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

An in situ sediment sound speed An in situ 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 in situ geoacoustic properties of the geoacoustic properties of the Obtain in situ seabed within the topmost 3 meters. seabed within the topmost 3 meters. • Design philosophy: Design philosophy: Measurements at at precise depth with minimum precise depth with minimum Measurements 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 0 0.5 1 Depth (m) 1.5 2 2.5 3 0 1 2 3 4 5 6 Time (ms)

Water sound speeds determined from calibration data Water sound speeds determined from calibration data 3 3 MF HF 2.5 2.5 Arrival time (ms) Arrival time (ms) 2 2 1.5 1.5 1 1 Sound speed: 1502.1 ± Sound speed: 1503.1 ± 2.7 m/s 3.4 m/s 0.5 0.5 1 1.5 2 2.5 3 3.5 4 4.5 1 1.5 2 2.5 3 3.5 4 4.5 Propagation distance (m) Propagation distance (m)

Sediment data: waveforms received for sources No. 1 and 10 at Sediment data: waveforms received for sources No. 1 and 10 at MF, 2 nd nd deployment deployment MF, 2 Source No. 1 Source No. 10 -0.2 -0.2 0 0 0.2 0.2 0.4 0.4 Depth (m) Depth (m) 0.6 0.6 0.8 0.8 1 1 1.2 1.2 1.4 1.4 1.6 1.6 0 1 2 3 4 0 1 2 3 4 Time (ms) Time (ms)

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

Sediment sound speed Sediment sound speed results results 1640 Cb (m/s) LF 1630 MF Position 1 LF 1614.8 ± 8.7 1620 MF 1622.1 ± 12.5 cb (m/s) 1610 Position 2 LF 1597.7 ± 11.0 1600 MF 1598.1 ± 9.7 1590 Position 3 LF 1588.2 ± 15.8 1580 MF 1611.6 ± 24.7 1570 1 2 3 Position

Direct measurement and geoacoustic inversion of sediment sound speed in SW06 1 km boxed SAMS (direct, APL- Geo Probe (direct, UW): Turgut): area: 1618 ± 11 1550, 1605, 1640 1598 ± 10 Jiang, Chapman & Choi, Dahl & Gerstoft: Goff: 1594 ± 11 1630 ± 20 3 ' 1680 SAMS: Yang, Tang & Williams Geo Probe: Turgut Jiang, Chapman & Gerstoft 1660 -80 Choi, Dahl & Goff 1640 Sound speed (m/s) 2 ' 1620 1600 1 ' -80 1580 1560 39 o N 4 ' 73 o W 2' 1' 1540 1 2 3 4 3.00'

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 ± ± 11, 1598 11, 1598 ± ± 10, and 1600 10, and 1600 ± ± 20 m/s 20 m/s 3 are 1618 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.

SAMS: work accomplished in SW06 and work as future directions In situ sediment sound speed in SW06 Design of SAMS 1640 LF 1630 MF 1620 VIBROHEAD DRIVER cb (m/s) 1610 ON 3 METER MAST 1600 SUBSEA ELECTRONICS 1590 10 SOURCES 1580 SUSPENDED ABOVE WATER-SEDIMENT TOWER PADS REST 1570 INTEFACE ON SEDIMENT 1 2 3 SURFACE Position In situ sediment attenuation for future studies Intensity fluctuation of direct arrivals using calibration data 10-21 kHz 2 SINGLE ELEMENT RECEIVER ARRAY IS DRIVEN INTO SEDIMENT 1 Intensity fluctuation (dB) 0 -1 -2 -3 Exterior view Interior view -4 20 30 40 50 60 70 80 90 Angle with vertical (degree)