An in situ sediment sound speed An in situ sediment sound speed - - PowerPoint PPT Presentation

An An in situ in situ sediment sound speed sediment sound speed measurement platform: measurement platform: Design, operation, and experimental results Design, operation, and experimental results

Jie Yang, Dajun Tang, and Kevin L. Jie Yang, Dajun Tang, and Kevin L. Williams Williams

Outline Outline

• The design of the

The design of the Sediment Acoustic-speed Sediment Acoustic-speed Measurement System (SAMS) Measurement System (SAMS)

• Field measurement at SW06

Field measurement at SW06

• Data analysis and results for SW06

Data analysis and results for SW06

• Summary and future directions

Summary and future directions

The design of SAMS The design of SAMS

• Scientific goal:

Scientific goal: Obtain Obtain in situ in situ geoacoustic properties of the geoacoustic properties of the seabed within the topmost 3 meters. seabed within the topmost 3 meters.

• Design philosophy:

Design philosophy: Measurements Measurements at at precise depth with minimum precise depth with minimum intrusion. intrusion.

Deployment during SW06 off New Jersey coast

A view at the sea bottom… A view at the sea bottom…

Locations where SAMS sediment data were taken

Field Data Field Data

• Four data sets: one for calibration; three in sediments at

Four data sets: one for calibration; three in sediments at different locations (1 and 2 are close to each other) different locations (1 and 2 are close to each other)

• Three frequency bands: 2-11 kHz, 10-21 kHz, and 20-35

Three frequency bands: 2-11 kHz, 10-21 kHz, and 20-35 kHz (referred to as LF, MF and HF) kHz (referred to as LF, MF and HF)

• Sediment maximum penetration depth for all three

Sediment maximum penetration depth for all three deployments: 1.6 meters deployments: 1.6 meters

Calibration data: waveforms received from source No. 10 at Calibration data: waveforms received from source No. 10 at MF MF

1 2 3 4 5 6 3 2.5 2 1.5 1 0.5 Time (ms) Depth (m)

Water sound speeds determined from calibration data Water sound speeds determined from calibration data

1 1.5 2 2.5 3 3.5 4 4.5 0.5 1 1.5 2 2.5 3 Arrival time (ms) Propagation distance (m)

Sound speed: 1502.1 ± 2.7 m/s

1 1.5 2 2.5 3 3.5 4 4.5 0.5 1 1.5 2 2.5 3 Arrival time (ms) Propagation distance (m)

Sound speed: 1503.1 ± 3.4 m/s MF HF

Sediment data: waveforms received for sources No. 1 and 10 at Sediment data: waveforms received for sources No. 1 and 10 at MF, 2 MF, 2nd

nd deployment

deployment

1 2 3 4 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2

• 0.2

Source No. 1 Time (ms) Depth (m) 1 2 3 4 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2

• 0.2

Source No. 10 Time (ms) Depth (m)

Comparison of curve fitting results between sediment and calibration data Comparison of curve fitting results between sediment and calibration data

0.5 1 1.5 2 2.5 3 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Arrival time (ms) Propagation distance (m) Sound speed: 1502.1 ± 2.7 m/s Water sound speed, calibration MF Data points: 214 0.5 1 1.5 2 2.5 3 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Propagation distance (m) Arrival time (ms) Position 1 Sediment sound speed: 1622.1 ± 12.5 m/s Data points: 119 0.5 1 1.5 2 2.5 3 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Propagation distance (m) Arrival time (ms) Position 2 Sediment sound speed: 1598.1 ± 9.7 m/s Data points: 122 0.5 1 1.5 2 2.5 3 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Propagation distance (m) Arrival time (ms) Position 3 Sediment sound speed: 1611.6 ± 24.7 m/s Data points: 100

Sediment sound speed Sediment sound speed results results

1 2 3 1570 1580 1590 1600 1610 1620 1630 1640 Position cb (m/s) LF MF

Cb (m/s)

Position 1 LF

1614.8 ± 8.7

MF

1622.1 ± 12.5

Position 2 LF

1597.7 ± 11.0

MF

1598.1 ± 9.7

Position 3 LF

1588.2 ± 15.8

MF

1611.6 ± 24.7

Direct measurement and geoacoustic inversion

• f sediment sound speed in SW06

SAMS (direct, APL- UW): 1618 ± 11 1598 ± 10 Jiang, Chapman & Gerstoft: 1594 ± 11 Choi, Dahl & Goff: 1630 ± 20 Geo Probe (direct, Turgut): 1550, 1605, 1640

1 km boxed area:

1 2 3 4 1540 1560 1580 1600 1620 1640 1660 1680 Sound speed (m/s)

SAMS: Yang, Tang & Williams Geo Probe: Turgut Jiang, Chapman & Gerstoft Choi, Dahl & Goff 4 '

73oW 3.00'

2' 1'

39oN

1 ' 2 ' 3 '

• 80
• 80

Summary Summary

• The overall system uncertainty is 3 m/s from the

The overall system uncertainty is 3 m/s from the calibration data. calibration data.

• The sediment sound speeds found at positions 1, 2, and

The sediment sound speeds found at positions 1, 2, and 3 are 1618 3 are 1618 ± ± 11, 1598 11, 1598 ± ± 10, and 1600 10, and 1600 ± ± 20 m/s 20 m/s respectively. respectively.

• The sediment sound speed is homogeneous within the

The sediment sound speed is homogeneous within the top 1.6 meters. top 1.6 meters.

• Little dispersion in sediment sound speed was observed.

Little dispersion in sediment sound speed was observed.

SUBSEA ELECTRONICS TOWER PADS REST ON SEDIMENT SURFACE SINGLE ELEMENT RECEIVER ARRAY IS DRIVEN INTO SEDIMENT 10 SOURCES SUSPENDED ABOVE WATER-SEDIMENT INTEFACE VIBROHEAD DRIVER ON 3 METER MAST

Interior view Exterior view

Design of SAMS In situ sediment attenuation for future studies

SAMS: work accomplished in SW06 and work as future directions

1 2 3 1570 1580 1590 1600 1610 1620 1630 1640 Position cb (m/s) LF MF

In situ sediment sound speed in SW06

20 30 40 50 60 70 80 90

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• 3
• 2
• 1

1 2 Angle with vertical (degree) Intensity fluctuation (dB) Intensity fluctuation of direct arrivals using calibration data 10-21 kHz