Educação Superior::Ciências Exatas e da Terra::GeoCiênciasEnsino Médio::GeografiaWintry weather brings cold temperatures and brown landscapes. This change in vegetation can be measured by satellites. Using satellites data, an index of the vegetative state of the surface can be computed, also called Normalized Difference Vegetation Index (NDVI). NDVI values that are close to zero represent bare land, while values close to one are heavily vegetated. This image compares the NDVI of June and December 2010. As is expected, a much greater proportion of the Northern Hemisphere changes to low NDVI values as the seasons change from summer to winter. Alternatively, in the Southern Hemisphere, values tend to increase from June to December as those areas begin their summer season