快猫短视频

SOMETIMES the old-fashioned ways are the best. It turns out that
photographing forest canopies with digital cameras rather than old-fashioned
film can produce misleading results.

Forest researchers use cameras with 鈥渇isheye鈥� lenses to obtain a 180掳
view of the canopy. They then process the images on computers to measure
structural details and the amount of light that penetrates the canopy. This
reveals things such as the age of the forest, or changes in vegetation due to
climate change.

In the past, researchers used photographic film and special high-quality
lenses to take their pictures. But many have now switched over to digital
cameras, says Gordon Frazer, a postgraduate student at the University of
Victoria in British Columbia. This is because digital cameras are quicker and
easier to use, and also because the scientific lenses for film cameras are
expensive and difficult to obtain.

But forestry scientists now often use digital cameras and lenses that are
intended for everyday use. Frazer says there is a problem with this. He has
noticed that the digital images often have unexpected distortions, especially at
the edges of the picture, with coloured haloes often appearing there.

Frazer processed images from digital and film cameras on a computer, and
found that the digital images overestimated how open the canopy was, making the
worst errors in thick canopies. This could give scientists a false idea of the
structure of the canopy and how much sunlight is reaching the forest
floor鈥攖he very things they are trying to measure.

Frazer thinks the distortions in the images from a digital camera are caused
partly by the lens and partly by the light-sensitive detector that captures the
image. He adds that the distortion can be reduced if pictures are taken on
overcast days, the camera is set to black and white, and the forest canopy is
fairly open. But the lesson is clear, he concludes: 鈥淒on鈥檛 use cheap stuff for
scientific work.鈥�

John Battles, a forest scientist at the University of California in Berkeley,
says the work highlights an important problem. But he thinks consumer-grade
digital cameras can still be useful in canopy studies, provided that researchers
bear Frazer鈥檚 cautions in mind. 鈥淎 digital camera with a fisheye lens is still a
practical alternative,鈥� he says.