Nature Correspondence on Satellite data use

Satellites: make data freely accessible

doi:10.1038/498037c

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.

Satellites: ambition for forest initiative

doi:10.1038/498037d

We disagree strongly with the suggestion by Jim Lynch and colleagues that the outputs of the Global Observation of Forest and Land Cover Dynamics panel and the Global Forest Observations Initiative “lack ambition and an understanding of the potential of satellites” (Nature 496, 293–294; 2013).

As participants in these programmes and in the United Nations Programme on Reducing Emissions from Deforestation and Forest Degradation (UN-REDD), we aim to show how remote sensing can help systematic global monitoring to make REDD+ a reality in the context of wider societal engagement. (REDD+ is a climate-mitigation initiative under the UN Framework Convention on Climate Change (UNFCCC).)

We also question the feasibility of Lynch and colleagues' call for rapid-response satellite monitoring of deforestation to be enshrined in international law under the UNFCCC, given national sovereignty concerns and the fact that we are not yet in a position to mitigate the problems of cloud cover. Although radar can penetrate cloud, the technology cannot yet capture changes in forest ecosystems in a systematic and repeatable way.