In the last decades there has been a growing interest in the study of natural phenomena due to the climate global changes and the intensification of natural disasters. The international community, through the international organizations and the research institutes, started to study and analyze the impact of the mankind on the environment since the end of the last century. Although some groups (mainly bound to the oil lobbies) claims that the results of the studies were controversial, the Intergovernmental Panel on Climate Changes, IPCC, found that there was evidence that the greenhouse gasses produced by human activities has led to the climate changes and global warming. Among all the themes investigated by the researchers, a special attention have been paid to the cryosphere (the portion of Earth covered by water in a solid form) because it represents one of the most important indicator of the global warming. Many glaciers, the Greenland ice sheet, permafrost and frozen ground, snow cover and Arctic sea ice are exhibiting dramatic changes which alter the ecosystems and consequently the human life. In particular the Earth climate is affected by the polar ice caps which contain more than the 95% of fresh water on Earth and directly influence the gas and particle fluxes, energy surface exchange, clouds, precipitation, hydrological conditions, atmospheric and ocean dynamics. In this scenario, Antarctica plays a fundamental role on the global climate due to its extension (more than the double of the surface of Europe), temperatures (which ranges from -90° up to -25°) and quantity of ice (the mean ice thickness is 1500 meters). Despite its high importance on the environment, Antarctica is the most unexplored and under-sampled area of the Earth due to the extremely conditions which let almost impossible the human life and consequently its monitoring. The latter problem can be partially overcome by the use of remote sensing techniques, which rely mainly on the satellite measured data. Up to now, only the surface temperature of snow can be estimated (mainly by means of optical satellite sensors) on wide areas such the Antarctic Plateau, but no evaluations on the sub-surface temperature are available, so far. The measurement of the temperature of the deep snow layers is carried out only in few sites by means of local probes. The use of microwave passive satellite instruments data (collected by AMSR-E or alternatively SSM/I and Windsat sensors) will make it possible to realize sub-surface snow temperature maps, which could be useful to determine the spatial and temporal trends of the energy contained in the snowpack and therefore the evolution of the global warming. Thus the proposed work aims at investigating the evolution of the Antarctica surface and sub-surface temperatures by means of microwave passive remote sensing data because they are almost insensitive to the clouds coverage and can penetrate the snow surface. The electromagnetic emission of a body strongly depends on its thermodynamic temperature, hence it is possible to estimate it by using electromagnetic models (such the Strong Fluctuation Theory of the Dense Medium Radiative Transfer Theory) and empirical relationships. Several analyses and experiments have been carried out by the IFAC Microwave Remote Sensing Group of the National Research Council, in order to investigate how the electromagnetic brightness temperature of snow is related to the thermodynamic temperature. The obtained results were very promising showing that the surface and subsurface temperatures of the snow in the Antarctic plateau can be estimated with an error lower than 2%. These analyses were carried out in the area surrounding Concordia Station, the Italian-French base on the Antarctic Plateau at Dome-C, and concerned three years of daily measured data, both on the snow and from satellite. The research work, carried out during the post-doc, was organized in four phases. In the first one, a further analysis of the relationships found between electromagnetic and thermodynamic data was carried out in order to extend the results obtained in the past years. Since the microwave satellite data are available since the 80's, in the second phase of the work the study was focused on the estimation of the snow temperature around Dome-C during the past decades. Such study will be useful to assess the decennial trend of the Antarctic temperature, especially with regards to the variation on a long-term basis. The third step was devoted to the extension of the estimates in a larger area of the Antarctic plateau, surrounding Dome-C, with the aim to study the spatial effect of the snow temperature variations. Finally, the last phase of the work has been dedicated to the study of the relationships between the air temperature (which drives the thermal changes in the snowpack) and the snow one. The rationale for this task resides in the lack of snow temperature data while the air temperature is measured at each research station in the continent and the data are widely available. Depending on the results found, the estimation of the snow temperature could be potentially extended to the entire Antarctica making it possible to give estimations of the sub-surface snow temperature trend for the entire continent. During the post-doc research there has been a strong interaction with other researchers of the University of Florence, the Avalanches Center of Arabba, (Italy), the WSF Institute for Snow and Avalanche Research (SLF) of Davos, Switzerland, the Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), Saint Martin d'Hères, France, and of the ENEA institute, which are expert of the Antarctic environment and could help to interpret the obtained data.
Study of the temperature evolution in Antarctica by means of microwave remote sensing data: a contribution to the global warming monitoring
Marco Brogioni
2010
Abstract
In the last decades there has been a growing interest in the study of natural phenomena due to the climate global changes and the intensification of natural disasters. The international community, through the international organizations and the research institutes, started to study and analyze the impact of the mankind on the environment since the end of the last century. Although some groups (mainly bound to the oil lobbies) claims that the results of the studies were controversial, the Intergovernmental Panel on Climate Changes, IPCC, found that there was evidence that the greenhouse gasses produced by human activities has led to the climate changes and global warming. Among all the themes investigated by the researchers, a special attention have been paid to the cryosphere (the portion of Earth covered by water in a solid form) because it represents one of the most important indicator of the global warming. Many glaciers, the Greenland ice sheet, permafrost and frozen ground, snow cover and Arctic sea ice are exhibiting dramatic changes which alter the ecosystems and consequently the human life. In particular the Earth climate is affected by the polar ice caps which contain more than the 95% of fresh water on Earth and directly influence the gas and particle fluxes, energy surface exchange, clouds, precipitation, hydrological conditions, atmospheric and ocean dynamics. In this scenario, Antarctica plays a fundamental role on the global climate due to its extension (more than the double of the surface of Europe), temperatures (which ranges from -90° up to -25°) and quantity of ice (the mean ice thickness is 1500 meters). Despite its high importance on the environment, Antarctica is the most unexplored and under-sampled area of the Earth due to the extremely conditions which let almost impossible the human life and consequently its monitoring. The latter problem can be partially overcome by the use of remote sensing techniques, which rely mainly on the satellite measured data. Up to now, only the surface temperature of snow can be estimated (mainly by means of optical satellite sensors) on wide areas such the Antarctic Plateau, but no evaluations on the sub-surface temperature are available, so far. The measurement of the temperature of the deep snow layers is carried out only in few sites by means of local probes. The use of microwave passive satellite instruments data (collected by AMSR-E or alternatively SSM/I and Windsat sensors) will make it possible to realize sub-surface snow temperature maps, which could be useful to determine the spatial and temporal trends of the energy contained in the snowpack and therefore the evolution of the global warming. Thus the proposed work aims at investigating the evolution of the Antarctica surface and sub-surface temperatures by means of microwave passive remote sensing data because they are almost insensitive to the clouds coverage and can penetrate the snow surface. The electromagnetic emission of a body strongly depends on its thermodynamic temperature, hence it is possible to estimate it by using electromagnetic models (such the Strong Fluctuation Theory of the Dense Medium Radiative Transfer Theory) and empirical relationships. Several analyses and experiments have been carried out by the IFAC Microwave Remote Sensing Group of the National Research Council, in order to investigate how the electromagnetic brightness temperature of snow is related to the thermodynamic temperature. The obtained results were very promising showing that the surface and subsurface temperatures of the snow in the Antarctic plateau can be estimated with an error lower than 2%. These analyses were carried out in the area surrounding Concordia Station, the Italian-French base on the Antarctic Plateau at Dome-C, and concerned three years of daily measured data, both on the snow and from satellite. The research work, carried out during the post-doc, was organized in four phases. In the first one, a further analysis of the relationships found between electromagnetic and thermodynamic data was carried out in order to extend the results obtained in the past years. Since the microwave satellite data are available since the 80's, in the second phase of the work the study was focused on the estimation of the snow temperature around Dome-C during the past decades. Such study will be useful to assess the decennial trend of the Antarctic temperature, especially with regards to the variation on a long-term basis. The third step was devoted to the extension of the estimates in a larger area of the Antarctic plateau, surrounding Dome-C, with the aim to study the spatial effect of the snow temperature variations. Finally, the last phase of the work has been dedicated to the study of the relationships between the air temperature (which drives the thermal changes in the snowpack) and the snow one. The rationale for this task resides in the lack of snow temperature data while the air temperature is measured at each research station in the continent and the data are widely available. Depending on the results found, the estimation of the snow temperature could be potentially extended to the entire Antarctica making it possible to give estimations of the sub-surface snow temperature trend for the entire continent. During the post-doc research there has been a strong interaction with other researchers of the University of Florence, the Avalanches Center of Arabba, (Italy), the WSF Institute for Snow and Avalanche Research (SLF) of Davos, Switzerland, the Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), Saint Martin d'Hères, France, and of the ENEA institute, which are expert of the Antarctic environment and could help to interpret the obtained data.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
