Investigating the use of UAV systems for photogrammetric applications : a case study of Ramla Bay (Gozo, Malta)

In this study, we present the 3D digital model of Ramla Bay (Gozo) obtained by using photograms taken from drones. The high-resolution 3D model of Ramla Bay allowed the construction of a detailed Digital Elevation Model (DEM). Comparison of an earlier LIDAR data derived DEM (ERDF 156 Data, 2013) and the photogrammetric DEM developed in this study allowed to make preliminary observations regarding the potential evolution of the coastal area over the last 5 years. This study serves as a proof of concept to demonstrate that coastal evolution can be quantitatively analysed in terms of changes of the sand dune systems. Furthermore, the technique used in this paper represents a good compromise in terms of cost effectiveness and a valid substitute for laser scanner survey. It is also useful for monitoring the dynamics of the beach-dune system and the characterization of the coast for the mitigation of coastal erosion.peer-reviewe

Assessing Shallow Soft Deposits through Near-Surface Geophysics and UAV-SfM: Application in Pocket Beaches Environments

This study employs a multimethod approach to investigate the sediment distribution in two pocket beaches, Ramla Beach and Mellieha S Beach, in Malta. Both study sites were digitally reconstructed using unmanned aerial vehicle (UAV) photogrammetry. For each case, an ERT and a dense network of ambient seismic noise measurements processed through a horizontal-to-vertical spectral ratio (HVSR) technique were acquired. Electrical resistivity tomography (ERT) analysis enables the estimation of sediment thickness in each beach. HVSR analysis revealed peaks related to beach sediments overlying limestone rocks in both sites and also indicated a deeper stratigraphic contact in Mellieha S Beach. Based on ERT measurements, sediment thickness is calculated for each HVSR measurement. Interpolation of results allows for bedrock surface modelling in each case study, and when combined with digital terrain models (DTMs) derived from photogrammetric models, sediment volumes are estimated for each site. The geometry of this surface is analyzed from a geological perspective, showing structural control of sediment distribution due to a normal fault in Mellieha S Beach and stratigraphic control facilitated by a highly erodible surface in Ramla Beach. The results emphasize the importance of adopting a three-dimensional perspective in coastal studies for precise sediment volume characterization and a deeper understanding of pocket beach dynamics. This practical multimethod approach presented here offers valuable tools for future coastal research and effective coastal management, facilitating informed decision making amidst the growing vulnerability of coastal zones to climate change impacts

Evaluating characteristics of an active coastal spreading area combining geophysical data with satellite, aerial, and unmanned aerial vehicles images

The northern region of the Maltese archipelago is experiencing lateral spreading landslide processes. This region is characterized by cliffs with a hard coralline limestone outcropping layer sitting on a thick layer of clay. Such a geological configuration causes coastal instability that results in lateral spreading which predispose to rockfalls and topplings all over the cliff slopes. The aim of this research was to develop a methodology for evaluating cliff erosion/retreat using the integration of geomatics and geophysical techniques. Starting from a 3D digital model of the Selmun promontory, generated by unmanned aerial vehicle (UAV) photogrammetry, it was possible to map the fractures and conduct geophysical measurements such as electrical resistivity tomography and ground penetrating radar for the identification and mapping of vertical fractures affecting the hard coralline limestone plateau, and to create a 3D geological model of the study area. In addition to this, high-accuracy orthophotos from UAV that were captured between 1957 and 2021 were georeferenced into a GIS and compared to aerial and satellite images. The movement and evolution of boulders and cracks in rocks were then vectorized to highlight, track and quantify the phenomenon through time. The results were used to derive a qualitative assessment of the coastal variations in the geometric properties of the exposed discontinuity surfaces to evaluate the volumes and the stop points of the observed rockfalls. The outcomes of this research were finally imported in a GIS which offers an easy approach for the collection and processing of coastal monitoring data. In principle, such a system could help local authorities to address social, economic and environmental issues of pressing importance as well as facilitate effective planning in view of a risk mitigation strategy

Seismic Monitoring Tool for Tidal-Forced Aquifer Level Changes in the Río de la Plata Coastal Plain, Argentina

Ambient seismic noise has gained extensive applications in seismology and plays a pivotal role in environmental seismic studies. This study focuses on the Río de la Plata Coastal Plain, employing the horizontal-to-vertical spectral ratio (HVSR) method on ambient seismic noise records to analyze subsurface dynamics. The region’s hydrogeology is complex, featuring partially interconnected coastal aquifers. The HVSR analysis reveals two peaks, with P0 associated with the sediment-basement interface and P1 linked to a shallower stratigraphic discontinuity. Temporal analysis of P1 highlights cyclical patterns correlated with estuarine levels, suggesting a relationship between variations in seismic velocities and tidal dynamics. Comparisons with aquifer data support the hypothesis that tidal variations influence subsurface mechanical properties, impacting the HVSR function. The study hints at the potential of ambient seismic noise analysis as a non-invasive and cost-effective method for studying coastal aquifers and understanding groundwater dynamics. Ongoing research aims to further explore these relationships for enhanced groundwater resource management

Integrated geophysical and geomatic studies at Ghar Dalam Cave, Malta’s oldest prehistoric site

The Ghar Dalam cave, southern Malta, hosts the oldest human evidence in the Maltese archipelago. Although the internal stratigraphy of the cave and its biotic record is well studied, the possibility of archaeological / paleontological prospects in the surrounding areas requires additional studies. In this work we use aerial and ground-based photogrammetry to reconstruct the interior and the surface of the cave, and various geophysical techniques (GPR, passive seismic and ERT) to study the subsurface of the cave and its surroundings. The results have clarified the geometry of the soil-rock contact above and at the entrance of the cave and possible karstic structures have been identified. The authors conclude that this multidisciplinary methodology allows more reliable results to be achieved and is essential for studies where direct observation is not possible.peer-reviewe

Evaluación de las reservas en lentes de agua dulce en el estuario exterior del río de la Plata

El objetivo del trabajo fue definir la morfología de la lente de agua dulce asociada a depósitos de espigas y crestas de playa arenosas formados durante la evolución cuaternaria del estuario exterior del Río de la Plata y el litoral marino adyacente.Centro de Investigaciones del MedioambienteCentro de Investigaciones Geológica

Use of UAVs and deep learning for beach litter monitoring

Stranded beach litter is a ubiquitous issue. Manual monitoring and retrieval can be cost and labour intensive. Therefore, automatic litter monitoring and retrieval is an essential mitigation strategy. In this paper, we present important foundational blocks that can be expanded into an autonomous monitoring-and-retrieval pipeline based on drone surveys and object detection using deep learning. Drone footage collected on the islands of Malta and Gozo in Sicily (Italy) and the Red Sea coast was combined with publicly available litter datasets and used to train an object detection algorithm (YOLOv5) to detect litter objects in footage recorded during drone surveys. Across all classes of litter objects, the 50%–95% mean average precision (mAP50-95) was 0.252, with the performance on single well-represented classes reaching up to 0.674. We also present an approach to geolocate objects detected by the algorithm, assigning latitude and longitude coordinates to each detection. In combination with beach morphology information derived from digital elevation models (DEMs) for path finding and identifying inaccessible areas for an autonomous litter retrieval robot, this research provides important building blocks for an automated monitoring-and-retrieval pipeline.peer-reviewe

Proximity remote sensing : preliminary results at the Batia Church (Tortorici, Sicily)

The paper presents the results of scientific investigations carried out at the Batia Church located in the small village of Tortorici (Messina, Sicily). We performed several geophysical surveys and reconstruct 2D and 3D digital models of the monument using digital photogrammetry. From the 3D model accurate digital elevation models. A detail mapping was carried out using the derived 3D digital model identifying mayor fractures as well as quantifying the extent of original pain and the modern interventions.peer-reviewe

Integrating near-surface geophysical methods and remote sensing techniques for reconstructing fault-bounded valleys (Mellieha valley, Malta)

The island of Malta (central Mediterranean) is dissected by several WSW-trending fault-line valleys related to Miocene-Pliocene extensional tectonics. Some valleys host remnants of alluvial deposits that could provide information on possible Quaternary faulting, but the thickness of these deposits and their subsurface extent is poorly constrained. Our study aimed to investigate the structural configuration of the southern sector of the Mellieha valley, which is located in the north-west part of the island and is limited by the ENE-WSW general trending Mellieha and Ghadira faults, and their relation with a thin layer of infill sediments. We employed different near-surface geophysical techniques (electrical resistivity tomography, active and passive seismic methods, ground-penetrating radar), as well as remote sensing techniques (unmanned aerial vehicle digital photogrammetry and ground-based Light Detection and Ranging) to complement classic structural surveys. The valley structure has an asymmetric graben configuration, being bounded by a normal fault to the southeast (Mellieha Fault) and other to the north-west (Ghadira Fault). Our study provides insights of possible Quaternary fault displacements and revealed the presence of an additional fault splay, the previously unmapped NNW-dipping Mellieha Fault 2 at the south-eastern edge of the valley. Additionally, by integrating results from geophysical surveys, we estimated the thickness of the valley's recent deposits, being thicker towards the Mellieha Bay sector, with maximum values of 8–10 m. Our study aligns with the general model of horst and graben structuring with associated regional tilting since the late Miocene, and supports the hypothesis that some segments of NW-trending normal faults within the North Malta Graben exhibit Quaternary activity, although with minimal throw rates (<< 0.1 mm/yr).peer-reviewe

Diagnostic investigation of the Cycle of the new church of Sarria (Floriana, Malta) by Mattia Preti

In the present paper, we present the main results of a diagnostic investigation on different paintings by Mattia Preti, belonging to the Cycle of the New Church of Sarria, located inside the Church of the Immaculate Conception of Sarria (Floriana) in Malta. The analysis was carried out on the occasion of the restoration process and, due to the short time available, only on some representative areas of each painting. A multi-technique approach was applied in situ, employing X-ray fluorescence spectroscopy (XRF) and Raman microscopy. The aim was to achieve information on the execution technique, in a completely non-invasive way, following the requirements of the restorers.peer-reviewe