The ASCII telemetry data that is transmitted by the Signature / Generation 2 series of instruments is quality controlled before it is sent, and any data that is deemed unreliable is flagged. The criteria for one data point being flagged as unreliable is by default the correlation being less than 50% for the measurement, and if more than 50 % of the data points within an average interval is considered bad the whole cell is flagged in the outputted data. The flag values are as follows:
- Velocity: -32.767 m/s
- Speed: 46.34 m/s
- Direction: 225°
All ASCII telemetry data formats go through this QC and it is not possible to disable this. If you need the unflagged data, this must be retrieved from the instrument recorder. The correlation threshold can however be adjusted during configuration to a different value. For Aquadopp 2 and AWAC 2 this can be done directly in the software, for Signatures the change has to be done by custom commands. We recommend keeping the correlation threshold to the default 50 % to ensure robust data quality.
Example reasons that the correlation might be < 50% (this is not an exhaustive list):
- Sidelobe interference near the surface
- Acoustic or electrical interference
- Obstructions in the path of the beams
- The instrument is measuring in air
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