Digital outcrop research (Utilising LiDAR (Light Detection and ranging))
The LiDAR (Light detection and ranging) is a state of the art laser imaging system which can build 3D georeferenced models of outcrop from distances of up to 800m. This is accomplished through the building of a 3D point cloud of LASER energy reflected from the target outcrop. Measurement rates of up to 12,000 emitted and reflected points per second are accomplished over a field of view of 80° vertically by 360° horizontally. A measurement accuracy of up to 2cm can be accomplished, although more often a lower resolution gives the required results.
The LiDAR has been used extensively since its acquisition by the Basin research Group, with projects including;
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The Basins group LiDAR system is available for hire in a consulting role. For more information please contact Dr Dave Hodgetts
- The LiDAR system
The LiDAR system is composed of several pieces of equipment:
The Scanner itself is a LMS-Z420i, manufactured by Austrian company RIEGL. Developed initially for industrial and surveying work, the LiDAR has proved extremely adept at geological field work, particularly quantifying large scale, and hard to reach outcrops. The scanner uses a Class 1 LASER with a maximum measurement rate of 12,000 points per second. The 3D representation outcrop is produced by measuring "time of flight" for the reflected LASER pulse, measuring distance, tilt and azimuth, and reflected light intensity.
A Nikon D100 Digital SLR camera provides high resolution colour images to provide colour and texture for the initial scan. The Camera is mounted above the Scanner and photographs are taken automatically to coincide with the scan data through a controlling Laptop. The Nikon D100 has a 6 megapixel resolution and uses 3 lenses, 14mm wide angle, plus 85 and 180mm lenses for detail. Photographs are overlaid upon the 3D LASER point cloud to provide photo realistic textural models of the outcrop that preserves colour and shadow data. This allows interpretation of LiDAR in a style similar to seismic interpretation.
In order to Fully georeference the LiDAR data (accurately place the data in a 3D virtual world), a Trimble Differential Global Positioning System (DGPS) is mounted upon the scanner head. With global coverage and centimeter scale accuracy, this allows scan positions to accurately mapped such that each data point's position in space is very accurately known. This means the data can be used for linear and volume measurements after leaving the outcrop site, and many scans can be merged together, creating models of extremely large outcrops.
The LiDAR system is controlled by a Panasonic Toughbook laptop. This laptop is ruggedised for field work, incorporating a touch screen which allows successful viewing even with direct sunlight. The laptop runs software to initiate and control the scan, including the Camera and DGPS. It also acts as a portable data storage device to record the scan data. The whole system is powered by a modified Car battery.
Post scan processing is generally performed in the laboratory, although this can be done in the field such that the scanning process can optimised as it is being done. The software used is PolyWorks by InnovMETRIC which provides engineering grade editing and merging of 3D point cloud data. Processing involves 3 main phases; 1) Merging of individual scans to create large outcrop wide data sets 2)A Polyworks algorithm produces a triangulated mesh surface from data points 3) Photographs are contoured over the 3D surface to provide a coloured/textured 3D surface.
- Uses of the LiDAR system
From the final model, 3D geological data can be extracted such as strikes/dips, lengths, directional data (palaeocurrents, fault azimuth, fracture orientations etc), and volumes. This is possible using VRGS (Virtual Reality Geological Studio) a software package developed inhouse by Dave Hodgetts (see screenshot right).
This is an immensely powerful tool for the creation of high resolution reservoir models which can be taken directly from outcrop data, therefore obeying the spatial orientations and heterogeneities of reservoirs. LiDAR is interpreted within VRGS much in the same way as seismic, such that
key surfaces can be picked and geostatistics can also be extracted to quantify geological systems such as sinuosity of channels, and structural data for modeling of folding and fault geometries. Combinations of scan position can allow geometries of very large bodies to be determined when this is not possible from outcrop. Work at Manchester is currently looking at combining interpreted LiDAR data with hydrocarbon reservoir modeling software so that fluid simulations can be run through the simulated reservoir.
Slightly more unusually the LiDAR has also produced very high resolution models of Dinosaur track imprints. Believed to be the first such trial, volume maps produced of the track imprints show the Dinosaurs gait, speed and characteristic of the foot. A further use of this is conservation of information long after the detail of the outcrop has been worn away.
LiDAR also proves a powerful teaching tool for the Petroleum Geoscience MSc at Manchester. Students benefit from being able to study world class outcrops without leaving the classroom, and also following the workflow from outcrop study to reservoir modeling.
- NARG LiDAR case studies
PhD research by Ivan Fabuel-Perez, Dr Jonathan Redfern and Dr Dave Hodgetts (Current research)
The aim of the project is the comparison and modeling of different Triassic fluvial systems using the combination of digital outcrop images obtained with LIDAR technology (Light Detection and Ranging) and field sedimentological data such as sedimentary logs, paleocurrent information, in order to analyse the basin evolution, depositional system, climate cycles and controls on reservoir quality and distribution. Click here to download a NARG LiDAR report from First Break (pdf 1.6Mb)
Sedimentology, third order sequence stratigraphy and controlling factors on facies distribution in the Triassic of North Africa
PhD research by Nadine Mader and Dr Jonathan Redfern (Finished research)
The study aims to assess the temporal and spatial distribution of the continental fluvio-aeolian sequences. Controlling factors on sediment distribution and related cyclicity are investigated to establish a cyclostratigraphic framework, and hence to improve correlation between and within the prolific reservoir intervals of North Africa. Outcrop, core and well-log data are integrated on a basin-by-basin scale.