Anti/-Submarine Warfare and Underwater Acoustics

[Anmdt]

Anti submarine warfare and underwater acoustics are interlocked, despite of researches in 21st century regarding to the ecological concern, majority of studies in underwater acoustics are still related to the military purposes which consists of;
-acoustic mapping
-bathymetry, sea bottom mapping-submarine geological studies (effects behavior of how sounds is traveled, absorbed /reflected)
-long range very low frequency- acoustic signature detection
-deep sound channel
-underwater currents, reflections
-target strength (linked to submarine detection by active sonar usage)
i will share a few sources which i believe would be useful for general understanding.

Submarine warfare:

Submarine Warfare - Navy Ships

why it matters to dive deep, why variable depth sonar - dip sonar matters, SOFAR* and Thermocline*:

Run Silent, Run Deep - Navy Ships

Underwater acoustics:

Underwater Acoustics - Navy Ships

Noise characteristics of Submarines:

What is known about the character of noise created by submarines? Appendix 1 - The Future of Russia's Strategic Nuclear Forces - E.V. Miasnikov

Terminology:
SOFAR is a layer in ocean which acts as a waveguide, in short, the sound traveling/entrapped in SOFAR sustains less losses thus transmitted at greater distance.

SOFAR channel - Wikipedia

en.wikipedia.org

Thermocline is a term used to define change of temperature by depth, usually the variance gets rapid below a depth, since temperature effects velocity of the speed,it both results in SOFAR and also sometimes a layer which reflects the sound.

Thermocline - Wikipedia

en.wikipedia.org

 

[Anmdt]

detection by noise is slowly being old-fashioned, here is the new techniques:

Wake detection has been used since ever, mainly to track wakes-disturbances in water, a singature left behind of ships and submarines , in earlier times it has relied on visual detection, helped airplanes to find their targets and engage in WWII, with improved instruments nowadays it can be used to detect anything which moves by measuring disturbances in water, which remains behind of a vessel, in its wake longer. These instruments also can be used to detect nuclear remains.
The technique is also used on torpedoes, which homes onto their targets by following wake of the target in combination with acoustic detectors.
What is wake:

Wake - Wikipedia

en.wikipedia.org

A source to read:

Rising importance of Non- Acoustic detection technologies of Stealthy submarines in Anti Submarine Warfare - International Defense Security & Technology

Ship detection for offshore production operations, military activities, transportation and other mar

idstch.com

Magnetic anomaly detection (MAD) is often seen by instruments placed on MPAs, as an extending probe at the tail. The subject is indeed vast, and it is not only related to disturbanced in magnetic field of earth because of presence of magnetic material (hull of submarine) but also linked to equipments, self-magnetization and Eddy currents generated along the hull.

Magnetic anomaly detector - Wikipedia

en.wikipedia.org

Beside those EMR detection is a thing, a submarine scatters EMW which is dissipated in short distances but still may result in detection.

 

[Gary]

 

[Anmdt]

Wake Features of Moving Submerged Bodies and Motion State Inversion of Submarines

The interaction between a moving submerged body and a homogeneous/stratified fluid generates a Bernoulli hump, a Kelvin wake, and an internal wake on the water surface. The height distribution of wakes is directly related to the location and motion state of the submerged body. Thus, it is...

ieeexplore.ieee.org

A glimpse of how a wake remains in place, scatters & visible in long distances. Don't mind the equations, visuals are enough to understand.
SAR may easily detect and classify those, whether it belongs to a surface or submerged vehicle, rough size and speed &heading.
The speed is high ~23 knots and high for the vehicle's size.

Different depth, same speed:

Different speeds, same depth:

In the end, one may find the author guesses submerged depth and speed of the object studying simple parameters' correlation. Imagine more parameters, Image processing algorithms combined with imaging/radar techniques.

One again may claim the study was assuming a calm sea, up to a certain sea state the water waves are permeable, and wake of different objects may pass through each others with minimal loss. A computer algorithm can detect and differ those.

 

[Anmdt]

Extension of Ship Wake Detectability Model for Non-Linear Influences of Parameters Using Satellite Based X-Band Synthetic Aperture Radar

The physics of the imaging mechanism underlying the emergence of ship wakes in Synthetic Aperture Radar (SAR) images has been studied in the past by many researchers providing a well-understood theory. Therefore, many publications describe how well ship wakes are detectable on SAR under the...

www.mdpi.com

Another study, adopted sensing by satellite based SAR data for surface vessels.
Note that, heading-speed information can be retrieved.

 

[Anmdt]

Thermal surface signatures of ship propeller wakes in stratified waters | Request PDF

Request PDF | Thermal surface signatures of ship propeller wakes in stratified waters | When a ship moves in temperature stratified water, e.g., in the ocean diurnal thermocline, the propeller(s) as well as the turbulent boundary... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

The article is closed-can be requested, but it claims a propeller's wake can leave trace of heat wake-signature. Studied for surface vessels, also valid for submarines. Temperature along depth varies, and 1~2 degree difference would be seen by IR sensors for long distance, and durations.

 

[Anmdt]

Seeking for studies on heat signature of submarines, since by HVAC or cooling cycles they dissipate some heat into the water. Such a heat difference tends to remain in wake for awhile, not mixing up or loosing its heat-energy as in calm condition.
It will be hard to find, may not be even avaliable.
US (ONR) in 1969 has classified thermal wake in three ways:
Essentially thermal (induced by submarine)
Non-essentially thermal (induced by disturbance of submarine, not by itself)
Non-thermal (non thermal disturbance)

And wake of a submarine is given as:
"More than forty phenomena that potentially could be associated with submarine wakes have been classified into categories such as thermal, optical, mechanical, electrical, ! magnetic, electromagnetic, chemical, biological and nuclear."

https://apps.dtic.mil/dtic/tr/fulltext/u2/c955796.pdf

I would love to see a study how it effects if cooling cycle water is dissipated quiescently towards -into propeller wake or avoided it by discharging farther from body.

 

[Turko]

@anmdt What would you say about it?is it feasible? Sinking them every 10 miles you could monitor your all shores.

 

[Anmdt]

@anmdt What would you say about it?is it feasible? Sinking them every 10 miles you could monitor your all shores.

Could work well, but i think would be better at the open seas and EEZs which is hard to draw a power-line from shore.