Level 1 data (velocity point-measurements)

From Atomix

The required dimensions and variables for the first processing level within NetCDF ATOMIX format for velocity measurements are described below. This processing level contains the raw measurements recorded by the instrument. If sampling is in burst mode, the measurements from individual bursts are appended together.

Only a few attributes for each variable are listed since the page's purpose is to describe the information layout within each NetCDF file. Please refer to the complete list for the additional attributes related to each variable (e.g., units, bounds, cell_methods).


Dimensions


The number of velocity instruments [N_VEL_INSTRUMENT] is here for completeness, but the benchmarks examples will have measurements only from one instrument stored.

Short name Standard name Dimensions Comments
TIME time TIME Units in Days since 1950-01-01T00:00:00Z
TIME_HPR time_of_heading_pitch_roll TIME_HPR Heading, pitch and roll (tilt) sensors measure always at 1Hz for Vector ADV
N_VEL_COMPONENT unique_identifier_for_each_velocity_component N_VEL_COMPONENT Maximum of 3 for u,v, w (east, north, up) velocities
Optional variables [math]\displaystyle{ \ddagger }[/math]
N_VEL_INSTRUMENT unique_identifier_for_each_velocity_instrument N_VEL_INSTRUMENT Required only if storing multiple synchronized instruments in the same file

Variables


Required variables

Short name Standard name Dimensions Comments and units
XYZ_VEL [math]\displaystyle{ \ddagger }[/math] water_velocity_measured_in_

instrument_coordinates

TIME, N_VEL_COMPONENT, N_VEL_INSTRUMENT Units in m/s variables are water_velocity_measured_in_

geographical_coordinates (ENU)

beam_coordinates (BEAM)

XYZ_VEL_FLAGS water_velocity_measured_in_

instrument_coordinates_status_flags

TIME, N_VEL_COMPONENT, N_VEL_INSTRUMENT CF-compliant 8-bit (0-255) boolean flag that designates why a velocity sample was discarded.
HEIGHT or DEPTH[math]\displaystyle{ \dagger }[/math] See table below TIME, N_VEL_INSTRUMENT Units always in meters
BURST_NUMBER[math]\displaystyle{ \dagger\dagger }[/math] unique_identifier_for_each_burst TIME Integers of 1, 2, etc to designate which burst the velocities are associated with.
Platform motion variables
HEADING platform_yaw_angle TIME_HPR, N_VEL_INSTRUMENT degrees, clockwise from true North
PITCH platform_pitch_angle TIME_HPR, N_VEL_INSTRUMENT degrees
ROLL platform_roll_angle TIME_HPR, N_VEL_INSTRUMENT degrees
Quality-control variables usually available with acoustic-Doppler instruments
ABSIC backscatter_intensity_from_each_acoustic_beam TIME, N_VEL_COMPONENT, N_VEL_INSTRUMENT count
SNR signal_noise_ratio_from_each_acoustic_beam TIME, N_VEL_COMPONENT decibel
CORRN noise_correlation_percent_from_each_acoustic_beam TIME, N_VEL_COMPONENT, N_VEL_INSTRUMENT percent
[math]\displaystyle{ \ddagger }[/math] Some manufacturers record quality-control variables (e.g., CORRN) in the instrument coordinate system. For example, Nortek records these variables in the instrument XYZ frame of reference. It's best to record the data in that coordinate system.

[math]\displaystyle{ \dagger }[/math]A variable situating the instruments in the water column is required. This may be a nominal depth (or height) or a time-varying depth or height above the bottom.

[math]\displaystyle{ \dagger\dagger }[/math] Variable required only when measuring in bursts e.g., 18 min of continuous measurements every hour.

Required height variable

Height or depth-related variables (only 1x is required). These variables locate the instrument vertically from a boundary (e.g, surface or ice). A negative value implies it's below the boundary. Units are always in meters. Can also provide a constant value in time representing the nominal height and/or depth.

Short name Standard name Dimensions
HEIGHT_AB height_above_bottom TIME, N_VEL_INSTRUMENT
DEPTH depth_below_surface TIME, N_VEL_INSTRUMENT

Optional ancillary variables

Short name Standard name Dimensions Comments
PRES sea_water_pressure TIME, N_VEL_INSTRUMENT dbar, equals 0 at the sea surface and positive down.
TEMP* sea_water_temperature TIME degrees_Celsius, in-situ temperature ITS-90 scale
*Data from concurrent sensors may be optionally included e.g., salinity, dissolved oxygen (e.g., eddy-correlation system). Kinematic viscosity of seawater needs to be calculated during processing,

Group attributes (metadata)


This section describes attributes that may provide additional information about how the data was processed and manipulated at this stage.

Attribute name Purpose Suggested content
processing_level Boilerplate about the ATOMIX Level 1 content.

This group includes the raw measurements from the recorder and ancillary measurements required for quality-controlling them using the manufacturer's recommendations.

despiking_method Specify which despiking technique (if any) was applied to the dataset. Include citation if possible.

Velocities were despiked using Goring Nikora phase-space thresholding technique applied on detrended timeseries. Time series were detrended using XX technique.

comment (optional) Information is pertinent to problems in the raw data files during collection. Examples: Stitching of files, corruption of binary files that were recovered by the manufacturer, etc.

Return to NetCDF velocimeters format

Go to next level: Level 2 quality controlled and segmented