Quantifying forest biomass carbon stocks from space

The monitoring of carbon stored in living aboveground biomass (AGB) of forest is of key importance to understand the global carbon cycle, and for the functioning of international economic mechanisms aiming to protect and enhance forest carbon stocks. The main challenge to monitor AGB lies in the difficulty of obtaining field measurements and allometric models in several parts of the world due to geographical remoteness, lack of capacity, data paucity, or armed conflicts. Spaceborne remote sensing in combination with ground measurements is the most cost-efficient technology to undertake the monitoring of AGB. This review presents cutting-edge methods and current and forthcoming satellite remote sensing technologies to map AGB. These approaches face several challenges: lack of ground data for calibration/validation purposes, signal saturation in high AGB, coverage of the sensor, cloud cover persistence, or complex signal retrieval due to topography. New spaceborne sensors to be launched in the coming years will allow accurate measurements of AGB in high biomass forests (> 200 t ha-1 ) for the first time across large areas.