Attenuation Of Microwave Signals In Snow-Covered Boreal Forest
Abstract
The presence of snow cover on the ground modifies significantly the interactions between the surface and the atmosphere. In the actual context of possible climate warming it is critical to monitor snow cover properties at different scales, including its extent, water equivalent and depth. The knowledge of these properties is of great interest not only to climate issues, global and regional water cycle hydrology, but also to agriculture management and hydroelectricity production in northern latitudes. Traditionally, snowpack physical properties are determined from snow coring, at more or less dispersed sampling points. However, the significant spatial heterogeneity of landscapes coupled to the high temporal variability of snow cover make traditional methods less effective, particularly for large and inaccessible areas. In the last decades several algorithms using remote sensing data were developed to estimate snow extent, depth and water equivalent. The determination of snow water equivalent in open areas such as Canadian Prairies, by remote sensing means is becoming more and more operational. However, in forested regions, such as boreal forests, the development of efficient algorithms remains challenging. Among other problems encountered, forest canopy transmissivity of the microwave signal emanating from the underlying snow layers is not well known in the literature. In this study, ground-based measurements using 19 and 37 GHz passive microwave radiometers were conducted in order to estimate forest transmissivity. The experiment was held in February 2003 in the former BOREAS southern study area in Saskatchewan (Central Canada). Various forest types, conditions and densities were considered. For each site two sets of microwave measurements were taken: the downwelling brightness temperature through the canopy cover and the sky brightness temperature. The canopy physical temperature was also measured. These measurements were used to estimate the transmission factor for each site. The results obtained show that depending on the forest type and structure, canopy transmittance can be as low as 15% to 20% especially in dense black spruce and old jack pine forest. Highest values (up to 90%) appear in less dense deciduous and sparsely distributed young forests.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.C12A0868G
- Keywords:
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- 1640 Remote sensing;
- 1645 Solid Earth;
- 1827 Glaciology (1863);
- 1863 Snow and ice (1827)