Engineering News
February 3, 2003 Vol.73, no. 3S
POLAR BEAR GOES FROM WHITE TO INFRARED: ME grad student Jessica Preciado unlocked the mystery of why polar bears appear invisible in infrared vision. Her paper on the subject recently won a prize.

ME student discovers a unique fact about polar bears

Everyone knows that polar bears are furry and cute, but few know that sometimes they can also be invisible.

While still an ME undergrad at Berkeley, Jessica Preciado plumbed the icy depths of a question that already had the whole natural science community buzzing.

A few years ago, scientists doing an aerial census of the polar bear population in the arctic encountered a problem. The polar bears being counted were hard to spot because their white fur blended into the snow. Scientists decided to use infrared, heat sensing technology for the survey, but found that curiously, the polar bears became invisible. Scientists could see the eyes, nose and breath, but not the bear.

“Everyone got really excited about this, particularly the military because it could have ramifications for creating infrared camouflage in cold climates,” says Preciado.

The excitement calmed when it was hypothesized that the reason for the invisibility was the polar bear’s deep layers of blubber and fur, which trap body heat below their skins, making the polar bears’ surface temperatures the same as the snow.

As an undergrad working in Lawrence Berkeley National Laboratory (LBNL), Preciado decided to further pursue a mystery that the scientific world so quickly shrugged off.

“Infrared detection functions not only by surface temperature, but also by the radiative properties of hair and skin. The last time people measured the radiative properties of polar bear hair was 50 years ago, and now we have much better equipment,” she says.

Preciado took advantage of the advanced light-source technology at LBNL (one of the few in the country) to take a closer look at polar bear hair procured from the San Francisco Zoo. “Not many people have access to the technology they need to measure something this small, I was lucky to have the advanced light-source telescope so close,” she adds.

What she found earned her an honorary mention at a bioengineering undergraduate paper competition at the International Mechanical Engineering meeting in New Orleans last semester. She discovered that polar bear hair has the same radiative properties as snow.

While interesting, her polar bear discovery has little practical application to spur further research. The military quickly lost interest in the subject when they discovered that the polar bears could easily be seen using ultraviolet detection technology.

Preciado, now a second year ME grad student at Berkeley, says that the project helped satisfy her own scientific curiosity. “It’s strange, though, that everyone decided to look at just one half of the equation and completely dismissed the other half,” she says. “What I learned might not be useful but it helps explain why something happens.”

Her paper also rated high in originality at the ME conference. “People at these conferences usually present on dry things. This research had a high coolness factor and coolness factor usually counts for a lot at ME conferences,” she adds.

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