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- Geografia Física em regiões de montanha: a Ilha da Madeira e as Serras da Arrábida e da Estrela. Homenagem a Orlando RibeiroPublication . Mora, Carla; Alcoforado, Maria João; Jansen, Jan; Fragoso, Marcelo; Lopes, António; Lopes, Sérgio; Vieira, GonçaloO presente livro é composto por dois textos, partindo de alguns trabalhos de Orlando Ribeiro e mostram como o Zephyrus tem estudado os temas seleccionados. O primeiro trata do clima e da vegetação da Arrábida e da Madeira, embora estes não sejam temas centrais na obra de Orlando Ribeiro. O. Ribeiro dedicou-se primeiro à investigação sobre a Arrábida, tema da sua tese de doutoramento em 1935 e estudou a Madeira em 1947 e 1948, quando preparava o livro-guia de uma das excursões do XVIº Congresso Internacional de Geografia, que o CEG de Lisboa organizou em 1949, sob a sua orientação. O segundo texto refere parte de uma investigação, feita na sequência do Projecto ESTRELA, liderado pelo Professor António de Brum Ferreira, falecido em 2013, que lembramos com saudade e admiração, e que muito contribuiu para o conhecimento da Geografia Física de Portugal, em particular no campo da Geomorfologia. Apresenta-se um estudo de unidades de paisagem, em que se investigam as interacções entre o clima, a dinâmica geomorfológica e as comunidades vegetais no circo glaciário do Covão Cimeiro, na Serra da Estrela, cuja glaciação quaternária foi inicialmente estudada por E. Fleury e H. Lautensach e, posteriormente, por Suzanne Daveau. O trabalho é feito a uma escala muito detalhada, com o objectivo de delimitar unidades de paisagem, adaptadas ao sistema de classificação de habitats Natura2000. A metodologia pode ser extrapolada e permite aplicação no ordenamento e na gestão do território. A ligação com o trabalho de Orlando Ribeiro tem aqui a ver com a selecção da metodologia (seguindo-se uma perspectiva de Geografia naturalista, focada nas inter-relações entre os elementos físicos e biofísicos da paisagem) e com os trabalhos que desenvolveu na Cordilheira Central, onde guiou excursões de numerosas gerações de geógrafos. Os dois textos mostram que, apesar da evolução dos conceitos em torno da paisagem, os trabalhos de Orlando Ribeiro são muito inovadores para a época, apresentando já a paisagem como um conceito dinâmico, resultado das relações entre geomorfologia, clima e vegetação e incluindo a marca do Homem.
- Evaluation of the use of very high resolution aerial imagery for accurate ice-wedge polygon mapping (Adventdalen, Svalbard)Publication . Lousada, Maura; Pina, Pedro; Vieira, Gonçalo; Bandeira, Lourenço; Mora, CarlaThe main objective of this paper is to verify the accuracy of delineating and characterizing ice-wedge polygonal networks with features exclusively extracted from remotely sensed images of very high resolution. This kind of mapping plays a key role for quantifying ice-wedge degradation in warming permafrost. The evaluation of mapping a network is performed in this study with two sets of aerial images that are compared to ground reference data determined by fieldwork on the same network, located in Adventdalen, Svalbard (78°N). One aerial dataset is obtained from a photogrammetric survey with RGB+NIR imagery of 20cm/pixel, the other from an UAV (Unmanned Aerial Vehicle) survey that acquired RGB images of 6cm/pixel of spatial resolution. Besides evaluating the degree of matching between the delineations, the morphometric and topological features computed for the differently mapped versions of the network are also confronted, to have a more solid basis of comparison. The results obtained are similar enough to admit that remotely sensed images of very high resolution are an adequate support to provide extensive characterizations and classifications of this kind of patterned ground.
- Penultimate Glacial Cycle glacier extent in the Iberian Peninsula: new evidence from the Serra da Estrela (Central System, Portugal)Publication . Vieira, Gonçalo; Palacios, David; Andrés, Nuria; Mora, Carla; Vázquez Selem, Lorenzo; Woronko, Barbara; Soncco, Carmen; Úbeda, Jose; Goyanes, GabrielThe objective of this work is to present a first assessment on the age of the glacial features of the Serra da Estrela, in the central Portugal, Iberian Peninsula (40°19′ N, 7°37′ W, 1993 m), using Cosmic-Ray Exposure dating (in situ cosmogenic 36Cl). A total of 6 samples were dated, 4 extracted from exposed moraine boulders and 2 from glacially polished bedrock surfaces. Despite the low number of samples, the results are consistent, reinforcing previous dating obtained by other methods and geomorphological and paleoclimatic information. The maximum extension of the glaciers occurred at the end of the Penultimate Glacial Cycle (Marine Isotope Stage 6), during Heinrich Stadial 11, around 140 ka. At the end of the Last Glacial Cycle, slightly before the Last Glacial Maximum, at around 30 ka, the Estrela glaciers reached again a similar extent. Finally, the glaciers disappeared fromthe Serra da Estrela at the beginning of the Bølling-Allerød Interstadial, at around 14.2 ka. These data confirm a certain synchronicity in the major glacial phases in most the Mediterranean and also European mountains, although there are notable differences in the maximum extent in the two cycles.
- A trained Mask R-CNN model over PlanetScope imagery for very-high resolution surface water mapping in boreal forest-tundraPublication . Freitas, Pedro; Vieira, Gonçalo; Canário, João; Vincent, Warwick F.; Pina, Pedro; Mora, CarlaSmall water bodies (< 0.01 km2) showing diverse limnological properties occur in great abundance across the boreal forest and tundra landscapes of the Arctic and Subarctic. However, their classification, geographical distribution and collective importance for water, heat, nutrient, contaminant and carbon cycles are still poorly constrained. One important step for better understanding the role and evolution of small water bodies in the fast-changing northern landscapes is to develop image analysis protocols that allow their automatic remote sensing detection, delineation and inventory. In this study, we set an image analysis protocol (High Latitude Water – HLWATER V1.0) based on a trained supervised Mask R-CNN deep learning model over PlanetScope imagery for the automatic detection and delineation of small lakes and ponds that were absent in existing datasets. Most of our training dataset comprised water bodies smaller than 0.01 km2 (97%) and spanned a wide range of environmental and hydrological settings, from the sporadic to the continuous permafrost zones of Canada. The model was tested as a fully autonomous approach for eastern Hudson Bay, Nunavik (Subarctic Canada), a region that poses challenges for water remote sensing given the abundance and variety of small water bodies. These are mainly permafrost thaw and glacial basin ponds in the boreal forest-tundra in challenging optical settings influenced by vegetation or topography shadowing, or revealing peat water logging, fen and bog pond conditions. A multi-scale validation approach was developed using water body delineations from PlanetScope imagery and ultra-high resolution orthomosaics from Unoccupied Aerial Systems. This procedure allowed a sub-pixel assessment and identified the limitations and strengths of the trained model for detecting small and large water bodies. The results varied according to different landscape units, with mean Intersection over Union (IoU) 0.5 F1 Scores of 0.53 to 0.71 and mean F1 Scores of 0.62 to 0.95. Considering 166 m2 as the minimum pond size detection threshold, the IoU 0.5 F1 Scores were 0.7 to 0.91 and F1 Scores were 0.76 to 0.83, evaluated by comparing the model results with ultra-high resolution manual delineations. The image analysis protocol and trained model show high potential for extension to other boreal forest-tundra regions of the Arctic and Subarctic, allowing for detailed inventories of optically and morphologically diverse small water bodies over large areas of the circumpolar North.
- Permafrost conditions in the Mediterranean region since the Last GlaciationPublication . Oliva, Marc; Žebre, M.; Guglielmin, M.; Hughes, P.D.; Çiner, A.; Vieira, Gonçalo; Bodin, X.; Andrés, N.; Colucci, R.R.; García-Hernández, C.; Mora, Carla; Nofre, J.; Palacios, D.; Pérez-Alberti, A.; Ribolini, A.; Ruiz-Fernández, J.; Sarıkaya, M.A.; Serrano, E.; Urdea, P.; Valcárcel, M.; Woodward, J.C.; Yıldırım, C.The relatively warm climate conditions prevailing today in the Mediterranean region limit cold geomorphological processes only to the highest mountain environments. However, climate variability during the Late Pleistocene and Holocene has led to significant spatio-temporal variations of the glacial and periglacial domain in these mountains, including permafrost conditions. Here, we examine the distribution and evolution of permafrost in the Mediterranean region considering five time periods: Last Glaciation, deglaciation, Holocene, Little Ice Age (LIA) and present-day. The distribution of inactive permafrost-derived features as well as sedimentary records indicates that the elevation limit of permafrost during the Last Glaciation was between 1000 m and even 2000 m lower than present. Permafrost was also widespread in non-glaciated slopes above the snowline forming rock glaciers and block streams, as well as meter-sized stone circles in relatively flat summit areas. As in most of the Northern Hemisphere, the onset of deglaciation in the Mediterranean region started around 19-20 ka. The ice-free terrain left by retreating glaciers was subject to paraglacial activity and intense periglacial processes under permafrost conditions. Many rock glaciers, protalus lobes and block streams formed in these recently deglaciated environments, though most of them became gradually inactive as temperatures kept rising, especially those at lower altitudes. Following the Younger Dryas glacial advance, the Early Holocene saw the last massive deglaciation in Mediterranean mountains accompanied by a progressive shift of permafrost conditions to higher elevations. It is unlikely that air temperatures recorded in Mediterranean mountains during the Holocene favoured the existence of widespread permafrost regimes, with the only exception of the highest massifs exceeding 2500-3000 m. LIA colder climate promoted a minor glacial advance and the spatial expansion of permafrost, with the development of new protalus lobes and rock glaciers in the highest massifs. Finally, post-LIA warming has led to glacial retreat/disappearance, enhanced paraglacial activity, shift of periglacial processes to higher elevations, degradation of alpine permafrost along with geoecological changes.
- UAV-based very high resolution point cloud, digital surface model and orthomosaic of the Chã das Caldeiras lava fields (Fogo, Cabo Verde)Publication . Vieira, Gonçalo; Mora, Carla; Pina, Pedro; Ramalho, Ricardo; Fernandes, RuiFogo 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 https://doi.org/10.5281/zenodo.4718520 (Vieira et al., 2021).
- Landscapes and Landforms of PortugalPublication . Vieira, Gonçalo; Zêzere, José; Mora, CarlaLandscapes and Landforms of Portugal volume presents, for the first time, a series of synthesis chapters on landscape highlights of mainland Portugal, covering a wide diversity of geomorphological settings. These are presented with language and graphic styles that try to bridge-the-gap from professional scientists to undergraduate students, while being also accessible to all those interested in the earth sciences, to help for a better understanding of landscape evolution and specific features of the Portuguese landforms. The authors are physical geographers and geologists, mostly from Portuguese research institutions, all of them having had conducted research in the regions which they present. The main objective of the book is to provide a good overview of the geomorphology of Portugal, but also of its links with human occupation of the territory, geohazards and geoheritage management. This book is a tribute to Prof. António de Brum Ferreira, who has been an inspiration for generations of geomorphologists and students. Landforms and Landscapes of Portugal volume is organized in five thematic parts, i.e. 1. geomorphological setting, dynamics and hazards, 2. coasts, 3. mountains and valleys, 4. urban areas, 5. geoconservation and geoparks. In each part, chapters are ordered geographically from north to south, covering most of mainland Portugal (Fig. 1) [...]
- The climate of PortugalPublication . Mora, Carla; Vieira, GonçaloPortugal shows a Mediterranean climate with, predominantly, a wet cool season and a dry summer. Despite the concentration of the precipitation in winter, there is a high inter-annual variability, resulting from the latitudinal position in the south-western façade of Europe. The prevailing weather conditions are anticyclonic, with Portugal’s seasonality being marked by the influence of either the subtropical anticyclonic belt or the zonal circulation. Despite the relatively small area of the country, its geographical position in the interplay between the Atlantic and Mediterranean influences, as well as its relief differences, with mountainous north and central regions and a flatter south, generates a diverse mosaic of regional climates. In this chapter, we show the main climate characteristics of Portugal, followed by a brief presentation of the main climatic scenarios for the end of the twenty-first century. The chapter closes with a synthesis of the palaeoenvironmental evolution of Portugal since the last glacial stage.
- Frozen ground and snow cover monitoring in Livingston and Deception islands, Antarctica: preliminary results of the 2015-2019 PERMASNOW projectPublication . De Pablo, M.A.; Jiménez, J.J.; Ramos, M.; Prieto, M.; Molina, A.; Vieira, Gonçalo; Hidalgo, M.A.; Fernández, S.; Recondo, C.; Calleja, J.F.; Peón, J.J.; Corbea-Pérez, A.; Maior, C.N.; Morales, M.; Mora, CSince 2006, our research team has been establishing in the islands of Livingston and Deception, (South Shetland archipelago, Antarctica) several monitoring stations of the active layer thickness within the international network Circumpolar Active Layer Monitoring (CALM), and the ground thermal regime for the Ground Terrestrial Network-Permafrost (GTN-P). Both networks were developed within the International Permafrost Association (IPA). In the GTN-P stations, in addition to the temperature of the air, soil, and terrain at different depths, the snow thickness is also monitored by snow poles. Since 2006, a delay in the disappearance of the snow layer has been observed, which could explain the variations we observed in the active layer thickness and permafrost temperatures. Therefore, in late 2015 our research group started the PERMASNOW project (2015-2019) to pay attention to the effect of snow cover on ground thermal This project had two different ways to study the snow cover. On the first hand, in early 2017 we deployed new instrumentation, including new time lapse cameras, snow poles with high number of sensors and a complete and complex set of instruments and sensors to configure a snow pack analyzer station providing 32 environmental and snow parameters. We used the data acquired along 2017 and 2018 years with the new instruments, together with the available from all our already existing sensors, to study in detail the snow cover. On the other hand, remote sensing data were used to try to map the snow cover, not only at our monitoring stations but the entire islands in order to map and study the snow cover distribution, as well as to start the way for future permafrost mapping in the entire islands. MODIS-derived surface temperatures and albedo products were used to detect the snow cover and to test the surface temperature. Since cloud presence limited the acquisition of valid observations of MODIS sensor, we also analyzed Terrasar X data to overcome this limitation. Remote sensing data validation required the acquirement of in situ ground-true data, consisting on data from our permanent instruments, as well as ad hoc measurements in the field (snow cover mapping, snow pits, albedo characterization, etc.). Although the project is finished, the data analysis is still ongoing. We present here the different research tasks we are developing as well as the most important results we already obtained about the snow cover. These results confirm how the snow cover duration has been changing in the last years, affecting the ground thermal behavior.
- Monitoring recent changes of vegetation in Fildes Peninsula (King George Island, Antarctica) through satellite imagery guided by UAV surveysPublication . Miranda, Vasco; Pina, Pedro; Heleno, Sandra; Vieira, Gonçalo; Mora, Carla; E.G.R. Schaefer, CarlosMapping accurately vegetation surfaces in space and time in the ice-free areas of Antarctica can provide important information to quantitatively describe the evolution of their ecosystems. Spaceborne remote sensing is the adequate way to map and evaluate multitemporal changes on the Antarctic vegetation at large but its nature of occurrence, in relatively small and sparse patches, makes the identification very challenging. The inclusion of an intermediate scale of observation between ground and satellite scales, provided by Unmanned Aerial Vehicles (UAV) imagery, is of great help not only for their effective classification, but also for discriminating their main communities (lichens and mosses). Thus, this paper quantifies accurately recent changes of the vegetated areas in Fildes Peninsula (King George Island, Antarctica) through a novel methodology based on the integration of multiplatform data (satellite and UAV). It consists of multiscale imagery (spatial resolution of 2 m and 2 cm) from the same period to create a robust classifier that, after intensive calibration, is adequately used in other dates, where field reference data is scarce or not available at all. The methodology is developed and tested with UAV and satellite data from 2017 showing overall accuracies of 96% and kappa equal to 0.94 with a SVM classifier. These high performances allow the extrapolation to a pair of previous dates, 2006 and 2013, when atmospherically clear very high-resolution satellite imagery are available. The classification allows verifying a loss of the total area of vegetation of 4.5% during the 11-year time period under analysis, which corresponds to a 10.3% reduction for Usnea sp. and 9.8% for moss formations. Nevertheless, the breakdown analysis by time period shows a distinct behaviour for each vegetation type which are evaluated and discussed, namely for Usnea sp. whose decline is likely to be related to changing snow conditions.