Skip to main content
U.S. flag

An official website of the United States government

Eyes on Earth Episode 4 - Cataloging Earth Observation Satellites

Right-click and save to download

Detailed Description

Earth observation used to be the province of a handful of countries with satellite technology. Today, hundreds of satellites built all over the world are launched every year. This episode of Eyes on Earth talks about the explosive growth in the civilian and commercial remote sensing and EROS’ role in it.




Public Domain.


HULT: Hello everyone. My name is John Hult and I am your host for today's episode of Eyes on Earth, a podcast of the US Geological Survey's Earth Resources Observation and Science Center. Today we are talking about the past and future of earth observation. A movie camera attached to a captured German V-2 rocket got the first images of the earth from space in 1946. But it took another 13 years to get imagery from an orbital satellite and 13 more after that to launch the first Landsat. For years, Landsat was the only game in earth observation. Other government space agencies launched satellites slowly with years passing between each launch. Fast forward to the present day, and the game has changed dramatically. More than 1,000 satellites were launched between 2012 and 2017. 335 launched in 2017 alone. How do we keep track of all these birds? And more importantly, how do we keep track of how good they are? What they are good for? And how they might work together to monitor the Earth's surface in the interest of science. Our guest today wrote a guide designed to answer questions like that. Or as we call them in the USGS, a circular. His name is Jon Christopherson. Jon, welcome to Eyes on Earth.


HULT: So, let's start by having you tell us a little bit about what you do here at EROS and how you got into the game of earth observation.

CHRISTOPHERSON: I've got plenty of grey hairs so I've got a rather long career. I've been involved with electro optical imaging since I got out of college, my first job. Originally doing it for defense work and then shifting the company I was working for in California, made all of the sensors for the first 7 Landsat Satellites. And I got involved with creating or helping to build the Enhanced Thematic Mapper Plus for Landsat 7. I came out here originally to help work with the quality assurance efforts, the calibration efforts for Landsat 7.

HULT: Can you give me just a sense of what you mean when you say "calibration"? What are we talking about doing to make them the best calibrated, what does that mean?

CHRISTOPHERSON: Calibration is just a way of ensuring that it is of the highest quality. I like to say that Landsat and other satellites don't take images of the earth, they take measurements of the earth. So the two big ones are geometric and radiometric accuracy. Are those pixels precisely where they should be? And are they reporting back what they are measuring? 

HULT: World of difference from a movie camera on a rocket.

CHRISTOPHERSON: Yes, yes, (laughter). You have to start somewhere. 

HULT: Right, yes, you have to start somewhere.

Let's talk a little bit about how earth observation has evolved from a movie camera on a rocket to the point where you are at today talking about calibration, radiometry and geometry. How many earth observation satellites are up right now? Do you have that on the tip of your tongue?

CHRISTOPHERSON: It is varying day by day. The Union of Concerned Scientists keeps a nice operational catalogue of satellites in the air right now. And they are tracking over 2,000 operational satellites of which 758-800 are operational earth observing satellites.

HULT: When we started, when Landsat started it was 1? There was just a handful of satellites?

CHRISTOPHERSON: There was 1 plus the military.

HULT: But in terms of the satellites that were up that we knew about that civilians had access to...

CHRISTOPHERSON:    Civilian satellites? Civilian remote sensing, if you look at earth observation actually started much earlier with the first weather birds. But for land imaging, which is near and dear to Eros' heart, Landsat was truly the first civilian dedicated land remote sensing satellite to serve land science.

HULT: We are not looking for weather, we're not looking at clouds, we are looking at what is happening on the ground.

CHRISTOPHERSON: Right, weather and clouds get in our way. (laughter)

HULT: Right, we are not quite as big of fans of those. So, we started with Landsat, and I think I mentioned in the intro, it used to be years, right, between the launch of an earth observation satellite.

CHRISTOPHERSON: It was Landsat and SPOT, the 2 main things until the late'90's.

HULT: And then we pass 1999, 2000 and a few more earth observation satellites come on line, and something called JACIE appears, is that right?


HULT: JACIE, is that one of Frank Zappa's kids? What is a JACIE? What's that?

CHRISTOPHERSON: (laughter) Well, some interesting things happened in the late 90's. First, the planning for the mission of planet earth which is an effort to get multiple satellites with multiple instruments measuring broad earth conditions, to get a more holistic picture of what's happening on our earth. That was an exciting time, but then also, in late'99, early 2000, we saw the launch of the first commercial high resolution satellites. IKONOS offered 1-meter resolution imagery which was astounding to us at the time. The digital globe corporation launched the first quick birds, other satellites, and there were questions about, well, are these data any good. And so JACIE was formed. JACIE stands for Joint Agency Commercial Imagery Evaluation.

HULT: That's quite the mouthful.

CHRISTOPHERSON: Yes. That's why we say JACIE. (laughter) 

HULT: So, this group came together to answer these questions about just a couple of a commercial satellites. So, at that point we had Landsat, we had SPOT, there were a few other sort of civilian government satellites out there. These commercial players come in, but we're still talking about a pretty low number of actual systems that are collecting imagery over the earth.

CHRISTOPHERSON: Right. Of the systems we could get our hands on data from you could still count them on 2 hands, even up through most of the first decade of this century. 

HULT: So, in 2000, you are talking to these people and you can still, like you say, 

use your hands to count the number of satellites. Last year there was a JACIE conference, a JACIE gathering, get together....

CHRISTOPHERSON: Right, this is ongoing, annual

HULT: How many satellites were you talking about? Or could you have potentially been talking about last year at your JACIE conference?

CHRISTOPHERSON: Potentially, we could have been talking about hundreds, but in actuality what we did report on, I'd have to go back and look at last year's agenda to see what we reported on. But, a dozen or less. They were the Landsats, the Centennial. The Europeans now have, it follows on almost in the spirit to the original mission of planet earth, earth observing system. They now have their Copernicus System. And then we also have commercial players there. Digital globe is very active in this. Over 50 countries have land observing satellites. 

HULT: Wow. A big leap. A big jump from where we were even 20 years ago. Well, so I suppose that brings us to the book. Tell us about the book. Why a compendium? What makes this product useful and unique for land imaging satellites?

CHRISTOPHERSON: There are a number of resources out on the web where you can find out different satellite characteristics. But they also have certain limitations to them. One, the CEOS, the Committee on Earth Observing Satellites, they have a great database, but that leaves out the commercial birds. There is a site maintained by ESA.

HULT: By ESA, you are talking about the... 

CHRISTOPHERSON: European Space Agency. We live by acronyms here.

HULT: Right.

CHRISTOPHERSON: They have a lot of very, very, very detailed information but, it's hard to pour through there and just find the basics that you need. And then again, they are missing a few satellites. Union of Concerned Scientists has their database but they don't have the technical details or remote sensing details that we like to have in there. So we decided to put together a book of these.

HULT: Why are there so many satellites? How has it become such an explosive thing? Let's talk about maybe, CubeSat? Is that....

CHRISTOPHERSON: Oh, that's all part of it. Numerous factors have come together for this. First of all, dealing with earth observing data in the last two decades has gotten so much easier. In the early days of EROS, the majority of users got their data on printed pieces of film. And it was around the late 90's that finally pc's became powerful enough, you know, desktop, laptop computers powerful enough to deal with massive amounts of data that is a Landsat scene. Which now, we don't think anything of. There is a confluence of technological developments that are driving this. One, the ease of computing. We can deal with this data so much easier now. So much easier than in the past. Launch vehicles have become cheaper. There are well over a hundred different launch systems under development, different systems being developed right now. Everybody and their brother is trying to build a rocket to space. Satellites can be made smaller with a lot of new technology advances in microelectronics and so you can make satellites smaller. You can put multiple satellites on one launch. Not long ago India launched over a hundred satellites 

in one launch.


CHRISTOPHERSON: It must have looked like popcorn coming out of there. So now you are only paying for one-one hundredth of the cost of a rocket and the launch is cheaper to begin with.

HULT: You say one-one hundredth of the cost of a rocket, I think again we are talking CubeSats which are loaf of bread size or larger kind of satellite.

CHRISTOPHERSON: On that launch vehicle that launched over 100, some of them were CubeSats, quite a few of them were, some were small sats, there are different classes. CubeSat is a buzz word that is bantered around right now. Basically what we are talking about is a satellite that weighs anywhere from a few pounds to a couple thousand pounds.

HULT: Which again allows you to put a whole bunch of them on one rocket.

CHRISTOPHERSON: Exactly. And now you can divide the cost of that launch among many passengers going up there. If we each had to pay for the entire jet when we flew across the country, none of us would fly. But, because we are dividing that cost with a couple hundred other passengers, it's pretty affordable. 

HULT: So we are literally to the point where satellites on a rocket are like passengers on a jet airplane and that's what's making this possible. That's what's making the economics work to get so many satellites.

CHRISTOPHERSON: Right. It's opened up economically access to space to far more people than ever before, particularly small companies, commercial companies. People are seeing niches that they are hoping they can fill with this.

HULT: When you say there are a lot of players, it's not just commercials, like you're talking about commercials is kind of like the big area where we are seeing the growth. But, colleges? I feel like I've read stories about high school students putting together satellites and hitching a ride on these things? 

CHRISTOPHERSON: If you've got $5,000 dollars, you can buy all the parts to build your own satellite, one of these little CubeSats. Which, by the way, a CubeSat means it is 10 centimeters by 10 centimeters by 10 centimeters, about 4 inches on a side. A little box.

HULT: Yes. 

CHRISTOPHERSON: That costs about $4,000-$5,000 dollars. You can buy it online with a credit card and assemble it yourself. And then you've got to go find a launch vehicle. But, NASA is very generous with education support and so on. You can catch a ride up to the Space Station. Space Station has ejectors that can eject satellites from it into fairly low earth orbit. They don't last too long up there but you can live for a year or two.

HULT: So how do you go about getting approval if you are a high school teacher and your class builds a satellite. Can you just call NASA and say, "Hello" and then they give you a form or something? Do you need permission to do that?

CHRISTOPHERSON: Yes. It's a fairly long and harrowing series of regulatory hoops you have to jump through. Within the United States, it's governed by the Department of Commerce. Permission logs and so on. The FCC also weighs in on that. We've got people at the USGS Headquarters who sit on the board to approve these launch license applications.

HULT: It's not quite as simple as like calling up a rocket like an uber...(laughter) There are several steps that need to happen. 

CHRISTOPHERSON: Yes, we don't have Uber for space yet. But yes, you've got to make sure that there are some rules for operating up there. You must deorbit, you must have certain capabilities to be safe. One of the reasons CubeSats are 10 centimeters by 10 centimeters and not smaller, we can make satellites even smaller, but that gets difficult to detect on a radar. And they want to be able to track all of these things up in space so you can avoid collisions, intersections and so on. So, yes, they just made that arbitrary limit 10 centimeters. By golly, everybody is building CubeSats. This is the most exciting time. Things like the cloud bringing computing power, unimaginable amounts of computing power to bear on this, access to data, measurements of the earth being taken at higher frequencies and greater densities than ever before. Science is going to be possible with all of these data, is mind boggling.

HULT: Again, it's got to be good, it's got to be trustworthy, and it's got to be able to work together. Jon Christopherson, thanks for talking with us about the past, present and future of earth observation. It's been fascinating. We hope that you come back for the next episode of Eyes on Earth. This podcast is a product of the US Geological Survey Department of Interior. Thanks for joining us.

Show Transcript