Level 3 data (velocity point-measurements)
| Page status: Draft | |
|---|---|
| Author(s): | Cynthia |
| Reviewer(s): | |
| Comment: | |
The required dimensions and variables associated with the Level 3 spectra processing level (NetCDF group) for velocity measurements are described below.
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).
Dimensions
The number of velocity instruments (N_VEL_INSTRUMENT) is here for completeness, but the benchmarks examples will have measurements only from one instrument stored.
| Short name | Standard name | Dimensions | Comments |
|---|---|---|---|
| TIME | time | TIME | Units in Days since 1950-01-01T00:00:00Z, time-centered |
| FREQ | frequency | FREQ | Frequency in Hz for the spectra |
| N_VEL_COMPONENT | unique_identifier_for_each_velocity_component | N_VEL_COMPONENT | Maximum of 3 for u,v, w (east, north, up) velocities |
| N_VEL_INSTRUMENT | unique_identifier_for_each_velocity_instrument | N_VEL_INSTRUMENT | Required only if storing multiple synchronized instruments in the same file |
Variables
| Short name | Standard name | Dimensions | Comment |
|---|---|---|---|
| UVW_VEL_SPEC | XXXX
_in_the_analysis_frame_or_reference |
TIME, FREQ, N_VEL_COMPONENT, N_VEL_INSTRUMENT | This may be rotated in the direction of the mean flow, or left in XYZ_VEL if relying only on the vertical component when estimating [math]\displaystyle{ \varepsilon }[/math]. Please specify the analysis frame of reference in the variable attribute and/or group's attribute. |
| UVW_VEL_SPEC_FLAGS | status_flag | TIME, N_SAMPLE, N_VEL_COMPONENT, N_VEL_INSTRUMENT | Enumerated flag that denotes if and how missing samples were replaced |
| HEIGHT or DEPTH[math]\displaystyle{ \dagger }[/math] | See Level 1 table | TIME, N_VEL_INSTRUMENT | |
| Optional variables [math]\displaystyle{ \ddagger }[/math] | |||
| BURST_NUMBER [math]\displaystyle{ \dagger\dagger }[/math] | unique_identifier_for_each_burst | TIME, N_VEL_INSTRUMENT | Only required when measuring in burst-mode. Integers of 1, 2, etc to designate which burst the velocities are associated with. |
|
[math]\displaystyle{ \ddagger }[/math] One could re-write for convenience the optional variables in Level 1 after segmenting them into smaller chunks. For instance, PRES (pressure) would be fairly common in surface wave studies. [math]\displaystyle{ \dagger }[/math] A variable situating the instruments in the water column is required. This may be a nominal depth (or height) or a time-varying depth or height above the bottom. [math]\displaystyle{ \dagger\dagger }[/math] Variable required only when measuring in bursts e.g., 18 min of continuous measurements every hour. | |||
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. |
| |
| spectral_calculation_type | |||
| spectral_windowing | |||
| spectral_fft_length | |||
| Optional group attributes [math]\displaystyle{ \ddagger }[/math] | |||
| stationarity_testing | |||
| noise_testing | |||
| comment (optional) | Any additional information pertinent to other users who test their algorithms against the file. | ||
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