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 (http://www.globalforestwatch.
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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