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  • Sensor Detects Red Algae Growth

Photonics Spectra
Feb 1999
Hank Hogan

What do Hong Kong and Corpus Christi, Texas, have in common? They've both been hit by algae red tides in the last two years. The mysterious bloom of toxic algae pops up in oceans around the world, threatening public health and wreaking economic havoc. Traditionally there has been little warning, but a company far from any ocean is developing a detector to remedy this.

To detect toxic algae, Apprise Technologies combines its sensor with its Remote Underwater Sampling System, which lowers sensors as much as 100 m below the water's surface.

Apprise Technologies Inc. -- a spin-off of the University of Minnesota's Natural Resources Research Institute -- is developing the sensor under a National Science Foundation grant. It's an adaptation of techniques created by NASA to quickly scan the reflected spectrum of planets for atmospheric composition. Because each algal species has a distinct optical fingerprint, identifying the signature is a problem similar to that of identifying the gases in a planet's atmosphere.

Therefore, the same spectral analysis techniques can be used for bloom onset identification and tracking. The sensors being developed target identification of pigments in water, utilizing a narrowband sensor that looks for reflection, absorption and fluorescence.

"We can come up with a fingerprint that has a high probability of determining if there's presence or absence of a red-tide algal bloom," said Christopher J. Owen, Apprise Technologies' president.

However, algae blooms follow the sun, rising and falling in the water; simply sampling a given water depth will not provide effective detection. So Apprise combines the sensor with its commercially available Remote Underwater Sampling System, which lowers sensors as much as 100 m below the surface to an accuracy of 0.2 m. Wireless technologies link the system to shore for data and instruction exchange.

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