5 ms·
Correct. The magnetic signatures seen are the permanent magnetic moments embedded in the steel of the ships, which are picked up by passive magnetic-anomaly det
by drostie 11y ago
Correct. The magnetic signatures seen are the permanent magnetic moments embedded in the steel of the ships, which are picked up by passive magnetic-anomaly detectors. These have to be removed by randomization in a normal all-at-once degaussing process.
It is hypothetically possible to have an active-detection process too, but presumably that would take the form of emitting a pulse of electromagnetic radiation and looking for its echoes, in other words it's just another form of vision. The standard problem applies: find a frequency at which water is mostly transparent. Unfortunately the absorption spectrum for water is https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water#/media/File:Absorption_spectrum_of_liquid_water.png https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_... , it has a minimum in the visible range.
In addition to being one of the more stunning confirmations of evolution (of course our eyes are only sensitive to the least-absorbed wavelengths of light in water -- our ancestors evolved eyes in the ocean! there weren't many other useful wavelengths down there!) this has the nasty property that it's unlikely that we'd be able to detect a sub this way with any better approach than shining a bright laser or spotlight or what have you, and watching what's reflected back with our own eyes.
- zimmund 11y agoThanks for your aclaration, it helped me understand the idea :)
- Flammy 11y agoThe ships undergoing this look kinda crazy. Couldn't find the exact image I was thinking of but here is a sub with wires wrapped around it: http://systems.polyamp.com/images/stories/DepermingSub.jpg http://systems.polyamp.com/images/stories/DepermingSub.jpg
- PhasmaFelis 11y agoHuh. It's like naval rope bondage. (Which is probably somebody's fetish)
- CamperBob2 11y agoI'm a bit unclear on how degaussing the hull prevents the sub from showing up as a magnetic anomaly. All that would do is keep the vessel from affecting nearby compasses. It still distorts the local geomagnetic field, doesn't it, just by virtue of being made from a ferromagnetic material...?
- dnautics 11y ago"All that would do is keep the vessel from affecting nearby compasses." "It still distorts the local geomagnetic field." These two statements are trivially identical.
- CamperBob2 11y agoQualitatively, but not quantitatively. A large metal object might not affect a conventional compass reading in a noticeable way, but if the enemy is flying around with cryocooled Josephson-junction magnetometers or whatever, they'll still see a distortion in the local field. I'd think that the permeability of a submarine hull -- magnetized or not -- would be very different from that of the surrounding seawater.
- dnautics 11y agoOh it doesn't completely erase the signal, but it minimizes it. P8 Orions have a plasma induction magnetometer in the back that is supposed to be able to see the degaussed submarines. The Russians did something even simpler: they took photographs from space and saw where submarine propellers were causing churn in the ocean cyanobacteria.
- dnautics 11y agoI think your understanding of evolution is a bit off, since there are other creatures with common ancestor (birds) that can see into long UV.
- madaxe_again 11y agoAnd magnetic anomalies, apparently, if they're migratory, via polarisation of uv iirc.
- dnautics 11y agoanother hypothesis is that spin-coupled electrons preferentially and directionally emit photons from a cryptochrome protein. But tbh, we don't really know yet. http://www.ks.uiuc.edu/Research/cryptochrome/ http://www.ks.uiuc.edu/Research/cryptochrome/