View source for Level 4 data (velocity profilers)

{{ReviewStage
|toreview=Ready for review
|authors=Cynthia
|instrument_type=Velocity profilers
}}
This will dictate the data required at the final processing level, where we store the estimated dissipation estimates <math>\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 {{FontColor|bg=#fca1fd|text= [[NetCDF_parameter|complete list]]}} for the additional attributes related to each variable (e.g., units, bounds, cell_methods).

__TOC__

=Dimensions=
{| class="wikitable sortable"
|-
! 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 ([http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html#methods-applied-to-a-timeseries-ex 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)
|}
</div>

=Variables=
<div class="mw-collapsible" id="raw" data-collapsetext="Collapse" data-expandtext="Expand variables">
<br>
{| class="wikitable" 
|-
! 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]. {{FontColor|fg=white|bg=red|text=best to state cell_methods attribute to indicate what was averaged}} e.g., [http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html#methods-applied-to-a-timeseries-ex "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 [[Processing your ADCP data using structure function techniques | Compute structure functions and dissipation estimates]]). 
|-
| colspan="4" style="text-align:center; font-weight:bold; background-color:#f9eddd"|  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 | 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) {{FontColor|fg=red|text=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) {{FontColor|fg=red|text=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>\delta\varepsilon</math> to the value of <math>\varepsilon</math>. Computed from the confidence intervals as <math>\frac{\delta\varepsilon}{\epsilon} = \frac{3\ (\text{SLOPE_CI_HIGH}\ -\ \text{SLOPE_CI_LOW})}{4\ \text{REGRESSION_COEFF_A1}}</math> {{FontColor|fg=red|text=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>^{2/3}</math>
|-
| REGRESSION_COEFF_A0
| structure_function_regression_intercept
| TIME,  Z_DIST, N_BEAM
| Constant term in regression, i.e. <math>A_0</math> in <math>D_{LL} = A_1 r^{2/3} + A_0</math>. Units are m<math>^2</math>s<math>^{-2}</math> and value is proportional to instrument noise. (see [[Processing your ADCP data using structure function techniques | 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>A_1</math> in <math>D_{LL} = A_1 r^{2/3} + A_0</math>. Units are m<math>^{4/3}</math>s<math>^{-2}</math>
|-
| REGRESSION_R2
| regression_goodness_of_fit_adjusted_for_number_of_terms
| TIME,  Z_DIST, N_BEAM
| <math>R^2</math> computed from the regression of <math>D_{LL}</math> vs <math>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>D_{LL}</math> vs <math>r^{2/3}</math>
|-
| colspan="4" style="text-align:center; font-weight:bold; background-color:#f9eddd"|  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>A_1</math> in <math>D_{LL} = A_3 r^2 + A_1 r^{2/3} + A_0</math>. Units are s<math>^{-2}</math>
|} 
</div>

=Group attributes (metadata)=
<div class="mw-collapsible"  id="raw_att" data-expandtext="Expand group attributes" data-collapsetext="Collapse attributes">

This section describes attributes that may provide additional information about how the data was processed and manipulated at this stage.


{| class="wikitable" 
|-
! Attribute name
! Purpose
! Suggested content
|-
| processing_level
| Boilerplate about the content of the NetCDF group.
| <blockquote>''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.''</blockquote>
|-
| regression_model
| model regressed against the data to determine <math>\varepsilon</math>
| Examples include:
	standard model, i.e. <math>D_{ll} = a_0 + a_1 (\delta r)^{2/3}</math> <br /><br />
	modified model, i.e. <math>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.
| 
|}
</div>

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Return to [[Level 3 data (velocity profilers)|Level 3 structure function]]

Go back to the beginning [[Dataset requirements for ADCP structure function]]