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Data Series 1039


Coastal Single-Beam Bathymetry Data Collected in 2015 from the Chandeleur Islands, Louisiana

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Citation Page
Abstract
Introduction
Survey Overview
Data Acquisition
Data Processing
Error Analysis
Survey Products
Data Downloads
Logs
Abbreviations
References Cited
 

Data Acquisition

Navigation

Three Geographic Positioning Systems (GPS) base stations were occupied during this survey. Benchmark MRK3 was located in the northern part of the survey area on the sound side of the islands near the Pelican fishing camp, benchmark SM01 was located in the middle of the survey area in the middle of the island at Monkey Bayou, and benchmark GRIG was located in the southern end of the survey on an abandoned oil drilling platform (fig. 2). The base stations were equipped with Ashtech Proflex GPS receivers (table 2) recording 12-channel, full-carrier-phase positioning signals (L1/L2) from satellites via Thales Choke-ring antennas, recording every 0.1 seconds (s).

This GPS instrumentation was duplicated on all survey vessels (rovers) with the exception of the R/V Chum (15BIM03) on which an Ashtech Global Navigation Satellite System (GNSS) antenna was used instead of a choke-ring antenna. The base and rover receivers recorded positions concurrently at all times throughout the survey. Rover R/V Chum and R/V Jabba Jaw recoded at intervals of 0.1 s and 0.2 s respectively, for the duration of the survey. R/V Sallenger recorded at intervals of 1.0 s for the first 4 days, and 0.2 s thereafter.

Soundings

Depth soundings were recorded at 50-millisecond (ms) intervals on all survey platforms using ODOM Echotrac CV100 fathometers (table 3) and eChart software version 1.4. All components including the GPS antenna, motion sensor, and the echo sounder transducers were mounted in-line vertically to avoid error resulting from offsets, helping to maintain low overall error for the survey. On each vessel, all data from the GPS receiver, motion sensor, and fathometer were recorded in real-time to a single raw data file (.raw) within the hydrographic survey software HYPACK (version 14.0.9.47 for 15BIM01 and 15BIM02; version 13.0.09.17 for 15BIM03), with each device string referenced by an identification code and a Coordinated Universal Time (UTC) time stamp to the nearest millisecond. HYPACK software was also used in conjunction with eChart software to monitor sounding data quality at all times throughout the survey.

Vessel Motion

Boat motion was recoded on the R/V Sallenger and R/V Jabba Jaw only, using Teledyne TSS Dynamic Motion Sensor “DMS-25” and Teledyne TSS Dynamic Motion Sensor “DMS-05” sensors, respectively, every 50 ms (table 4). A motion sensor was not used on the R/V Chum. To minimize motion errors on this vessel, a rapid GPS recording interval of 0.1 s, a minimal vertical distance of 1.29 m from antenna to sounding device, and a narrow 4 degree transducer beam were utilized.

Sound Velocity

Sound velocity profile (SVP) measurements were collected using two SonTek CastAway conductivity, temperature, and depth (CTD) instruments (table 5) as well as a Valport Mini Sound Velocity Profiler (SVP) (table 6). The instruments were periodically cast overboard to observe changes in the speed of sound (SOS). A total of 188 successful sound velocity casts were taken throughout the survey in water depths ranging from 0.13 to 13.96 m. The average sound velocity recorded was 1527.93 meters per second (m/s), and values ranged from 1519.85 to 1539.23 m/s. The recorded profiles were later incorporated into the post-processing software to correct the depth for temporal and spatial changes in the speed of sound (SOS) throughout the water column.

Table 2. Specifications for the Ashtech ProFlex 500 and ProFlex 800 GPS receivers used during the single-beam bathymetry survey (Ashtech_ProFlex500, 228-KB PDF; Ashtech_ProFlex800, 194-KB PDF). Abbreviations: feet (ft), millimeters (mm), parts per million (ppm).

GPS Receiver Specifications Ashtech ProFlex 500 and 800
Static horizontal 3 mm (0.009 ft) + 0.1 ppm
Static vertical 3.5 mm (0.011 ft) + 0.4 ppm
Kinematic horizontal 10 mm (0.033 ft) + 1 ppm
Kinematic vertical20 mm (0.065 ft) + 1 ppm


Table 3. Specifications for the ODOM CV100 Echosounder used during the single-beam bathymetry survey (Odom_Echotrac_CV100, 116-KB PDF). Abbreviations: centimeters (cm), hertz (Hz), meters (m), root mean square (RMS).

ODOM Echotrac CV100 Specifications
Water depth range >0.30–600 m (depending on frequency)
Output power Up 300 watts RMS
<1 watt minimum
Resolution 1.0 cm
Vertical (depth) accuracy 0.01 m +/- 0.1 percent depth value (200 Hz)


Table 4. Specifications for the Teledyne TSS-DMS-05 motion sensor used during the single-beam bathymetry survey (TSS-DMS-05, 202-KB PDF). Abbreviation: centimeters (cm).

Teledyne TSS-DMS-05 Specifications
Roll and pitch 0.05 degrees
Heave 5 percent of heave amplitude or 5 cm, whichever is greater


Table 5. Specifications for the SonTek CastAway CTD profiler used during the single-beam bathymetry survey (CastAway-CTD, 520-KB PDF). Abbreviations: conductivity, temperature, depth (CTD); meters per second (m/s).

SonTek CastAway CTD
Range 1,400–1,730 m/s
Resolution 0.01 m/s
Accuracy +/- 0.15 m/s
Measured or derived Speed of sound in sea water at high pressures (Chen and Millero, 1977)


Table 6. Specifications for the Valeport Mini Sound Velocity Profiler (SVP) used to collect positional sound velocity profiles through the water column (Valport MiniSVP, 136-KB PDF). Abbreviations: hertz (Hz), meters per second (m/s).

Valeport Mini SVP
Range 1,375–1,900 m/s
Resolution 0.001 m/s
Accuracy

Sound Velocity, +/- 0.02 m/s
Temperature, +/- 0.01 degrees Celsius
Pressure, +/- 0.05 percent range

Acoustic frequency 1 Hz

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