Acoustic survey Yangtze Freshwater Dolphin Expedition 2006

1
Acoustic survey Yangtze Freshwater Dolphin
Expedition 2006
Two towing survey systems are applied. 1 First
towing system focuses on baiji's whistle. It
consists of a monaural hydrophone with 87 m
cable, a frequency filter to eliminate towing
flow noise, a real time sonagram on a PC. The
sound will be recorded and also transmitted by FM
wireless system that enables to monitor the
underwater audible sound anywhere on the
ship. 2 Second towing system focuses on
ultrasonic clicks from baiji and finless
porpoises. It consists of stereo broadband
hydrophone (16 m cable, relatively easy to
handle), envelope and heterodyne converter
(similar to the Bat Detector to convert
ultrasonic clicks to 0-48kHz signals), 96kHz A/D,
recording and detection software (RainbowClick by
IFAW, which was recommended by Jay). Real-time
bearing angle and spectrum of each pulse appears
on a PC screen. Difference of spectrum shape of
broad (baiji) and narrow (finless porpoise)
clicks possibly help to discriminate these
species.
2
1
Whistle of baiji !
Cool Edit Pro
44.1 kHz A/D
rope and tension meter
hydrophone
Float every 2.5 m
5m
87m
3
2
one baiji and one finless porpoise, southwest, at
1423
Real-time spectrum analysis
Stereo heterodyne circuit
96 kHz A/D
Rainbow Click
Sound source direction
hydrophone
hydrophone
2m
16m
4
Special thanks to
Marine Micro Technology
Little Leonardo
Yangtze Freshwater Dolphin Expedition 2006,
Acoustic Team