An objective approach for feature extraction: distribution analysis and statistical descriptors for scale choice and channel network identification

A statistical approach to LiDAR derived topographic attributes for the automatic extraction of channel network and for the choice of the scale to apply for parameter evaluation is presented in this paper. The basis of this approach is to use distribution analysis and statistical descriptors to identify channels where terrain geometry denotes significant convergences. Two case study areas with different morphology and degree of organization are used with their 1 m LiDAR Digital Terrain Models (DTMs). Topographic attribute maps (curvature and openness) for various window sizes are derived from the DTMs in order to detect surface convergences. A statistical analysis on value distributions considering each window size is carried out for the choice of the optimum kernel. We propose a three-step method to extract the network based (a) on the normalization and overlapping of openness and minimum curvature to highlight the more likely surface convergences, (b) a weighting of the upslope area according to these normalized maps to identify drainage flow paths and flow accumulation consistent with terrain geometry, (c) the standard score normalization of the weighted upslope area and the use of standard score values as non subjective threshold for channel network identification. As a final step for optimal definition and representation of the whole network, a noise-filtering and connection procedure is applied. The advantage of the proposed methodology, and the efficiency and accurate localization of extracted features are demonstrated using LiDAR data of two different areas and comparing both extractions with field surveyed networks

INVESTIGATING THE PERFORMANCE OF A HANDHELD MOBILE MAPPING SYSTEM IN DIFFERENT OUTDOOR SCENARIOS

In recent years, portable Mobile Mapping Systems (MMSs) are emerging as valuable survey instruments for fast and efficient mapping of both internal and external environments. The aim of this work is to assess the performance of a commercial handheld MMS, Gexcel HERON Lite, in two different outdoor applications. The first is the mapping of a large building, which represents a standard use-case scenario of this technology. Through the second case study, that consists in the survey of a torrent reach, we investigate instead the applicability of the handheld MMS for natural environment monitoring, a field in which portable systems are not yet widely employed. Quantitative and qualitative assessment is presented, comparing the point clouds obtained from the HERON Lite system against reference models provided by traditional techniques (i.e., Terrestrial Laser Scanning and Photogrammetry)

Air temperature variability over three glaciers in the Ortles-Cevedale (Italian Alps): Effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

Glacier mass balance models rely on accurate spatial calculation of input data, in particular air temperature. Lower temperatures (the so-called glacier cooling effect), and lower temperature variability (the so-called glacier damping effect) generally occur over glaciers, compared to ambient conditions. These effects, which depend on the geometric characteristics of glaciers and display a high spatial and temporal variability, have been mostly investigated on medium- to large-size glaciers so far, while observations on smaller ice bodies are scarce. Using a dataset from 8 on-glacier and 4 off-glacier weather stations, collected in summer 2010 and 2011, we analyzed the air temperature distribution variability and wind regime over three different glaciers in the Ortles-Cevedale. The magnitude of the cooling effect and the occurrence of katabatic boundary layer (KBL) processes showed remarkable differences among the three ice bodies, highlighting suggesting the likely existence of important reinforcing mechanisms during glacier decay and disintegration. None of the methods proposed in the literature for calculating on-glacier temperature from off-glacier data fully reproduced our observations. Among them, the more physically-based procedure of Greuell and B\uf6hm [1998] provided the best overall results where the KBL prevail, but it was not effective elsewhere (i.e. on smaller ice bodies and close to the glacier margins). The accuracy of air temperature estimations strongly impacted the results from a mass balance model which was applied to the three investigated glaciers. Most importantly, even small temperature deviations caused distortions in parameter calibration, thus compromising the model generalizability

Automatic measurement of glacier ice ablation using thermistor strings

In this work we tested the suitability of thermistor strings as automatic tools for the continuous measurement of glacier ice ablation. Experimental data collected in summer 2017 over an Italian glacier provided ice ablation readings with accuracy similar to manual measurements with ablation stakes and other automatic systems, like the draw-wire method and the B\uf8ggild ablatometer. Thermistor strings have potential for future applications in remote glacier monitoring, thanks to their flexibility, simple construction, and robustness

4D-SFM photogrammetry for monitoring sediment dynamics in a debris-flow catchment: Software testing and results comparison

In recent years, the combination of Structure-from-Motion (SfM) algorithms and UAV-based aerial images has revolutionised 3D topographic surveys for natural environment monitoring, offering low-cost, fast and high quality data acquisition and processing. A continuous monitoring of the morphological changes through multi-temporal (4D) SfM surveys allows, e.g., to analyse the torrent dynamic also in complex topography environment like debris-flow catchments, provided that appropriate tools and procedures are employed in the data processing steps. In this work we test two different software packages (3DF Zephyr Aerial and Agisoft Photoscan) on a dataset composed of both UAV and terrestrial images acquired on a debris-flow reach (Moscardo torrent - North-eastern Italian Alps). Unlike other papers in the literature, we evaluate the results not only on the raw point clouds generated by the Structure-from- Motion and Multi-View Stereo algorithms, but also on the Digital Terrain Models (DTMs) created after post-processing. Outcomes show differences between the DTMs that can be considered irrelevant for the geomorphological phenomena under analysis. This study confirms that SfM photogrammetry can be a valuable tool for monitoring sediment dynamics, but accurate point cloud post-processing is required to reliably localize geomorphological changes

The current deglaciation of the Ortles-Cevedale massif (Eastern Italian Alps): impacts, controls and degree of imbalance.

The Ortles-Cevedale is the largest glacierized mountain group of the Italian Alps hosting 112 ice bodies, with a total area of 76.8 km2. Since the 1980\u2019s, this massif is undergoing a rapid deglaciation, as most of the mountain ranges in the European Alps. The aims of this work were: i) to quantify area and volume change of the Ortles- Cevedale glacier system from the 1980s to the 2000s; ii) to improve the knowledge of factors controlling the spatial variability of the deglaciation; and iii) to assess the degree of imbalance of individual glaciers with respect to the present climate conditions. Two inventories were created, based on Landsat5 TM scenes of 20-09-1987 and 31-08-2009. Contrast-enhanced composites (bands TM5, TM4 and TM3), aerial photos and field surveys (for the most recent period) were used to correct the automatic delineation of glaciers derived from a hard classification based on a threshold applied to a TM3/TM5 ratio image. Since Landsat scenes were acquired at the end of the ablation seasons and fresh snow was absent, the accumulation areas could be roughly determined by mapping the snow covered area. This region was identified from the difference in reflectance between snow and ice in the near infrared band of Landsat (TM4), and mapped after correcting topographic effects to determine surface reflectance. The area-averaged geodetic mass budget was then calculated for the individual glaciers by differencing two Digital Terrain Models (2000s minus 1980s, derived from LiDAR and aerial photogrammetry) and combining the result with the glacier outlines. Afterwards, we examined the mass balance data using statistical analyses (Correlation matrices, Principal Component Analysis, Cluster Analysis). This allowed us highlighting clusters of glaciers, which exhibit a similar behavior, identify the outlayers and the relative influence of the factors controlling spatial variability of the mass losses. Finally, we assessed the degree of imbalance of individual glaciers by comparing the current Accumulation Area Ratios (AAR) with the balanced-budget AAR (AAR0), the latter also accounting for the debris cover of glaciers. We found that the total area loss of the Ortles-Cevedale glaciers from 1987 to 2009 amounts to 23.5 km2, i.e. 23.4% of the initial area. On the other hand, the AAR of the entire glacier system was 0.3 in both investigated years. The overall debris cover increased from 10.5% to 16.3%. The geodetic mass balance rate was -0.7 m w.e. y1(as an average on 112 ice bodies), ranging from -0.1 to -1.7 m w.e. y1. We also found that the main controls of the differing change of single glaciers are related to their hypsometry (elevation range and slope), AAR, feeding source and debris cover. Interestingly, a significant correlation was found between AAR, AAR0 and debris cover. This information was used to assess and visualize the needed additional reduction of individual glaciers to reach equilibrium with the current size of their accumulation areas. This amounts on average to a further reduction of 40% of the current areal extent of glaciers

Modello morfo-energetico di fusione

software versione Win98 e manuale per l'utent

Progetto di massima e sperimentale rivolto al riordino del vincolo idrogeologico all\u2019interno di un bacino idrogeografico campione situato nel Collio Goriziano

Regione Friuli Venezia-Giulia, Direzione Regionale delle Risorse Agricole, Forestali e Natural