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    463 points bookofjoe | 11 comments | | HN request time: 0s | source | bottom
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    supernova87a ◴[] No.45131847[source]
    Hey, I heard about how utility pole inspecting helicopters are able to tell the good/rotten state of wooden telephone poles by the reverb pattern of sound waves coming off the poles from the rotors -- it seems to me the whole field of non-invasive sensing (and using existing/ambient emission sources) is getting pretty impressive.
    replies(7): >>45132413 #>>45132699 #>>45132844 #>>45133389 #>>45133942 #>>45137337 #>>45137440 #
    1. nashashmi ◴[] No.45132413[source]
    What kind of helicopter of what size are we talking about here that can actually get close to a utility pole with wires going across?
    replies(4): >>45132571 #>>45132678 #>>45132790 #>>45133877 #
    2. trhway ◴[] No.45132571[source]
    I think you can do it from a distance, just need to have directed microphone (or use laser “microphone”)
    replies(1): >>45132705 #
    3. gerdesj ◴[] No.45132678[source]
    I live near a helicopter factory and when the spinning towers are in use, you hear all sorts of auditory patterns as you move around the town. When they are test flying - similar and the Police have one and there is an air ambulance too. My Dad's other staff car in the '80s was a Gazelle and in the '70s he whizzed around in a Sioux. I've seen and heard a lot of helos!

    I have absolutely no doubt that with some funky signal processing you can do all sorts of things.

    replies(1): >>45134332 #
    4. shitpostbot ◴[] No.45132705[source]
    That makes sense. It's probably less "doing crazy convolution calculations on how sampled ambient noise changes as the helicopter gets close to a pole", and more "rotten wood vibrates slower"
    replies(1): >>45133129 #
    5. trenchpilgrim ◴[] No.45132790[source]
    Look up "Helicopter tree trimming" and prepare to be amazed.
    replies(1): >>45132962 #
    6. fsckboy ◴[] No.45132962[source]
    also look up "helicopter high voltage wire"
    7. gregoryl ◴[] No.45133129{3}[source]
    FYI, you've been hellbanned for seemingly 6 years. Probably the account name triggering a spam filter?

    Email hn@ycombinator.com, they may be willing to unban you, so other people can see your posts.

    8. privatelypublic ◴[] No.45133877[source]
    HV transmission line inspection routinely has the linesmen crawl out of helicopters onto the lines and back. Granted, as far as I know its the highest skill and most difficult helicopter job.
    replies(1): >>45134056 #
    9. jacquesm ◴[] No.45134056[source]
    I've seen that in person while in Canada and it is most impressive. The moment they discharge the differential between the helicopter and the line is just awesome. The firebreak clearing operations are also something to behold. From a very safe distance.
    10. morkalork ◴[] No.45134332[source]
    And here I thought living behind a few garages that rev engines all day long was disturbing
    replies(1): >>45144754 #
    11. gerdesj ◴[] No.45144754{3}[source]
    Its much less disturbing than living under a flight path to an airport. I actually like the sound of a helo - its variable and interesting, as is a piston powered fixed wing aircraft.

    Mind you I also lived near RAF, USAAF and Luftwaffe bases back in the day and several flights of Phantoms, Starfighters, Jaguars and Tornadoes and the rest can make quite a din. Phantoms were pretty huge engined beasts with minimal effort made for noise reduction. A "finger four" lighting up their after burners to gain altitude really fast is ear splitting.