Direct measurement of
in situ sediment sound speed at SW06
Jie Yang, Dajun Tang, and Kevin L. Williams
Outline
• The design of the Sediment AcousticAcoustic-speed
Measurement System (SAMS)
• Field measurement at SW06
• Data analysis and results for SW06
• Summary and future directions
The design of SAMS
• Scientific goal:
Obtain in situ geoacoustic properties of the
seabed within the topmost 3 meters.
• Design philosophy:
Measurements at precise depth with minimum
intrusion.
Deployment during SW06 off New Jersey coast
A view at the sea bottom…
Locations where
SAMS sediment
data were taken
Field Data
• Four data sets: one for calibration; three in sediments at
different locations (1 and 2 are close to each other)
• Three frequency bands: 22-11 kHz, 1010-21 kHz, and 2020-35
kHz (referred to as LF, MF and HF)
• Sediment maximum penetration depth for all three
deployments: 1.6 meters
Calibration data: waveforms received from source No. 10 at MF
0
0.5
Depth (m)
1
1.5
2
2.5
3
0
1
2
3
Time (ms)
4
5
6
Water sound speeds determined from calibration data
3
3
MF
HF
2.5
Arrival time (ms)
Arrival time (ms)
2.5
2
1.5
1
0.5
1
Cw: 1502.2 ± 2.7 m/s
1.5
2
2.5 3
3.5
4
Propagation distance (m)
4.5
2
1.5
1
0.5
1
Cw: 1503.1 ± 3.4 m/s
1.5 2 2.5 3 3.5 4
Propagation distance (m)
4.5
Sediment data: waveforms received at sources No. 1 and 10 at
MF, 2nd deployment
Source No. 10
-0.2
-0.2
0
0
0.2
0.2
0.4
0.4
Depth (m)
Depth (m)
Source No. 1
0.6
0.8
0.6
0.8
1
1
1.2
1.2
1.4
1.4
1.6
1.6
0
1
2
Time (ms)
3
4
0
1
2
Time (ms)
3
4
-0.2
-0.2
0
0
0.2
0.2
0.4
0.4
Depth (m)
Depth (m)
Two half-space Green’s function simulation
0.6
0.8
0.6
0.8
1
1
1.2
1.2
1.4
1.4
1.6
1.6
0
1
2
Time (ms)
3
4
0
1
2
Time (ms)
3
4
Sediment sound speed results
1640
Cb (m/s)
LF
MF
1630
Position 2
Position 3
LF
1614.8 ± 8.7
MF
1622.1 ± 12.5
LF
1597.7 ± 11.0
MF
1598.6 ± 9.8
LF
1588.2 ± 15.8
MF
1611.6 ± 24.8
1620
cb (m/s)
Position 1
1610
1600
1590
1580
1570
1
2
Position
3
Summary
• The overall system uncertainty is 3 m/s from the
calibration data.
• The sediment sound speeds found at positions 1, 2, and
3 are 1618 ± 11, 1598 ± 10, and 1600 ± 20 m/s
respectively.
• The sediment sound speed is homogeneous within the
top 1.6 meters.
• Little dispersion in sediment sound speed was observed.
Future directions
• On
On--going sediment attenuation study using
current data set from SW06
• Overall improvement of system uncertainty in
sediment sound speed
• Investigation of sediment attenuation dispersion
relation
• Depth dependence of sediment geoacoustic
properties.