Re: Can a satellite detect a submarine?

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Question ID Number 1187943216.Ph

Greetings Javier:

References:

1. Mad Science Archived Question : Can submarine's heat signature be detected while it is submerged ?

http://www.madsci.org/posts/archives/2005- 05/1115410201.Ph.r.html

2.Landolt-Bornstein , Oceanography, New Series, group 5, Volume 3, part A.

3.Cureio, Petty, Optical absorption of pure water,
Journal of the Optical Society of America, (JOSA) V41, pp 302-304

4.DARPA Blue Laser for Submarine Laser Communications (SLC) and Non-Acoustic Anti-Submarine Warfare (ASW)

http://www.darpa.mil/sto /maritime/slc.html

Microwave RADAR (RAdio Detection And Ranging) cannot penetrate salt water and can only detect surfaced submarines
or their periscopes above water. SONAR (Sound NAvigation and Ranging) and LIDAR (LIght Detection And Ranging) are
the only technologies that can penetrate water.

The answer to the question in Reference 1. in the Mad Science Archives is part of the answer to your question
because satellites do use heat sensors at infrared wavelengths from 1 to 10 micrometers to form images of the
weather and sea and land temperatures maps. These types of sensors could detect a submarine near the surface of
the water but not at greater depths.

The data in References 2 and 3 present data for clear fresh water and clear sea water and show that the water is
most transparent at visible blue - green wavelengths between 0.4 to 0.5 micrometers (micrometers are 1/1,000,000
of a meter) where the attenuation (loss) of electromagnetic energy is about - 0.1 dB per meter (about 2% loss,
98% transmission/meter). However, the attenuation rapidly increases for both longer and shorter light wavelengths.

We know that in clear water we can visually see a submarine at a much greater depth than a few meters because of
the blue - green "window" in water; however, the thermal radiation from the submarine at these wavelengths is
negligible.

After the invention of powerful blue - green lasers during the 1960s there has been a great deal of research in
using LIDAR to detect the ocean's depth. The US National Oceanic and Atmospheric Administration (NOAA)
is using Blue-green laser LIDARs from aircraft to measure the depth of water near the coast of land masses.
Obviously these systems could also detect submarines; however, information about this subject is remains a secret.

In Reference 4 we find that the US Defense Advanced Research Projects Agency (DARPA) has a task for developing
an efficient solid state laser for submarine communications and detection. The following development of an airborne
laser sensor could be extended to space if a more powerful and efficient blue- green laser could be developed for use
in space.

Quotation from Reference 4.

“Blue Laser for Submarine Laser Communications (SLC) and Non- Acoustic Anti-Submarine Warfare (ASW)
The goal of the DARPA Blue Laser for Submarine Laser Communications (SLC) and Non-Acoustic Anti-Submarine Warfare
(ASW) program is to develop a high wall-plug efficient, Blue Light (0.455 micrometers, 455 nanometers), Solid-state
Laser.

Foreign submarines are quieter than ever before, and there is a pressing need for improved ASW capabilities,
particularly in shallow water (above the thermocline) and littoral areas of operations. Coordination between multiple
assets such as aircraft, surface ships, and submarines is critical to an effective ASW campaign. Integration of
submarines into an overall ASW effort, arguably the most effective platform for wide area search and tracking, has
traditionally been hampered by lack of or minimal communications to the submarine while deep.

The Navy is currently investing in new and previously demonstrated techniques for communicating with submarines at
speed and depth for coordinated ASW operations. These techniques most commonly use either trailing wires or towed
buoys for submarine communications, which impose limitations on the submarine's maneuverability and stealth, and
therefore negatively impact the submarine's ability to fully conduct ASW operations. An airborne laser which could
penetrate shallow water would permit submarine communications without the restrictions of floating wires or buoys.
This program is intended to develop the world's first wall-plug efficient laser that operates both at an optimum
water transmission band of open ocean water and at the wavelength of a Cesium Atomic Line Filter. This laser has the
potential to improve the detection depth of a NAASW LIDAR system by a significant factor for the same reasons it
could improve submarine communications.”

Best regards, Your Mad Scientist
Adrian Popa