Since the opening of the Landsat archive in 2008, medium spatial resolution data have been available for use in alert-based applications.  Since 2013, two Landsat sensors, the Enhanced Thematic Mapper Plus (ETM+) onboard Landsat 7, and the Operational Land Imager (OLI) onboard Landsat 8, have been systematically acquiring global multi-spectral observations at a 30m spatial resolution.  The orbits of the two spacecraft are coordinated to enable potential 8-day repeat coverage globally.   Given this cadence, the use of Landsat as a near-real time source of land change information is possible. The data displayed and made available here quantify forest disturbance events for the tropics using ETM+ and OLI data as an input.  Daily updates are made for areas where quality land observations are acquired.  We define forest cover as 5m tall trees with a canopy closure exceeding 30%.  An alert is defined as any Landsat pixel that experiences a canopy loss in excess of 50% cover. 

This alerting system is meant to complement a current annual global forest cover loss product, implemented in collaboration with Google and World Resources Institute as part of Global Forest Watch.  The annual product is based on a calendar year update, first prototyped using Landsat 7 data from 2000 through 2012 and annually updated thereafter ( and   The interim alert system provides forest disturbance updates as observed, with the objective of providing a conservative change detection system absent of errors of commission.  In other words, the alert system should not be used to provide area estimates, but event-based information for areas experiencing forest cover loss.  Such information is useful for forest management activities and enforcement.

For the full description of forest alert methodology please refer to the following publication: Hansen et al. (2016) Humid tropical forest disturbance alerts using Landsat data. Environmental Research Letters 11 034008

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