Join Opposing Pings
Joins the ping data from two transducers which are pointing in opposite directions. The output ping has the same orientation and sample thickness as operand 1, with the ping data from operand 2 projected onto the output and resampled if required.
The output pings are no data if the magnitude of the operands' transducer orientation is less than 90°.
Important: The ping samples' range in the output does not reflect the true range from the transducer face, and may therefore produce unexpected results in downstream operators. Hence, we recommend using the Join opposing pings operator at the end of your dataflow as a visualization tool.
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Operand 1 |
Operand 2 |
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Settings
The Join opposing pings Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:
Operands page
Join Opposing Pings
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Setting |
Description |
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Maximum acceptable time difference (milliseconds) |
Specifies the maximum ping time difference in milliseconds between candidate pings. |
Algorithm description
For each ping in operand 1, Echoview identifies the matched ping in operand 2—if the ping time difference between the two is less than the Maximum acceptable time difference (milliseconds). Otherwise, there is no matched ping and Echoview does not produce an output ping.
Each output ping has the same sample thickness and transducer orientation as the ping from operand 1. However, the start range of the output ping extends (into negative ranges if required) to accommodate the ping samples from operand 2.
The operator then copies the samples from operand 1 into the output ping. As for operand 2, the joining operation projects the samples onto the output ping, resampling as required using a weighted mean (refer to the resampling algorithm). Hence, expect to see distortions in ping samples from operand 2.
Depending on the positional offset between the two transducers and their direction, the operator may output no data ping samples, or overwrite operand 1 ping samples with that of operand 2 (if the direction of the transducers is toward each other).
Visualization recommendations
Where AUV or glider data is used and a glider depth time line is available, use the line as a Platform Heave source. Use the downward pointing variable as operand 1. See also: Scenario: Moving glider or AUV with a transducer pointed up and a transducer pointed down
Where the upward pointing variable is operand 1, use Echogram Display, Flip echogram vertically to orient the output echogram correctly.