Abstract:

The dataset contains current-meter records from 5 deployments of a floating sediment trap during the ECOGIG-2 EN600 water-column cruise. The instrument was an ALEC Electronics electromagnetic current meter, suspended beneath the sediment trap at a depth of ~150m. Samples were collected in the Gulf of Mexico from June 4th to 19th, 2017.

Suggested Citation:

Andreas Thurnherr. 2018. Current Meter Data from a Floating Sediment Trap, Gulf of Mexico, June 4 to 19, 2017. Distributed by: Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC), Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N79W0D21

Purpose:

To provide measurements of the velocity field in close proximity to the drifting sediment trap.

Data Parameters and Units:

Each data file contains a time series (8s sampling interval) of the current meter records from a single deployment (002, 006, 008, 013 and 015) of the floating trap. The file names are based on the deployment number --- the file 008.nc contains the data from the 3rd deployment. Each time series contains the following Metadata: mag_decl: correction for magnetic declination in degrees that was applied during processing; SondeName: ALEC instrument name (id); SondeNo: ALEC serial number; SensorType: ALEC sensor information; SensorType2: ALEC sensor information; Interval: sampling interval in milliseconds; depth: deployment depth in meters; SampleCnt: number of samples in file; vx.bias: applied x-axis sensor bias correction determined during post-cruise calibration; vy.bias: applied y-axis sensor bias correction determined during post-cruise calibration; Each time series contains the following data: dn: 2017 decimal day (0.5 indicates noon of Jan 1); date: date of sample; time: time of sample; speed: horizontal current speed in meters per second; dir: horizontal current direction in clockwise degrees from north; u: eastward velocity component in meters per second; v: northward velocity component in meters per second; temp: uncalibrated temperature in degC id deployment lon/lat recovery lon/lat --------------------------------------------------------------- 002 -96.3283 26.7473 -96.4343 26.7151 006 -91.9799 27.4985 -92.2308 27.5034 008 -91.4976 27.7805 -91.4867 27.9066 013 -90.0369 27.2871 -89.8466 27.156 015 -91.8216 27.3513 -92.0585 27.5304

Methods:

The following data processing steps were applied to each file: 1. Trim out-of-water records from beginning and end of file. 2. Correct velocity measurements for sensor biases determined during post-deployment calibration. 3. Apply magnetic declination correction of 2 degrees.

Instruments:

ALEC Electronics AEM-USB electromagnetic current meter.

Error Analysis:

After the cruise the biases of the two acoustic sensor paths were determined in the laboratory, following the manufacturer-recommended protocol. The corrections have only a minor effect on the velocities, largely because of the strong velocities encountered in the northeastern Gulf. A basic analysis was carried out combining the current-meter records with simultaneous ADCP data from the upper 100m of the water column. The data from the two instruments are mutually consistent, which allows interpolation to be used to fill the gap between 100 and 150m.

Individual Files: