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High resolution images underwater

07/26/2022 7:11 AM

I remember reading,years ago , about a system that could transmit high resolution images underwater.Previous attempts were limited by the ability of the crystals to oscillate above a certain frequency underwater.

The new method used a laser to create cavitation bubbles to generate the pulses,increasing the frequency band.I have not been able to find anything on it in a recent search.Perhaps Solar Eagle could help,since the is the Guru of searches.

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#1

Re: High resolution images underwater

07/26/2022 8:05 AM

I'm assuming you're referring to high bandwidth. With low bandwidth, you can still transmit high resolution if you are patient, just as they do for space probes.

Possibly this..https://www.mit.edu/~millitsa/resources/pdfs/oc05.pdf

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#2
In reply to #1

Re: High resolution images underwater

07/26/2022 10:09 AM

No,I am talking about real time data.Maybe it has been removed by government agencies because of it's value to the military.

The article I read showed real time full color images transmitted to a submarine under water,but I can not find it now,but nothing ever really dies on the internet,so it is out there somewhere in the Netland Universe.

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#6
In reply to #2

Re: High resolution images underwater

07/27/2022 5:31 AM

I think that what Rixter is getting at is:

Is this a technology specific to imaging, or, just any high bandwidth data?

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#3

Re: High resolution images underwater

07/26/2022 7:21 PM

Well, it depends on how far you want to communicate. With a good blue laser, you can get 10-100 Mb/s at 100 meters or maybe a GigaBit/sec close in, depending on how clear the water is.

https://www.researchgate.net/publication/233669755_High-Bandwidth_Underwater_Communications

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#4

Re: High resolution images underwater

07/26/2022 8:52 PM

I suspect you remembered the hopes and not the results of old research. If high-speed data could be transmitted through mirky(?) waters then underwater robotics would only need power tethers.

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#5

Re: High resolution images underwater

07/27/2022 4:40 AM

There was a facility in Australia, owned by the USA military to transmit to their submarines when submerged at a place called Pine Gap and the supposed transmission range was global.

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#10
In reply to #5

Re: High resolution images underwater

07/27/2022 10:56 PM

If I recall correctly, that was an ELF (Extremely Low Frequency) system. Obviously (for those who know something about communications theory), the bandwidth limits it to text messaging for anything sent in a useful time frame.

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#7

Re: High resolution images underwater

07/27/2022 8:02 AM

I do remember some details about the method,and it depended on temperature and salinity of the water as well as depth and pressure.There was a lot of buffering of the signal at the receiver,and the data was digital.If a scene did not change,the image was not refreshed.. a form of compression at the source..in other words,a stationary back ground was not repeated,only the active parts of the video,and the range was definitely limited .The digital format served also to filter out background noise and reflections.

That is about all I recall about the technology at the time.This has been many years ago,and I am sure the methods have improved.

Some amazing technologies have occurred over the years,such as supercavitating torpedoes,that travel faster than the speed of sound underwater,and supercavitating projectiles for destroying underwater mines from above.

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#8
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Re: High resolution images underwater

07/27/2022 1:47 PM

Sending just changes is pretty standard for image compression. Dependence on temperature, salinity, depth, and pressure sounds like the transmission was very likely acoustical. I suspect they were using a number of signal processing "tricks", knowing the characteristics of the signal being received, to tease the signal out of the ambient noise.

Maybe something like this.

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#9
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Re: High resolution images underwater

07/27/2022 1:55 PM

I figure they were sending info in packets,with preamble and eop for each packet,containing the number of bits,spaces,and data length,etc.

And I am sure there are many other very sophisticated error detection/correction methods being used also.

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#11

Re: High resolution images underwater

07/28/2022 11:48 AM

CAILabs claim to have an adaptive optics underwater laser communications solution. There's no mention of using cavitation (which would be dangerously noisy for submarines to use, unless somehow disguised as cavitation from pistol shrimp).

TILBA improves the reliability of underwater laser communication by compensating for turbulence.

There are several other companies with similar technology.

Crystal oscillators aren't limited by being underwater so long as they stay nice and dry inside a waterproof housing along with the rest of the electronics. The problem is that the radio frequencies at which they oscillate are not readily transmitted in water. Thus, electromagnetic communication is pretty much limited to ELF or blue-green light, or (maybe) near-surface operation to pick up above-water radio, typically with an antenna protruding from the water. Blue-green light is still relatively short range - probably not much more than 200 meters in ocean water.

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#12
In reply to #11

Re: High resolution images underwater

07/28/2022 1:13 PM

I accept this can provide communication for a short range of fewer than 300 meters but particulate scattering by everything from plankton, algae, bubbles, fish schools, etc. will attenuate the carrier signal. Increasing the source's luminous intensity to reach 300 meters will mean detectable light will get to the surface and remove the stealth nature of submarines.

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#13

Re: High resolution images underwater

07/28/2022 3:48 PM

https://cr4.globalspec.com/thread/117438/Hi-Def-Underwater-Image-Transmission

..."Sea-Eye’s system solves previous limitations by combining new advances in signal processing and video compression – available only in the past couple of years – and have made real time full color undersea broadcasts a reality.

The modem developed by the Sea-Eye team allows a data transmission rate of up to 150kbits/sec on carrier frequency between 300KHz and 1MHz, rates which are much more robust than is available elsewhere. In addition, Sea-Eye has developed algorithms to cope with underwater signal transmission problems such as multi-path reflection and Doppler effects, enabling streaming video or voice broadcasting to proceed unimpeded. This ensures much higher quality real time communication.

Vainstein plans to market modems in the near future with transmission ranges of up to 300-500 meters. “For divers that need to be in communication with a ship above them, this is perfect, because they will have much greater flexibility than they would if they were connected by cable, and they won’t have to contend with the limitations of other wireless systems or the inconvenience or danger of cabled connections,” Vainstein says."...

https://www.israel21c.org/israeli-sea-eye-takes-streaming-video-underwater-2/

After this 2008 article the company goes dark....until a combination with Saab emerges...

https://www.offshore-energy.biz/video-seaeye-sabertooth-showcased-at-nasa/

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#14
In reply to #13

Re: High resolution images underwater

07/29/2022 7:49 AM

Thanks,SE.You are the master of the internet searches!

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