Target Strength of Southern Resident Killer Whales ... - BioSonics, Inc

Code:46.2008-final-Feb9
which equals 6.64 neper/m. For our analysis we chose to use values of of 4.45 neper/m at 67 kHz, 1.53
neper/m at 23 kHz, and 13.28 neper/m at 200 kHz.
The plane wave reflection coefficients for a three-layer model of water–blubber–lung at three different
frequencies are shown in Figure 2 for an angle of incidence of 90 normal to the surface of the blubber. It
also shows the variability in the reflection coefficient as a function of blubber thickness, which increases
with frequency. Depending on the thickness of blubber layer, the difference in reflection coefficient
between the frequencies of 67 kHz and 200 kHz could vary from 4 dB up to 15 dB. These reflection
coefficient values can be used to estimate the TS of killer whales at 200 kHz.
III.
RESULTS
A. Whale Behavior
Figure 3 shows the averaged distance, depth, and swimming speed estimates for the killer whales
observed a Lime Kiln Point. There were some unrealistic values for whale depth (above surface),
possibly due uncertainty in the tilt angle of the split beam transducer in the horizontal direction or
propagation effect such as multipath off the ocean surface of the transmitter pulse and/or echo. Other than
these observations, the trends in whale depth appear to be realistic given the visual observations of the
whales. The whales were initially detected by the sonar at a range of about 100 m, swimming at a depth
of about 2 or 3 m. They approached to within about 30 m from the sonar transducer at a depth of about 5
m. At this range from the transducer they turned and swam away at a deeper depth. The killer whales
were also observed to slow on their approach to the transducer then speed up after they turned and were
swimming away from the transducer.
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