The international effort to map global rain forests in not limited to the Amazon, nor is it limited to SAR (Synthetic Aperture Radar) data exclusively. Since radar can image day or night, cloudy or clear, SAR data make it possible to study seasonal changes. Mapping of floodplain vegetation and sediment concentrations of river channels and lakes is also being carried out by Brazilian and American scientists using Landsat Thematic Mapper data. Landsat data offer a much longer data record, dating from the 1970s, offering researchers more detailed information on land use changes. But the optical instrument can take years to acquire cloud-free coverage over the entire basin.