View source for 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 sampling|burst mode]], the measurements from individual [[Burst sampling|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 {{FontColor|bg=#fca1fd|text= [[NetCDF_parameter|complete list]]}} for the additional attributes related to each variable (e.g., units, bounds, cell_methods).


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

{| class="wikitable sortable"
|-
! 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
|-
| colspan="4" style="text-align:center; font-weight:bold; background-color:#f9eddd"|  Optional variables <math>\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 
|}

</div>

=Variables=
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<br>
==Required variables==
{| class="wikitable"
|-
! Short name
! Standard name
! Dimensions
! Comments and units
|-
| XYZ_VEL <math>\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_ <blockquote>''geographical_coordinates (ENU)''</blockquote>  <blockquote>''beam_coordinates (BEAM)''</blockquote>
|-
| 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. 
|-
| [[Level_1_data_(velocity_point-measurements)#Required_height_variable|HEIGHT or DEPTH]]<math>\dagger</math> 
| See [[Level_1_data_(velocity_point-measurements)#Required_height_variable|table below]]
| TIME, N_VEL_INSTRUMENT
| Units always in meters
|-
| BURST_NUMBER<math>\dagger\dagger</math>
| unique_identifier_for_each_burst
| TIME
| Integers of 1, 2, etc to designate which [[Burst sampling|burst]] the velocities are associated with.
|-
| colspan="4" style="text-align:center; font-weight:bold; background-color:#f9eddd" | '''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
|-
| colspan="4" style="text-align:center; font-weight:bold; background-color:#f9eddd" | '''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
|-
| colspan="4" | <math>\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>\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>\dagger\dagger</math> Variable required only when measuring in [[Burst sampling|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.

{| class="wikitable sortable" 
|-
! 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==


{| class="wikitable sortable" 
|-
! 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
|-
| colspan="4" | *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,
|}
</div>

=Group attributes (metadata)=
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<br>
This section describes attributes that may provide additional information about how the data was processed and manipulated at this stage.
{| class="wikitable" 
|-
! Attribute name
! Purpose
! Suggested content
|-
| processing_level
| Boilerplate about the ATOMIX Level 1 content.
| <blockquote>''This group includes the raw measurements from the recorder and ancillary measurements required for quality-controlling them using the manufacturer's recommendations.''</blockquote>
|-
| despiking_method
| Specify which despiking technique (if any) was applied to the dataset. Include citation if possible.
| <blockquote>''Velocities were despiked using Goring Nikora phase-space thresholding technique applied on [[Detrended time series|detrended timeseries]]. Time series were detrended using XX technique.''</blockquote>
|-
| 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.
|}
</div>

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Return to [[NetCDF velocimeters format]]

Go to next level: [[Level_2_data_(velocity_point-measurements)|Level 2 quality controlled and segmented]]
[[Category:Velocity point-measurements]]