Level 1 data (shear probes)
Minimum and desirable data set
- 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.
Level 1 data (shear probes)
Level 1 data refers to the full resolution data in physical units, e.g. the regularly sampled time series of converted shear probe data. If needed, a transfer function for shear is given. Below, a table with parameters included in the level 1 data set is compiled. The parameter names and definitions fit the NetCDF parameter attributes.
In the standard names, "sea_water" can be replaced with "water" if working in freshwater environments. This is specified in some entries below but not all.
Dimensions
| Dimension short name | description |
|---|---|
| TIME | Time axis for the microstructure sampling rate |
| TIME_CTD | Time axis for the CTD sampling rate. |
| TIME_*** [math]\displaystyle{ ^a }[/math] | Time axis for the *** sensor sampling rate |
| N_SHEAR_SENSORS | number of shear channel |
| N_***_SENSORS | number of *** channel (e.g., N_VIB_SENSORS, N_ACC_SENSORS) |
[math]\displaystyle{ ^a }[/math] Typically we assume TIME for the fast-sampled microstructure channels, and eventually _SLOW or _CTD for slower sampled channels such as CTD and tilt sensors. If the application requires different time stamps for different sensors, this can be utilized like TIME_PITCH, TIME_ACC etc.
Required Variables
| Parameter Name | Standard Name | Units of measurement | dimension |
|---|---|---|---|
| TIME | time | Days since YYYY-MM-DDT00:00:00Z | TIME |
| SHEAR | sea_water_velocity_shear (or water_velocity_shear) |
s-1 | [TIME, N_SHEAR_SENSORS] |
Optional Level 1 Variables
| Parameter Name | Standard Name | Units of measurement | dimension |
|---|---|---|---|
| PSPD_REL | platform_speed_wrt_sea_water | m s-1 | TIME[math]\displaystyle{ ^a }[/math] |
| VIB | platform_vibration | NA | [TIME, N_VIB_SENSORS] |
| ACC | platform_acceleration | m s-2 | [TIME[math]\displaystyle{ ^b }[/math], N_ACC_SENSORS] |
| TEMP | sea_water_temperature (water_temperature) |
degree_Celsius | [TIME_CTD[math]\displaystyle{ ^b }[/math], N_T_SENSORS] |
| CNCD | sea_water_electrical_conductivity (water_electrical_conductivity) |
S m-1 | [TIME_CTD[math]\displaystyle{ ^b }[/math], N_C_SENSORS] |
| GRADT | temperature_gradient | [TIME, N_GRADT_SENSORS] | |
| GRADC | conductivity_gradient | [TIME, N_GRADC_SENSORS] | |
| PITCH | platform_pitch_angle | degree | TIME[math]\displaystyle{ ^a }[/math] |
| ROLL | platform_roll_angle | degree | TIME[math]\displaystyle{ ^a }[/math] |
[math]\displaystyle{ ^a }[/math]or TIME_SLOW or TIME_CTD [math]\displaystyle{ ^a }[/math]or TIME_SLOW
return to Dataset requirements for shear probes.
