Major EM122 interference from unknown source

[kjerram]

Credit to Brian Calder (UNH) for all information and images, adapted/paraphrased by MAC for posting here.

Context:
Major interference in EM122 data on I/B Oden in 400-500 m in Nares Strait (see images). This system is synchronized with other acoustic systems on board using a K-Sync. Operators and technicians are highly experienced multibeam users.

Symptoms:

1. Intermittent blanking / interference affecting water column data and bottom detection (see screenshots)
2. Occasionally the entire water column display goes blank (purple / low amplitude)
3. No obvious source of interference or relationship to sea state or icebreaking
4. Each RX interference 'ring' appears to start with very low / zero amplitude followed by very high amplitude
5. Rings appear intermittently in sets of varying numbers, not resembling TX patterns from any known sources

Troubleshooting:

1. Symptoms may improve after system is turned off and allowed to cool, but this has not been observed consistently
2. Other systems have been operated with and without synchronization to confirm their impacts on the EM122; no relationship found to the interference rings shown here
3. Dual Swath turned off/on to test for internal synchronization issue (no change)
4. Depth mode reduced to lower TX strength as a test for some unlikely multipath / multiple return issue (no change)

Next steps:

1. Checking all TX and RX cables; reseating boards if directed by Kongsberg support