Dataset requirements for shear probes

This page provides an overview of the NetCDF format of benchmark dataset for instruments that measure microstructure shear using airfoil probes.

Benchmark datasets: Shear probe measurements

ATOMIX provides several benchmark datasets consisting of four processing levels.

1. Raw timeseries
   • full resolution data in physical units
2. Quality-controlled and segmented timeseries
   • full resolution cleaned and despiked parameters from level 1, subdivided in individual sections.
3. Spectra
   • raw and cleaned spectra
4. Dissipation [math]\displaystyle{ \varepsilon }[/math] estimates
   • dissipation estimates and corresponding quality parameter as time series

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• The absolute minimum signals and information required to estimate the rate of dissipation of kinetic energy consists of:

• a sampled shear-probe signal,
• a means of determining the speed of flow past the shear probe, and
• a means to estimate the temperature of the fluid so that you can determine its kinematic viscosity.

The sampling rate of the shear-probe signal should exceed significantly (by a factor of 2 to 4) the value of 150U, where U is the speed of the flow past the shear-probe. This speed is often called the speed of profiling, even when the probe is fixed in space and the current causes fluid to flow past the shear probe. The value of 150 cpm equals the spatial resolution of the commonly used shear probe.

• The desirable data set

A far more desirable, but not absolutely necessary, set of data consists of the following.

• Two or more shear probes for measurement redundancy.
• Vibration sensors or accelerometers that are sensitive to the directions of sensitivity of the shear probes.
• An accurate thermometer.
• A pressure transducer.
• A signal that can be used to estimate the speed of flow past the shear probe.
• Pitch and roll sensors.

Most commonly available instruments carry two shear probes that are frequently oriented so that they measure orthogonal components of the shear and, thus, provide two independent estimates of the rate of dissipation that you should agree statistically.

Recommended data format

For sharing a data set, we recommend providing four processing levels of data in a single netCDF file per instrument file. The processing levels include

• L1_converted (level 1)
• L2_cleaned (level 2)
• L3_spectra (level 3)
• L4_dissipation (level 4)
• Ancillary

The data format recommended is summarized in standard dimensions and should include necessary meta data. ATOMIX provides several benchmark data sets following these guidelines.

This section provides an overview of the NetCDF format of benchmark dataset for instruments that measure microstructure shear.

Raw timeseries

Dimensions

Example of collapsible list

• TIME
• HEIGHT_AS

Example of collapsible table

Short name	Standard name
TIME	days since 1950-01-01 00:00:00 UTC
n_shear_sensors	number of shear channel

These dimensions are defined for the raw group level but have a caption.

Short name	Standard name
Content	Goes
In Here	Please

Required Variables

Parameter Name	Standard Name	Units of measurement	dimension
PRES	sea_water_pressure water_pressure	dbar	TIME	1,2
TIME	time	days since 1950-01-01 00:00:00 UTC	TIME	1
SHEAR	water_velocity_shear	s-1	[TIME, n_shear_sensors]	1

Optional Variables

Parameter Name	Standard Name	Units of measurement	dimension
VIB	platform_vibration	NA	[TIME, n_vibration_sensors]
ACC	platform_acceleration	m s-2	[TIME, n_acc_sensors]
TEMP	sea_water_temperature (water_temperature)	degree_Celsius	[TIME,n_T_sensors]
CNCD	sea_water_electrical_conductivity (water_electrical_conductivity)	S m-1	[TIME_FAST,n_C_sensors]
GRADT	temperature_gradient		[TIME, n_gradT_sensors]
GRADC	conductivity_gradient		[TIME, n_gradC_sensors]
PITCH	platform_pitch_angle	degree	[TIME]
ROLL	platform_roll_angle	degree	[TIME]

Group Attributes (metadata)

Required

• Att 1
• Att2

Optional

• Enter here

Quality-controlled and segmented timeseries

Insert info here in the same format as Raw

Spectra

Dissipation

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