Level 4 data (velocity profilers)

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

This will dictate the data required at the final processing level, where we store the estimated dissipation estimates [math]\displaystyle{ \varepsilon }[/math] along with quality metrics.

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 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)

Variables

Short name	Standard name	Dimensions	Comment
EPSI	specific_turbulent_kinetic_energy_dissipation _in_sea_water	TIME, Z_DIST, N_BEAM	Dissipation rate of turbulent kinetic energy per unit mass of water [W/kg] estimated from individual beams.
EPSI_FINAL	specific_turbulent_kinetic_energy_dissipation _in_sea_water	TIME, Z_DIST	Final (beam-averaged) dissipation rate of turbulent kinetic energy per unit mass of water [W/kg]. best to state cell_methods attribute to indicate what was averaged e.g., "cell_methods= N_BEAM:mean" for averages across beams.
C2	constant_used_in_the_second_order_structure_function	Scalar [1 value]	This constant appears when estimating the dissipation rate of turbulent kinetic energy from the regression coefficients (see Compute structure functions and dissipation estimates).
Quality-control metrics
EPSI_FLAGS	specific_turbulent_kinetic_energy_dissipation_ in_sea_water_status_flag	TIME, Z_DIST, N_BEAM	For details see Velocity Profiler data flags
EPSI_CI_HIGH	specific_turbulent_kinetic_energy_dissipation_ in_sea_water_high_confidence_limit	TIME, Z_DIST, N_BEAM	Computed from the confidence interval of the regression slope as EPSI_CI_HIGH = (SLOPE_CI_HIGH/C2)^(3/2) To be verified.
EPSI_CI_LOW	specific_turbulent_kinetic_energy_dissipation_ in_sea_water_low_confidence_limit	TIME, Z_DIST, N_BEAM	Computed from the confidence interval of the regression slope as EPSI_CI_HIGH = (SLOPE_CI_HIGH/C2)^(3/2) To be verified.
EPSI_DEL_RATIO	specific_turbulent_kinetic_energy_dissipation_in_sea_water_error_ratio	TIME, Z_DIST, N_BEAM	Ratio of the uncertainty, [math]\displaystyle{ \delta\varepsilon }[/math] to the value of [math]\displaystyle{ \varepsilon }[/math]. Computed from the confidence intervals as [math]\displaystyle{ \frac{\delta\varepsilon}{\epsilon} = \frac{3\ (\text{EPSI_CI_HIGH}\ -\ \text{EPSI_CI_LOW})}{4\ \text{REGRESSION_COEFF_A0}} }[/math] Link to derivation
R_MAX	maximum_separation_distance_for_DLL_regression	TIME, Z_DIST, N_BEAM	maximum R_DEL separation distance [m] used when computing the regression of DLL vs r[math]\displaystyle{ ^{2/3} }[/math]
REGRESSION_COEFF_A0	structure_function_regression_intercept	TIME, Z_DIST, N_BEAM	Constant term in regression, i.e. [math]\displaystyle{ A_0 }[/math] in [math]\displaystyle{ D_{LL} = A_1 r^{2/3} + A_0 }[/math]. Units are m[math]\displaystyle{ ^2 }[/math]s[math]\displaystyle{ ^{-2} }[/math] and value is proportional to instrument noise. (see Compute structure functions and dissipation estimates)
REGRESSION_COEFF_A1	structure_function_regression_coefficient for_r^2/3	TIME, Z_DIST, N_BEAM	Linear term in regression, i.e. [math]\displaystyle{ A_1 }[/math] in [math]\displaystyle{ D_{LL} = A_1 r^{2/3} + A_0 }[/math]. Units are m[math]\displaystyle{ ^{4/3} }[/math]s[math]\displaystyle{ ^{-2} }[/math]
REGRESSION_R2	regression_goodness_of_fit_adjusted_for_number_of_terms	TIME, Z_DIST, N_BEAM	[math]\displaystyle{ R^2 }[/math] computed from the regression of [math]\displaystyle{ D_{LL} }[/math] vs [math]\displaystyle{ r^{2/3} }[/math]. Specific method should be described in group attributes.
REGRESSION_N	structure_function_regression_number_of_observations	TIME, Z_DIST, N_BEAM	number of data points used in the regression of [math]\displaystyle{ D_{LL} }[/math] vs [math]\displaystyle{ r^{2/3} }[/math]
Optional variables
REGRESSION_COEFF_A3	structure_function_regression_coefficient for_(r^2/3)^3	TIME, Z_DIST, N_BEAM	Linear term in regression for modified method, i.e. [math]\displaystyle{ A_1 }[/math] in [math]\displaystyle{ D_{LL} = A_3 r^2 + A_1 r^{2/3} + A_0 }[/math]. Units are s[math]\displaystyle{ ^{-2} }[/math]

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 results associated with fitting the structure function to data in level 3. The results for each beam, along with quality indicators and errors are provided. A final estimate for the turbulent kinetic energy dissipation is also provided.
regression_model	model regressed against the data to determine [math]\displaystyle{ \varepsilon }[/math]	Examples include: standard model, i.e. [math]\displaystyle{ D_{ll} = a_0 + a_1 (\delta r)^{2/3} }[/math] modified model, i.e. [math]\displaystyle{ D_{ll} = a_0 + a_1 (\delta r)^{2/3}+a_3((\delta r)^{2/3})^3 }[/math]
regression_method	method used to regress the model against the data	Examples include: Least-squares using evaluated separation distances to r_max.
EPSI_FINAL_method	method used to calculate EPSI_FINAL from EPSI	Examples include: arithmetic mean across beams of resolved EPSI after all EPSI_FLAGS applied.
rsquared_method	method used to calculate the goodness of fit	Examples include: ????
comment (optional)	Any additional information pertinent to other users who test their algorithms against the file.

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