The cost of accessing satellite data is hampering the widespread application of satellite monitoring, a vital tool for controlling deforestation (Jim Lynch et al. Nature 496, 293–294; 2013) and for biodiversity assessments. We urge government agencies that produce taxpayer-funded satellite images to make these available free of charge and in user-friendly formats.

Lynch and colleagues' call for daily satellite observations of forests worldwide would mean aggregating information from numerous satellites that are operated by many countries. Assembling the large data sets needed for global monitoring would be prohibitively expensive, however, because national governments do not have a free-access policy for their satellite images.

One solution would be to combine data from the US Landsat satellites with those from the European Space Agency's planned Sentinel-2 satellites, which could deliver optical imagery with global coverage every 3–5 days. The distribution of Landsat imagery has increased by two orders of magnitude since 2008, when the US Geological Survey made all the data free to access online. Data from NASA's MODIS and all of their Earth-observation imagery are also available for free, as are data from the China–Brazil Earth Resources Satellite programme.