This is the first ever map of global forest health. NASA used lasers to measure tree heights in a fashion similar to sonar. LIDAR uses a pulse of light from space at a spot on the earth to measure how long it takes to bounce back. Tall trees bounce the light back faster.
Here’s a closer view of the United States of America. The Eastern US has more forest coverage, but the West Coast has much taller trees, judging by the darker shades of green there. Maine and Wisconsin appear to be shorter forests.
There wasn’t a good zoom in on Africa, but here’s a Biomass map from 2008: Thank the academics Baccini, Laporte, Goetz, Sun, and Dong for analyzing satellite imaging. They write in their paper, “The region is characterized by a diverse range of moist tropical forest, seasonal and semi-arid woodland, savanna, and wetland forests.” Green blobs are areas of dense biomass.
National Geographic’s blog notes that this method can be used for carbon accounting. You could also use this method to verify that a group of people you are paying in a foreign land NOT to cut down their local forest (in fact you are paying “protection money” in a sense), are indeed protecting the lands. Satellite LIDAR imaging would reveal any changes in the area’s trees, keeping them honest.