The development of a new dielectric model of tundra and forest-tundra for remote probing from space is being performed by Russian researchers from the L.V. Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences (Krasnoyarsk) jointly with the US colleagues from Michigan. The researches are sponsored by the U.S. Civilian Research & Development Foundation (CRDF) and the Federal Agency for Science and Innovation (Rosnauka). The new model will make basis for more accurate and trustworthy climatic forecasts.
Northern sub-polar areas, these being not only boundless lands of Siberia, but also vast territories of Canada and Alaska, are going through hard times. Consequences of global warming make the strongest impact on them. The temperature is rising, ice cover is decreasing, permafrost is thawing, flora is changing, arctic birds and animals are migrating. The majority of sub-polar areas is remote and difficult of access. Therefore remote probing from space is becoming now the main method of their investigation. This includes microwave and radar sounding and radiometry. Radiosounding data can provide information about streams of warm and moisture between the surface of the earth and atmosphere taking into account soil thawing and freezing. Researchers state that trustworthiness of global climate models can be increased if they take into account changes in moisture and heat streams. Reliability of moisture and heat streams determination by radiosounding depends in principle on physical reliability of the so-called soil and flora dielectric models. Russian researchers have set about to develop this particular model for tundra and forest-tundra.
The soil, per se, represents a dielectric, the properties of which may be characterized by permittivity. The latter mainly depends on water content in the soil. When soil moisture freezes and then thaws out, the soil permittivity changes abruptly. Magnitude of such sudden changes depends significantly on the content of the so-called bound soil moisture not frozen at temperatures below freezing. These fluctuations are reflected in sudden changes of brightness temperature and radar signals at microwave probing of soil. Brightness temperature – is one of important characteristics of thermal balance of the surface. It is equal to the temperature of absolute black body, which would create irradiation of the same strength in the investigated frequency band. As strength of microwave irradiation is proportionate to the black body temperature, introduction of the brightness temperature notion noticeably simplifies radiometry methods and data interpretation.
Sergey Komarov | alfa
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