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- Registadores automáticos de baixo-custo para a monitorização de temperaturas do ar, da rocha e do soloPublication . Vieira, Goncalo; Mora, Carla; Ramos, MiguelRegistadores automáticos de temperatura do tipo Tiny Talk II® foram transformados no laboratório do Centro de Estudos Geográficos, com o objectivo de monitorizar as variações de temperatura do ar, rocha e solo. Tratam-se de registadores de 8 bits, com capacidade para armazenar até 1800 dados de temperatura medida a intervalos pré-definidos. A principal vantagem do sistema reside no baixo custo dos instrumentos, na sua pequena dimensão e na simplicidade das adaptações necessárias para que sejam medidos os parâmetros referidos. Descrevem-se na presente nota todos os procedimentos necessários para a construção dos três tipos de sistema de aquisição de dados.
- Accurate determination of surface reference data in digital photographs in ice-free surfaces of Maritime AntarcticaPublication . Pina, Pedro; Vieira, Goncalo; Bandeira, Lourenço; Mora, CarlaThe ice-free areas of Maritime Antarctica show complex mosaics of surface covers, with wide patches of diverse bare soils and rock, together with various vegetation communities dominated by lichens and mosses. The microscale variability is difficult to characterize and quantify, but is essential for ground-truthing and for defining classifiers for large areas using, for example high resolution satellite imagery, or even ultra-high resolution unmanned aerial vehicle (UAV) imagery. The main objective of this paper is to verify the ability and robustness of an automated approach to discriminate the variety of surface types in digital photographs acquired at ground level in ice-free regions of Maritime Antarctica. The proposed method is based on an object-based classification procedure built in two main steps: first, on the automated delineation of homogeneous regions (the objects) of the images through the watershed transform with adequate filtering to avoid an over-segmentation, and second, on labelling each identified object with a supervised decision classifier trained with samples of representative objects of ice-free surface types (bare rock, bare soil, moss and lichen formations). The method is evaluated with images acquired in summer campaigns in Fildes and Barton peninsulas (King George Island, South Shetlands). The best performances for the datasets of the two peninsulas are achieved with a SVM classifier with overall accuracies of about 92% and kappa values around 0.89. The excellent performances allow validating the adequacy of the approach for obtaining accurate surface reference data at the complete pixel scale (sub-metric) of current very high resolution (VHR) satellite images, instead of a common single point sampling.
- Evaluation of Envisat ASAR IMP imagery for snow mapping at varying spatial resolution (Deception Island, South Shetlands – Antarctica)Publication . Mora, Carla; Vieira, Goncalo; Ramos, MiguelAdvanced synthetic aperture radar image mode precision (ASAR IMP) scenes of Deception Island from December 2008 to September 2010 have been analysed to assess its potential for snow cover classification. Backscattering was checked against ground truth. Despite the good spatial resolution of the ASAR, its applicability for detecting snow cover, and especially wet snow, was only possible at much lower resolutions, since noise was found to be very high. Scenes with bare ground or with dry snow cover showed highest backscattering, with averages from 210 to 212 dB. Wet snow showed a shift towards lower values, peaking at 215 dB. A threshold of 213 to 214 dB was identified between dry/bare ground and wet snow scenes at Crater Lake. The backscatter difference to a reference snow-free scene usually provided better classification results, and a threshold ranging from 22 to 23 dB was found. Results show that, despite the relative ease of use of C-band ASAR, special care is necessary since the results show significant noise, and it should only be applied to large areas. Large seasonal patterns of snow melt were identified on Deception Island.
- Oblique rainfall and contemporary geomorphological dynamics (Serra da Estrela, Portugal)Publication . Vieira, Goncalo; Mora, Carla; Gouveia, Maria ManuelCoarse sand accumulations are polygenic microforms that attain a width of several metres, a height up to 30 – 40 cm,a gradient of 8–12°and a slope length up to 1 m. These accumulations are frequent in the gruss-covered plateausof the granite mountains of central and northern Portugal,but they have been described in other mountain areas (i.e.Cairngorms, Scotland). Though these microforms are frequent features, studies on them are rare. They have beenattributed to complex genesis controlled primarily byaeolian processes, but also by wash and cryogenic dynamics.Results presented here add new insights into the origin of the sand accumulations and emphasize the importance ofrainsplash-saltation induced by oblique rainfall as the main transportation mechanism. The study was conducted inthe Serra da Estrela, a granite mountain in central Portugal (1993 m above sea level) and is supported by a detailedmapping of the orientation of the accumulations, monitoring of the surface material and analysis of meteorologicaldata. The results are particularly significant since they indicate that the coarse sand accumulations are very activefeatures that show a clear climatic and ecological signal.
- Evaluation of water resources in a high-mountain basin in Serra da Estrela, central Portugal, using a semi-distributed hydrological modelPublication . Espinha Marques, J.; Samper, J.; Pisani, B.; Alvares, D.; Carvalho, J. M.; Chaminé, H. I.; Marques, J. M.; Vieira, Goncalo; Mora, Carla; Sodré Borges, F.High-mountain basins provide a source of valuable water resources. This paper presents hydrological models for the evaluation of water resources in the highmountain Zeˆzere river basin in Serra da Estrela, Central Portugal. Models are solved with VISUAL BALAN v2.0, a code which performs daily water balances in the root zone, the unsaturated zone and the aquifer and requires a small number of parameters. A lumped hydrological model fails to fit measured stream flows. Its limitations are overcome by considering the dependence of the temperature and precipitation data with elevation and the spatial variability in hydrogeomorphological variables with nine sub-basins of uniform parameters. Model parameters are calibrated by fitting stream flow measurements in the Zeˆzere river. Computed stream flows are highly sensitive to soil thickness, whereas computed groundwater recharge is most sensitive to the interflow and percolation recession coefficients. Interflow is the main component of total runoff, ranging from 41 to 55% of annual precipitation. High interflows are favored by the steep relief of the basin, by the presence of a high permeability soil overlying the fractured low permeability granitic bedrock and by the extensive subhorizontal fracturing at shallow depths. Mean annual groundwater recharge ranges from 11 to 15% of annual precipitation. It has a significant uncertainty due to uncertainties in soil parameters. This methodology proves to be useful to handle the research difficulties regarding a complex mountain basin in a context of data scarcity.
- Avaliação de recursos hídricos através de modelação hidrológica: aplicação do programa VISUAL BALAN v2.0 a uma bacia hidrográfica na Serra da Estrela (Centro de Portugal)Publication . Espinha Marques, J.; Samper, J.; Pisani, B.V.; Alvares, D.; Vieira, Goncalo; Mora, Carla; Carvalho, J. M.; Chaminé, H. I.; Marques, J. M.; Sodré Borges, F.Numerical models are needed to evaluate complex hydrological systems. VISUAL BALAN v2.0 is a lumped hydrological code which performs daily water balances in the soil, the unsaturated zone and the aquifer requiring a small number of parameters. VISUAL BALAN has been used to model the river Zêzere catchment upstream of Manteigas (Serra da Estrela, Central Portugal), in order to assess its water resources. Modelling started with the definition of sub-basins based on hydrogeomorphological units. Then, daily temperature and precipitation data from Manteigas meteorological station were extrapolated to each sub-basin considering vertical gradients. Finally, modelling with VISUAL BALAN was performed in four stages: (i) physical characterisation of each sub-basin; (ii) preliminary calculations of the daily water balance; (iii) model calibration by means of flow measurements in the river Zêzere; (iv) result analysis. This basin exhibits complex patterns in hydrometeorological variables such as rainfall and temperature. Several sub-basins have been defined in order to account for the spatial variability in hydrometeorological and geomorphological variables. The model reproduces observed flowrates while its results are coherent with the conclusions of previous studies in similar basins.
- Hydrogeological study of a high mountain area (Serra da Estrela, Central Portugal): a multidisciplinary approachPublication . Marques, J.; Espinha Marques, J. M.; Chaminé, H. I.; Afonso, M. J.; Carreira, P. M.; Fonseca, P. E.; Cabral, J.; Santos, F. A. Monteiro; Vieira, Goncalo; Mora, Carla; Gomes, A.; Teixeira, J.; Samper, Javier; Pisani, B. J.; Aguiar, C.; Gonçalves, J. A.; Almeida, P.The results ofa preliminary hydrogeological study ofthe river Zêzere catchment upstream ofManteigas(Serra da Estrela Natural Park,Central Portugal) are presented.In this mountain region,different types of groundwater and surface water (used in several economic activities) occur.The methodology adopted in thisstudy emphasizes the way how Geology,Geomorphology,Geophysics,Geochemistry,Soil Science andHydrogeology contribute to the description ofthe hydrological phenomena taking place in the catchment,such as infiltration and aquifer recharge and groundwater flow and geochemistry — allowing to develop bet-ter hydrogeologic conceptual models.The hydrological modelling in course includes the use ofthe VISU- AL BALAN code,which is being coupled to a GIS.The hydrogeochemical techniques are highlighted as well as its preliminary results concerning major and minor elements.The thermomineral water study includes the identification ofthe reservoir’s geologic material,the characterization ofwater-rock interactionand geothermometry.
- Régimen térmico y variabilidad espacial de la capa activa en Isla Decepcion, AntártidaPublication . Vieira, Goncalo; Caselli, Alberto; Mora, Carla; Ramos, Miguel; Pablo, Miguel Angel de; Neves, Mário; Santos, Fernando; Bernardo, Ivo; Gilichinsky, David; Abramov, Andrey; Batista, Vanessa; Melo, Raquel; Nieuwendam, Alexandre; Ferreira, Alice; Oliva, MarcEl programa de monitoreo de capa activa (CALM) fue desarrollado en las últimas décadas con la finalidad de comprender el impacto del cambio climático sobre los ambientes con permafrost. Este trabajo analiza los resultados obtenidos, en los últimos seis años, de los sitios CALM-S Irizar, Cráter Lake y Refugio Chileno, ubicados en Isla Decepción. En ellos se ha medido el espesor, el estado térmico y la distribución espacial de la capa activa. En los sitios Irizar y Refugio Chileno la evolución del espesor de capa activa varió interanualmente sin una clara tendencia dentro del corto período analizado; por el contrario, el sitio Cráter Lake evidenció una tendencia a la disminución de espesor. La distribución espacial como el espesor de dicha capa en los tres sitios de monitoreo, mostraron estar condicionados principalmente por la potencia de la cubierta de nieve, la litología y la exposición a los vientos. El relieve, la topografía de detalle, la orientación de las laderas frente a la radiación solar incidente, ejercieron un control menor sobre esta distribución. El estado térmico de la capa activa evidenció el control ejercido sobre ella de la temperatura del aire y de la cubierta nival. Así bajo reducidos espesores de nieve, el modelo de penetración en profundidad de la isoterma de 0 ºC, ha permitido aproximar satisfactoriamente el espesor de capa activa.
- Daily minimum air temperatures in the Serra da Estrela, PortugalPublication . Mora, Carla; Vieira, Goncalo; Alcoforado, Maria JoaoThe Serra da Estrela is part of the Iberian Central Cordillera and is the highest mountain in Portugal (1,993 m ASL). The Torre-Penhas Douradas and Alto da Pedrice-Malhada Alta plateaus with altitudes between 1,400 and 1,993m, which are separated by the Alforfa and Zêzere valleys dominate the highest part of the range. The central massif is dissected by several glacially sculpted valleys that originate reliefs from 200 to 700m. This morphological diversity controls to a great extent the local climates of the mountain. Nine air temperature data loggers were installed in contrasting topographic situations, with special emphasis to valley floors and interfluve sites. Data collection was made each 2-hours from 27th December 1999 to 27th March 2000. Minima temperature most of the times occurs at 7 UTC. The minimum air temperature patterns based on the data from the nine sites were classified using k-means. Two contrasting events were chosen for the centroids of the classification. Cluster 1 represents the stable events with thermal inversions in the valleys and higher temperature in the interfluves. The valley floors at higher altitudes present lower temperatures than the ones at lower positions. Cluster 2 groups the unstable episodes with more turbulence and a temperature decrease controlled by altitude. In this group temperature does not depends on the topographic position.
- Metodologias de análise e de classificação das paisagens: o exemplo do projecto EstrelaPublication . Ferreira, António Brum; Alcoforado, Maria Joao; Vieira, Goncalo; Mora, Carla; Jansen, JanAssiste-se actualmente ao renascimento dos estudos de «Ecologia da Paisagem», mas continua a verificar-se uma grande dispersão, não só nos métodos, mas também no próprio objecto e nas escalas espacial e temporal de análise. Os progressos dos métodos quantitativos e dos sistemas de informação geográfica têm conduzido muitas vezes a uma excessiva preocupação pelos padrões fisionómicos, em detrimento da dinâmica da paisagem. Por sua vez, o entendimento da paisagem como um «geossistema» tem enfrentado a dificuldade do cálculo dos fluxos de matéria e energia, que exige meios poderosos só ao alcance de alguns laboratórios. O estudo integrado do ambiente físico, mesmo num plano mais modesto, de análise mais descritiva e cartográfica do que quantitativa, exige uma investigação pluridisciplinar, defendida por muitos mas raramente posta em prática. O projecto de investigação ESTRELA tem como objectivo o estudo das relações entre a fisionomia e a dinâmica da paisagem, num ambiente de montanha, através da análise geomorfológica, climatológica e da vegetação, utilizando três escalas espaciais de análise. Referem-se os trabalhos efectuados em cada um desses domínios, dá-se um exemplo de tentativa de integração de pesquisas sectoriais e remata-se com uma perspectiva temporal da transformação da paisagem na Serra da Estrela. Um dos problemas ainda não resolvidos consiste nos critérios a adoptar na definição das unidades de paisagem.