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Stuart N Lane - One of the best experts on this subject based on the ideXlab platform.
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remote survey of large scale braided gravel bed rivers using Digital Photogrammetry and image analysis
International Journal of Remote Sensing, 2003Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:The use of conventional survey methods to monitor large, gravel river beds has traditionally led to a reliance on repeat measurements of cross-sections which, unless very closely spaced, may give unreliable information about three-dimensional channel morphology and morphological change. Provided certain technological limitations can be overcome, remote survey techniques, such as Digital Photogrammetry and airborne laser scanning, remove the spatial and temporal constraints typically associated with ground-based surveys, allowing high spatial resolution, distributed, elevation mapping of gravel river beds. This paper develops the use of Digital Photogrammetry for the survey of a 3.3 km reach of the braided Waimakariri River, New Zealand, which, when combined with image analysis of water colour to infer water depth, provides a Digital Elevation Model (DEM) of the entire river bed. Central to the successful application of this method is DEM post-processing. Errors take two forms: (i) individual point errors ...
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cost effective non metric close range Digital Photogrammetry and its application to a study of coarse gravel river beds
International Journal of Remote Sensing, 2003Co-Authors: Patrice E Carbonneau, Stuart N Lane, Normand BergeronAbstract:Digital Photogrammetry is now increasingly recognized as being a powerful tool in geomorphology. However, the high material costs and skills required by Digital Photogrammetry may deter non-photogrammetrists from using this technique in their research. This paper demonstrates the use of a close-range Digital photogrammetric methodology accessible to non-photogrammetrists and yet capable of yielding good quality topographic information on coarse gravel riverbeds at minimal cost. Digital Elevation Models (DEMs) were derived from 1:165 scale imagery obtained with a 35 mm film SLR camera, a commercial desktop scanner and a softcopy Photogrammetry package. Quality assessment based upon independent checkpoints and scaling analysis showed that the precision of the DEMs was consistently less than 10% of the D 50 of the bed particles. This translates into sub-centimetric precision. Whilst Photogrammetry is presently capable of a better data quality at this scale, quality must be judged with respect to the requirem...
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through water close range Digital Photogrammetry in flume and field environments
Photogrammetric Record, 2002Co-Authors: Justin B Butler, Stuart N Lane, Jim H Chandler, Ekaterini PorfiriAbstract:La determination de la structure de surface des graviers au fond des fleuves est essentielle pour une bonne comprehension de la rugosite du lit et du processus d'entrainement des sediments. On presente dans cet article une application de la photogrammetrie numerique rapprochee pour determiner et suivre les variations qui interviennent sur les graviers dans le lit des cours d'eau, tant dans des canaux d'amenee que sur le terrain. On a obtenu des modeles numeriques des altitudes (MNA) a haute resolution en corrigeant les effets de la refraction a la surface de separation des deux milieux (air/ eau). Bien que les modeles de refraction dont on dispose soient bien adaptes, se pose le probleme du retablissement de la colinearite dans la conception des logiciels generant automatiquement le MNA. Aussi a t-on developpe un algorithme simple de correction de la refraction, en s'appuyant sur la geometrie analytique. On presente cet algorithme qui doit etre utilise une fois acquis le MNA initial, ce qui permet de recourir ensuite a n'importe quel jeu de logiciels photogrammetriques pour la saisie des donnees. On ameliore ainsi la precision du MNA par la reduction du biais de refraction dependant systematiquement de la profondeur sous l'eau. On a pu tester cet algorithme sur un canal d'amenee et determiner la surface du lit lors d'une inondation et apres evacuation de l'eau. Les differences que l'on a trouvees entre l'etat a sec et en eau du MNA ne sont pas apparues systematiques; on pense qu'elles sont dues a une attenuation de la lumiere dans l'eau et a l'apparition d'une parallaxe residuelle et non a un biais de refraction. Ces resultats montrent que l'on peut utiliser la photogrammetrie rapprochee pour etablir des MNA de tres bonne qualite et determiner la topographie sous le niveau de l'eau dans les canaux d'amenee comme dans les fleuves, sur le terrain. Cela constitue une application qui devrait tout a fait interesser les geomorphologues specialises dans les cours d'eau.
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remote sensing of clear water shallow gravel bed rivers using Digital Photogrammetry
Photogrammetric Engineering and Remote Sensing, 2001Co-Authors: Richard M Westaway, Stuart N Lane, Murray D HicksAbstract:The Digital elevation model (DEM] quality that can be obtained from a Digital photogrammetric survey of a reach of the clear water, shallow, gravel-bed North Ashburton River, New Zealand is assessed. An automated correction procedure is used to deal with point errors associated with submerged topography, based on a correction for refraction at an air-water interface. The effects of collection parameter variation upon DEM quality are also considered. The accuracy and precision of DEMs of submerged topography are evaluated using an independent data set. Results show that Digital Photogrammetry, if used in conjunction with image analysis techniques, can successfully be used to extract high-resolution DEMs of gravel riverbeds, but that the quality of submerged topographic representation is heavily dependent upon the water depth at the time of image acquisition. It is suggested that differences between the Digital photogrammetric surface and the "actual" riverbed surface (as determined by terrestrial ground survey] will, in part, reflect the problem of defining what is the true elevation of a gravel-covered surface. A Digital photogrammetric survey will generally see the tops of gravel cobbles, while a hand-held survey staff will tend to record the elevation between stones. The nomenclature of errors is also discussed, and it is concluded that the measure of surface quality adopted should be consistent with the application for which the DEM is to be used.
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monitoring river channel and flume surfaces with Digital Photogrammetry
Journal of Hydraulic Engineering, 2001Co-Authors: Stuart N Lane, Jim H Chandler, K PorfiriAbstract:This paper describes and illustrates a technique for high resolution monitoring of the surface morphology of water-worked sediments. The monitoring uses close-range Digital Photogrammetry. While Photogrammetry is a long-established technique, more recent developments in Digital Photogrammetry allow application in fluvial research to be highly cost effective in both flume and natural river channel studies. Results are presented that involve two scales of laboratory flume: a smaller-scale application associated with sediment sorting processes in a straight channel; and a larger-scale application involving sediment transport and bed material feedbacks in a meandering channel subject to overbank flows. A preliminary assessment of data quality is undertaken with encouraging results. The precision of elevation estimates corresponds to the scale of the imagery acquired and hence may be controlled by design of the image acquisition process.
Jim H Chandler - One of the best experts on this subject based on the ideXlab platform.
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applying close range Digital Photogrammetry in soil erosion studies
Photogrammetric Record, 2010Co-Authors: B Peter C Heng, Jim H Chandler, Alona ArmstrongAbstract:Soil erosion due to rainfall and overland flow is a significant environmental problem. Studying the phenomenon requires accurate high-resolution measurements of soil surface topography and morphology. Close range Digital Photogrammetry with an oblique convergent configuration is proposed in this paper as a useful technique for such measurements, in the context of a flume-scale experimental study. The precision of the technique is assessed by comparing triangulation solutions and the resulting DEMs with varying tie point distributions and control point measurements, as well as by comparing DEMs extracted from different images of the same surface. Independent measurements were acquired using a terrestrial laser scanner for comparison with a DEM derived from Photogrammetry. The results point to the need for a stronger geometric configuration to improve precision. They also suggest that the camera lens models were not fully adequate for the large object depths in this study. Nevertheless, the photogrammetric output can provide useful topographical information for soil erosion studies, provided limitations of the technique are duly considered.
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Aerial photography and Digital Photogrammetry for landslide monitoring
Geological Society London Special Publications, 2007Co-Authors: Jan Walstra, Jim H Chandler, Neil Dixon, Tom DijkstraAbstract:A review is given of the techniques that are available to extract relevant information from multi-temporal aerial photographs for use in the monitoring stage of landslide assessments. It is shown that aerial photograph interpretation reveals qualitative information on surface characteristics, which is helpful in detecting landslide features and inferring the mechanisms involved. Photogrammetrically derived products can be used to quantify these processes, providing distinctive advantages. Comparison of Digital elevation models (DEMs) from different times provides detailed information on changes in surface topography, whereas orthophotos can be used to measure horizontal displacements. The various factors influencing the quality of the products are also identified. Examples from a case study on the Mam Tor landslide are used to illustrate the benefits of the different approaches. Aerial photographs are a generally accepted tool used in landslide studies. They not only provide a metric model from which quantitative measurements can be obtained, but also give a qualitative description of the Earth surface. These two capabilities are irrefutably related to each other, as ‘one must know what one is measuring’ (Lo 1976). The application of aerial photographs to landslide investigation provides a number of distinct advantages. Reconnaissance of the study area can greatly benefit from the 3D representation that is provided by stereoscopic viewing, thereby showing relationships between the various landscape elements more obviously than from a ground perspective. Furthermore, photographically based derivatives provide a suitable base on which boundaries can be delineated accurately. In addition, photographs support the efficient planning of field investigations and sampling schemes, without the need for visiting the site physically, which is especially useful in remote and inaccessible areas (Crozier 1984, Van Zuidam 1985). A final and important advantage is the quantitative topographic information contained, which can be unlocked by appropriate photogrammetric techniques. However, quantitative use of aerial photographs create some difficulties, such as the requirement of experienced analysts and appropriate equipment, combined with sufficient knowledge of the site under investigation (Lo 1976). Aerial photographs can be used in various stages of landslide investigations (Mantovani et al. 1996), and have been extensively used in the detection and classification of landslides. When properly interpreted they allow the identification of diagnostic surface features, such as morphology, vegetation cover, soil moisture and drainage pattern. Furthermore, recent photographs can be compared with historical imagery to assess landslide conditions over different periods of time and allow the progressive development to be examined. Characteristics of mass movements that can be monitored by sequential photographs are, for example, the areal extent of the landslide body, regression rate of the head scar, displacement velocity, surface topography, succession of vegetation and soil moisture conditions. Accurate quantification of change requires the application of rigorous photogrammetric techniques (Chandler 1989). Finally, aerial photography can be helpful in hazard mapping. The purpose of landslide hazard mapping is to analyse the susceptibility of the terrain to slope movements. Aerial photographs can be used to delimit terrain units and map the controlling factors affecting slope stability. The aim of this paper is to give an overview of the ways in which aerial photographs and Digital photogrammetric techniques can be used in the monitoring stage of landslide assessments. Particular attention will be paid to the quality of data derived from aerial photographs of differing type, when using the different techniques available. The various approaches can be roughly divided into three categories: those based on simple aerial photograph interpretations (APIs), those involving the extraction of Digital elevation models (DEMs), and those based on the creation of orthophotos. The underlying techniques will be described and illustrated with some results that were obtained from a case study focusing on the Mam Tor landslide (Derbyshire, UK). From: TEEUW, R. M. (ed.) Mapping Hazardous Terrain using Remote Sensing. Geological Society, London, Special Publications, 283, 53–63. DOI: 10.1144/SP283.5 0305-8719/07/$15.00 # The Geological Society 2007. The study area: Mam Tor The landslide of Mam Tor is situated on the eastern flank of this 517 m high hill, at the head of the Hope Valley, Derbyshire, UK [SK135835]. The former main road between Sheffield and Manchester (A625) was constructed across the slide, but abandoned in 1979 as a consequence of continuous damage caused by the moving ground mass (Fig. 1). The slope consists of predominantly sandstone sequences (Mam Tor Beds) overlying predominantly shale units (Edale Shales). The layers dip slightly inwards of the slope. From scarp to toe, the landslide measures c. 1000 m, and elevation varies from 510 to 230 m. The mean slope of the slipped mass is 128 and the maximum thickness 30–40 m (Skempton et al. 1989). The initial rotational failure has been dated back to 3600 BP (Skempton et al. 1989). While advancing downslope the mass broke into a complex of blocks and slices. Disintegration of the front slices created a debris mass, which slid further down. The unstable transition zone, overlying the steepest part of the basal shear, is the most active part, moving on average 0.35 m a over the last century (Rutter et al. 2003). There is evidence that the movements are not continuous but accelerate during wet winters, when rainfall exceeds certain limits; that is, more than 250 mm rain in a single month and over 750 mm in the preceding 6 months (Waltham & Dixon 2000). There are several information sources available that quantify displacements that have taken place over the last century. Notes about regular disturbance and repairs of the road, from 1907 until the final closure in 1979, are kept by Derbyshire and stability analysis was carried out (Skempton et al. 1989). Since closure of the road, temporary monitoring schemes were set up by Sheffield University (1981–1983; Al-Dabbagh & Cripps 1987), Nottingham Trent University (1990–1998; Waltham & Dixon 2000) and Manchester University (since 1996; Rutter et al. 2003).
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recording aboriginal rock art using cheap Digital cameras and Digital Photogrammetry
2005Co-Authors: Jim H Chandler, John G FryerAbstract:Archaeologists, conservators and rock-site managers need simple and cost effective methods to record and document rock art, including both petroglyphs and pictographs. Combined laser scanning and Photogrammetry can be effective but equipment remains expensive, is difficult to transport into the field and requires some expertise to use successfully during data capture. What is required is the development of a methodology that enables the inexpert, perhaps volunteer, field worker to acquire imagery suitable for photogrammetric measurement using cost effective Digital sensors. This paper describes the desired alternative in which a cheap Digital camera costing just US$300 is used to generate both accurate and dense DEMs and orthophotographs. These data are able to record detailed morphology, generate three dimensional visualizations and the ubiquitous fly through model. The methodology was developed and tested using a series of case studies, representing a diverse selection of aboriginal rock art. Imagery was acquired using a 3 Megapixel Nikon Coolpix 3100 costing US$300 and compared with imagery obtained using a Kodak DCS460, which originally cost US$ 30,000. Fieldwork was conducted at six field sites in Australia, including both petroglyphs and pictographs. Digital Photogrammetry was carried out using the Leica Photogrammetry System and an external self-calibrating bundle adjustment; the combination generating medium accuracy (±3mm), high-resolution DEMs and orthophotos. The petroglyphs were small, typically 1-2m in length and located on horizontal sandstone outcrops. Simple stereopairs acquired using the Nikon Coolpix and simple scaled control in the form of a survey staff, generated dense DEMs (5mm), appropriate to record detailed morphology. An image processing technique implemented in the form of an Erdas “Spatial Model” tool allowed identification of the pecked and engraved grooves from the surrounding rock surface. The pictographs sites were located on vertical and curved rock faces within rock shelters, typically 2-4m high. 3D control was provided using a reflectorless Total Station and rotation of the control coordinates enabled the LPS software to function correctly. Lower resolution DEMs (50mm) proved sufficient to record the simplified morphology. Colour orthophotographs could be generated and multiple images mosaiced together to allow 3D dimensional visualization and fly through generation. The merits of the developed approach will be discussed and implications arising from adoption outlined.
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monitoring river channel change using terrestrial oblique Digital imagery and automated Digital Photogrammetry
Annals of The Association of American Geographers, 2002Co-Authors: Jim H Chandler, Peter Ashmore, Chris Paola, Mike Gooch, Fred VarkarisAbstract:Imagery acquired using a high-resolution Digital camera and ground survey has been used to monitor changes in bed topography and plan form, and to obtain synoptic water surface and flow depth information in the braided, gravel bed Sunwapta River in the Canadian Rockies. Digital images were obtained during daily low flows during the summer melt-water season to maximize the exposed bed area and to map the water surface on the days with the highest flows. Images were acquired from a cliff top 125m above and at a distance of 235m from the riverbed and used to generate high resolution orthophotos and Digital elevation models (DEMs) at a ground resolution of 0.2m, within an area 80 x 125m. The creation of Digital elevation models (DEMs) from oblique and non-metric imagery using automated Digital Photogrammetry can be difficult, but a solution based on rotation of coordinates is described here. Independent field verification demonstrated that root mean square accuracies of 0.045m in elevation were achieved. The ground survey data representing river bed topography were merged with photogrammetric DEMs of the exposed bars. The high-flow water surface could not be surveyed directly because wading was dangerous but was derived by ground survey of selected accessible points and Photogrammetry. The DEMs and depth map provide high-resolution, continuous data on the channel morphology and will be the basis for subsequent 2D flow modeling of velocity and shear stress fields. The experience of using Digital Photogrammetry for monitoring river channel change allows the authors to identify other potential benefits of using this technique for fluvial research and beyond.
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through water close range Digital Photogrammetry in flume and field environments
Photogrammetric Record, 2002Co-Authors: Justin B Butler, Stuart N Lane, Jim H Chandler, Ekaterini PorfiriAbstract:La determination de la structure de surface des graviers au fond des fleuves est essentielle pour une bonne comprehension de la rugosite du lit et du processus d'entrainement des sediments. On presente dans cet article une application de la photogrammetrie numerique rapprochee pour determiner et suivre les variations qui interviennent sur les graviers dans le lit des cours d'eau, tant dans des canaux d'amenee que sur le terrain. On a obtenu des modeles numeriques des altitudes (MNA) a haute resolution en corrigeant les effets de la refraction a la surface de separation des deux milieux (air/ eau). Bien que les modeles de refraction dont on dispose soient bien adaptes, se pose le probleme du retablissement de la colinearite dans la conception des logiciels generant automatiquement le MNA. Aussi a t-on developpe un algorithme simple de correction de la refraction, en s'appuyant sur la geometrie analytique. On presente cet algorithme qui doit etre utilise une fois acquis le MNA initial, ce qui permet de recourir ensuite a n'importe quel jeu de logiciels photogrammetriques pour la saisie des donnees. On ameliore ainsi la precision du MNA par la reduction du biais de refraction dependant systematiquement de la profondeur sous l'eau. On a pu tester cet algorithme sur un canal d'amenee et determiner la surface du lit lors d'une inondation et apres evacuation de l'eau. Les differences que l'on a trouvees entre l'etat a sec et en eau du MNA ne sont pas apparues systematiques; on pense qu'elles sont dues a une attenuation de la lumiere dans l'eau et a l'apparition d'une parallaxe residuelle et non a un biais de refraction. Ces resultats montrent que l'on peut utiliser la photogrammetrie rapprochee pour etablir des MNA de tres bonne qualite et determiner la topographie sous le niveau de l'eau dans les canaux d'amenee comme dans les fleuves, sur le terrain. Cela constitue une application qui devrait tout a fait interesser les geomorphologues specialises dans les cours d'eau.
D M Hicks - One of the best experts on this subject based on the ideXlab platform.
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remote survey of large scale braided gravel bed rivers using Digital Photogrammetry and image analysis
International Journal of Remote Sensing, 2003Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:The use of conventional survey methods to monitor large, gravel river beds has traditionally led to a reliance on repeat measurements of cross-sections which, unless very closely spaced, may give unreliable information about three-dimensional channel morphology and morphological change. Provided certain technological limitations can be overcome, remote survey techniques, such as Digital Photogrammetry and airborne laser scanning, remove the spatial and temporal constraints typically associated with ground-based surveys, allowing high spatial resolution, distributed, elevation mapping of gravel river beds. This paper develops the use of Digital Photogrammetry for the survey of a 3.3 km reach of the braided Waimakariri River, New Zealand, which, when combined with image analysis of water colour to infer water depth, provides a Digital Elevation Model (DEM) of the entire river bed. Central to the successful application of this method is DEM post-processing. Errors take two forms: (i) individual point errors ...
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the development of an automated correction procedure for Digital Photogrammetry for the study of wide shallow gravel bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated correction procedure for dealing with point errors associated with through-water Photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The procedure involves combining Digital Photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The correction procedure was applied to raw Digital elevation models (DEMs) generated using Digital Photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that Digital Photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the correction procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
Richard M Westaway - One of the best experts on this subject based on the ideXlab platform.
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remote survey of large scale braided gravel bed rivers using Digital Photogrammetry and image analysis
International Journal of Remote Sensing, 2003Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:The use of conventional survey methods to monitor large, gravel river beds has traditionally led to a reliance on repeat measurements of cross-sections which, unless very closely spaced, may give unreliable information about three-dimensional channel morphology and morphological change. Provided certain technological limitations can be overcome, remote survey techniques, such as Digital Photogrammetry and airborne laser scanning, remove the spatial and temporal constraints typically associated with ground-based surveys, allowing high spatial resolution, distributed, elevation mapping of gravel river beds. This paper develops the use of Digital Photogrammetry for the survey of a 3.3 km reach of the braided Waimakariri River, New Zealand, which, when combined with image analysis of water colour to infer water depth, provides a Digital Elevation Model (DEM) of the entire river bed. Central to the successful application of this method is DEM post-processing. Errors take two forms: (i) individual point errors ...
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remote sensing of clear water shallow gravel bed rivers using Digital Photogrammetry
Photogrammetric Engineering and Remote Sensing, 2001Co-Authors: Richard M Westaway, Stuart N Lane, Murray D HicksAbstract:The Digital elevation model (DEM] quality that can be obtained from a Digital photogrammetric survey of a reach of the clear water, shallow, gravel-bed North Ashburton River, New Zealand is assessed. An automated correction procedure is used to deal with point errors associated with submerged topography, based on a correction for refraction at an air-water interface. The effects of collection parameter variation upon DEM quality are also considered. The accuracy and precision of DEMs of submerged topography are evaluated using an independent data set. Results show that Digital Photogrammetry, if used in conjunction with image analysis techniques, can successfully be used to extract high-resolution DEMs of gravel riverbeds, but that the quality of submerged topographic representation is heavily dependent upon the water depth at the time of image acquisition. It is suggested that differences between the Digital photogrammetric surface and the "actual" riverbed surface (as determined by terrestrial ground survey] will, in part, reflect the problem of defining what is the true elevation of a gravel-covered surface. A Digital photogrammetric survey will generally see the tops of gravel cobbles, while a hand-held survey staff will tend to record the elevation between stones. The nomenclature of errors is also discussed, and it is concluded that the measure of surface quality adopted should be consistent with the application for which the DEM is to be used.
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the development of an automated correction procedure for Digital Photogrammetry for the study of wide shallow gravel bed rivers
Earth Surface Processes and Landforms, 2000Co-Authors: Richard M Westaway, Stuart N Lane, D M HicksAbstract:This paper develops an automated correction procedure for dealing with point errors associated with through-water Photogrammetry, for application in the study of clear-water, shallow gravel-bed rivers. The procedure involves combining Digital Photogrammetry and image analysis techniques to: (i) correct for the effects of refraction at an air–water interface; and (ii) eliminate and reinterpolate points where the bed has not been ‘seen’. The correction procedure was applied to raw Digital elevation models (DEMs) generated using Digital Photogrammetry from 1:3000 scale aerial photography of a small reach of the North Ashburton River, New Zealand. The accuracy of corrected and uncorrected DEMs is evaluated using an independent data set. A measure of ‘geomorphological usefulness’ as well as DEM external reliability is obtained from calculations of water depth distributions and mean bed level. Results show that Digital Photogrammetry, used in conjunction with image analysis techniques, can successfully be used for extracting high-resolution DEMs of gravel river beds. In exposed areas, errors are small and random, tending to cancel out over large numbers of points. Where water is shallow, and following correction, point elevation errors are statistically no different from those for exposed zones. In deeper water, despite an improvement following application of the correction procedure, elevation errors scale with water depth. The geomorphological potential of photogrammetric survey of large, gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution (important for the assessment of a river's ecological and recreational characteristics) and mean bed level (important for the calculation of reach-scale sediment volumes). Copyright © 2000 John Wiley & Sons, Ltd.
Christian Ginzler - One of the best experts on this subject based on the ideXlab platform.
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Snow depth mapping in high-alpine catchments using Digital Photogrammetry
Cryosphere, 2015Co-Authors: Yves Buhler, Michael Marty, J. Veitinger, P. Thee, Lukas Egli, Tobias Jonas, Christian GinzlerAbstract:Information on snow depth and its spatial distribution is crucial for numerous applications in snow and avalanche research as well as in hydrology and ecology. Today, snow depth distributions are usually estimated using point measurements performed by automated weather stations and observers in the field combined with interpolation algorithms. However, these methodologies are not able to capture the high spatial variability of the snow depth distribution present in alpine terrain. Continuous and accurate snow depth mapping has been successfully performed using laser scanning but this method can only cover limited areas and is expensive. We use the airborne ADS80 optoelectronic scanner, acquiring stereo imagery with 0.25 m spatial resolution to derive Digital surface models (DSMs) of winter and summer terrains in the neighborhood of Davos, Switzerland. The DSMs are generated using photogrammetric image correlation techniques based on the multispectral nadir and backward-looking sensor data. In order to assess the accuracy of the photogrammetric products, we compare these products with the following independent data sets acquired simultaneously: (a) manually measured snow depth plots; (b) differential Global Navigation Satellite System (dGNSS) points; (c) terrestrial laser scanning (TLS); and (d) ground-penetrating radar (GPR) data sets. We demonstrate that the method presented can be used to map snow depth at 2 m resolution with a vertical depth accuracy of ±30 cm (root mean square error) in the complex topography of the Alps. The snow depth maps presented have an average accuracy that is better than 15 % compared to the average snow depth of 2.2 m over the entire test site.