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