opto_wele_oc_rtr_lo_dnic

brightness. The texture operator, called rier Reef and smaller segments cut from 79.7% and 79.3% recognition rates. “local binary patterns,” gets statistical the images for test, resulting in 185 im- The researchers note that the neural information from spatial relationships ages— 98 of live coral, 43 of dead coral, net will require retraining for videos of pixels. In the experiment, the neu- and 44 of sand (see figure). The neural- taken at different depths, because the ral-net classifier was compared against a net classifier achieved 86.5% and 82.7% blue-green tint of seawater changes the simpler two-step decision-tree classifier. recognition rates for analyses based on color properties. Underwater lighting

For test, preclassified image frames the two different color spaces, with the could also help. were taken from an underwater video of 2-D color space achieving the higher “At the moment we can classify living a small portion of Australia’s Great Bar- rate. The two-step classifier achieved and dead coral and sand,” says Saloma.

“However, it is also important to measure the amount of algae cover because it is an indicator of the reef’s robustness and resiliency. In essence, the applicability of the current performance of our system would depend on the problem of the marine scientist. If a need for rapid assessment of living and nonliving areas is desired, then our system would suffice.”

Increasing the number of categories analyzed by the neural net should boost the classification accuracy, he notes.

John Wallace

REFERENCE

1. Ma. Sheila Angeli C. Marcos et al., Optics Express 13( 22) (Oct. 31, 2005).

 

NEGATIVE REFRACTION Nanofabrication creates left-handed materials at optical wavelengths

The creation of an optical lens based on negative refraction, and thus capable of imaging features smaller than the light’s wavelength, has been hampered because the contribution that natural materials make to total magnetic flux density when placed in a magnetic field (magnetic susceptibility) becomes negligible at high frequencies, beginning in the microwave region. After being artificially extended into the microwave region five years ago using left-handed materials, however, magnetic properties were further extended into the visible spectrum last year using nanofabrication techniques.

In 2000, John Pendry at Imperial College (London, England) proposed the idea of exploiting the inductive response from structured nonmagnet-