Abstract
ABSTRACTTerrestrial laser scanning is the current technique of choice for acquiring high resolution topographic data at the site scale (i.e. over tens to hundreds of metres), for accurate volume measurements or process modelling. However, in regions of complex topography with multiple local horizons, restricted lines of sight significantly hinder use of such tripod‐based instruments by requiring multiple setups to achieve full coverage of the area. We demonstrate a novel hand‐held mobile laser scanning technique that offers particular promise for site‐scale topographic surveys of complex environments. To carry out a survey, the hand‐held mobile laser scanner (HMLS) is walked across a site, mapping around the surveyor continuously en route. We assess the accuracy of HMLS data by comparing survey results from an eroding coastal cliff site with those acquired by a state‐of‐the‐art terrestrial laser scanner (TLS) and also with the results of a photo‐survey, processed by structure from motion and multi‐view stereo (SfM‐MVS) algorithms. HMLS data are shown to have a root mean square (RMS) difference to the benchmark TLS data of 20 mm, not dissimilar to that of the SfM‐MVS survey (18 mm). The efficiency of the HMLS system in complex terrain is demonstrated by acquiring topographic data covering ~780 m2 of salt‐marsh gullies, with a mean point spacing of 4.4 cm, in approximately six minutes. We estimate that HMLS surveying of gullies is approximately 40 times faster than using a TLS and six times faster than using SfM‐MVS. © 2013 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.
Highlights
Many geomorphological studies have some form of topographic measurement at their heart
The terrestrial laser scanner (TLS) survey took longest to carry out, with both the held mobile laser scanner (HMLS) and structure from motion and multi-view stereo (SfM-multi-view stereo (MVS)) data collection taking less than 10 minutes each
The point-to-point differences calculated between the surveys and the TLS data show that the HMLS data are similar in accuracy to those from structure from motion (SfM)-MVS (Figure 2b), with root mean square (RMS) differences of 20 and 18 mm, respectively
Summary
Many geomorphological studies have some form of topographic measurement at their heart. Satellite navigation systems [e.g. Global Positioning System (GPS), Global Navigation Satellite System (GLONASS)] have added to the geomorphologist’s armory, allowing survey work to be positioned within a global coordinate system Such methods provide good accuracy and precision for the measurement of individual points, significant time is required to collect a sufficient density of data for useful digital elevation models (DEMs) of the landscape to be produced. Laser-based measurements require line of sight and, with TLS systems being tripod-mounted, this can significantly increase survey times in complex topographic environments In such scenarios, with few vantage points from which large proportions of the project site are observable, multiple scan positions must be used to cover the full area required. Time-consuming instrument repositioning must be repeatedly carried out and the complexity of the subsequent data processing is increased
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