Mooring data description

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1) BPR (bottom pressure recorders)

On the BG moorings, bottom pressure measurements are being made using either Sea-Bird Electronics SBE-16plus temperature and salinity recorders or SBE-53 BPR bottom pressure recorders, both with precision Paroscientific Digiquartz (6000 psia) pressure sensors. The recovered data processing procedure is fundamentally the same for either instrument.

Accuracy of the pressure sensor is 0.01% full-scale (~0.4 m for 6000 psia sensor), and the long term drift is on the order of 1 ppm per year. The resolution of the pressure measurement depends on the sensitivity of the sensor and the resolution of the counter. Integrating the pressure measurements increases the resolution of the pressure measurement, although this may be limited somewhat by sensor drift, recorder time base drift, and background noise. For the SBE-16plus recorders, a measurement integration of 70 seconds should resolve better than 1 mm. The SBE-53 BPR provides higher quality data by continuously powering the pressure sensor and ovenized reference oscillator to reduce startup transients, hence a measurement integration of 1 minute should resolve better than 0.2 mm. Battery life considerations dictate the configured sampling rate for each instrument so that the frequency of SBE16plus measurements is either 25 or 30 minutes between readings, and the frequency of the SBE 53 BPR measurements is 15 minutes.

After recovering the BPR, Sea-Bird SeaTerm software is used to download the data from the SBE16plus recorders in single binary hexadecimal (HEX) files, while SeaTermW software is used for the SBE53 BPRs. The hex files are converted to ASCII CNV files using the Sea-Bird Data Processing program for the SBE16plus recorders and using Seasoft for waves for the SBE53 BPRs. During this step, the instrument specific calibration adjustments are applied to the raw data. The CNV files include header information with all of the instrument specific information including the calibration coefficients used in the conversion, followed by the specific output data in columns. These data were plotted using the Sea-Bird software to visually check for obvious errors. Subsequently, the CNV files are imported into MATLAB, where deployment specific script routines operate on the data from every instrument in a single year.

The MATLAB routines truncate the time series for the period when the BPR is deployed on the ocean bottom, and output the data in ASCII files. The filename format is bgXXYY_bpr_Z.dat, where XXYY indicates the observation years and Z is the mooring identifier. The first two lines of the file are header information (preceded by a % character), the data follow in 3 columns, and the file terminates with %endofdat. The first line of the header includes the observation years, the mooring identifier and location, and the second line indicates the data variables and units [%date time(UTC) pressure(dbar) temperature(C) salinity(PSU)]. Dates and times are given in UTC, and temperature is determined according to the ITS-90 scale.

2) MMP (McLane Moored Profilers)

The results of the BGFE 2003-04 MMP EMCTD and ACM Data Processing [PDF] are digitally archived in three formats that are being made publicly available here along with documentation thoroughly describing the processing procedure. The data are identical regardless of the format.

The first format stores all of the processed data from all profiles from a single MMP into single Matlab-format files ending in .mat, where a, b, and c identify the mooring. Each file contains the following variables:

DPDT: array of profiling speeds cm/s
S: array of salinity pss
SIGTH: array of sigma-theta kg/m3
T: array of temperature deg C
THETA: array of potential temperature
TIME: array of time of each measurement (encoded with datenum.m)
U: array of east velocity cm/s
V: array of north velocity cm/s
W: array of measured vertical velocity (includes profiling velocity) cm/s
dates: vector string with profiler start date
day: vector of decimal year day (2003)
location: string with location of mooring
name: string with dataset name
number: vector of profile number
pgrid: vector of pressure grid m

The remaining two formats contain the same information in multiple ASCII text files with all the data from each profile in a single file, but differ in the method of storage to accommodate both PC and UNIX computer systems. In either case, the individual ASCII profile data files are named bg0304_mmp_a###.mat, bg0304_mmp_b###.mat, and bg0304_mmp_c###.mat, where a, b, and c identify the mooring and ### is the profile number. For PC systems, all of the files from a single MMP are zipped into single files that end in .zip. For UNIX systems, all of the files from a single MMP are compressed and tarred into single files ending in .Z. Each individual data files includes two lines of header information.

The first line provides general information:
project and mooring name: profile number, start date and time, location

The second line describes the columns of data:
hr:min:sec P(Dbar) T(degC) S(PSU) U(cm/s) V(cm/s) W(cm/s) DPDT(cm/s)

The remaining lines comprise the processed data from the profile in the following format:
'%02d:%02d:%02.0f %4d %6.3f %6.3f %6.2f %6.2f %6.2f %6.2f\n'

The lines of data increase sequentially based on the time of the observation, so downgoing profiles start at the shallowest depth and upgoing profiles start at the deepest depth. Grid points with no data (that were filled with NANs) are omitted in the ASCII files.

3) ULS (upward looking sonars)

A complete description of the processing used to derive ice drafts from the ULS data is given in BGOS ULS Data Processing Procedure [PDF]. The output of the processed ULS data is available in two formats: 1) the complete 2-second ice draft time series, and 2) daily averages draft statistics, temperature, water level, and sound speed. With velocities provided from an outside source, the complete draft time series can be converted to a spatial distribution, and the features in the ice cover can be clearly discerned and described. If high resolution is not required, the daily average ice draft (and ancillary) data provide a synopsis of the results in a convenient abbreviated format.

The complete draft time series are saved in separate ASCII text files for each mooring and year. The filename includes the deployment year and mooring identifier (for example uls03a_draft.dat). The first two lines of the file includes the experiment year, mooring location and data variable names (with units):

%BG 2003-2004 Mooring A: 75 00.449 N, 149 58.660 W
%date time(UTC) draft(m)

The remainder of the file includes all 15 million (2-second) draft estimates processed for the full year. Compressed versions of the text file are saved in .ZIP and TAR.Z formats.

Daily average draft, betas, temperature, and water level information for each mooring and year are saved in MATLAB format files (e.g. uls03a_daily.mat) with the following variables:

dates: date string timeseries
name: name of the mooring and dataset
yday: year day timeseries
BETA: final beta adjustment timeseries used in ice draft calculations
BTBETA: initial beta timeseries based on bottom temperature
ID: number of ice drafts binned daily every 0.1 m from 0.05 to 29.95 m
IDS: daily ice draft statistics: number, mean, std, minimum, maximum, median
OWBETA: beta timeseries determined from open water events
T: temperature timeseries (°C)
WL: water level timeseries (m)

3) ADCP (Acoustic Doppler Current Profilers)

Coming soon...

Last updated: April 2, 2013