Earth
Science in Space 6
Before we went into space, science fiction stories treated space travel as a
new form of air or sea travel. Nobody thought the real space program would be
like riding a Ferris wheel—we get on, go in circles, then come down, and while
we're up there we look mostly down at the ground. But the real payoff of space,
for Earth science and for every other human endeavor, has been the new vantage
point we get to look at Earth itself. The view from space is a synoptic, all-in-one-eyeful view of our home
world. We didn't take advantage of it right away for science, though. Space
imagery has been practical first and scientific a distant second, for the most
part. The earliest synoptic images were those taken by weather satellites and
military sky spies, and both activities are still going strong.
Satellite geology began in the 1970s with the Landsat program, which
returned detailed images of every spot on the globe every 18 days. The digital
images could be massaged and analyzed—for instance, to indicate geochemistry
for prospecting purposes. And everywhere geologists found subtle lineaments on
the ground that are too large even for aerial photos to encompass. (Most of
these are probably fault lines.)
The U.S. government's Earth Resources Observation Systems or EROS
center is the clearinghouse for Landsat imagery. They've got stuff ranging from
utilitarian—pictures of your region with no annotations, for instance—to
downright sensuous, like this false-color image of the MacDonnell Range in
Australia. They also have photos taken by astronauts.
SAR images can be made as detailed as visible-light pictures nowadays. Feast
your eyes on a set of geology-related
images from NASA's Jet Propulsion Laboratory. SAR also brings out subtleties
of the ocean surface that are being further studied.
The biggest Earth-watching satellite program is probably the Earth Observing
System (EOS) program. Check out the Earth
Observatory to see the scope of this enterprise, which is much bigger than I
have space to review. Among other things, there is a thorough treatment
of satellite imagery, as good as a full-fledged seminar on the subject.
Then go play in the mother lode: NASA's Visible
Earth site of satellite imagery that includes full-Earth pictures in true
color. Between there and the other sites in my Earth
Images from Space list, you'll never run out of things to see.
The first astronauts took
pictures out their little portholes. They were great documentary photos, but
about as useful for science as the snapshots I've taken through airliner
windows.
Another kind of synoptic image is that created by "lighting" the
Earth's surface with radar. By turning continuous radar satellite passes into a
sort of stereo vision, "synthetic aperture radar" or SAR can yield
greatly detailed black-and-white pictures of the ground surface. The Magellan
spacecraft mapped the whole surface of Venus that way; visit the Magellan
site at JPL to see some of the best images, including a stereopair of
a crater. If you're handy with your eyeballs, you can do what every freshman
geologist is taught . . . by crossing your eyes slightly to fuse the two images
together, then carefully focusing on the fused image, you can view it in stereo.
The secret key to space-based Earth research is the Global Positioning System of satellites. GPS allows any spot on the globe to be located to within meters instantly. With this tool, enormous amounts of data are being poured into the same digital pool as the imagery, and the magic of digital analysis is pulling more than rabbits out of more than hats. Here's a short list of recent GPS-related research from the University Navstar Consortium or UNAVCO, which has been in this business since 1984.