Level 1 data (velocity point-measurements)

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.

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