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.
discovers a unique fact about polar bears
Everyone knows that polar
bears are furry and cute, but few know that sometimes they can also
While still an ME undergrad at Berkeley, Jessica Preciado plumbed the
icy depths of a question that already had the whole natural science
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 bears 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,
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. Its
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.