The vast expanses of the Sahara and Sahel may be not as barren as was previously believed, after a combination of satellite imagery and deep learning apparently revealed the presence of a significant number of trees in those regions.
The efforts of a group of researchers revealed the existence of some 1.8 billion trees in the West African Sahara and Sahel regions, according to the survey's results that were published in Nature magazine.
"We were very surprised that there are quite (so) many trees growing in the Sahara desert," Martin Brandt, assistant professor of geography at the University of Copenhagen and lead author of the new study, told AFP. "Certainly there are vast areas without any trees, but there are still areas with a high tree density, and even between the sandy dunes there are here and there some trees growing".
The survey covered an area spanning some 1.3 million square kilometres and involved the analysis of over 11,000 images.
In order to properly count trees spread across such a vast expanse, scientists had to essentially train a computer program to perform this task, with the training process involving Brandt himself individually counting and labelling nearly 90,000 trees.
"The level of detail is very high and the model needs to know how all kind of different trees in different landscapes look," he explained. "I did not accept misclassifications and further added training when I saw wrongly-classified trees."
Jesse Meyer, a programmer at NASA's Goddard Space Flight Center who worked on the research, also remarked that "for preservation, restoration, climate change and so on, data like this are very important to establish a baseline".
"In a year or two or ten, the study could be repeated... to see if efforts to revitalise and reduce deforestation are effective or not," he said in a NASA press release.
