Level 2 data (velocity profilers)

Velocities have now been segmented and detrended. Each segment is stored separately from each other, which allows segmenting data using overlapping windows i.e., some velocity samples can belong to more than one segment. This processing level is only required when an overlapping window is used during segmenting. For all other cases, the segment number and detrended velocities can be provided in Level 2 qaqc velocities.

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

The dimensions and variables for this optional processing level within NetCDF ATOMIX format are described below. This processing level is only required when an overlapping window is used during segmenting. For all other cases, the segment number and detrended velocities can be provided in Level 2 qaqc velocities.

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

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Short name	Standard name	Dimensions	Comments
N_SEGMENT	unique_identifier_for_each_ segment_in_the_entire_available_timeseries	N_SEGMENT	Replacement for using TIME centred in the segment as dimension
N_SAMPLE	unique_identifier_for_each_ sample_within_the_segment	N_SAMPLE	Max sample number is the segment length (seconds) multiplied by the sampling rate
N_BEAM	unique_identifier_for_each_beam	N_BEAM	Array of 1 to number of beams (3 to 5 typically)
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

Variables

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Short name	Standard name	Dimensions	Comment
R_VEL	water_radial_velocity_of_scatterers_ towards_instrument	N_SEGMENT [or time], R_DIST,N_SAMPLE, N_BEAM
R_VEL_DETRENDED	water_radial_velocity_of_scatterers_ towards_instrument_detrended	N_SEGMENT, R_DIST, N_SAMPLE, N_BEAM	High-frequency content of the signal, which may include surface wave, motion contamination, in addition to the turbulence signal. Please specify how.
TIME	TIME	N_SEGMENT, N_SAMPLE	Units in Days since 1950-01-01T00:00:00Z
N_PROFILE	unique_identifier_for_each_profile	N_SEGMENT, N_SAMPLE	This variable identifies each record (velocity) profile
THETA	beam_angle_from_instrument_z_axis	N_BEAM	The angle for a beam pointing vertically up would be 0o, and typically between 20 to 30o for the other beams.
[math]\displaystyle{ \ddagger }[/math] One could re-write for convenience the optional variables in Level 1 after segmenting them into smaller chunks.

Group attributes (metadata)

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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.	In this group, quality-controlled velocities have been split into smaller segments for processing. The timeseries are also detrended to recover the turbulence, and potentially surface wave and motion contamination.
segment_length	Provide length in seconds of each segment	Usually about 300 to 600 s dependent on time and length scales of turbulence
segment_overlap_proportion	Provide proportion overlap of each segment, i.e., window overlap	Often set to 0 or 0.5
detrending_method	Specify which filter or technique was used to detrend velocities, which is required for spectral and turbulence analysis.	Some examples include High-pass YY order butterworth filter with XX seconds cutoff frequency on the entire burst/timeseries Linear detrending on each segment
Optional group attributes
comment (optional)	Any additional information pertinent to other users who test their algorithms against the file.

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Return to: Level 1 raw

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