Satellite view improves penguin head count

Caren B. Les, caren.les@photonics.com

Satellite imagery and pan-sharpening have shown researchers that there are twice as many emperor penguins marching around Antarctica than previously thought.

The ability to track the penguin population with this satellite mapping technology could help monitor the long-term impact of environmental change on the birds. There is the concern, for example, that early spring warming could affect the continent’s northerly penguin colonies.

A census of emperor penguins in Antarctica was taken using satellite imagery and a pan-sharpening technique. Courtesy of British Antarctic Survey.

“Current research suggests that emperor penguin colonies will be seriously affected by climate change,” said co-author and British Antarctic Survey (BAS) biologist Phil Trathan. “An accurate continentwide census that can be easily repeated on a regular basis will help us monitor more accurately the impacts of future change on this iconic species.”

Taking a penguin head count via space satellite is a reasonable solution, not only because the mostly black birds show up so well against their snowy environment, but also because their breeding grounds are remote and often inaccessible, with temperatures significantly below freezing.

Images from satellites initially were used to identify locations of penguin colonies. Where colonies were distinguished, very high resolution imagery was obtained. Pan-sharpening this imagery helped the international team to differentiate the birds from one another and from ice, shadow and guano.

Emperor penguins move along on their bellies. Courtesy of British Antarctic Survey.

The technique entails merging a higher-resolution panchromatic image (black and white, but sensitive to all wavelengths) with a lower-resolution color image to produce a single high-resolution (60 cm) color image. The process lowered statistical deviations between known and predicted penguin counts considerably, the scientists say. Ground counts and aerial photography were used to calibrate the analysis; 44 colonies were studied in all, and seven of these were previously unknown.

“We counted 595,000 [adult] birds, which is almost double the previous estimates of 270,000 to 350,000 birds,” said lead author and geographer Peter Fretwell of BAS. “This is the first comprehensive census of a species taken from space.”

This aerial view of a colony of emperor penguins was captured near British Antarctic Survey’s Halley Research Station. To estimate the number of penguins in Antarctica, scientists used satellite imagery and a pan-sharpening technique, the latter of which helped to differentiate penguins from each other, and from ice, shadow and guano. Courtesy of DigitalGlobe.

The research, which was published in PLoS ONE, represents a collaboration among BAS, the University of Minnesota, the National Science Foundation, Scripps Institution of Oceanography and the Australian Antarctic Division.

“The methods we used are an enormous step forward in Antarctic ecology because we can conduct research safely and efficiently with little environmental impact and determine estimates of an entire penguin population,” said co-author Michelle LaRue of the University of Minnesota. “The implications of this study are far-reaching: We now have a cost-effective way to apply our methods to other poorly understood species in the Antarctic, to strengthen ongoing field research, and to provide accurate information for international conservation efforts.”