Abstract
The easy and ready access to Landsat datasets and the ever-lowering costs of computing make it feasible to monitor the Earth’s land cover at Landsat resolutions of 30 m. However, producing forest-cover products rapidly and on a large scale, such as intercontinental or global, is still a challenging task. By utilizing the huge catalog of satellite imagery as well as the high-performance computing capacity of Google Earth Engine, we proposed an automated pipeline for generating 30-m resolution global-scale forest map from time-series of Landsat images. We describe the methods to create products of forest cover at a global scale. First, we partitioned the landscapes into subregions of similar forest type and spatial continuity. Then, a multisource forest/nonforest sample set was established for machine algorithm learning training. Finally, a random forest classifier algorithm was used to obtain samples automatically, extract the characteristics of satellite images, and establish the forest/nonforest classifier models. Taking Landsat8 images in 2018 as a case, a novel 30-m resolution global forest cover (GFC30) map has been produced. The result shows that by the end of 2018, the total forest area in the world was 3.71 × 109 ha. The accuracy evaluation of GFC30 for 2018 was carried out using verification points via stratified random sampling of a MODIS land cover map (MCD12C1 product in 2012) and verified on high-resolution satellite imagery (e.g., Google Earth). According to the validation result, the overall accuracy of GFC30 for 2018 is 90.94%.
Highlights
Forests cover about 30.6% of the Earth’s land area and constitute a critical terrestrial ecosystem
By utilizing the forest ecological zones (FEZs) as a processing unit, making full use of the existing data to obtain global forest sample points, as well as with the huge catalog of satellite imagery on Google Earth Engine (GEE), we proposed an automated pipeline method for generating 30-m resolution global-scale forest cover map
Zhang et al.: Rapid generation of global forest cover map using Landsat based on the forest ecological zones modified by reference to several global products primarily developed for land cover or forest cover
Summary
Forests cover about 30.6% of the Earth’s land area and constitute a critical terrestrial ecosystem. Forest cover change (FCC) is highly relevant to the global carbon cycle, water supplies, biodiversity richness, and for understanding the rates and causes of land use change. As global ecological environment changes and population growth and ensuing human activities intensify, global forest cover (GFC) has decreased from 4128 × 106 ha in 1990 to 3999 × 106 ha in 2015. There was a net loss of some 129 × 106 ha of forest between 1990 and 2015, which was about the size of South Africa, representing an annual net loss rate of 0.13%.1. Forest conversion to other land use, is more complicated than that. Forest cover mapping has important practical significance and scientific value in terms of the spatial and temporal detailed change on global-scale forest.[2]
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