High-resolution LiDAR and photogrammetric survey of the Fumanya dinosaur tracksites (Catalonia): implications for the conservation and interpretation of geological heritage sites

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High-resolution LiDAR and photogrammetric survey of the Fumanya dinosaur tracksites (Catalonia): implications for the conservation and interpretation of geological heritage sites
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  doi:10.1144/0016-76492007-033 2008; v. 165; p. 115-127 Journal of the Geological Society   Gawthorpe Karl T. Bates, Frank Rarity, Phillip L. Manning, David Hodgetts, Bernat Vila, Oriol Oms, Àngel Galobart and Robert L.  geological heritage sitestracksites (Catalonia): implications for the conservation and interpretation of High-resolution LiDAR and photogrammetric survey of the Fumanya dinosaur   Journal of the Geological Society   serviceEmail alerting  to receive free email alerts when new articles cite this article click here  requestPermission  to seek permission to re-use all or part of this article click here  Subscribe  to subscribe to Journal of the Geological Society or the Lyell Collection click here  Notes   Downloaded by University of Manchester on 15 January 2008  © 2008 Geological Society of London   Journal of the Geological Society ,  London , Vol.  165 , 2008, pp. 115–127. Printed in Great Britain.115 High-resolution LiDAR and photogrammetric survey of the Fumanya dinosaurtracksites (Catalonia): implications for the conservation and interpretation of geological heritage sites KARL T. BATES 1,2 , FRANK RARITY 2 , PHILLIP L. MANNING 2,3 , DAVID HODGETTS 2 , BERNATVILA 4,5 , ORIOL OMS 6 , A` NGEL GALOBART 4 & ROBERT L. GAWTHORPE 21  Adaptive Organismal Biology Research Group, Faculty of Life Sciences, University of Manchester, Jackson’s Mill, PO Box88, Sackville Street, Manchester M60 1QD, UK (e-mail: karl.bates@postgrad.manchester.ac.uk) 2 School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK  3 The Manchester Museum, University of Manchester, Oxford Road, Manchester M13 9PL, UK  4  Institut de Paleontologia ‘M. Crusafont’, Carrer Escola Industrial, 23, 08201, Sabadell, Barcelona, Spain 5  Former address: Consorci Ruta Minera, Carretera de Ribes, 20, 08698, Cercs, Barcelona, Spain 6  Department de Geologia, Facultat de Ciencies, Universitat Autonoma de Barcelona, 08193, Bellaterra, Spain Abstract:  Increasing political and social awareness of the importance of protecting the geological heritage iscompelling geoscientists to consider new methods for reconciling conservation and exploration of their research sites. Terrestrial Light Detection And Range (LiDAR) imaging is an accurate method of collecting3D spatial data that has so far been under-utilized in the geological sciences. This aim of this paper is toassess the value of integrated LiDAR and photogrammetric imaging as a tool for synchronizing scientificexploration with conservation of geological heritage sites.Fumanya (Catalonia) is one of the most important Cretaceous tracksites in Europe, but the nature of exposure of the track-bearing surface has hindered quantitative documentation of the ichnites. Using integrated Light Detection And Range (LiDAR) imaging and photogrammetry it has been possible to construct high-resolution Digital Outcrop Models (DOM) of the tracksites. Photo-textured DOMs are a powerful visualizationtool and function as fully 3D interactive databases that preserve information about the site that would otherwise be lost to erosion. LiDAR-derived DOMs have the potential to contribute profoundly to futuregeoconservation projects, particularly as a tool for documenting and monitoring heritage sites and promotingeducation and tourism. LiDAR scanning also provides sufficient resolution to perform robust quantitativeanalysis of dinosaur tracks. The long-term conservation of high-quality geological heritagesites has been a problematic issue for decades (Gillette 1986;Agnew  et al  . 1989; Oms  et al  . 2002), and in recent years therehas been collective effort to preserve elements of the Earth’sgeological history. This growing emphasis on geoconservation isreflected in the policies of national and international geologicalheritage organizations (e.g. UNESCO World Heritage, ProGEO,GEOSEE, GEOSITES, GeoPark), dedicated to establishing sys-tematic frameworks for protecting and managing geosites for the purpose of education, tourism and research (Cleal  et al  . 1999;Page 1999; Garcia-Cortes  et al  . 2001; Rohling & Schmidt-Thome´ 2004; Brilha 2005). Despite undoubted progress and numerous examples of successful conservation programmes (e.g.Agnew  et al  . 1989; Parkes & Morris 1999; Breithaupt  et al  .2004; Falcon-Lang & Calder 2004), concerns about the deteriora-tion of research sites persist (Barettino  et al  . 1999; Schulp &Brokx 1999; Clarkson 2001; Van Der Merwe 2003). Many keysites are susceptible to weathering, erosion and destruction byother means (quarrying, vandalism, etc.). The conservation and documentation of such sites requires new techniques to preventthe permanent loss of what is in many cases a finite naturalresource.LiDAR imaging is a highly accurate method of acquiring 3Dspatial data and has been widely applied in other areas of heritage conservation (Weibring  et al  . 1997; Mason  et al  . 2000;Louden 2002; Barnes 2003; Bewley  et al  . 2005). To date LiDAR has been under-utilized in geology, both as an analytical and as aconservation tool. Breithaupt  et al  . (2004) used terrestrial LiDAR imaging and digital photogrammetry separately to record and map small sections of outcrop in Wyoming and Colorado (USA)containing abundant dinosaur tracks and skeletal remains. The potential to integrate LiDAR and photographic data and collecthigh-resolution quantitative data from sites through remotesurveying suggests that the method may provide a means tomerge conservation with scientific exploration of heritage sites.To assess the value of integrated LiDAR imaging and digital photography as a geoconservation tool, a survey of the Maas-trichtian dinosaur tracksites at Fumanya (SE Pyrenees, Catalonia)was undertaken using established ground-based procedures. Theunique tracksites at Fumanya have undergone significant weath-ering since their exposure by open-air lignite mining in the1980s (Schulp & Brokx 1999; Oms  et al  . 2002). The LiDAR survey has provided sufficient data to construct a variety of high-resolution 3D DOMs of the localities. The 3D geometry of individual tracks within the DOMs can be viewed and quantita-tively analysed, providing the first comprehensive record of thetracksite in a 3D framework. The purpose of this paper is toreport the methods involved in collecting field data and building  high-resolution 3D DOMs, and to discuss the implications of theresults for the conservation and interpretation of geologicalheritage sites. Study area  Fumanya (SE Pyrenees, Catalonia) The Fumanya sites are located between the Figols and Vallcebrevillages, to the north of Berga (Barcelona province, Catalonia), by the western edge of the Llobregat river, in the foothills of Serra d’Ensija mountain in NE Spain (Fig. 1). The main localityis at Fumanya South, where more than 2000 tracks have beenidentified. Sites at Mina Esquirol, Fumanya North and MinaTumı´ are linked by a mountain road that runs from Coll deFumanya to Vallcebre village. Geological setting  The Pyrenees fold-and-thrust belt formed at the boundary be-tween the European and Iberian plates at the end of the Mesozoicand through the lower Tertiary. This belt is made up by Hercinian basement and a sedimentary cover that developed in foreland  basins at both the northern and the southern edge of the orogen.The Vallcebre basin belongs to the latter and contains the studied sites.The continental Late Cretaceous–Early Palaeocene sedimentsthat filled the southern Pyrenean basins are known as the TrempFormation or ‘Garumnian’ (see historical review by Rosell  et al  .2001). The Tremp Formation was deposited following a marineregression that began near the Campanian–Maastrichtian bound-ary, accumulating sediments in an east–west foreland troughconnected to the Atlantic Ocean. Above the Are´n sandstone (and other related marine formations) the general stratigraphy of theTremp Formation for the southern Pyrenees has the followingunits: unit a, a marine–continental transitional Grey Unit (marls,coals, limestones and sandstones); unit b, a fluvial Lower Red Unit (mudstones, sandstones, oncoliths and palaeosols); unit c,the lacustrine Vallcebre limestones and laterally equivalent strata;unit d, an Upper Red Unit (mudstones, sandstones, conglomer-ates and limestones). The age of these units is Maastrichtian(units a and b) and Palaeocene (units c and d). All these unitscan be recognized in the Vallcebre syncline, within the Pedrafor-ca thrust sheet, which is one of the main structural units in thesouthwestern Pyrenees. Along this syncline dinosaur tracks arefound throughout units a and b, with the Fumanya tracksiteslocated at the very base of unit a. In this stratigraphic position a5 m thick layer (the ‘concrete level’) contains the studied tracks,which are exposed in the footwall of the abandoned miningworks. Palaeontological remains (ostracodes, gastropods, charo- phytes, vertebrate remains, etc.) and sedimentological observa-tions suggest that the concrete layer represents an extensivecarbonate mudflat deposited in a marine–continental transitionalenvironment (Vila  et al  . 2005; Oms  et al  . 2007). The location of the tracks at the top of the concrete layer indicates that preservation occurred just before or as a result of a significantenvironmental change, specifically evolution to a more diversi-fied environment, with coals, charophyte limestones, siltstonesand fine-grained sandstones of limited lateral extent.  Palaeontology The Tremp and Aren formations have yielded a diverse verte- brate fauna including fish, turtles, rays, lepidosaurs, crocodilesand dinosaurs, including theropods, titanosaurs, hadrosaurs and ankylosaurs (Vila  et al  . 2006). Since 2001 more than 60localities with abundant vertebrate remains have been found, and the 14 sites excavated to date have produced over 500 bones(Galobart  et al  . 2003; Vila  et al  . 2006). The dinosaur track record consists of more than 15 localities, including sauropod trackways and hadrosaur tracks; dinosaur eggshells, eggs and clutches are also common (see **Lo´pez-Martinez 2000; Bravo  et al  . 2005).Much of this Late Cretaceous faunal diversity is present at theFumanya sites (Schulp & Brokx 1999; Oms  et al  . 2007). TheFumanya sites, however, are unique in their preservation of   c .3500 dinosaur tracks and 40 recognizable trackways. The majorityof tracks have been attributed to titanosaurid sauropods, alongsidea likely theropod trackway at Fumanya South (Le Loeuff &Martı´nez 1997; Schulp & Brokx 1999; Vila  et al  . 2005). Track preservation The track-bearing surface at the Fumanya sites forms a steepdipslope, inclined at 60 8 , that runs north–south to form thewestern face of the quarries (Fig. 2). The majority of tracks have been interpreted as undertracks (Vila  et al  . 2005), althoughSchulp & Brokx (1999) mentioned the presence of well-pre-served surface tracks (i.e. tracks formed at the foot–sedimentinterface; Romano & Whyte 2003) at the northern end of theFumanya South site. In addition to tilting the track-bearingsurface, Alpine tectonism has caused significant fracturing and veining, resulting in the displacement of a number of trackways.The track-bearing surface has also undergone significant physicalweathering since its exposure in the 1980s (Oms  et al  . 2002).Schulp & Brokx (1999, p. 243) noted: ‘Although the excavationof lignite ceased only a few years ago, even the prints that wereonly recently exposed are already being affected by erosion.’ Thetracks are preserved in soft, silty marl that is highly friable and has a fissile weathering texture. The altitude (over 1550 m) and  Fig. 1.  Location of the Fumanya tracksitesin the SE Pyrenees, near the town of theBerga (adapted from Vila  et al  . 2005).K. T. BATES  ET AL. 116  Pyrenean climate (high insulation indices, rain, ice, wind, etc.)mean that the site experiences extremes of temperature, and thesteepness of the slope results in falling overburden further damaging the track-bearing surface. The distinct pattern of fractures on the track-bearing surface allows recognition of corresponding areas in photographs taken at discrete intervalssince excavations ceased. These photographs clearly demonstratethe deterioration and loss of the ichnological record at Fumanya(Fig. 3).Although the condition of many tracks has deteriorated, asignificant number of tracks still clearly retain diagnostic featuressuch as digit impressions and claw marks (Vila  et al  . 2005). Thewealth of data available, and the rarity of Maastrichtian dinosaur tracksites (Lockley  et al  . 2002), makes Fumanya one of the mostimportant Cretaceous dinosaur tracksites in Europe. However, areview of previous research illustrates the logistical difficulty inquantitatively studying and archiving the Fumanya tracksites.  Previous work  Since its first description by Viladrich (1986), the FumanyaSouth site has been the focus of a number of cartographic studies(Le Loeuff & Martı´nez-Rius 1997; Schulp & Brokx 1999; Vila et al  . 2005). In these studies, the workers have experimented with a variety of novel approaches in an effort to overcome thefundamental difficulties of mapping the distribution and geome-try of tracks on the largely inaccessible, steep quarry face.Schulp & Brokx (1999) produced the first general cartography of the Fumanya South site using a combination of climbing, surfacegrids, photogrammetry and simple visual surveying through binoculars. In 2002 some of the present authors used similar methods to produce a more detailed map of Fumanya South(B. Vila, pers. comm.). By using 5 m marked ropes it was possible to make a narrower surface grid than those used in previous cartographic studies. Having created a dense surfacegrid a series of high-resolution photographs of the track-bearingsurface were taken, upon which track outlines and joints weremarked as reference points. This allowed correction for perspec-tive distortion to be achieved using photogrammetric software.At the northern extreme of the outcrop some of the authors wereable to use climbing equipment to measure a number of track-ways directly on the vertical surface. At Fumanya North, MinaEsquirol and Mina Tumi trackways were also mapped usingclimbing techniques and balloons. Fig. 2.  Photograph of the disused quarry atFumanya South. The track-bearing surfaceforms a steep dip slope exposed by open-air lignite mining in the 1980s. Fig. 3.  Serial photographs of the same area of the track-bearing surface at Fumanya South illustrate the rapid weathering of the horizon and the loss of theichnological record. Various features on the track-bearing surface (e.g. fractures, weathering patterns) allow recognition of common points (A, B and C) inthe photographs.FUMANYA DINOSAUR TRACKS, SPAIN 117  The distribution of tracks on the surface at Fumanya South has been qualitatively constrained, but to comprehensively archiveeach of these valuable sites, a quantitative record of thedistribution and 3D geometry of tracks is required. Integrated LiDAR imaging and digital photogrammetry, as a highly accurateremote method of collecting 3D spatial data, offers an idealsolution to the methodological difficulties that have so far  prevented quantitative documentation of the tracksites. Materials and methods  Fieldwork   Instrumentation.  The fully portable RIEGL LMS-Z420i 3D laser scanner was chosen for its ability to rapidly acquire spatial data (12000  x ,  y ,  z  and intensity points per second) under demanding environmental condi-tions. The LiDAR scanner has a range of 800 m, 80 8  vertical and 360 8 horizontal fields of view and can be powered by a 24 V or 12 V car  battery. The scanner uses a near-IR laser that is eye safe and requires noadditional safety precautions. A Panasonic Windows tough-book with aCentrino Pentium 1.6 GHz CPU, 1 gigabyte of RAM and the software package RiSCAN PRO allows the operator to acquire, view and process3D data in the field, thereby increasing the level of quality control onsurvey data. A digital camera (6.1 megapixel Nikon D100) was mounted on the scanner and, once calibrated, provided images that were used toextract an RGB colour channel and reflection intensity information for the point cloud; it was also used to texture map the final geoconservationmodel, to produce a photo-realistic representation of the outcrop. Preciseglobal positioning was provided by the Trimble PRO-XR DifferentialGlobal Positioning System (DGPS), which utilizes a fixed base station tocorrect for the effects of systematic errors on the receiver (e.g. atmo-spheric propagation, satellite clock offset) to give sub-metre accuracy.The scanner can be fitted with either a vertical mount or a tilt mount.A tilt mount was used in this survey and provided a full 180 8  rotationfrom the horizontal, giving a very wide field of view. The tilt-mounted scanner, digital camera and GPS were mounted on a heavy-dutysurveyor’s tripod (Fig. 4).  Data acquisition.  The LiDAR scanner emits a pulsed beam of light thatis backscattered by the target object(s) and recaptured by the detector.The two-way travel time is divided in half and multiplied by the speed of light to derive a  z   value, whereas the  x  and   y  positions are calculated vialaser deflecting mirrors within the detector (Bellian  et al  . 2005). Theintensity of the return for each laser point is also recorded, and isdetermined by the reflective properties of the target surface. Laser intensity is therefore particularly sensitive to colour and moisture contentof an exposure, as well as its distance from the scanner.Full coverage of the track-bearing surface required a number of scanstations at each locality. Multiple scan stations provide more detailed 3Dshape information by eliminating shadows (i.e. areas not visible to thelaser) in the data caused by irregularities in the exposure surface. Both perpendicular and oblique scan perspectives were therefore necessary inthis instance to prevent shadows occurring within the tracks themselves,which form features of negative relief (i.e. casts) on the scanned surface.Prior to surveying it was uncertain precisely what scan resolutionwould be required to accurately capture the 3D geometry and particularlythe depth (  z  ) perspective of the tracks. Scan resolution describes thenumber of   x ,  y  and   z   points per unit area in the scan (i.e. the density of  points within the resulting 3D point cloud). High-resolution scans arecharacterized by a small spacing between scan points, producing high-density 3D point clouds. Previous geological applications of LiDAR havefocused almost exclusively on mapping large-scale features withinexposures (e.g. bedding, fluvial channels, faults, etc.), relying ontraditional methods (e.g. sedimentary logging) to incorporate sub-metresedimentary structures into stratigraphic models (Bellian  et al  . 2005).Scan resolution is an important logistical constraint during fieldwork and data processing, as it determines the duration of the scan for a given area,and the size and manageability of the resulting dataset. The ability toview and process scans on a laptop in the field is crucial to findingappropriate scan resolutions for imaging 3D track geometry givenconstraints on field time and computer processing capability.At each scan station a standard 360 8  panorama scan (1998000 pointsusing the RIEGL LMS-Z420i) was used to acquire a single image of theentire exposure and its surrounding landscape. The panorama scan wascoloured using photographic images acquired from the camera and wide-angle 14 mm lens (full 360 8  requires seven images). The operationalsoftware package (RiSCAN PRO) allows the panorama to be viewed onthe laptop, and to serve as a template to select areas for higher resolutionscans. The track-bearing surface was subsequently selected and scanned from each station at a variety of resolutions (0.01–0.08 m pointspacings). At such fine resolutions, a single scan covering the entiretrack-bearing surface would have generated an unusable multi-gigabytedataset. Instead, a series of smaller, overlapping scans were acquired tocreate more manageable files for later processing and interpretative work.A series of high-resolution photographic images of the track-bearingsurface were taken using 85 mm and 180 mm lenses on the Nikon D100.The height of the exposure required use of the tilt mount to capture thefull vertical extent of the track-bearing face using both the 85 mm and 180 mm lenses. In both instances, the result was a high-resolution photographic mosaic of the exposure composed of horizontally and vertically overlapping images. The procedure was performed automati- Fig. 4.  The fully integrated scan unit (LiDAR, Nikon D100, laptop and DGPS) mounted on the tilt mount and surveyor’s tripod.K. T. BATES  ET AL. 118
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