Level 4 data (velocity profilers)
From Atomix
| 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{SLOPE_CI_HIGH}\ -\ \text{SLOPE_CI_LOW})}{4\ \text{REGRESSION_COEFF_A1}} }[/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. |
|
| 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] |
| 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. |
Return to Level 3 structure function
Go back to the beginning Dataset requirements for ADCP structure function
