Sizing up biomass from space

Much of the earth’s carbon is stored in forest biomass, which is thought to play a critical role in mitigating the effects of global climate change. It is therefore crucial that scientists are able to find an accurate and reliable way to estimate forest biomass to monitor the effects of deforestation that continue to occur on a global level.

In new research published in Carbon Balance and Management today Healey et al use lidar height data from the Geosciences Laser Altimeter System (GLAS) recorded during the Ice Cloud and Elevation Satellite (ICESat) mission to create a model for estimating global forest biomass. The authors propose a method to create a subset of lidar height data which can be treated as a random sample and therefore used to calculate a global estimate.

Dr Sean Healey from the Rocky Mountain Research Station explained, “We split the area to be evaluated up into a series of equal area, but not equal shape units, using a fractal-based approach. Each unit contained at least one GLAS shot and where there was more than one shot (on average each unit had 560 shots) only one was randomly chosen. We tested this method on California because the US Forest Inventory and Analysis program (FIA)  maintains extensive forestry records including biomass which we could compare our method to.”

When tested in the US state of California, the model provided an estimate within 1.4% standard error of the design-based estimate provided by the US National Forest Inventory (NFI). Furthermore, the GLAS-based approach costs almost nothing (excluding the costs for the satellite itself), in comparison with the US NFI estimate which cost approximately $10.5 million.

Co-Editor in Chief of Carbon Balance and Management, Dr Burke Hales said, “The GLAS approach shows promise in standardizing global forest biomass inventory, and in improving spatial and temporal coverage more quickly, easily, and most likely cheaply over traditional methods. We will probably need to rely on ‘boots on the ground’ estimates to refine the GLAS method for some time, but the addition of this approach will reduce the uncertainty currently overshadowing the inclusion of forest biomass in global carbon budgets.”

Dr Sean Healey continued, “In fact, this method has been adopted for just this purpose by a partnership between scientists participating in the NASA Carbon Monitoring System pilot project and the UN Food and Agriculture Organization (FAO). Over time, these data will also show how our forests continue to change and will allow scientists to calculate the impact of deforestation, or even reforestation schemes, on climate change.”

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