Fugro Cruise C16314 Line 0044, 75 kHz VMADCP

Program of vessel mount ADCP measurements comprising a combination of 300kHz and 75kHz ADCP data collected in the vicinity of the Loop Current and drilling blocks between 2004 and 2007.
_NCProperties=version=2,netcdf=4.7.4,hdf5=1.12.0,
acknowledgement=Data collection funded by various oil industry operators
cdm_data_type=TrajectoryProfile
cdm_profile_variables=time
cdm_trajectory_variables=trajectory
CODAS_processing_note=
CODAS processing note:
======================

Overview
--------
The CODAS database is a specialized storage format designed for
shipboard ADCP data. "CODAS processing" uses this format to hold
averaged shipboard ADCP velocities and other variables, during the
stages of data processing. The CODAS database stores velocity
profiles relative to the ship as east and north components along with
position, ship speed, heading, and other variables. The netCDF *short*
form contains ocean velocities relative to earth, time, position,
transducer temperature, and ship heading; these are designed to be
"ready for immediate use". The netCDF *long* form is just a dump of
the entire CODAS database. Some variables are no longer used, and all
have names derived from their original CODAS names, dating back to the
late 1980's.

Post-processing
---------------
CODAS post-processing, i.e. that which occurs after the single-ping
profiles have been vector-averaged and loaded into the CODAS database,
includes editing (using automated algorithms and manual tools),
rotation and scaling of the measured velocities, and application of a
time-varying heading correction. Additional algorithms developed more
recently include translation of the GPS positions to the transducer
location, and averaging of ship's speed over the times of valid pings
when Percent Good is reduced. Such post-processing is needed prior to
submission of "processed ADCP data" to JASADCP or other archives.

Full CODAS processing
---------------------
Whenever single-ping data have been recorded, full CODAS processing
provides the best end product.

Full CODAS processing starts with the single-ping velocities in beam
coordinates. Based on the transducer orientation relative to the
hull, the beam velocities are transformed to horizontal, vertical, and
"error velocity" components. Using a reliable heading (typically from
the ship's gyro compass), the velocities in ship coordinates are
rotated into earth coordinates.

Pings are grouped into an "ensemble" (usually 2-5 minutes duration)
and undergo a suite of automated editing algorithms (removal of
acoustic interference; identification of the bottom; editing based on
thresholds; and specialized editing that targets CTD wire interference
and "weak, biased profiles". The ensemble of single-ping velocities
is then averaged using an iterative reference layer averaging scheme.
Each ensemble is approximated as a single function of depth, with a
zero-average over a reference layer plus a reference layer velocity
for each ping. Adding the average of the single-ping reference layer
velocities to the function of depth yields the ensemble-average
velocity profile. These averaged profiles, along with ancillary
measurements, are written to disk, and subsequently loaded into the
CODAS database. Everything after this stage is "post-processing".

note (time):
------------
Time is stored in the database using UTC Year, Month, Day, Hour,
Minute, Seconds. Floating point time "Decimal Day" is the floating
point interval in days since the start of the year, usually the year
of the first day of the cruise.

note (heading):
---------------
CODAS processing uses heading from a reliable device, and (if
available) uses a time-dependent correction by an accurate heading
device. The reliable heading device is typically a gyro compass (for
example, the Bridge gyro). Accurate heading devices can be POSMV,
Seapath, Phins, Hydrins, MAHRS, or various Ashtech devices; this
varies with the technology of the time. It is always confusing to
keep track of the sign of the heading correction. Headings are written
degrees, positive clockwise. setting up some variables:

X = transducer angle (CONFIG1_heading_bias)
positive clockwise (beam 3 angle relative to ship)
G = Reliable heading (gyrocompass)
A = Accurate heading
dh = G - A = time-dependent heading correction (ANCIL2_watrk_hd_misalign)

Rotation of the measured velocities into the correct coordinate system
amounts to (u+i*v)*(exp(i*theta)) where theta is the sum of the
corrected heading and the transducer angle.

theta = X + (G - dh) = X + G - dh

Watertrack and Bottomtrack calibrations give an indication of the
residual angle offset to apply, for example if mean and median of the
phase are all 0.5 (then R=0.5). Using the "rotate" command,
the value of R is added to "ANCIL2_watrk_hd_misalign".

new_dh = dh + R

Therefore the total angle used in rotation is

new_theta = X + G - dh_new
= X + G - (dh + R)
= (X - R) + (G - dh)

The new estimate of the transducer angle is: X - R
ANCIL2_watrk_hd_misalign contains: dh + R

====================================================

Profile flags
-------------
Profile editing flags are provided for each depth cell:

binary decimal below Percent
value value bottom Good bin
-------+----------+--------+----------+-------+
000 0
001 1 bad
010 2 bad
011 3 bad bad
100 4 bad
101 5 bad bad
110 6 bad bad
111 7 bad bad bad
-------+----------+--------+----------+-------+

CODAS_variables=
Variables in this CODAS short-form Netcdf file are intended for most end-user
scientific analysis and display purposes. For additional information see
the CODAS_processing_note global attribute and the attributes of each
of the variables.

============= =================================================================
time Time at the end of the ensemble, days from start of year.
lon, lat Longitude, Latitude from GPS at the end of the ensemble.
u,v Ocean zonal and meridional velocity component profiles.
uship, vship Zonal and meridional velocity components of the ship.
heading Mean ship heading during the ensemble.
depth Bin centers in nominal meters (no sound speed profile correction).
tr_temp ADCP transducer temperature.
pg Percent Good pings for u, v averaging after editing.
pflag Profile Flags based on editing, used to mask u, v.
amp Received signal strength in ADCP-specific units; no correction
for spreading or attenuation.
============= =================================================================

contributor_name=RPS
contributor_role=editor
contributor_role_vocabulary=https://vocab.nerc.ac.uk/collection/G04/current/
Conventions=CF-1.6, ACDD-1.3, IOOS Metadata Profile Version 1.2, COARDS
cruise_id=Fugro_C16314_075_Line0044_0
description=Shipboard ADCP velocity profiles from Fugro_C16314_075_Line0044_0 using instrument wh75
Easternmost_Easting=-89.75908055555556
featureType=TrajectoryProfile
geospatial_bounds=LINESTRING (-90.97738055555556 27.296511111111112, -89.75908055555556 27.308366666666668)
geospatial_bounds_crs=EPSG:4326
geospatial_bounds_vertical_crs=EPSG:5703
geospatial_lat_max=27.308366666666668
geospatial_lat_min=27.296511111111112
geospatial_lat_units=degrees_north
geospatial_lon_max=-89.75908055555556
geospatial_lon_min=-90.97738055555556
geospatial_lon_units=degrees_east
geospatial_vertical_max=600.76
geospatial_vertical_min=16.76
geospatial_vertical_positive=down
geospatial_vertical_units=m
hg_changeset=2955:483f3262b192
history=Created: 2019-07-31 15:15:32 UTC
id=C16314_075_Line0044_0
infoUrl=ADD ME
institution=GCOOS
instrument=In Situ/Laboratory Instruments > Profilers/Sounders > Acoustic Sounders > ADCP > Acoustic Doppler Current Profiler
keywords_vocabulary=GCMD Science Keywords
naming_authority=edu.tamucc.gulfhub
Northernmost_Northing=27.308366666666668
platform=ship
platform_vocabulary=https://mmisw.org/ont/ioos/platform
processing_level=QA'ed and checked by Oceanographer
program=Oil and Gas Loop Current VMADCP Program
project=O&G LC VMADCP Program
software=pycurrents
sonar=wh75
source=Current profiler
sourceUrl=(local files)
Southernmost_Northing=27.296511111111112
standard_name_vocabulary=CF Standard Name Table v67
subsetVariables=time, longitude, latitude, depth, u, v
time_coverage_duration=P0Y0M0DT11H52M26S
time_coverage_end=2007-08-23T19:27:53Z
time_coverage_resolution=P0Y0M0DT0H5M1S
time_coverage_start=2007-08-23T07:35:27Z
Westernmost_Easting=-90.97738055555556
yearbase=2007

包含2004年至2007年间在Loop Current附近及钻井区块收集的300kHz和75kHz ADCP数据的船舶安装式ADCP测量程序。该数据集采用CODAS数据库格式，旨在存储船舶ADCP的平均速度和其他变量，并在数据处理过程中使用。CODAS数据库存储相对于船舶的东向和北向速度分量、位置、船速、航向以及其他变量。netCDF简短形式包含相对于地球的海洋速度、时间、位置、换能器温度和船速；这些数据设计为“可直接使用”。netCDF长形式是CODAS数据库的全部内容。一些变量已不再使用，所有变量名称均源自其原始的CODAS名称，追溯至20世纪80年代末后期。