Hurricanes wreak havoc not just on manmade infrastructre, but also on coastal shorelines, shifting large amounts of soil (through erosion or accretion) that can dramatically reshape coastlines, sometimes with serious environmental impacts. The US Navy worries constantly about avoiding collisions with other watercraft, not to mention avoiding underwater mines. And marine biologists would love more precise mapping and imaging methods to better delineate the structure and development of coral reefs.

Increasingly, researchers are turning to LIDAR imaging systems to produce the data-rich 3D images they need for all of these applications. LIDAR -- which stands for LIght Detection and Ranging -- is an optical remote sensing technology that exploits the same basic principle as radar and sonar. The system sends out pulses that bounce off objects and analyzes the returning signals to determine an object's distance from the source -- except it uses light wave pulses instead of radio waves.

A LIDAR instrument transmits pulses of light to a target, and the parts of the spectra that are not absorbed by the target are reflected back to the system, which then are detected, stored and analyzed. It's the changes in the properties of the light when it scatters back that enable scientists to measure specific properties of the target. The more frequent the light pulses emitted in a LIDAR system, the more information is gathered, and the more accurately a target area can be mapped.

Usually, a LIDAR system is mounted onto an aircraft equipped with a GPS receiver to track its exact location and altitude. It also needs a high-accuracy inertial measurement unit (IMU) to track the pitch and roll of the airplane so that movement can be accounted for in the final analysis. All the data collected from the various instruments, when combined, can give an elevation that is accurate to within 6 inches.

There's more than one kind of LIDAR system, and which one to use depends on the application. If you want to map a shallow river bed underwater, or use the system for mine detection, you're better off using differential absorption LIDAR. Underwater imaging in particular can be difficult using infrared and near-infrared preferred for terrestrial mapping, since water absorbs those wavelengths; only the blue-green end of the visible spectrum can penetrate water, for the most part.

Arete's Bruce Hubbard reported at Tuesday morning's IPF session on the development of his company's streak-tube imaging LIDAR (STIL). STIL uses a combination of air and underwater-borne platforms to produce very high resolution 3D images of ocean scenes from a remote platform. In particular, says Hubbard, it enables "unrivaled object detection and classification in turbid media" -- that is, the cloudy waters along coastal shorelines, or especially choppy waves. Arete uses STILL as the basis for its collision avoidance system, which allows high-speed water craft to detect and avoid floating obstacles, shallow bottoms, or submerged (or floating) military mines.

Another speaker at the session, Jennifer Wozencraft, is a scientist with the US Army and LIDAR Bathymetry Technical COE. She has been conducting various surveys around the world using a system developed in the 1980s known as SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey). Applications include shoreline mapping -- important before and after major storm surges like hurricanes to measure any topographical changes like soil erosion or accretion -- as well as mapping coral reefs, nautical charting, and flood water modeling.

Bathymetric LIDAR systems like SHOALS transmit two light waves, one in the infrared and one in the green spectrum, and are capable of detecting two returns that delineate the water surface and seabed. The infrared band is quickly absorbed, so it's perfect for detection on the surface of the water, while the green band is used as the optimum color to achieve maximum penetration in shallow water.

In 2003, Wozencraft began working with a new and improved system, called Compact Hydrographic Airborne Rapid Total Survey (CHARTS), which fused multiple sensors into one remote sensing system to better characterize coastal dynamics and update shallow water charts. Specifically, CHARTS incorporates a hydrographic laser system, topographic laser system and digital camera, with a future option being a hyperspectral imager.

Wozencraft has deployed these systems to map coastlines all over the globe. Her latest project, Coastal Zone Mapping and Imaging Lidar (CZMIL) employs a new state-of-the-art optical system for improved depth measurements, as well as streamlined data processing. The latter is particularly important to fill in key gaps in data -- the result of things like bubbles in breaking waves, or particles of sand stirred up in shallow coastline waters.

But the most striking part of Wozencraft's presentation were her before-and-after LIDAR images of shorelines post-Hurricane Ivan (2004) and Katrina (2005):

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Many years ago, as a budding young science writer, I attended a press conference at a physics meeting and heard John Sidles of the University of Washington describe a promising new imaging technique: magnetic resonance force microscopy (MRFM). He made a strong case that such a technique was needed, particularly for 3D imaging single biological molecules such as proteins at the atomic level, which can't really be done using more conventional methods like X-ray crystallography. MRFM was pretty much in its infancy at the time, but Sidles' lucid, impassioned championing of it stuck with me all these years.

I don't know what Sidles is up to these days, but the other impassioned scientist at that long-ago press conference was Dan Rugar of IBM Almaden Research Center, and he's been fighting the good fight on behalf of MRFM ever since. Rugar was a featured speaker during this morning's session on bio-Imaging, detailing the progress made to date on MRFM and outlining the challenges that (still) remain. Sidles had said it would take a good 10-15 years of R&D before the technique was ready for prime-time; looks like he was right. But it might just be on the brink of success at long last.

MRFM basically combines the concepts of magnetic resonance imaging (MRI) and atomic force microscopy (AFM) to detect the magnetic signal from electrons in a given sample. Electrons have a property known as "spin," causing it take like itsy-bitsy bar magnet, and either attract or repel the magnetic tip of an ultrathin cantilever made of silicon.

The interaction between the electron spin and the magnetic tip causes the cantilever to vibrate ever so slightly in response. A nearby coil generates a high-frequency magnetic field, causing the electron spin to "flip" back and forth between the "up" and "down" positions, alternating attraction and repulsion, causing the cantilever's frequency to change ever so slightly. This slight change can be measured very precisely by a laser beam (courtesy of an interferometer). The data can then be processed in a computer to produce a final image.

It's a complex system with lots of different pieces, each with its own set of technical challenges. Why is MRFM so necessary? Well, proteins, for example, tend to fold in very complex patterns that directly impact how they function, but to date, researchers have been quite limited in their ability to observe biomolecules (and atoms, for that matter) in three dimensions. In nanotechnology and materials science, the ability to precisely locate specific atoms -- to map a material's structure at the atomic level in 3D -- would give deeper insights into how to tailor them to exhibit preferred properties. (Materials derive most of their unique properties from atomic structure.)

Various incarnations of Rugar's MRFM instrument have been used to image the structure of tobacco mosaic virus and dengue virus, as well as hydrogen molecules in a multi-walled carbon nanotube. In 2004, Rugar's team made a critical breakthrough when they directly detected the faint magnetic signal from a single electron buried inside a solid sample -- a 10 million times improvement over conventional MRI machines used to image organs in the human body. It's still not the desired 3D snapshot of a single atom or molecule, it's a strong proof of principle that MRFM is capable of achieving atomic-scale imaging. His team has also demonstrated one-dimensional imaging of a sample with 24-nanometer resolution.

Among the more enabling advances for bringing MRI to the nanometer scale was fabrication of an ultrasensitive silicon cantilever -- a miniature diving board 1000 times thinner than a human hair capable of vibrating about 5000 times a second, with a powerful magnetic tip. (Rugar has his cantilevers tailor-fabricated by B.W. Chui's group at Stanford University.)

It hasn't been easy to get this far, and daunting obstacles still remain, but Rugar is still optimistic that the ultimate goal can be achieved through perseverance and sheer ingenuity -- and the payoff could be revolutionary if/when that happens. "Throughout history, the ability to see matter more clearly has always enabled important new discoveries and insights," Rugar said of these latest advances back in 2004. "This new capability should ultimately lead to fundamental advances in nanotechnology and biology."

Science is like that most of the time: you grind away at the minutiae year after drudge-filled year, until you finally reach a tipping point and make the Big Breakthrough. It's been a long wait for Rugar, Sidles and their many collaborators. Here's hoping MRFM finds its way into widespread lab use very soon, so they can finally break out the bubbly to celebrate much-deserved success.

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