Airborne LiDAR in support of geomorphological and hydraulic modelling

This paper considers the application of airborne laser altimetry (LiDAR) to the provision of elevation data at accuracies and spatial densities commensurate with the current generation of high-resolution hydraulic models. Three sets of issues are addressed with reference to a Telemac 2D model of a morphologically complex estuary in eastern England. First, the quality of airborne LiDAR data is assessed via multiscale calibration against surveyed sections and supplementary control points. Second, image processing techniques are used for (i) identification of multiple regions of interest within large LiDAR mosaics; (ii) subregional infilling of voids left by data 'drop-outs'; (iii) filtering and subsampling to match topographic information content with model resolution and the density of the computational mesh. Third, the implications of improved terrain data are considered with reference to the estimation of elevations and potential tidal volumes for a number of discrete flood compartments and the modelling of hypothetical inundation scenarios. After minor offset correction to ensure registration with local benchmarks, the quality of LiDAR elevation data within a 12 km x 4 kin coverage is found to be consistent with the published specification (+/-0.10 to +/-0.15 m). Image-processing tools provide an efficient means of managing information content and interfacing this with the GIS-based functionality of the preprocessing software used in conjunction with the hydraulic model. The accuracy and spatial resolution of the LiDAR data allow the identification of subtle but important topographic variations between adjacent flood compartments. In many cases, differences in model results obtained using these data relative to previously estimated average flood compartment elevations are small. Importantly, however, LiDAR provides topographic information at an accuracy and resolution close to the present limits of model representation. Reliable representation of form allows the modeller to concentrate on the physical aspects of model parameterization, whilst minimizing the conflation of parameter effects with those of poorly constrained geometric representation. Copyright (C) 2003 John Wiley Sons, Ltd.