EARTH SURFACE PROCESSES AND LANDFORMS Earth Surf. Process. Landforms 34, 1831–1838 (2009) Copyright © 2009 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/esp.1879 Letters to ESEX Application of boat-based laser scanning for river survey P. Alho, 1 * A. Kukko, 2 H. Hyyppä, 3 H. Kaartinen, 2 J. Hyyppä 2 and A. Jaakkola 2 1 University of Turku, Department of Geography, FI-20014 University of Turku, Finland 2 Finnish Geodetic Institute, Department of Remote Sensing and Photogrammetry, Geodeetinrinne 2, P.O. Box 15, FI-02431 Masala, Finland 3 Helsinki University of Technology, Research Institute of Modelling and Measuring for the Built Environment, P.O. Box 1200, FI-02015 TKK, Finland Received 12 December 2008; Revised 22 June 2009; Accepted 29 June 2009 *Correspondence to: P. Alho, University of Turku, Department of Geography, FI-20014 University of Turku, Finland. E-mail: petteri.alho@utu.fi Abstract: The boat-based, mobile mapping system (BoMMS) with a laser scanner allows the derivation of detailed riverine topo- graphical data for fluvial applications. Combined with data acquisition from static terrestrial LiDAR (light detection and range) or mobile terrestrial LiDAR on the ground, boat-based laser scanning enables a totally new field mapping approach for fluvial studies. The BoMMS approach is an extremely rapid methodology for surveying riverine topography, taking only 85 min to survey a reach approximately 6 km in length. The BoMMS approach also allowed an effective survey angle for deep river banks, which is dif- ficult to achieve with aerial or static terrestrial LiDAR. Further, this paper demonstrates the three-dimensional mapping of a point- bar and its detailed morphology. Compared with the BoMMS surface, approximately, 80% and 96% of the terrestrial LiDAR points showed a height deviation of less than 2 cm and 5 cm, respectively, with an overall standard deviation of ± 2·7 cm. This level of accuracy and rapidity of data capture enables the mapping of post-flood deposition directly after a flood event without an extensive time lag. Additionally, the improved object characterisation may allow for better 3D mapping of the point bar and other riverrine features. However, the shadow effect of the BoMMS survey in point bar mapping should be removed by additional LiDAR data to acquire entire riverine topography. The approach demonstrated allowed a large reach to be surveyed compared with static terrestrial LiDAR and increased the spatial limit of survey towards aerial LiDAR, but it maintains the same or even better temporal resolution as static terrestrial LiDAR. Copyright © 2009 John Wiley & Sons, Ltd. KEYWORDS: laser scanning; LiDAR; river morphology; TLS; mobile mapping Introduction and background In fluvial studies, different survey and modelling approaches have been used to study the interaction of landscape and flow processes, including response thresholds, feedback elements and other such complexities, requiring high-quality topo- graphical and bathymetrical data at different scales. Currently, synoptic aerial photogrammetry, tachymetry and GPS surveys are widely used in fluvial geomorphology (Brasington et al., 2000; Fuller et al., 2003, Lane et al., 2003), while more sophisticated survey methods such as close-range photogram- metry (Lane et al., 1994; Butler et al., 1998; Smith et al., 2009) and terrestrial LiDAR (Heritage and Hetherington, 2007) are less common. Fluvial processes have been efficiently simulated using hydraulic models, which require digital terrain models or digital elevation models (DTMs, DEMs) as input data. The effects of DTM characteristics in fluvial studies and particu- larly in flood inundation modelling have been investigated in a number of studies (Néelz et al., 2006; Sanders, 2007). More recently, remote sensing techniques have also been utilised to acquire high-resolution digital terrain models using aerial LiDAR, or in reconstructing past inundations with either air- borne synthetic aperture radar (SAR) or airborne photogram- metry (Néelz et al., 2006). In a number of studies, it has been reported that DTM accuracy is crucial for fluvial geomorpho- logical mapping and hydraulic modelling (Cobby et al., 2001; Bates, 2004; Alho et al., 2009). Therefore, a number of researchers have sought to develop better approaches for acquiring topographic data for fluvial studies (Alsdorf et al., 2000; Cobby et al., 2001; Bates et al., 2003, Hudson and Colditz, 2003; Fonstad and Marcus 2005; Heritage and Hetherington, 2007). Promising results have been obtained by various authors using satellite remote sensing data (Bates, 2004) or highly accurate aerial LiDAR DTMs (Cobby et al., 2001; French, 2003; Mason et al., 2007), rather than the more traditional ground or national survey maps. Nevertheless, ground surveys could be applied using terrestrial LiDAR, based on distance measurements and the precise orientation of these measure- ments between a sensor at a known position and a reflecting object (the position to be defined). This technique has been shown to be useful in producing high-quality 3-D models of forested environments (Hyyppä et al., 2001; Yu et al., 2006;