Continued

                                              Submerged navigation and data transfer.

In our modern world, we are blessed with the results of years and years of technology developments, starting with the atomic clock, giving us the most accurate time keeping, essential for the coordination of data, transmitted up and down satellites and circuits.
(See section “Atomic Clock” below for details.)

Only thanks to this precision timing, could we achieve the high position accuracies of today’s technologies. (Wave frequencies and Global navigation) In our daily lives we navigate with precision thanks to GPS.

Unfortunately, GPS is not waterproof.

The navigation system relies on (radio) waves, which break down rapidly in liquids.
To track underwater, lower frequency acoustic signals are used.
The good news is that those lower frequencies travel faster through liquids than air.

    Typical frequencies and its behaviors in air and liquids.
Humans can detect sounds in the frequency range from about 20 Hz to 20 kHz.
Sonar acoustical frequencies are typically between 500 kHz and 1 MHz
Radar frequencies are typically 400 MHz and 36 GHz.
Radio Frequencies (RF) are typical HF: 3-30 MHz; VHF: 30-300 MHz; UHF: 300 MHZ- 3GHz.
Some radio frequencies can go as low as 3 Hz or as high as 3 THZ.
Laser frequencies are typically between 180 and 400 nm. (Ultra Violet to Visible blue light) 3 x 10 to the 15th Hz to 7.5 x 10 to the 14th Hz)

Transmitting through a liquid has its limitations for Sound or energy waves.
Waves at higher frequencies will be absorbed and/or dispersed at a higher rate than at lower frequencies. 

       Lower frequencies
So, how do we navigate underwater?

Underwater we experience similar phenomenon's like Doppler shifts, reverberations, propagations and fluctuations, just all on different levels.
Understanding and using these are the gate to navigation and communicate underwater.

One base principle for submerged Navigation is using pulse generators (Transmitters) and a reflector or transponder. Both returns the signal, the reflector in a passive (non powered) way and the transponder in a powered way. By placing multiple transmitters on marked locations, with a single responder, the location of the responder can be triangulated.
Basically, this is the Ultra-Short Baseline System.
Our navigation system is an expansion on the USBL principles, with additional, state of the art, technology, supported with, and by, powerful software. We call this an inverted USBL system.

Communicating through a liquid in a (metal) tank comes with a whole set of challenges.
The walls, and levels, will cause reflections, the liquids
The robot in the tank, as well as Many ROV applications require that the operator know the position of the ROV with varying degrees of precision.
However, precise navigation for small ROVs is actually a very difficult task to achieve.
There are three basic positioning techniques that are practical for use on ROVs: dead reckoning, Global Positioning System (GPS), and Ultra-Short Baseline (USBL).

We will look at each of them in turn.
Dead reckoning is the navigational method used by mariners all over the globe before the invention of compasses, chronometers and sextants. In dead reckoning, the navigator starts with a known (or estimated) position, and from there attempts to gauge the vehicle’s position by applying the vehicle’s heading and speed. Depending on the tools available, dead reckoning can be a surprisingly effective form of navigation. In the modern era, where the starting position of an ROV may be known with great precision and the heading and speed of the vehicle are also known quantities, dead reckoning can be sufficient for many applications. However, dead reckoning has one fatal defect: it cannot account for currents in the water. If the current is significant, the position of the ROV at the end of a run can be vastly different than the reckoned position. Atomic Clock An atomic clock is a clock whose timekeeping mechanism is based on the interaction of electromagnetic radiation with the excited states of certain atoms. Specifically, either a hyperfine transition in the microwave region, or an electron transition in the optical or ultraviolet region, of the emission spectrum of an atom is used as a frequency standard for the timekeeping element. Atomic clocks are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, to control the wave frequency of television broadcasts, and in global navigation satellite systems such as GPS. Since 2004, more accurate atomic clocks first cool the atoms to near absolute zero temperature by slowing them with lasers and probing them in atomic fountains in a microwave-filled cavity. An example of this is the NIST-F1 atomic clock, one of the national primary time and frequency standards of the United States. One of these clocks, the strontium atomic clock, is accurate to within 1/15,000,000,000 of a second per year. This is so accurate that it would not have gained or lost a second if the clock had started running at the dawn of the universe. It promises to be as much as 1000 times more accurate than the world's current standard in time measurement-cesium-based clocks. Light frequencies are in the 600 Terra Herz range, whereby sonar typically works in 850 K Herz range. In the last 15 years, streaming multibeam sonars have been introduced, working at 1 Meg Herz range. Their range is short, but their resolution is high. As we have said to track exact location a method of triangulation is used from signals received, so what is this method? While orbiting the earth, satellites broadcast their own location and timestamp, when at least three satellites are in line of sight of the object that is tracked, a GPS receiver receives signals and calculates the The receiver calculates the distance between itself and the satellite and then sends the information to a monitoring device. Since precision is of utmost importance and cannot be compromised in GPS tracking, the method of triangulation with zero margin of error ensures the accuracy of the data received from multiple satellites. Calculating data through triangulation methods ensures a high level of accuracy in any device. 2. Cellular Network: PAJ GPS Tracker uses cellular network and cellular networks are the best method to transmit data of the location to monitoring service without any delay. Always opt for devices that use sim cards. 3.Differential GPS (DGPS): To enhance GPS Accuracy, a correction technique called DGPS is used. In this additional ground-based reference stations are used to enhance GPS accuracy. DGPS can significantly improve accuracy in certain applications. What is DGPS? DGPS (Differential GPS) is essentially a system to provide positional corrections to GPS signals. DGPS uses a fixed, known position to adjust real time GPS signals to eliminate pseudorange errors. An important point to note is that DGPS corrections improve the accuracy of position data only. Ground reference station Sonar: Sonar: The principle used to measure the distance between a source and a reflector (target) based on the echo return time Active Sonar: Emitting pulses of sound and listening for echoes. Passive Sonar: Does not Emit/transmit a pulse; only listens for the sounds made by vessels or other sources. Transponder: device that, upon receiving a signal, transmits a different signal in response Transducer: Device that converts energy from on form to another. Usually a transducer converts a signal in one form of energy. (For instance pressure into an electrical signal). Electro-acoustic transducer/array: Pulse: Active sonars create a pulse of sound, often called a “Ping” Speed of Sound: (SoS through a column of water) Average is 1531 m/sec in Seawater. (SoS through air is 343 m/sec; Kerosene: 1324m/sec; Benzene: 1298 m/sec. And just for fun: Through Diamond is 12Km/sec) (General: Less dense =Slower speed) Color: The different colors used to represent the varying echo return strength. Echo: The reflected sound wave Echo Return: The time required for the echo to return to the source of the sound Echo Sounding: When active sonar is used to measure the distance from the sonar head to the bottom, this is known as Echo Sounding. Wave measurement: Same principle as echo sounding, but now with active sonar measuring he distance from the sonar head to the surface. Target: The object that you wish to obtain information about. Sonar Gain: The gain settings controls the sensitivity of the Sonar receiver to compensate for water depth and water clarity. Increasing the gain shows more detail and decreasing the gain reduces clutter. (Reflections and Noise) Beam: Sonar pulse, shaped into a beam pattern. Fan shaped for Imagine sonar ( Width and height to be narrow 1.7 by 30 D) and Conical ( 1.7 deg) for profiling sonars. Comms Protocol: The sonar communicates with a computer or laptop using RS485 or Rs 232. Both are a communications protocol, enabling the transfer of all data to the computer using 2 conductors. Protocols cover authentication, error detection and correction, and signaling. Sonar reflections: When used in a small metal base, the walls reflect the sonar signals and induce “noise” for the sonar transducer (Receiver). The first recorded use of the sonar technique was by Leonardo da Vinci, in 1490, who used a tube inserted into the water to detect vessels by ear. This was, of course, an example of a rudimentary and passive principle. It was developed in World War 1 to counter the growing threat of (German) submarines. Modern active sonar systems use a sound transmitter and a receiver to generate and receive a sound wave, which is reflected back from targeted objects. A Sonar works with sound waves to “see” / identify objects and more In comparison, a camera works with light (and therefor with light waves, which works with very high frequencies. (4.3x 10 to the 14th Hz) Light used for photographic imagery, uses a wide spectrum (Band width) and, by filtering out specific frequencies, can identify colors through absorption and reflections of the light waves.

For instance: White objects reflect light (back) and black objects absorb light. For this reason the human eye sees the white and black colors Sonar is helpful for navigation and mapping because these sound waves travel farther in water and related medias than light waves. Lower frequencies travel farther but have less capability to carry information, so longer range with less resolution. Light frequencies are in the 600 Terra Herz range, whereby sonar typically works in 850 K Herz range. In the last 15 years, streaming multibeam sonars have been introduced, working at 1 Meg Herz range. Their range is short, but their resolution is high.

Some of the manufacturers are: Didson, Seattle Washington; Blue View Seattle Washington; Imagenex Vancouver Canada; Tritech Aberdeen Scotland; R2 Sonic Austin Texas; Coda Octopus Tampa Florida; Reson Denmark.