Level 2 data (velocity profilers)
Velocities have now been segmented and detrended. Each segment is stored separately from each other, which allows segmenting data using overlapping windows i.e., some velocity samples can belong to more than one segment.
The dimensions and variables for this processing level 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, bounds, cell_methods).
Dimensions
| Short name | Standard name | Dimensions | Comments |
|---|---|---|---|
| N_SEGMENT | unique_identifier_for_each_segment_in_the_
entire_available_timeseries |
N_SEGMENT | Array of 1 to number of segments into which the data has been separated (Note TIME variable) |
| 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) |
| N_SAMPLE | unique_identifier_for_each_sample_within_
the_segment |
N_SAMPLE | Array of 1 to number of samples in each segment (segment length in seconds multiplied by the sampling rate in Hz) |
Variables [math]\displaystyle{ \ddagger }[/math]
| Short name | Standard name | Dimensions | Comment |
|---|---|---|---|
| R_VEL | water_radial_velocity_of_scatterers_
towards_instrument |
N_SEGMENT, Z_DIST, N_BEAM, N_SAMPLE | Along beam velocity [m/s] for each of the beams. |
| R_VEL_DETRENDED | water_radial_velocity_of_scatterers_
towards_instrument_detrended |
N_SEGMENT, Z_DIST, N_BEAM, N_SAMPLE | High-frequency content of the along-beam velocities [m/s], which may include surface wave, motion contamination, in addition to the turbulence signal. Calculated from R_VEL by removing the segment mean or trend. Detrending method should be specified by detrending_method in group attributes (see below). Link to own detrending page |
| TIME | TIME | N_SEGMENT, N_SAMPLE | Units in Days since reference time specified in variable attribute |
| PROFILE_NUMBER or N_PROFILE (agree as group) | unique_identifier_for_each_profile | N_SEGMENT, N_SAMPLE | This variable identifies each record (velocity) profile |
| THETA | beam_angle_from_instrument_z_axis | N_BEAM | Units in degrees, positive (usually ~20-30[math]\displaystyle{ ^\circ }[/math]) except vertical-pointing beams (0[math]\displaystyle{ ^\circ }[/math]) |
| BIN_SIZE | instrument_measurement_volume_bin_size | N_BEAM | Vertical size of the ADCP bins [m]. Usually the same for diverging beams. |
|
[math]\displaystyle{ \ddagger }[/math] One could re-write for convenience the optional variables in Level 1 after restructuring into segments. | |||
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. |
| |
| segment_length | Provide length in seconds of each segment | Usually about 300 to 600 s dependent on time and length scales of turbulence | |
| segment_overlap_proportion | Provide proportion overlap of each segment, i.e., window overlap | Often set to 0 or 0.5 | |
| detrending_method | Specify which filter or technique was used to detrend velocities, which is required for spectral and turbulence analysis. | Some examples include
| |
| Optional group attributes | |||
| comment (optional) | Any additional information pertinent to other users who test their algorithms against the file. | ||
Return to: Level 1 raw
