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RSEHN >> Publicaciones >> Bol. R. Soc. Esp. Hist. Nat. 99 (1-4), 2004 >> Trabajos presentados en la VI Reunión de la IPA España

Bol. R. Soc. Esp. Hist. Nat. 99(1-4), 2004


Trabajos presentados en la VI Reunión de la IPA España

Balance radiactivo de los altiplanos de la Sierra de la Estrella (Portugal) en una mañana de invierno. Metodología y primeros resultados


Radiation balance of the plateaus of Serra da Estrela (Portugal) in a winter morning. Methodology and first results

Carla Mora y Gonçalo Teles Vieira

Bol. R. Soc. Esp. Hist. Nat. 99 (1-4): 37-45, 2004

Resumen

El balance radiactivo de la superficie es una componente importante para determinar el régimen térmico del suelo, y es un parámetro frecuentemente utilizado en el ámbito de investigaciones de geomorfología periglaciar y crionival. En este trabajo, se calculan las distintas componentes del balance radiativo instantáneo de los altiplanos de la Sierra de la Estrella (Sistema Central Ibérico-Portugal), a partir de una imagen del satélite Landsat 5TM del 3 de Febrero de 1992. Se presentan los datos obtenidos en dos perfiles topográficos representativos de las condiciones de los altiplanos de Torre –Penhas Douradas (1.400-1.993 m) y de Alto da Pedrice– Curral da Nave (1.400-1.600 m). La imagen de satélite muestra unas condiciones con el suelo cubierto de nieve en amplias áreas, pero ya en un estadio adelantado de fusión, traducido en patrones determinados por el relieve y radiación solar incidente. El albedo de la nieve es el principal factor condicionante del balance radiativo de la superficie, y las zonas con nieve son las que presentan un balance radiativo mas bajo (pero positivo). Los valores de balance radiativo mas elevados son coincidentes con las laderas sur y sureste, con pendiente media, y sin nieve. En las zonas de los altiplanos con nieve, existen sectores circunscritos con balance radiativo más positivo que el entorno. Se tratan de las convexidades topográficas, donde el barrido del viento es más significativo. Los primeros resultados del análisis de esta imagen Landsat insinúan un elevado potencial para estudios de periglaciarismo, en especial en áreas remotas donde los datos medidos en el campo son escasos y de carácter espacial discontinuo.

Palabras clave: Periglaciarismo, Balance Radiactivo del Suelo, Teledetección, Landsat 5TM, Sierra de la Estrella, Portugal.

Abstract

The surface radiation budget is an important factor controlling ground temperature regimes and is therefore frequently used in studies of periglacial geomorphology. In this paper the main components of the radiation budget of the plateaus of Serra da Estrela (Portugal) are calculated. The altitude of the plateaus ranges from 1400 to 1993 m. A Landsat 5TM image of 3 February 1992 at 9.30 LST, together with a digital terrain model, was used for the calculations. The shadow-effect algorithm by VIEIRA (2000) was used to compute shaded areas at satellite overpass. Incoming short-wave radiation was calculated using the model SWIM (Short-Wave Irradiation Model) by PARLOW (1996a). The radiation budget and its components (albedo, incoming long-wave radiation and outgoing long-wave radiation) were calculated applying the algorithms collection SEBAL (Surface Energy Balance Algorithms for Land) by WATERS et al. (2002). The results were analyzed along two south-north cross-sections that allow the characterization of the two main plateau areas of Serra da Estrela. As one would expect, short-wave radiation shows the largest spatial variations in its values, and seems to be the main factor controlling snow melt in the period that precedes the image. The pattern of the snow distribution reflects clearly the influence of aspect, a fact that suggests a melting pattern linked to high insolation periods. Outgoing long-wave radiation shows the lowest values in the plateau areas without snow cover, showing a cooler ground surface than in the lower areas of the plateau. In what respects to the all-wave radiation budget, the high snow albedo appears as a very influent factor, giving origin to the lowest values. The highest values occur in the south and south-east facing slopes that are snow free. It is interesting to note that in the snow-covered plateaus, peaks of positive radiation budget occur in terrain convexities, where the snow was blown away and melted earlier. The geomorphic significance of this situation is under evaluation. The first results presented in this paper show that Landsat 5TM scenes are valuable data sources in supporting research on periglacial geomorphology. Despite the instantaneous nature of the data, other authors (e.g. PARLOW, 1996b; LOPES & VIEIRA, 2000) showed that there is generally a high correlation between all-wave radiation budget and potential incoming short-wave radiation. Since it is possible to calculate the later variable for different hours of the day, a model of the all-wave radiation budget can be derived. However, in scenes with snow-covered and snowfree areas, albedo influence must be accounted for. It is significant to note that the wide-spatial coverage of satellite scenes offers invaluable information of terrain characteristics (not only climatic), allowing to derive good quality maps, a step that will be attempted in future research by the authors. The overpass interval of Landsat 5 scenes is 16 days, therefore allowing a reasonable interval for time-dependent monitoring. Finally, since most of the periglacial regions are remote areas, where field-work is done in extreme conditions and very expensive, the use of remote sensing, becomes specially useful and valuable, for example to fill gaps in field data, for modeling or model enhancement and validation, or in assessing terrain characteristics.

Keywords: Periglacial processes, Surface Radiation Balance, Remote Sensing, Landsat 5TM, Serra da Estrela, Portugal.





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(c) Real Sociedad Española de Historia Natural. Facultades de Biología y Geología. Universidad Complutense de Madrid. 28040-Madrid - e-mail: rsehno@bio.ucm.es