Abstract
Abstract. The work stems from a joint study between the Laboratory ASTRO (Department of Civil and Industrial Engineering – University of Pisa), the municipality of Pisa and the province of Arezzo on the advanced analysis and use of digital elevation data. Besides, it is framed in the research carried on by ASTRO about the definition of the priority informative layers for emergency management in the territory, as of PRIN 2008. Specifically, this work is in continuity with other already published results concerning rigorous accuracy checks of LIDAR data and testing of the procedures to transform raw data in formats consistent with CTR and survey data. The analysis of sections of riverbed, derived from interpolation by DTMs featuring different grid density with those detected topographically, is presented. Validation by differential GNSS methodology of the DTMs used showed a good overall quality of the model for open, low-sloping areas. Analysis of the sections, however, has shown that the representation of small or high-sloping (ditches, embankments) morphological elements requires a high point density such as in laser scanner surveys, and a small mesh size of the grid. In addition, the correct representation of riverside structures is often hindered by the presence of thick vegetation and poor raw LIDAR data filtering.
Highlights
The work stems from a joint study, between the ASTRO Laboratory of the Department of Civil and Industrial Engineering – University of Pisa, the municipality of Pisa and the province of Arezzo, about analysis and advanced use of digital elevation data, and is included in the research that the Laboratory ASTRO is carrying on about the definition of the primary informative layers for emergency management in the territory, as defined by PRIN 2008 project
The present work suggests some conclusions. It confirms the good overall accuracy of digital elevation models obtained from Lidar measurements
The results are not always optimal in the presence of thick vegetation. Both problems are common in the study of riverside areas the sections obtained by interpolation from digital elevation models (DTMs) have often proved of good quality, differing from those detected topographically only in some cases
Summary
Some insights are provided on the integration between the different topographical databases and the implications that these additions may have on aspects of planning, that play some important economic interests For these purposes, FEMA (Federal Emergency Management Agency) recommends using a high-density, high-precision model. In Italy, thanks to the Lidar-based national remote sensing plan for the updating of the database of the National Cartographic Portal (NCP) digital elevation models of some river courses, all shorelines and areas of high hydrogeological criticality have been produced. These models can be considered compliant with the requirements of FEMA. Validation of the test area used for checking in the present work, the shaft of Sovara Creek, a right-hand tributary of the Tiber River, involved a hundred points distributed in the area with particular attention in order to homogenize the GNSS validation surveys with DTM regarding the framing in planimetric and altimetric data and exclude in advance some possible systematic errors (Figure 1)
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