About transmission characteristic data
The active transmission impedance of a transducer may vary from the manufacturer's measured value due to physical or enviromental changes at or near the transducer.
The ICES CRR326 Calibration of Acoustic instruments report mentions that changes in transducer impedance may be an indicator of:
- echosounder performance
- the physical integrity of a transducer or transducer cabling
- the state of the transducer face (biofouling/entrained air in the water)
Some hydroacoustic systems may record active transmission characteristics and save them to a file.
Echoview supports Simrad EK80 narrowband/contiunous wave active transmission characteristics per ping saved to file by the following systems:
- EK80 WBAT and EK80 WBT systems that save characteristics with complex samples.
- EK80 WBT systems that save characteristics with power/angle samples starting with v21.15 of the EK80 data acquisition software (released in 2022). Note, Power/angle data acquired with EK80 data acquisition software versions prior to v21.15 did not record impedance information.
Notes:
- Transducer impedance tolerances and manufacturer's values are specified in the transducer data sheet and the manufacturer's Reference manual.
- WBT includes WBT, WBT Tube, WBT Mini, WBT Portable which are all run via the “EK80” data acquisition software.
- WBAT systems run acquisition software known as 'Mission Planner'.
- Echoview may fail to read transmission characteristics saved in WBAT files with dates around 2017 and 2018.
Transmission characteristics variables
Derived raw transmission characteristic variables contain ping, date/time and source data file information. The derived raw variable is associated a transducer. The transducer can't be deleted. When the Platform is assigned as None for the transducer, the transmission characteristic raw variable becomes unavailable.
Extract transmission characteristic operator
Active transducer impedance statistics are output by the Extract transmission characteristic virtual variable. The operand is a transmission characteristic variable. Be aware that the operator statistics are different from the statistics displayed on the Transducer Diagnostics section of Simrad EK80 acquisition software. See also: Extract transmission statistics equations.