MapQuest for Mars

June 18, 2008

It's summer, time for the great American tradition of the family vacation road trip! When I was a kid, our entire family criss-crossed the country one summer, from Seattle to Maine, in an old Buick station wagon, stopping off at Yellowstone National Park, the Grand Canyon, and a few other landmarks along the way. But mostly, I recall the tedium of 8-hour drives, punctuated by arguments between me and my siblings: "Are we there yet?" "Mom, he keeps looking at me!" Even my parents had their share of arguments, usually while looking over a map in the gigantic atlas that weighed more than my baby sister. Because of course my father wouldn't dream of asking for directions (that's my mom's story and she's sticking to it).

These days, the standard big atlases of my youth are pretty much obsolete, thanks to online resources like MapQuest and GoogleMaps -- both of which I use regularly. But what's a plucky space explorer to do when trying to land a spaceship on Mars (or the moons of Jupiter) sometime in the distant future? Our current "maps" of the red planet leave a lot to be desired in terms of the minute details, especially changing variables like wind speed, atmospheric pressure, and temperature. Sure, our little space probes have done an outstanding job giving us a rough idea of Martian topography, but frankly, the resolution just isn't good enough yet. You don't want to confuse a big boulder with a small pebble -- not when you're trying to land a multi-million-dollar space craft.

What we need is a 3D "super road map" giving us location-specific, detailed information about changing planetary surfaces and conditions. If only we had an imaging technique capable of producing such a map! Lucky for our future astronauts, scientists at the Rochester Institute of Technology (RIT) in upstate New York are developing such an imaging system based on LIDAR (Light Detection and Ranging), in collaboration with MIT's Lincoln Laboratory.

LIDAR is very similar to radar in concept, except it uses laser light instead of radio waves to determine distances, by measuring the time it takes for light to travel from a laser beam to an object and then back again. Not only could such a system prove invaluable for mapping out the surface of the moon, Mars, or other planetary surfaces and atmosphere, it can also probe the environments of comets or asteroids. The RIT scientists will test their prototype system under conditions that mimic those likely to be encountered during NASA space missions.

Improved resolution is the key. Generally speaking, we can usually only image objects roughly the same size as the wavelength of light being used, or larger. The radio waves used in radar, for instance, are terrific at detecting metallic objects, but rocks, or even raindrops, might not produce much in the way of detectable reflections, so these sorts of things would be pretty much invisible to radar. LIDAR uses much shorter wavelengths (eg, in the optical and ultraviolet regimes of the electromagnetic spectrum), and thus the system can detect very small objects, even tiny particles in the atmosphere. In fact, LIDAR is already being used to study atmospheric conditions here on Earth.

Lasers also have a very narrow, focused beam, so LIDAR enables the mapping of physical features with much higher resolution than conventional radar. Its "footprint" can be less than one meter, making it possible to map the floor underneath a thick forest canopy in the Amazon, or details in narrow urban canyons obscured by tall buildings. Such systems were used in the aftermath of the terrorist attacks on September 11, 2001, to map out the debris from the collapsed World Trade Center at Ground Zero in New York City. The resulting detailed topographical "maps" helped rescue workers navigate the often treacherous terrain by identifying unstable areas likely to shift or collapse. The maps also showed the locations of foundation-support structures, elevator shafts and so forth. (You can read more about LIDAR and its many terrestrial applications here.)

According to RIT scientist Donald Figer, his team's LIDAR imaging detector will be able to distinguish topographical details of a planetary surface that differ in height by as little as 1 centimeter. And its imaging system will be able to swiftly capture wide swaths of entire scenes as the laser beams sweep across the terrain. Current LIDAR systems use a single pixel, which must be moved across a scene bit by bit to slowly build up an image. Accuracy is important in space navigation, but so is speed: you've got to be able to adapt to changing conditions quickly, after all. That's why Figer believes his team's LIDAR system could become "a workhorse for a wide range of NASA missions" -- thereby sparing our future astronauts the embarrassment of having to ask local planetary inhabitants for directions.

Photo: LIDAR image of Ground Zero in New York City, September 27, 2001. NOAA/U.S. Army JPSD