Skip Links

USGS - science for a changing world

Data Series 848

Coastal Bathymetry Data Collected in 2011 from the Chandeleur Islands, Louisiana

Survey Overview and Acquisition



Geophysical survey data were collected during two cruises covering an area of approximately 83 square kilometers (km2). Single-beam data (11BIM02) were collected June 6-16, 2011, aboard the 22-foot (ft) R/V TwinVee (fig. 2), from which 446 line-km of bathymetry data were collected. Tracklines (158 lines) were primarily perpendicular to shore and spaced approximately 100 meters (m) apart (fig. 3). Additional single-beam data were also acquired along six long-term change lines spaced approximately 1 km apart extending 6 km offshore on both the gulf and sound sides of the islands. These lines were designed to reoccupy previously collected single-beam bathymetric survey lines, allowing for comparison of bathymetric profiles from multiple surveys independent of larger scale mapping efforts.

Interferometric swath and seismic data (11BIM01) were collected June 2-15, 2011, aboard the 26-ft R/V SurveyCat (fig. 4). A total of 572 line-km of data were collected utilizing an integrated suite of geophysical instruments capable of mapping the nearshore environment around the island, including an interferometer that provided swath bathymetry (this report) and a high-resolution chirp subbottom profiler that imaged the shallow subbottom (Forde and others, 2013). Swath bathymetry and chirp tracklines (133 lines) were generally shoreline parallel, and line spacing varied from 50 m to 250 m, depending on water depth (fig. 5). Tie lines, or tracklines perpendicular or oblique to shoreline orientation, were also surveyed as a check on bathymetric soundings and to provide dip or apparent dip lines for the chirp profiles. The North American Vertical Datum of 1988 (NAVD88) orthometric elevation range for all of the bathymetric data was -0.548 m to -16.446 m, derived by the National Geodetic Survey's (NGS) geoid model of 2009 (GEOID09).


Navigation and Motion

A Geographic Positioning System (GPS) base station was assembled at a temporarily installed USGS benchmark (TMRK), located on a wide sand flat on the sound side of the island within about 15 km of the farthest single-beam trackline (fig. 3). GPS receivers recorded the 12-channel full-carrier-phase positioning signals (L1/L2) from satellites via a Thales choke-ring antenna. This GPS instrument combination was duplicated on the survey vessel (rover). The base receiver and the rover receiver recorded their positions concurrently at 1-second (s) intervals throughout the survey. Boat motion was recorded at 50-millisecond (ms) intervals using a Teledyne TSS Dynamic Motion Sensor (TSS DMS-05) (table 1). HYPACK® version 10, a marine surveying, positioning, and navigation software package, managed the planned-transect information and provided real-time navigation, steering, correction, data quality, and instrumentation-status information to the boat operator.


Aboard the R/V TwinVee, depth soundings were recorded at 50-ms intervals using a Marimatech E-SEA-206 echosounder system with dual 208-kilohertz (kHz) transducers (fig. 2) (table 2). Data from the GPS receiver, motion sensor, and fathometer were recorded in real time and merged into a single raw data file (.raw) in HYPACK, with each device string referenced by a device identification code and time stamped to Coordinated Universal Time (UTC).

Sound Velocity

Sound velocity measurements were collected using an Applied Microsystems Smart Sound Velocity Profiler (SVP). The instrument was cast overboard periodically throughout the survey to observe changes in water-column speed of sound (SOS). The recorded daily mean sound velocity for the duration of the survey was 1524.75 meters/second (m/s).

Photo showing survey equipment set up on RV TwinVee

Figure 2. The Research Vessel (R/V) TwinVee, mobilized with the Marimatech single-beam bathymetry equipment configuration.

    Map showing single-beam bathymetry survey tracklines around the Chandeleur Islands

Figure 3. Single-beam bathymetry tracklines for Chandeleur Islands survey in 2011. Island extent is derived from USGS lidar data collected in 2011. [Click to enlarge]

Table 1.  Specifications for the Teledyne TSS-DMS-05 motion sensor used during the single-beam bathymetry survey (, 202 KB).

Teledyne TSS-DMS-05 Specifications
Roll and pitch 0.05 degrees
Heave 5 percent of heave amplitude or 5 centimeters

Table 2.  Specifications for the Marimatech E-SEA SOUND 206 fathometer used during the single-beam bathymetry survey (, 246 KB).

Marimatech E-SEA SOUND 206 Specifications
Transmitter and bottom pulse output TX and RX pulse
Water depth range 0.5 – 1,600 meters
Transmission power 600-2,000 watts
Resolution 2.0 centimeters
Vertical (depth) accuracy 1.0 centimeter, +/- 0.1 percent of depth value (200 hertz)


Navigation and Motion

The position data string was integrated in real time using a Coda-Octopus F190R Precision Attitude and Positioning System, which includes a waterproof inertial measurement unit (IMU). The IMU is mounted underwater between the transducer heads to minimize lever arm geometry errors between the observed depths and associated vessel motion. Real-time corrected positions were acquired via the use of the OmniSTAR HP (High-Precision differential global navigation satellite system) satellite constellation subscription. In addition to the position string, the F190R records heave, roll, and pitch of the vessel during acquisition (table 3), which are all used to calculate the precise position of the measured reference point near the head of the transducers. Equipment offsets were entered into the F190 software prior to the survey and instrument calibration. Planned survey tracklines were loaded into HYPACK for survey orientation, providing a navigation guide for the boat operator.


Interferometric swath bathymetry was collected aboard the R/V SurveyCat using a 234-kHz Systems Engineering and Assessment, Ltd. (SEA), SWATHplus-M (medium frequency) interferometric sonar system (table 4). The transducers were mounted on a sled attached to a rail system fastened between the catamaran hulls, allowing the instrument to align directly below the GPS antennae in order to minimize geometry errors (fig. 4). OmniSTAR HP position correction data and motion data from the IMU were integrated with interferometric soundings in the SWATHplus software package with positional and calibration offsets predefined by a session file (.sxs), allowing for real-time-corrected depths. Prior to deployment, all equipment offsets were surveyed in dry dock with the use of a laser total station. During the survey all swath tracklines were recorded in SEA raw data format (.sxr).

Sound Velocity

A Valeport® Mini Sound Velocity Sensor (SVS) was attached to the transducer mount and collected continuous SOS measurements at the depth of the transducers. These values were directly read and incorporated into the SWATHplus acquisition software giving real-time speed of sound at the transducer while underway (table 5). In addition, a separate sound velocity profiler (Valeport miniSVP) was used to collect speed of sound profiles (water surface to seafloor) at intervals throughout the survey (table 6). Accurate SOS values throughout the water column are essential to accurately map the seafloor with a swath system, particularly at swath beam range extents, and most notably at depths greater than 3 m where SOS has commonly demonstrated variability due to thermoclines and changes in salinity. If SOS is inaccurate, water column refraction will significantly decrease data precision and accuracy throughout the beam range, but particularly at the far range, increasing manual post-survey processing time and interpolation uncertainty upon creation of a Digital Elevation Model (DEM).

Photo showing survey equipment on the RV SurveyCat

Figure 4.  The Research Vessel (R/V) SurveyCat mobilized with roof-mounted navigation bracket and interferometric swath bathymetry transduces and IMU wetpod cradle mounted to a sled and rail system between the catamaran hulls.

    Map showing swath bathymetry survey tracklines around the Chandeleur Islands

Figure 5. Swath bathymetry tracklines for Chandeleur Islands survey in 2011. Island extent is derived from USGS lidar data collected in 2011. [Click to enlarge]

Table 3. Specifications for the Coda Ocotopus F190R inertial measurement unit (IMU) used during the swath bathymetry survey (Coda Octopus Group, Inc.) (

Coda Octopus F190 Specifications
Positional accuracy 0.1 meters with OmniSTAR HP subscription
Velocity 0.014 meters/second
Roll and Pitch <0.025 degrees
True Heading 1 m baseline – 0.1 degrees
2 m baseline – 0.05 degrees
4 m baseline – 0.025 degrees
Heave 5 percent of heave amplitude or 5 centimeters

Table 4. Specifications for the SWATHplus-H sonar system (SEA Ltd.) transducers used to collect interferometric swath bathymetry during the survey (

SWATHplus-M Sonar Specifications
Sonar Frequency 234 kilohertz
Maximum Water Depth 100 meters
Maximum Swath Width 300 meters
Resolution Across Track (best case) 2.0 centimeters
Transmit Pulse Length 8.5 – 500 microseconds
Ping Repetition Rate (300m Swath Width) 7.5 pings per second
Vertical (depth) Accuracy (Range Dependent)
57 meter range        0.1 meters

Table 5. Specifications for the Valeport Mini Sound Velocity Sensor (SVS) used to collect continuous sound velocity, co-located with the bathymetry transducers and IMU (Valeport, Ltd.).

Valeport MiniSVS Specifications
Range 1,375-1,900 meters/second
Resolution 0.001 meters/second
Accuracy (100 millimeter path length)
Last factory calibration error 0.001 meters/second
Total maximum theoretical error +/- 0.017 meters/second
Acoustic frequency 1 hertz

Table 6. Specifications for the Valeport Mini Sound Velocity Profiler (SVP) used to collect positional sound velocity profiles through the water column (Valeport, Ltd.).

Valeport MiniSVP Specifications
Range 1,375-1,900 meters/second
Resolution 0.001 meters/second
Sound velocity +/- 0.02 meters/second
Temperature +/- 0.01 °Celsius
Pressure +/- 0.05 percent range
Acoustic frequency 1 hertz

Note: Any use of trade names is for descriptive purposes only and does not imply endorsement by the U.S. Government. To view PDF documents, you will need the latest version of Adobe Acrobat Reader or similar software.

(back to top)

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo logo U.S. Department of the Interior | U.S. Geological Survey
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Monday, 28-Nov-2016 19:35:55 EST