. >> reporter: there is a good reason marine scientist chris roelfsema studies coral reefs. >> billionsf people are depending on coral reefs. >> reporter: you're not just talking about things that are pretty to look at. >> no, no, this is also a food resource. 25% of marine species depends on coral reefs. >> reporter: but now to study what's happening down there, scientists are going up. they're using hundreds of shoebox-sized mini-satellites already in orbit to try to save the world's coral reefs. all of them? >> all of them. every one. how can you love something if you don't know how much you have? >> reporter: the satellites circle over the north and south poles as the earth spins underneath and send back pictures of every square inch of the planet every day, including pictures of the 150,000 or so coral reefs. it's a game changer. until now, scientists have had to visit individual reefs to monitor their health-- or lack of it. this group was heading to australia's great barrier reef. as research, it's expensive, it's time consuming, and it's incomplete. what's the difficulty in tryi

. >> reporter: there is a good reason marine scientist chris roelfsema studies coral reefs. >> billions of people are depending on coral reefs. >> reporter: you're not just talking about things that are pretty to look at. >> no, no, this is also a food resource. 25% of known marine species depends on coral reefs. >> reporter: but now to study what's happening down there, scientists are going up. they're using hundreds of shoebox-sized mini-satellites already in orbit to try to save the world's coral reefs. all of them? >> all of them. every one. how can you love something if you don't know how much you have? >> reporter: the satellites circle over the north and south poles as the earth spins underneath and send back pictures of every square inch of the planet every day, including pictures of the 150,000 or so coral reefs. it's a game changer. until now, scientists have had to visit individual reefs to monitor their health-- or lack of it. this group was heading to australia's great barrier reef. as research, it's expensive, it's time consuming, and it's incomplete. what's the difficulty