distributed mass balance modelling on two neighbouring glaciers in ortles cevedale italy from 2004 to 2009

AbstractA 6 year application of an enhanced temperature-index mass-balance model to Careser and La Mare glaciers, Eastern Italian Alps, is presented. The two glaciers exhibit very different characteristics, and a comprehensive dataset of distributed mass-balance measurements was used to test the model performance. The model was run using meteorological data acquired outside the glaciers. The work was focused on two main aspects: (1) the development of a morphological redistribution procedure for snow, and (2) the comparison of three different melt algorithms proposed in the literature. The results show that the simple method proposed for snow redistribution can greatly improve simulation of winter balance, and further improvements would be achievable by collecting data on inaccessible and high-altitude areas. All three melt formulations displayed a good skill level and very similar results in modelling the mass-balance distribution over glacier areas, with slightly better results from a multiplicative algorithm in capturing the vertical balance gradient. The simulation errors are related to aspect and elevation, and tend to be spatially aggregated. Some assumptions concerning the spatial and temporal distribution of air temperature and incoming solar radiation, although reasonable and widely used in the literature, may be responsible for this aggregation. Hence, there is a need to further investigate the processes that regulate the distribution of melt energy, and that appear to control the current deglaciation phase in this area

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

Downstream hydraulic geometry relationships: Gathering reference reach-scale width values from LiDAR

This paper examines the ability of LiDAR topography to provide reach-scale width values for the analysis of downstream hydraulic geometry relationships along some streams in the Dolomites (northern Italy). Multiple reach-scale dimensions can provide representative geometries and statistics characterising the longitudinal variability in the channel, improving the understanding of geomorphic processes across networks. Starting from the minimum curvature derived from a LiDAR DTM, the proposed algorithm uses a statistical approach for the identification of the scale of analysis, and for the automatic characterisation of reach-scale bankfull widths. The downstream adjustment in channel morphology is then related to flow parameters (drainage area and stream power). With the correct planning of a LiDAR survey, uncertainties in the procedure are principally due to the resolution of the DTM. The outputs are in general comparable in quality to field survey measurements, and the procedure allows the quick comparison among different watersheds. The proposed automatic approach could improve knowledge about river systems with highly variable widths, and about systems in areas covered by vegetation or inaccessible to field surveys. With proven effectiveness, this research could offer an interesting starting point for the analysis of differences betweenwatersheds, and to improve knowledge about downstream channel adjustment in relation, for example, to scale and landscape forcing (e.g. sediment transport, tectonics, lithology, climate, geomorphology, and anthropic pressure)

Impiego di DTM ad alta risoluzione per la misura automatica di larghezze al bankfull

The study of the morphological characteristics of rivers and of their degree morphological alterations, is a basis for a proper management of mountain watershed: the availability of detailed topographic data is a key tool. The evaluation of channel geometry variability, determined by hydrodynamic and geomorphological processes, is usually gathered through field surveys, or through visual interpretations of digital orthophotos. However, the topographic data obtained through visual interpretation are not sufficiently accurate to allow the identification and the correct mapping of channel geometries. On the other hand, even if they provide more reliable data, field surveys require considerable time and financial resources, and they are often challenged by the inaccessibility of the areas under analysis. It is therefore strategic to adopt new and more accurate methods to estimate channel geometries, based on the availability of high-resolution data, such as the one derived from airborne laser scanner (LiDAR). LiDAR technology enables the acquisition of high resolution topographic data over large areas, with vertical and horizontal accuracy of a few centimeters (10-20 cm for the vertical component and 0.5-2 m for horizontal), contributing to a better representation the Earth's surface at more affordable costs. In mountain areas many studies have explored the potential of LiDAR DTM for the proper characterization of the network and the objective of this paper is to highlight their potential in the automatic determination of values representative of bankfull widths. The analysis is based on a topographic index (Elevation Percentile) used to measure the variability of the elevation from 1 m DTM resolution. This index is derived by calculating within a moving window the number of cells with elevation higher than the central pixel. This number is then normalized to the extension of the moving window: channelized areas have an EP value greater than convex areas. Applying a statistical threshold to the EP, it is possible to obtain a Boolean map of potential river bed. The geometries derived from this map are approximated due to the resolution of the DTM, but it is possible to consider the topographic representation of the banks and to approximate the bankfull width. In an automatic manner, moving downstream along the thalweg, it is possible to estimate perpendicularly to the flow directions, the bankfull width at each point of the network, with the above-mentioned limit of the DTM resolution. Automatically derived widths show a good agreement with those detected in the field, with low values of RMSE, and the range of the estimated values is compatible with the surveyed ones

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

recognition of surface flow processes influenced by roads and trails in mountain areas using high resolution topography

AbstractRoad networks in mountainous forest landscapes have the potential to increase the susceptibility to erosion and shallow landsliding. The same issue is observed also for minor trail networks, with evidences of surface erosion due to surface flow redistribution. This could be a problem in regions such as the Italian Alps where forestry and tourist activities are a relevant part of the local economy. This is just one among the several effects of modern anthropogenic forcing: it is now well accepted by the scientific community that we are living in a new era where human activities may leave a significant signature on the Earth, by altering its morphology, and significantly affecting the related surface processes. In this work, we proposed a methodology for the automatic recognition of roads and trails induced flow direction changes. The algorithm is based on the calculation of the drainage area variation in the presence, or in the absence of anthropic features such as roads and trails on hillslopes. T..

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

Il servizio WCTS del Geoportale Nazionale

The 2007/2/CE INSPIRE directive requires every Member State to implement a set of services to facilitate the interchange of spatial data; the Coordinate Transformation Service (CTS) is one of the geometric transformation services required by the directive. The Italian National Geoportal (GN) has recently published a new set of public access services that enable the users to transform and convert the coordinate reference system of geographic data within the Italian territory using the high-accuracy correction data provided by the Istituto Geografico Militare Italiano (IGM). This article will illustrate these newly published services: a browser-based web application to transform raster and vector files or sets of coordinates and an OGC-compliant Web Coordinate Transformation Service (WCTS) that performs on the fly transformation of GML (Geography Markup Language) data

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)