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Aerial frames and satellite imagery are widely recognized data sources from which to produce maps. For volcanoes, maps enable the quantification of erupted ash and the destruction caused. The last eruptive sequence on Deception Island was endured from 1967 to 1970. Analogue maps were produced via classical photogrammetric methods with a high degree of human intervention mainly to analyse the volcanic-centres areas only. However, historical aerial frames cover the whole of Deception Island. Structure from motion photogrammetry, a near-automated compilation of digital image processing strategies, minimizes the degree of human intervention to produce orthographic mosaics and digital elevation models from digital aerial frames. Orthographic mosaics were produced from historical aerial frames of 1956 and 1968, and a Kompsat-3 image of 2020. Their shared root-mean-square deviation was 1.8 m and 1.7 m in easting and northing, respectively, at ground control points measured with phase-differential global navigation satellite systems. The digital elevation models were processed with a root-mean-square deviation of 2.3 m and 3.6 m from 1956 and 1968 aerial frames, respectively. As the first application, erupted ashfall and the subsequent destruction, mainly at the former Chilean and British bases, were identified, and the volume of erupted ash was assessed to be over 0.16 km3 within the area mapped by these new digital cartographic products. [ABSTRACT FROM AUTHOR]

Thermokarst lakes and ponds are a common landscape feature resulting from permafrost thaw, but their intense greenhouse gas emissions are still poorly constrained as a feedback mechanism for global warming because of their diversity, abundance, and remoteness. Thermokarst waterbodies may be small and optically diverse, posing specific challenges for optical remote sensing regarding detection, classification, and monitoring. This is especially relevant when accounting for external factors that affect water reflectance, such as scattering and vegetation shadow casts. In this study, we evaluated the effects of shadowing across optically diverse waterbodies located in the forest–tundra zone of northern Canada. We used ultra-high spatial resolution multispectral data and digital surface models obtained from unmanned aerial systems for modeling and analyzing shadow effects on water reflectance at Earth Observation satellite overpass time. Our results show that shadowing causes variations in reflectance, reducing the usable area of remotely sensed pixels for waterbody analysis in small lakes and ponds. The effects were greater on brighter and turbid inorganic thermokarst lakes embedded in post-glacial silt–clay marine deposits and littoral sands, where the mean reflectance decrease was from -51 to -70%, depending on the wavelength. These effects were also dependent on lake shape and vegetation height and were amplified in the cold season due to low solar elevations. Remote sensing will increasingly play a key role in assessing thermokarst lake responses and feedbacks to global change, and this study shows the magnitude and sources of optical variations caused by shading that need to be considered in future analyses. [ABSTRACT FROM AUTHOR]

Fogo in the Cabo Verde archipelago off western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard both to local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1800 ma.s.l. The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. During December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle (UAV) and real-time kinematic (RTK) global navigation satellite system (GNSS), with the objective of improving the terrain models and visible imagery derived from satellite platforms, from metric to decimetric resolution and accuracy. The main result is a very high resolution and quality 3D point cloud with a root mean square error of 0.08 m in X , 0.11 m in Y and 0.12 m in Z , which fully covers the most recent lava flows. The survey comprises an area of 23.9 km2 and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. The dense point cloud, digital surface models and orthomosaics with 25 and 10 cm resolutions, a 50 cm spaced elevation contour shapefile, and a 3D texture mesh, as well as the full aerial survey dataset are provided. The delineation of the 2014/15 lava flows covers an area of 4.53 km2 , which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km2. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of the flow geometry and to the exclusion of the areas corresponding to kīpukas (outcrops surrounded by lava flows). Our study provides a very high resolution dataset of the areas affected by Fogo's latest eruption and is a case study supporting the advantageous use of UAV aerial photography surveys in disaster-prone areas. This dataset provides accurate baseline data for future eruptions, allowing for different applications in Earth system sciences, such as hydrology, ecology and spatial modelling, as well as to planning. The dataset is available for download at 10.5281/zenodo.4718520 (Vieira et al., 2021). [ABSTRACT FROM AUTHOR]

Fogo in the Cape Verde archipelago off Western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard to both local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1,800?m above sea level The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. In December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle and RTK GNSS, with the objective of improving the mapping accuracy derived from satellite platforms. The main result is an ultra-high resolution 3D point cloud with a Root Mean Square Error of 0.08 m in X, 0.11 m in Y and 0.12 m in Z, which provides unprecedented accuracy. The survey covers an area of 23.9 km2 and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. A digital surface model and an orthomosaic with 25 cm resolution are provided, together with elevation contours with an equidistance of 50 cm and a 3D texture mesh for visualization purposes. The delineation of the 2014-15 lava flows shows an area of 4.53 km2 by lava, which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km2. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of flow geometry and the exclusion of the areas corresponding to kipukas. Our study provides an ultra high-resolution dataset of the areas affected by Fogo's latest eruption - crucial for local planning - and provides a case study to determine the advantages of ultra high-resolution UAV surveys in disaster-prone areas. [ABSTRACT FROM AUTHOR]

The mountainous and ice-free terrains of the maritime Antarctic generate complex mosaics of snow patches, ranging from tens to hundreds of metres. These can only be accurately mapped using high-resolution remote sensing. In this paper we evaluate the application of radar scenes from TerraSAR-X in High Resolution SpotLight mode for mapping snow patches at a test area on Fildes Peninsula (King George Island, South Shetlands). Snow-patch mapping and characterization of snow stratigraphy were conducted at the time of image acquisition on 12 and 13 January 2012. Snow was wet in all studied snow patches, with coarse-grain and rounded crystals showing advanced melting and with frequent ice layers in the snow pack. Two TerraSAR-X scenes in HH and VV polarization modes were analysed, with the former showing the best results when discriminating between wet snow, lake water and bare soil. However, significant overlap in the backscattering signal was found. Average wet-snow backscattering was --18.0 dB in HH mode, with water showing --21.1 dB and bare soil showing --11.9 dB. Single-band pixel-based and object-oriented image classification methods were used to assess the classification potential of TerraSAR-X SpotLight imagery. The best results were obtained with an object-oriented approach using a watershed segmentation with a support vector machine (SVM) classifier, with an overall accuracy of 92% and Kappa of 0.88. The main limitation was the west to north-west facing snow patches, which showed significant error, an issue related to artefacts from the geometry of satellite imagery acquisition. The results show that TerraSAR-X in SpotLight mode provides high-quality imagery for mapping wet snow and snowmelt in the maritime Antarctic. The classification procedure that we propose is a simple method and a first step to an implementation in operational mode if a good digital elevation model is available. [ABSTRACT FROM AUTHOR]

Serra da Estrela is an elevated granite massif in central Portugal, characterized by extensive plateau surfaces incised by deep valleys affected by Quaternary glaciation, bounded by steep fault-generated escarpments. The presence of seven major textural variants of granite provides an opportunity to study the relationships between lithology and relief, whereas DEM analysis helped to show the relationships between lithology and topography objectively. The higher ground is associated with fine- to medium-grained granites and is typified by planar surfaces of low gradient, with occasional angular tors and rock pedestals. Block fields built by angular material are common in the parts that were not previously glaciated. Less elevated parts of the plateau are supported by medium- to coarse-grained granites and show more varied topography, with an abundance of tors, boulder piles, and depressions. Lithological boundaries locally coincide with slope breaks but this is not the rule. In the northern part of the massif a deep topographic basin has evolved in biotite granite, whereas deeply incised valleys follow major fault lines. Geological controls show a hierarchy, in that gross relief reflects the pattern of tectonic uplift and subsidence, whereas lithology and then fracture patterns become more and more important if one focuses on smaller and smaller landforms. [ABSTRACT FROM AUTHOR]

The warming of high latitudes climate is enhancing the degradation of ground-ice and inducing important landscape changes across the Arctic. This new Arctic state affects geomorphological dynamics, hydrology, and ecosystems, and poses challenges to the stability of infrastructure and livelihoods of Arctic communities. This study focuses on the hamlet of Paulatuk within the Inuvialuit Settlement Region of the Amundsen Gulf, south Darnley Bay, in northern Canada. In the summer of 2019, an ultra-high resolution aerial survey with a fixed-wing Unmanned Aerial Vehicle (UAV) was conducted, generating a 5 cm spatial resolution orthomosaic and Digital Surface Model (DSM). These, together with field observations were used to produce a very-high resolution geomorphological map of the settlement and surrounding coastal areas. Landscape changes were analyzed using historical aerial imagery of 1975 and 1993, the 2019 UAV survey and a very-high resolution Pléiades satellite scene from 2020. The area is a tundra terrace made up of sandy fluvioglacial sediments affected by a dense network of ice-wedge polygons, mostly high-centered, but also low-centered, showing signs of permafrost degradation. Air and ground temperatures have increased respectively by 0.8 and 1.9 °C over last two decades at Paulatuk, and inter-polygon ponds surface increased by 23,000 m2 since 1975 due to ice-wedge thawing. The airstrip enhanced thaw pond formation on its margins, especially after 1993. The DSM reveals a depression south of the airstrip, which can be potentially flooded due to its proximity to the coastal waters. • Air and ground temperatures increased significantly over the two last decades leading to permafrost degradation. • Infrastructures participate in increasing surficial water retention at their margin, disrupting ground-thermal regime. • High-centered ice-wedges polygons and inter-polygon ponds revealed advanced signs of degradation due to ground-ice thawing. • A low depression basin is subject to marine submersion associated with relative sea level rise scenarios by 2100. [ABSTRACT FROM AUTHOR]