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  • An Olympian Feat in the Sky

Photonics Spectra
Nov 2008
The 2008 summer Olympics in Beijing showcased world-class athletic prowess side by side with spectacular new green technologies. While the aquatics center called the Water Cube appeared to undulate with light, thanks to LEDs, in the Olympic Village, photovoltaics (PV) and thermal solar systems were providing hot water for the athletes, and PV panels were powering the LED street lamps.


The Beijing National Aquatics Center, known as the water cube, was designed with special LED lighting effects.

But not all the glamour and cutting-edge photonics innovations were at the Olympics. High above the razzle-dazzle of the photonics displays, unbeknownst to many spectators, unmanned aircraft called autonomous unmanned aerial vehicles, or AUAVs, were prowling the skies to monitor the infamous Beijing air quality.

Before the games, the Chinese government had attempted to clear the air by imposing traffic sanctions and halting industrial manufacturing. Scientists saw a rare opportunity to study an atmosphere that was less polluted than is typical, although during the Olympics the characteristic hazy brown glow continued to hover overhead.

A multipronged attack

To study these atmospheric brown clouds, which reduce photosynthetically active radiation and broadband solar radiation, the Cheju ABC Plume-Asian Monsoon Experiment (CAPMEX) combined information gathered during the flights with data from observatories on the ground and from satellites. The exploratory flights, funded by the National Science Foundation, originated in the South Korean island of Cheju, 725 miles from Beijing.

The aircraft – essentially a tiny flying laboratory – used in the study was designed by Advanced Ceramics Research Inc. of Tucson, Ariz. Called the Manta, it can carry up to 6.8 kg on a 5-hour flight, it can climb to 10,000 ft in just less than 15 minutes, and it has a service ceiling of 16,000 ft. Equipped with a differential global positioning system, the vehicle was designed to launch, fly and recover automatically.

Monitoring equipment onboard was developed at Scripps Institution of Oceanography in La Jolla, Calif., by the unmanned aerial vehicles group in the Center for Clouds, Chemistry and Climate. Many of the miniature instruments were designed first for tests conducted in 2006, but the group added to the payload new advanced photonics, microelectromechanical systems, nanosensors and other devices.

An autonomous unmanned aerial vehicle loaded with miniaturized photonics equipment takes flight during an experiment conducted by researchers from the Scripps Institution of Oceanography.

One new device is a spectroradiometer that measures shortwave flux divergence as a function of altitude and time. Using a pair of spectroradiometers, both fitted with cosine collectors, researchers simultaneously measured solar light penetrating the Earth’s atmosphere and radiation reflected from the Earth’s surface. This data set gives researchers an idea of the atmospheric heating rate from shortwave radiation. The miniature tools are made by StellarNet Inc. of Tampa, Fla., and can scan 200 to 1100 nm at 1 nm.

According to Will Pierce, chief scientist at StellarNet, these miniature spectroradiometers are ruggedized to be vibration tolerant and shock resistant for everyday use or for flight onboard an AUAV. The optics are one-of-a-kind concave gratings for high sensitivity and uniform resolution from UV-blue through near-IR to red (220 to 1100 nm). The instruments have no internal mirrors, which keeps stray light at a minimum and increases sensitivity.

Another tool onboard was a TruPulse 200 laser altimeter from Laser Technology Inc. of Centennial, Colo. Using airborne altimetric lidar, the device determines how far from the Earth the AUAV is by measuring the time of flight of a short flash of infrared laser radiation. Use of the altimeter for measuring cloud and atmospheric conditions as well as sea ice thickness also is being studied.

The group at Scripps is testing prototype nanocrystal volatile organic compound sensors, which use porous silicon photonic crystals that can change color in the presence of chemical agents. As volatile organic compounds are collected in the pores of the crystal, the crystal’s color change is measured by a photodetector. The researchers are redesigning these sensors so that they’re small and light enough for use on the unmanned vehicles.

The CAPMEX study, like the Olympics, offers the technological world an opportunity to demonstrate the latest innovations. Combining photonics-based instruments with other measurement tools enabled research that profiled dust, organics and sulfates and helped identify the major type of absorbing aerosol in cloud droplets. Data from the study will show how atmospheric brown clouds affect weather and possibly contribute to global warming. The information also will help investigators assess the impact of the Chinese government’s effort to clean up the air.

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