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Doppler differs from the simple NetCDF time series structures previously commented on in that the depth dimension is larger than one. The current velocities are therefore multidimensional in depth and time. If the water depth is deep enough, a full 30 bins can be realistically recorded. When relayed back via GOES, usually fewer than 30 bins are sent.
As an example, see the structure for the GOES doppler NetCDF file for E0106.
The post-recovery-sensor-raw data has numerous additional variables that are particular to the nature of the RDI ADCP instrument. An example is given in the appendix The m-file rdradcp.m written by <GENUFLECT>Rich Pawlowicz</GENUFLECT> that reads the data provides a number of instrument parameters that are tacked on to the NetCDF file as global attributes. Many of the definitions are ripped right out of Table 27 in [ WORKHORSE_COM_FOR ] . These are defined as follow.
Attribute Definitions
Always wh-adcp.
Corresponds to CPU firmware version number and CPU firmware revision number in xx.yy format.
Bit mask defining the Workhorse hardware configuration, represented as by a string, LSB first, then MSB. The information conveyed by the bitmask is given by the beam_angle, beam_freq, beam_pattern, and orientation attributes.
Either 15E, 20E, 30E, or other.
Either 75, 150, 300, 600, 1200, or 2400 kHz.
Up or down.
Concave or convex.
Should always be real.
Contains the number of beams used to calculate velocity data (not physical beams). The Workhorse needs only three beams to calculate water-current velocities. The fourth beam provides an error velocity that determines data validity. If only three beams are available, the Workhorse does not make this validity check.
Contains the number of depth cells over which the Workhorse collects data. Usually this is 30.
Contains the number of pings averaged together during a data ensemble.
The length of one depth cell. Usually 4.
Contains the blanking distance used by the Workhorse to allow the transmit circuits time to recover before the receive cycle begins.
Signal processing mode. Should be 1.
Contains the minimum threshold of correlation that water profile data can have to be considered good data. Range of 0 to 255 counts.
Contains the number of code repetitions in the transmit pulse.
Contains the minimum percentage of water-profiling pings in an ensemble that must be considered good to output velocity data. Range 1 to 100 percent.
This field contains the actual threshold value used to flag water-current data as good or bad. If the error velocity value exceeds this threshold, the Workhorse flags all four beams of the affected bin as bad. Range is 0 to 5000 mm/s.
Time in seconds between ping groups in the ensemble.
Bit mask whose information is conveyed by the attributes coord_sys, use_pitchroll, use_3beam, and bin_mapping.
One of beam, instrument, ship, or earth.
no, or yes.
no, or yes.
no, or yes.
Heading Alignment field, contains a correction factor for physical heading misalignment. In degrees.
Sensor Source field, contains the selected source of environmental sensor data. These firmware switches indicate the following.
Bit Flags
Calculates EC (speed of sound) from ED, ES, and ET.
Uses ED from depth sensor.
Uses EH from from transducer heading sensor.
Uses EP from transducer pitch sensor.
Uses ER from transducer roll sensor.
Uses ES (salinity) from conductivity sensor.
Uses ET from transducer temperature sensor.
This field reflects if the Speed of Sound sensor is available. The bit pattern is the same as listed above, and is also converted into a string.
The distance to the middle of the first depth cell (bin) in meters rather than cm.
The length of the transmit pulse in meters rather than cm.
Contains the starting depth cell and the ending depth cell used for water reference layer averaging. Range = 1 to 128 depth cells.
Contains the threshold value used to reject data retrieved from a false target, usually fish (WA-command). Range = 0 to 255 counts.
This field, determined mainly by the setting of the WM-command, contains the distance between pulse repetitions. In meters.
CPU board serial number.
The depth to the middle of each bin. This usually does not take into account the instrument depth itself, which usually isn't dead on accurate itself. A good rule of thumb here is to add the instrument depth to this attribute, and if the depth values are within half the cell width of the ranges values, then we're probably ok. Good enough for government work, anyway. Oh wait, we're not government...
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