley, Lincolnshire: an assessment of new remote sensing techniquesARCHAEOLOGICAL PROSPECTION, Issue 4 2006Simon 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] Comparison of LiDAR waveform processing methods for very shallow water bathymetry using Raman, near-infrared and green signalsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2010Tristan Allouis Abstract Airborne light detection and ranging (LiDAR) bathymetry appears to be a useful technology for bed topography mapping of non-navigable areas, offering high data density and a high acquisition rate. However, few studies have focused on continental waters, in particular, on very shallow waters (<2,m) where it is difficult to extract the surface and bottom positions that are typically mixed in the green LiDAR signal. This paper proposes two new processing methods for depth extraction based on the use of different LiDAR signals [green, near-infrared (NIR), Raman] of the SHOALS-1000T sensor. They have been tested on a very shallow coastal area (Golfe du Morbihan, France) as an analogy to very shallow rivers. The first method is based on a combination of mathematical and heuristic methods using the green and the NIR LiDAR signals to cross validate the information delivered by each signal. The second method extracts water depths from the Raman signal using statistical methods such as principal components analysis (PCA) and classification and regression tree (CART) analysis. The obtained results are then compared to the reference depths, and the performances of the different methods, as well as their advantages/disadvantages are evaluated. The green/NIR method supplies 42% more points compared to the operator process, with an equivalent mean error (,4·2,cm verusu ,4·5,cm) and a smaller standard deviation (25·3,cm verusu 33·5,cm). The Raman processing method provides very scattered results (standard deviation of 40·3,cm) with the lowest mean error (,3·1,cm) and 40% more points. The minimum detectable depth is also improved by the two presented methods, being around 1,m for the green/NIR approach and 0·5,m for the statistical approach, compared to 1·5,m for the data processed by the operator. Despite its ability to measure other parameters like water temperature, the Raman method needed a large amount of reference data to provide reliable depth measurements, as opposed to the green/NIR method. Copyright © 2010 John Wiley & Sons, Ltd. [source] Stream network modelling using lidar and photogrammetric digital elevation models: a comparison and field verificationHYDROLOGICAL PROCESSES, Issue 12 2008Paul N. C. Murphy Abstract A conventional, photogrammetrically derived digital elevation model (DEM; 10 m resolution) and a light detection and ranging (lidar)-derived DEM (1 m resolution) were used to model the stream network of a 193 ha watershed in the Swan Hills of Alberta, Canada. Stream networks, modelled using both hydrologically corrected and uncorrected versions of the DEMs and derived from aerial photographs, were compared. The actual network, mapped in the field, was used as verification. The lidar DEM-derived network was the most accurate representation of the field-mapped network, being more accurate even than the photo-derived network. This was likely due to the greater initial point density, accuracy and resolution of the lidar DEM compared with the conventional DEM. Lidar DEMs have great potential for application in land-use planning and management and hydrologic modelling. The network derived from the hydrologically corrected conventional DEM was more accurate than that derived from the uncorrected one, but this was not the case with the lidar DEM. Copyright © 2007 John Wiley & Sons, Ltd. [source] Measurement sampling and scaling for deep montane snow depth dataHYDROLOGICAL PROCESSES, Issue 4 2006S. R. Fassnacht Abstract The resolution of snow depth measurements was scaled from a nominal horizontal resolution of approximately 1·5 m to 3, 5, 10, 20, and 30 m using averaging (AVG) and resampling with a uniform random stratified sampling (RSS) scheme. The raw snow depth values were computed from airborne light detection and ranging data by differencing summer elevation measurements from winter snow surface elevations. Three montane study sites from the NASA Cold Lands Processes Experiment, each covering an 1100 m × 1100 m area, were used. To examine scaling, log,log semi-variograms with 50 log-width bins were created for both of the different subsetting methods, i.e. RSS and AVG. From the raw data, a scale break, going from a structured to a nearly spatially random system, was observed in each of the log,log variograms. For each site, the scale break was still detectable at slightly greater than the resampling resolution for the RSS scheme, but at approximately twice the subsetting resolution for the AVG scheme. The resolution required to identify the scale break was still from 5 to 10 m, depending upon the location and sampling method. Copyright © 2006 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 datasetsHYDROLOGICAL PROCESSES, Issue 2 2006D. 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] A network-index-based version of TOPMODEL for use with high-resolution digital topographic dataHYDROLOGICAL PROCESSES, Issue 1 2004S. N. Lane Abstract This paper describes the preliminary development of a network-index approach to modify and to extend the classic TOPMODEL. Application of the basic Beven and Kirkby form of TOPMODEL to high-resolution (2·0 m) laser altimetric data (based upon the UK Environment Agency's light detection and ranging (LIDAR) system) to a 13·8 km2 catchment in an upland environment identified many saturated areas that remained unconnected from the drainage network even during an extreme flood event. This is shown to be a particular problem with using high-resolution topographic data, especially over large appreciable areas. To deal with the hydrological consequences of disconnected areas, we present a simple network index modification in which saturated areas are only considered to contribute when the topographic index indicates continuous saturation through the length of a flow path to the point where the path becomes a stream. This is combined with an enhanced method for dealing with the problem of pits and hollows, which is shown to become more acute with higher resolution topographic data. The paper concludes by noting the implications of the research as presented for both methodological and substantive research that is currently under way. Copyright © 2004 John Wiley & Sons, Ltd. [source] Sulfachlorpyrazine residues depletion in turkey edible tissuesJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 4 2010EBKOWSKA-WIERUSZEWSKA ,ebkowska-Wieruszewska, B.I., Kowalski, C.J. Sulfachlorpyrazine residues depletion in turkey edible tissues. J. vet. Pharmacol. Therap. doi: 10.1111/j.1365-2885.2009.01147.x. Sulfachlorpyrazine (SCP) is currently used to treat coccidian infections in turkeys; however, there is no information available about the withdrawal period necessary for the turkey to be safe for human consumption. A high performance liquid chromatography method with ultraviolet-visible light detection was adapted and validated for the determination of SCP in turkey tissues. The procedure is based on isolation of the (SCP sodium) compound from edible turkey tissues (muscles, liver, kidneys, and fat with skin) with satisfactory recovery (72.80 ± 1.40) and specificity. The residue depletion of SCP in turkeys was conducted after a dose of 50 mg/kg body weight/day had been administrated orally for 3 days. After treatment has been discontinued residue concentrations were detected in tissues on the 7th day. The highest SCP concentrations were measured in muscles. Based on the results presented in this study, it could be assumed that a withdrawal period of 21 days, before medicated turkeys could be slaughtered, would be sufficient to ensure consumer safety. [source] Light detection and ranging (lidar) in the Witham Valley, Lincolnshire: an assessment of new remote sensing techniquesARCHAEOLOGICAL PROSPECTION, Issue 4 2006Simon 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] Principle of adaptive opticsACTA OPHTHALMOLOGICA, Issue 2009PG SÖDERBERG Purpose To provide an overview of adaptive optics imaging of the retina. Methods In ophthalmoscopical imaging, the two dimensional spatial radiance variation of the back scattered light from the retinal surface is measured. Perfect imaging would require that light backscattered from one point on the retina examined is refocused to one point on the detector. Due to diffraction, light scattering and aberrations, some of the light, injected into the eye examined and some of the light back scatted from the retina examined, are deviated. This leads to loss of contrast. Aberrations induced are, for each individual, specific to the optics of the eye examined. In AOSLO, in addition to confocal illumination and light detection, aberrations induced by the optics of the eye examined are individually measured by wave front sensing and corrected for. Results In the AOSLO, a wave front sensor is introduced between the light source and the eye examined. The information from the wave front sensor is fed back to a deformable mirror, also placed in between the light source and the eye examined. The deformable mirror corrects the wave front aberrations induced by the optics of the eye examined. This allows the injected light to form a point on the retinal surface and simultaneously, the backscattered light from the retina of the eye examined to be focused to a point on a detector. An x-y scanner in front of the eye allows sequential illumination and capturing of aberration minimized back scattered light from an x-y matrix of the retinal surface of the eye examined. The relative radiances measured in the x-y matrix represent the image. Conclusion Adaptive optics in ophthalmoscopy improves contrast in the image of the retina examined by correcting for aberrations induced by the optics of the eye examined. [source] | ||||||||||||||||