4 ms·

Wonder if we’ll be able to make something equivalent to a gravitational camera at some point.

by nynx 5y ago

pa7x1 5y ago
That's what LIGO is, in essence.
fmajid 5y ago
The French navy is going to equip 4 ships with ONERA's GIRAFE quantum interference gravimeters, starting in 2023, based on a prototype developed in 2012: https://www.capital.fr/economie-politique/la-marine-francaise-pourrait-etre-la-premiere-au-monde-a-utiliser-cette-technologie-revolutionnaire-1429014 https://www.capital.fr/economie-politique/la-marine-francais... One of the goals is to be resistant to GPS jammers.
- arlort 5y ago
  Maybe it's explained in the article but my french isn't great But how would that work to replace (?) GPS?
  - plafl 5y ago
    Not french speaking but I will guess that by using extremely precise inertial navigation. Accelerometers measure acceleration + gravity. You need to subtract the gravity.
  - mdturnerphys 5y ago
    Submarines have been using gravity gradiometers for navigation for decades. Tom Clancy revealed what was then classified information about these in The Hunt for Red October. They can serve as passive collision avoidance systems or let the navigators use geological features to correct drift in inertial navigation. The later application requires gravity gradient maps. They are useful for submarines because they are completely passive, unlike active sonar that produces a signal others can detect.
petermcneeley 5y ago
I did some simulations of doing this (in Qbasic). The issues that I ran into was that effectively the matrices were singular. I think this might not be mathematically possible for static gravity measurements.
- nynx 5y ago
  Interesting! Perhaps that could’ve been a numerical accuracy issue? Do you have code somewhere you’d be willing to share?
  - petermcneeley 5y ago
    I dont have my qbasic code from 1998. I wish I did. The setup was like a sensing array vs a much smaller array of test gravity sources (all in 2d).
jubjubbird 5y ago
Apologies for the paywall, but this paper describes imaging cargo containers with gravity gradient sensors (to look for, e.g., plutonium): https://ieeexplore.ieee.org/document/4215058 https://ieeexplore.ieee.org/document/4215058 Basically you can image anything if there is a density contrast, it's "just" a matter of how good your sensor and inversion algorithm is. I spend my day-to-day working on measuring gravitational changes to determine groundwater storage change. There's a huge difference between demonstrating something in the lab vs. building an actual field instrument you can use in the real world.
deleted 5y ago
[deleted]

Wonder if we’ll be able to make something equivalent to a gravitational camera at some point.

by nynx 5y ago

Wonder if we’ll be able to make something equivalent to a gravitational camera at some point.

pa7x1 5y ago

That's what LIGO is, in essence.

fmajid 5y ago

The French navy is going to equip 4 ships with ONERA's GIRAFE quantum interference gravimeters, starting in 2023, based on a prototype developed in 2012: https://www.capital.fr/economie-politique/la-marine-francaise-pourrait-etre-la-premiere-au-monde-a-utiliser-cette-technologie-revolutionnaire-1429014 https://www.capital.fr/economie-politique/la-marine-francais... One of the goals is to be resistant to GPS jammers.

arlort 5y ago
Maybe it's explained in the article but my french isn't great But how would that work to replace (?) GPS?
- plafl 5y ago
  Not french speaking but I will guess that by using extremely precise inertial navigation. Accelerometers measure acceleration + gravity. You need to subtract the gravity.
- mdturnerphys 5y ago
  Submarines have been using gravity gradiometers for navigation for decades. Tom Clancy revealed what was then classified information about these in The Hunt for Red October. They can serve as passive collision avoidance systems or let the navigators use geological features to correct drift in inertial navigation. The later application requires gravity gradient maps. They are useful for submarines because they are completely passive, unlike active sonar that produces a signal others can detect.

petermcneeley 5y ago

I did some simulations of doing this (in Qbasic). The issues that I ran into was that effectively the matrices were singular. I think this might not be mathematically possible for static gravity measurements.

nynx 5y ago
Interesting! Perhaps that could’ve been a numerical accuracy issue? Do you have code somewhere you’d be willing to share?
- petermcneeley 5y ago
  I dont have my qbasic code from 1998. I wish I did. The setup was like a sensing array vs a much smaller array of test gravity sources (all in 2d).

jubjubbird 5y ago

Apologies for the paywall, but this paper describes imaging cargo containers with gravity gradient sensors (to look for, e.g., plutonium): https://ieeexplore.ieee.org/document/4215058 https://ieeexplore.ieee.org/document/4215058 Basically you can image anything if there is a density contrast, it's "just" a matter of how good your sensor and inversion algorithm is. I spend my day-to-day working on measuring gravitational changes to determine groundwater storage change. There's a huge difference between demonstrating something in the lab vs. building an actual field instrument you can use in the real world.

deleted 5y ago

[deleted]