Sperm whale seismic study in Gulf of Mexico-acoustics focus General background My role: 3D tracking...
-
Upload
patrick-malloy -
Category
Documents
-
view
214 -
download
1
Transcript of Sperm whale seismic study in Gulf of Mexico-acoustics focus General background My role: 3D tracking...
Sperm whale seismic study in Gulf of Mexico-acoustics focus
General background My role: 3D tracking tagged/untagged
animals—working a few months at a time Single array localization-2000 Tag/array integration-2001 Dual-array localization-2002-?
Upcoming plans
Aaron Thode, Marine Physical Lab, SIO, UCSD
MMS
Minerals Management ServiceMarine Fisheries Service
Background-SWAMP cruises 2000-2001
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
photo: Keith Mullin,SE Fisheries Service
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
Three different towed array systems 30-100m depth, give ~6km range
Source:MATLABKRAKEN(should alsoBe repeatedWith Bellhop)
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,Outgrowth of Jay Barlow work,SWFSC.SWFSC.Also arrays from Ecologic,Also arrays from Ecologic,WHOIWHOI
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:
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
• 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 md
s
b
t
tds tdbtdt
Bearing 1
Bearing 2
R
zw
za
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
Simultaneous recordings on tag/array corrects pseudotrack.
Acoustics does not have control of ship during most tagging operations, with interesting results.
Time (sec)
Arr
ay b
earin
g (d
eg)
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
RdsdddRds
FdsdFds
Ra
Fa
PPPP
PPP
z
z
,,
,,
,
,
22
2
Restrictions: Array depths known (difficult!) Depths > 40 m (slow towing speed) Doesn’t work broadside. Assumes straight-line propagation
Sept. 5 proof-of-concept
trial demonstrated
results● 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.
broadside
endfire
Range vs. time
Depth vs. time
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?