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	Segment midpoint time. Units in Days since reference time specified in variable attribute. Provide bounds attribute to designate the variable containing the limits of each segment (see CF-compliant example).
Z_DIST	distance_from_sensor_along_vertical	Z_DIST	bin centre distance (in meters) from the transducer along the instrument's vertical axis
N_BEAM	unique_identifier_for_each_beam	N_BEAM	Array of 1 to number of beams (3 to 5 typically)
N_DEL	along-beam_separation_distance_over_ which_DLL_is_evaluated_in_number_of_bins	N_DEL	Number of bins separating two velocity measurements used to calculate DLL

Variables

Short name	Standard name	Dimensions	Comment
DLL	second_order_structure_function	TIME, Z_DIST, N_BEAM, N_DEL	Differences in velocities squared have been time-averaged (units of m2/s2).
DLL_FLAGS	second_order_structure_function_ status_flag	TIME, Z_DIST, N_BEAM, N_DEL	To be linked, when boolean flags defined
R_DEL	along-beam_separation_distance_at_ which_structure_function_is_evaluated	TIME, Z_DIST, N_BEAM, N_DEL	Estimated quantity (in meters) from N_DEL (Level 3), BIN_SIZE (Level 2) and THETA (Level 2).
R_DIST	distance_from_sensor_along_beams	Z_DIST, N_BEAM	Along-beam bin centre distance (in meters) from the transducer
DLL_N	second_order_structure_function_number_ of_observations	TIME, Z_DIST, N_BEAM, N_DEL	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
Optional variables [math]\displaystyle{ \ddagger }[/math]
ENU_VEL	east_north_up_error_water_velocity	TIME, Z_DIST, N_BEAM	This variable provides burst-averaged water velocity in geographical coordinates where N_BEAM = [1 2 3 4] corresponding to east, north, up components and error velocities for determining background flow.

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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