Civilian Layman learning about SONAR
To clarify, I'm European, my background is in IT, but I have a wide technical interest and spent some time learning about modern-ish submarines (Between WW2 and 1970s, before digital signal processing/beamforming).
I have a digital copy of Norman Friedmans "US Submarines since 1945" and researched on public sources on the internet regarding some surface search SONAR like SQS-23 and found some sources linking German Balkongerät with BQR-7, not sure how reliable that is.
I also learned how the sonar signal is displayed and processed in the sub with BTR, TMA etc. but that's where it starts to get spotty, for example I fail to understand how TMA can give you anything close to distance.
On the more technical side, I understand transducers are special microphones/speakers, I was somewhat able to follow the analog beamforming on a Balkongerät, but without studies in electronics, it stops there.
I've seen the YT videos of smarter every day on the 688i Toledo and found it interesting how the XO wanted to stop the interview when discussing parts of SONAR that are widely public. Is my understanding correct that it's hard for a serviceman to understand which part is public known and where the classified content starts?
Now to the core question: Are there any unclassified sources that I could use to learn more, especially on how the data was used and processed to track contacts? Or is anything used in the 60s still so relevant today (just digital) that it's in the deeply classified drawer?
Thanks to anyone who is able to answer and thanks for the community here in general, even as an outsider, I really enjoy this subreddit.