Seasonal Variation - Early Spring
Seasonal variations in a landscape are revealed in satellite images. Sometimes patterns of light reflected differently from snow and bare soil can be useful in interpretation. This scene is from early March when snow and ice remain in some parts of the scene and bare soil in others.Estonia generally has mild winters compared to countries of similar latitude because of proximity to the sea. In early March 2003, the scene shows some ice and snow on the ground especially in the higher elevations. Lower elevations may be sheltered from windblown snow. The image is an ASTER composite of bands 1, 2, and 3, which is broadly comparable to an ETM+ composite of bands 2, 3, and 4 but with a resolution of 15-meters. The lowest areas seem to be free of snow though the drainage channels may still be frozen. What is striking is that some low-lying land appears black with a reddish tint. This may indicate early vigorous plant growth. A possible explanation is that the black soil absorbs sunlight and thus warms more quickly in spring, especially in places sheltered from the wind by higher ground.
The ASTER dataset contains two bands that form a stereo pair. These can be used to prepare a digital elevation model (DEM). Unfortunately, though such a DEM would be useful for analyzing topography and landuse, demand is so great that processing delay is now about six months.
