Remote sensing to survey deserts

This Landsat 7 image shows the Namib-Naukluft National Park, an ecological preserve in Namibia's vast Namib Desert.

The park is the largest game park in Africa, and a surprising collection of creatures manage to survive in this hyper-arid region, including snakes, geckos, unusual insects, hyenas, and jackals.

Coastal winds create the tallest sand dunes in the world here, with some dunes reaching 300 meters in height.

Question : How do satellites track desertification ?