Level 3 data (velocity profilers)

Page status: Ready for review
Author(s):	Cynthia
Reviewer(s):
Comment:

Schematic of ADCP processing nomenclature

The required dimensions and variables for the structure-function processing level within NetCDF ATOMIX format for velocity ADCP measurements are described below. This NetCDF group contains the structure function (DLL) calculated as a function of the along-beam separation for the available/usable ADCP bins.

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

Short name	Standard name	Dimensions	Comments
TIME	time	TIME	Units in Days since 1950-01-01T00:00:00Z. Provide bounds attribute to designate the variable containing the limits of each segment (see CF-compliant example).
Z_DIST	distance_from_sensor_along_z_instrument_axis	Z_DIST	bin centre distance (in meters) from the transducer along the instrument's vertical axis
R_DEL	along-beam_separation_distance_ at_which_structure_function_is_evaluated	R_DEL	Estimated from bin sizes and theta in Level 2 qaqc variables
N_BEAM	unique_identifier_for_each_beam	N_BEAM	Array of 1 to number of beams (3 to 5 typically)

Variables

Short name	Standard name	Dimensions	Comment
DLL	second_order_structure_function	TIME, R_DIST, R_DEL, N_BEAM	Differences in velocities squared have been time-averaged (units of m2/s2).
DLL_FLAGS	second_order_structure_function_status_flags	TIME, R_DIST, R_DEL, N_BEAM	To be linked, when boolean flags defined
DLL_N	second_order_structure_function_number_of_observations	TIME, R_DIST, R_DEL, N_BEAM	Measure the number of available measurements in each segment i.e., data quality.
N_SEGMENT	unique_identifier_for_each_segment_ in_the_entire_available_timeseries	TIME	Enables backtracking to previous processing level
BURST_NUMBER [math]\displaystyle{ \dagger\dagger }[/math]	unique_identifier_for_each_burst	TIME	Only required when measuring in burst-mode. Integers of 1, 2, etc to designate which burst the velocities are associated with.
Optional dimensions for 5-beam ADCP
DLL5	second_order_structure_function_in_beam_5	TIME, R_DEL5, R_DIST5	Only necessary for 5-beam ADCP
DLL5_FLAGS	second_order_structure_function_in_beam_5_status_flags	TIME, R_DEL5, R_DIST5	Same as DLL_FLAGS but for the 5th vertical beam when present.
DLL5_N	second_order_structure_function_in_beam_5_number_of_observations	TIME, R_DIST, R_DEL, N_BEAM	Measure the number of available measurements in each segment i.e., data quality.
[math]\displaystyle{ \dagger\dagger }[/math] Variable required only when measuring in bursts e.g., 18 min of continuous measurements every hour.

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 content of the NetCDF group.	This group includes the structure function Dll as a function of the separation distance. Any ancillary information required for estimating the dissipation of turbulent kinetic energy may also be stored here.
dll_calculation_type	Specify differencing technique used to estimate DLL	Examples include: Central-differencing Forward-differencing
Optional group attributes [math]\displaystyle{ \ddagger }[/math]
stationarity_testing	Any testing done on the segment to verify stationarity?	To be revisited once testing begins. Tentatively refer to demo yaml file.
noise_testing	Details of testing the noise levels, or if the signal comprises mostly of noise?
comment (optional)	Any additional information pertinent to other users who test their algorithms against the file.

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