Transcript Notes on sperm whale seismic studies in Gulf of Mexico

Sperm whale seismic study in Gulf of
Mexico-acoustics focus
Aaron Thode, Marine Physical Lab, SIO, UCSD
 General background
 My role: 3D tracking tagged/untagged
animals—working a few months at a time
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Single array localization-2000
Tag/array integration-2001
Dual-array localization-2002-?
 Upcoming plans
MMS
Minerals Management Service
Marine Fisheries Service
Background-SWAMP cruises 2000-2001
photo: Keith Mullin,
SE Fisheries Service
 Sponsors
 Minerals Management Service
 International Association of Geophysical Contractors
 Marine Fisheries, SE, 2000-2001
 Focus: effect of seismic exploration on sperm whales
 Endangered species
 Acoustically active
 “Resident” populations
 Mississippi Canyon
 De Soto
Present SWSS study centers on
two types of tags
 Bruce Mate’s satellite tag (STAG)
 Long duration deployments—long-term habitat shift?
 Over 15 animals tagged, mostly on one day
 WHOI digital recording tag (DTAG)
 Also pressure, orientation, acceleration
 High-resolution behavioral responses, energy studies,
3D pseudeotracks
 Visual, biopsy, acoustic component
 Nineteen animals tagged in 2002, three simultaneously
under controlled seismic exposure, many more under
uncontrolled exposures.
Gulf of Mexico an acoustically
unfavorable propagation environment
Measured and computed detection
ranges predict 3-10km, depending on
source depth
Source:
MATLAB
KRAKEN
(should also
Be repeated
With Bellhop)
Three different towed array systems 30-100m depth, give ~6km range
Bottom-mounted sensors have
similar predicted ranges
Stennis Space Center (George Ioup) has placed bottom-mounted
sensors in general vicinity of SWSS. Some coordination, little overlap
so far.
To date passive acoustic data collection program uses
towed arrays with few elements->close range work
Outgrowth of Jay Barlow work,
SWFSC.
Also arrays from Ecologic,
WHOI
My focus has been tracking untagged
animals, under various conditions
 Goal: statistically significant samples of low-
resolution dive profiles under tagging/seismic
conditions

Complements high-resolution low volume
tagging runs.
 Three branches:
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Single array localization-2000
Tag/array integration-2001
Dual-array localization-2002-?
SWSS acoustic work involves
close follows at slow speeds
NOAA ship Gordon Gunther 0.5-1.5 kts
s
t
d
b
• Overnight tracking allowed biopsy, tagging in morning
• July 3 typical-slow tow through middle of traveling pod
• Silty/muddy flat bottom, depth measured with fathometer
• Pod composition assumed to be females and juveniles
• TDR was NOT attached during this particular sequence
930 m
tdt
tdb
tds
Bearing 1
Bearing 2
q
zw
R
za
a
 Example from one dive:
 Good depth resolution
from 100 m depth
 Range uncertainty
increases with animal
depth
 Tracking ends when
bottom returns vanish
Ray refraction may be neglected
for ranges less than 1 km
True range (m)
 During first stage of dive
cycle inter-click interval is
closely related to two-way
travel time from whale to
bottom.
 During second stage
bottom bounces vanish
and timing becomes
irregular.
 Why so many clicks
related to bottom? (New
Zealand counterexample)
Some work has been performed
on merging tag/array data
recordings on
tag/array corrects
pseudotrack.
 Acoustics does
not have control
of ship during
most tagging
operations, with
interesting results.
Array bearing (deg)
 Simultaneous
Time (sec)
The inter-click interval (ICI) used to
identify tagged whale out of 7-13 other
animals
Using surface reflections only gives
three different time-of-arrivals, with
two arrays
Ishmael display: David Mellinger
Two arrays can eliminate need for bottom
reflection, if array depths measured
za,F
za,R

Pds ,F 2 Pd  Pds ,F 
Pds ,R 2 Pd  2 Pdd  Pds ,R 
 Restrictions:
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Array depths known (difficult!)
Depths > 40 m (slow towing speed)
Doesn’t work broadside.
Assumes straight-line propagation
Range vs. time
broadside
Sept. 5 proofof-concept trial
demonstrated
results
endfire
Depth vs. time
● Array depth had to be
estimated for one array.
●Measured descent rate
of 91 meters per minute,
similar to 88 meter per
minute measurements
from next-day tag.
Two arrays plus tag refines
localization-”leverages” tag info
2001-Array depths still the bug-bear!
Everything seems up in the air,
as opposed to in the water
 What ship for seismic playback?
 There was a lot of uncontrolled seismic exposures in
2002
 What ship for research?
 Last year’s ship was way too noisy
 What “holes” are there?
 The off axis acoustic signature of seismic vessels is
not known.
 Modeling by IAGC free-space only, no waveguide
effects included.
 Better arrays needed
 Bottom-mounted sensors? Stennis?