contact classification by radiated lines
- blade rate = shaft rpm/60 * #blades. harmonics stack on top.
- merchant: low shaft rpm, 4-5 blades, strong low harmonics
- small craft: high rpm, cavitation broadband hiss
- detect tonals (DEMON/LOFAR), track harmonic family, estimate blade count -> class
library match handoff to ALDER as (bearing, class, confidence)