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 International Conference on Complex Systems (ICCS2007)

Stereoscopic Reconstruction and Analysis of Infrared Videos of Bats

Lisa Premerlani
Department of Computer Science, Boston University

Margrit Betke
Department of Computer Science, Boston University

Stan Sclaroff
Department of Computer Science, Boston University

Thomas Kunz
Department of Biology, Boston University

     Full text: Not available
     Last modified: September 19, 2007

Brazilian free-tailed bats (Tadarida brasiliensis) form some of the
largest known aggregations of mammals. In south-central Texas, these
bats disperse nightly from their roosts to feed on aerial insects,
including those from agricultural crops. One of the least understood
aspects of the biology of these bats is the behavior of individuals
when they emerge from their roosts and forage for food. We have
developed algorithms for analyzing infrared videos of bats in
flight. We compared two tracking approaches, an alpha-beta and a
Kalman filter, and analyzed the performance of two data-association
approaches, a greedy method and the Hungarian Method. Our analysis
revealed similar results for both filters and more accurate results
for the Hungarian Method. We applied the algorithms to video data of
bats that foraged over a small pond. We computed stereoscopic
reconstructions of bat flight paths from videos that were recorded
simultaneously from two uncalibrated infrared cameras placed
approximately 14 meters apart. To locate the three-dimensional
coordinates of each bat along its flight trajectory, we calibrated the
two cameras spatially using Horn's relative orientation algorithm and
then performed a triangulation. From the trajectories, we calculated
velocities and changes in flight direction of the bats. Our analysis
indicates that the minimum, maximum, and average speeds of these bats
were 1.53, 20.24, and 8.42 m/s, respectively. The minimum, maximum,
and average changes in flight direction in 1/60 seconds were 0.2,
96.1, and 6.4 degrees, respectively. Our results provide the first
stereoscopic analysis of the foraging behavior of free-ranging bats
based on thermal imaging technology.

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