The use of stationary smart sound receivers as part of a network-centric system

This article is a continuation of the article “Design of a smart sound receiver as part of a network-centric system for establishing the coordinates of a sound source”

1 Problems of using modern sound-receiving equipment.

In the article [1] the following is said (we apologize for the command-military phraseology of constructing phrases):

“Experience in practical application, as well as theoretical studies show that meeting, with a probability of at least 0.95–98, consumer requirements for the accuracy of determining the coordinates of targets and discontinuities, regardless of the influence of meteorological conditions, terrain and properties of underlying surfaces, is possible at a distance to sound-receiving equipment not more than 2-3 km.”

This revelation came as a surprise to us. A range of 2-3 km is very short. Against the textbook [2] the range is underestimated by a factor of 5. Apparently, this should be considered a declaration of the goal of the upcoming modernization of means to improve existing standards (0.7–0.9)% of the range and 0-03-0-05 d.u. towards.

“This is explained by the fact that at these ranges atmospheric factors do not have time to have a significant influence on the change in the structure of the original sound signals, which ensures the detection and determination of their parameters necessary for accurate location determination with a probability close to one.”

It turns out that the whole point is in the heterogeneity of the sound propagation medium! However, what is noteworthy is the desire of the respected author of the article to remain within the spherical front of the sound wave, and as we know, the wave front undergoes deformation into an ellipsoidal shape.

As in the article [1] is it proposed to solve the problem of increasing the definition of coordinates?

“the reduction in the influence of turbulent processes in the surface layer of the atmosphere, arising under the influence of the relief and underlying surfaces, which have the strongest influence on the change in the structure of the original acoustic signals, can be somewhat reduced when the sound-receiving equipment is raised to a height of at least 150-200 m.”

2 Factors influencing the accuracy and efficiency of determining target coordinates

Let us first consider the turbulence factor. According to review [3] In theoretical studies, vortices in acoustics can be neglected if the dimensionless vorticity is small compared to the dimensionless velocity, i.e.

|rot u|/ω >> u/c

where u is wind speed,

ω is the frequency of sound.

We do not have statistical data on the value on the left half of this inequality, so we consider the issue of the influence of turbulence open for further study.

Most likely we are talking about dispersion and frequency distortion of the sound wave in general on atmospheric inhomogeneities, i.e. about the sound absorption coefficient in air. We will talk more about the absorption coefficient below.

But why is it really necessary to lift sound-receiving equipment into the air on drones? Let's consider the vertical wind gradient factor. Let us turn to the previous article “Constructing the hodograph of a sound wave point…”, namely to diagram 4. With all the previously indicated imperfections of the said diagram, we have that:

• on the windward side at a distance of 2.5 km, drones with sound-receiving equipment must be raised to a height of at least 500 m in order to remove them from the acoustic shadow zone;

  Conclusion: from the diagram it follows that in order to double the range of determining the coordinates of targets, it is necessary to have drones with a loitering altitude of 2 km.

• on the leeward side, there is no need to raise the sound-receiving equipment to a height on drones, because the main beam of sound rays is “grounded” at a distance of up to 10 km; then the sound wave sharply loses intensity;

  Conclusion: in order to increase the reliability and accuracy of determining the coordinates of targets, it is necessary to locate sound receivers, if possible, behind the line of contact on the territory of the opposite side.

3 Receiver elimination configuration

On the battalion's defense front, 5 km away. It is advisable to place smart sound receivers across the entire width of the front. With the standard number of receivers being 6 pcs. The distance between receivers will be 1 km. Receivers are arranged in a special order.

There is a theoretical limitation on the configuration of receivers. Incorrect location of the receivers leads to a system stop, namely, to a failure of the analyzer. One could call this arrangement an exception, because… at the program level, this will cause precisely an exception that is caught, but there is a successful biological concept of elimination, which means the death of a biological population. Therefore, we will say that the “culprits” of the exception are in the elimination configuration, and the geometric location in which the “culprits” are located will be called the elimination zone.

For clarity, let's draw points 1 and j on the plan and draw a straight line through these points. This line will be the elimination zone for the 3-receiver configuration. An additional receiver placed on this line will render the existing population of receivers inoperable.

Those. When planning artillery reconnaissance, it is necessary to avoid placing 3 or more receivers on a straight spatial line. It is acceptable to place receivers in a straight line on a topographic map if, for example, two receivers are on a hill and one is in a valley.

Theoretically, it is advantageous to place the receivers on a hypothetical surface of a sphere or ellipsoid.

4 Receiver configurations for combat escort of ships

We will look at an example of the maritime application of smart receivers, because… their use for guarding the parking of a warship is very well demonstrated by the construction of smart sensors to detect and prevent penetration into a closed territorial zone.

It is necessary to adapt smart receivers to the marine environment:

· receivers are placed on floating buoys.

· microphones are replaced with passive sonars.

· buoys with smart receivers are located on a circle around the ship's anchorage, as shown in Fig. 2.

It is known that sound travels much better in water than in air. This is due to the low sound absorption coefficient in water.

There are two types of sound energy loss.

In the first type, the energy loss of an acoustic wave occurs due to geometric expansion as it moves away from the source: for air and water they are the same. The dependence of acoustic loss on expansion is called the 6 dB rule: “For every doubling of the distance from the sound source, the sound pressure decreases by 6 dB.”

The second type of sound absorption is associated with viscosity, thermal conductivity of the medium, and chemical relaxation molecules.

Next, the reduction in sound level due to absorption was assessed for a frequency of 1 kHz, since Acoustic noise direction finding devices operate most effectively at frequencies below 1 kHz, at which noise from propellers is most powerfully emitted.

For water, the reduction in sound level with a frequency of 1 kHz at a distance of 1 kHz is ~0.06 dB/km according to the online calculator [7].

According to Gosta [2] the reduction in the level of a flat monophonic sound with the same frequency in air at normal atmospheric pressure and 50% humidity is equal to 4.66 dB/km.

In practice, for a rough quick estimate of the propagation range of sound in water, you can use a very simple formula:

d=(40/f)^3/2

As far as we can understand from the source [8], this formula gives a “cautious” but more or less accurate estimate of the propagation range of sound with a frequency of 1–5 kHz from a source developing a pressure of 200–400 Pa, with reliable sound reception in conditions of extraneous noise. Using this formula for a frequency of 1 kHz d is 252 km. This is more than enough to protect the anchorage.

Although sound travels well in water, there are subtleties in ensuring the reception and processing of a sound signal in sea water. This is primarily due to the refraction of sound caused by the vertical temperature change in water. If the temperature, and therefore the speed of sound, decreases with depth, sound rays are deflected downward, resulting in the formation of a zone of silence, similar to what happens for the atmosphere, including under conditions of a vertical wind gradient.

Therefore, sonars are made with variable immersion depth and they try to lower them deeper.

Another feature of the marine application of smart sound receivers is the reception of an audio signal from a moving source. The Doppler effect occurs, which must be “deciphered” in the FFT block.

The current level of sonar technology is very high. But there is also a significant drawback: as a rule, only the direction to the target is set.

When using smart sound receivers as part of a network-centric system, it is possible to establish the exact coordinates of the sound source on and in the water. When organizing a combat guard for a ship at anchor, a preemptive artillery strike is launched at the identified target coordinates without waiting for eye contact.

What is another important difference between the proposed network-centric system and existing ship security systems? We risk incurring a barrage of criticism, but we are confident that existing systems are built on the principle of consolidating data in memory before processing it, which is illustrated in Fig. 2 in the article CAN bus based smart sound sensor receiver design concepts.

If we analyze Western open sources of information, over the past 15 years the West has headed towards systems with streaming data processing.

conclusions

Stationary smart sound receivers are passive, operate in standby mode and practically do not detect themselves.

The rules for the tactical construction of stationary smart sound receivers as part of a network-centric system for establishing 3-dimensional coordinates of a sound source at the battalion or artillery division level have been determined.

The tactical construction of stationary smart sound receivers to detect and prevent penetration into a closed territorial zone is shown.

The next article will talk about converting a passive network-centric system of smart sound receivers into an active system to counter low-noise flying objects.

Literature

1. N.M. PARSHIN, Development and condition of sound means of artillery reconnaissance in the Armed Forces of the Russian Federation, “Military Thought”, 2024, No. 1

2. Artillery sound reconnaissance, ed. MO, M., 1993

3. Chernov L.A. “Acoustics of a moving medium. Review“, Acoustic Journal, 1958, 4, issue 4, With. 299-306

4. GOST 31295.1-2005 (ISO 9613-1:1993) Noise. SOUND DAMPING DURING LOCAL PROPAGATION Part 1. Calculation of sound absorption by the atmosphere

5. Ainslie M. A., McColm J. G., “Simplified formula for viscous and chemical absorption in seawater,” Journal of the Acoustical Society of America, 103(3), 1671-1672, 1998.

6. Fisher, F. H., and Simmons, W. P., “Sound Absorption in Seawater,” Journal of the Acoustical Society of America, 62, 558-564, 1977.

7. Francois R. E., Garrison G. R., “Sound Absorption from Ocean Measurements: Part I: Contributions of Pure Water and Magnesium Sulfate,” Journal of the Acoustical Society of America, 72(3), 896-907, 1982.

8. Francois R. E., Garrison G. R., “Sound Absorption from Ocean Measurements: Part II: Contribution of Boric Acid and Equation for Total Absorption,” Journal of the Acoustical Society of America, 72(6), 1879-1890, 1982.

9. //resource.npl.co.uk/acoustics/techguides/seaabsorption/

10. Why does sound dampen in water? https://habr.com/ru/articles/696738/