"I think the primary emphasis now is getting REDD+ accepted, implemented and financed as part of the climate negotiations going on in Paris this week, and in the months that follow," Goetz told environmentalresearchweb. "Space-based missions like GEDI will only make those capabilities better, so there is no reason to – and in fact little time – to delay action."

Under REDD+, countries will receive money according to how many carbon emissions they prevent by protecting or adding forest. So good monitoring systems are essential. "The key challenges in forest monitoring are related to providing consistent measurements through time so that change can be assessed with the least error and with the highest confidence," said Goetz, who believes his review will be useful to both scientists and decision makers when assessing their options for consistent forest monitoring and reporting to the UNFCCC in the context of REDD+.

GEDI – the Global Ecosystems Dynamics Investigation – is a LiDAR instrument that will sit on the International Space Station. Goetz says GEDI will revolutionize our ability to map forest biomass from space, and thereby estimate emissions from deforestation and forest degradation with even greater accuracy.

LiDAR shoots a laser beam from a spaceborne – or airborne – platform. Recording the light bounced back enables measurement of the three-dimensional structure of tree canopies, including their height and the variability of biomass elements such as leaves, twigs, branches and stems. "It also allows us to map the ground surface topography beneath the trees," said Goetz. "When LiDAR is coupled with field plot measurements it is possible to estimate the aboveground biomass (or carbon stock) of forested landscapes with uncertainties on the order of 20% or less."

According to Goetz there are multi-fold ways to achieve consistency and accuracy in forest monitoring. "First, satellite observations have to be systematically corrected for various effects like cloud cover, and this has to be done for tens of thousands of images when covering large areas," he said. "Second, satellite observations need to be calibrated and validated with both field measurements and very high resolution imagery, the latter being comparable to aerial photographs." As technology advances, scientists must incorporate those advances while maintaining consistency with the baselines established before the technology became available. Yet all of these challenges have been overcome and capabilities are in place to monitor the world's forests and inform both national and international policies.

Goetz reckons it’s astonishing how far Earth observation technology has come in the past 50 years (he reviewed this progress in 2008). "Now anyone can buy a drone online and equip it with sensors that collect multispectral imagery and stereo-photography," he said. "I can hardly imagine what we'll be flying 50 years from now, but they will certainly include three-dimensional imaging LiDAR from space that will allow holographic fly-through capabilities so you can virtually walk through the Amazonian or Congolese rainforest and look around you and up through the trees."

Goetz hopes that our actions now will ensure those forests are still standing, providing all the services they currently do to humanity and to all the life that depends on them. "If we accomplish that we will have succeeded in ways our decendants will certainly appreciate," he said.

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