Abstract
In volcanic areas, where it can be difficult to perform direct surveys, digital photogrammetry techniques are rarely adopted for routine volcano monitoring. Nevertheless, they have remarkable potentialities for observing active volcanic features (e.g., fissures, lava flows) and the connected deformation processes. The ability to obtain accurate quantitative data of definite accuracy in short time spans makes digital photogrammetry a suitable method for controlling the evolution of rapidly changing large-area volcanic phenomena. The systematic acquisition of airborne photogrammetric datasets can be adopted for implementing a more effective procedure aimed at long-term volcano monitoring and hazard assessment. In addition, during the volcanic crisis, the frequent acquisition of oblique digital images from helicopter allows for quasi-real-time monitoring to support mitigation actions by civil protection. These images are commonly used to update existing maps through a photo-interpretation approach that provide data of unknown accuracy. This work presents a scientific tool (Orthoview) that implements a straightforward photogrammetric approach to generate digital orthophotos from single-view oblique images provided that at least four Ground Control Points (GCP) and current Digital Elevation Models (DEM) are available. The influence of the view geometry, of sparse and not-signalized GCP and DEM inaccuracies is analyzed for evaluating the performance of the developed tool in comparison with other remote sensing techniques. Results obtained with datasets from Etna and Stromboli volcanoes demonstrate that 2D features measured on the produced orthophotos can reach sub-meter-level accuracy.
Highlights
In active volcanic areas, the continuous monitoring of surface variations provides a fundamental contribution for a better understanding of the dynamics of the system
A number of tests were conducted in active volcanic areas for evaluating the performance of the Orthoview tool and for assessing the effects of operational constraints, such as not-optimal acquisition views and lack of recent maps for measuring Ground Control Points (GCP)
Recent eruptions of Etna and Stromboli volcanoes were selected as test cases according to the availability of oblique helicopter photos, acquired during or after the active phases, as well as of high resolution reference digital orthophotos and Digital Elevation Models (DEM) acquired before the beginning of the eruptions
Summary
The continuous monitoring of surface variations provides a fundamental contribution for a better understanding of the dynamics of the system. Ground deformations are typically measured through geodetic methods, such as Global Positioning System (GPS), total stations and leveling surveys, clinometers, terrestrial radar interferometry These methods track localized deformation processes, provided that fixed networks/stations have been established in quiescent periods. By comparing DEMs at subsequent epochs, mass balance analysis can be performed (volume estimation, erosion/accumulation rates, etc.), Digital orthophotos can be used to produce and update maps relevant for understanding the evolution of the volcanic processes. This type of monitoring approach was recently applied to volcanic areas in the world during eruptive and post-eruption phases [1,2,3,4,5]. Such rigorous surveys allow obtaining high quality data but they require a great effort both for data processing and for measuring a well-distributed
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