Thank you for video (i watched it earlier)
I think you should remind something about TACTAS. Most ASW warships in DW uses TA sonar. This sonar can be deployed under layer. For example Perry's TA can reach*:
1030 ft (315 m) at 15 kts
1230 ft (375 m) at 10 kts
1480 ft (450 m) at 5 kts
It means: shallow layer can be penetrated easily by FFG TA
Of course greater speed (needed for tactical operations) sets TA antenna shallower. Sometimes surface ASW group cannot reach under layer and in this case shadow zone works like in your video
Would be nice to see sound propagation for antenna below layer.
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This is my sound propagation drawing for DW
It's little simplified because main reason was to use it as hint for understanding sound velocity gradient.
(Red lines for TA are more accurate for VDS with active regime of work than passive TACTAS - but it's still good hint for DW)
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Here is gif from database srceens for AI SQR-19 Towed Array (like on Perry class FFG)
Blue marked on left shows sensor used for
Shallow,
Medium or
Deep position of TA
Green means maximum speed for this position of TA antenna
Blue on right shows depth in meters at current speed (green value)
[Yes - sensor for specific speed range is physically changed in DW for AI warships]
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* in RA mod