What is Dead Reckoning?

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- everything RF

May 11, 2023


Dead Reckoning is a navigational technique that has been used for centuries by mariners, pilots, and explorers to determine their position and direction of travel when other navigational aids, such as maps or GPS, are unavailable. The method involves estimating one's position based on the direction and speed of travel from a known starting point.

The term "dead reckoning" is believed to have originated from the Old English phrase "ded reckoning," which meant "deduced reckoning." The technique was originally used by seafarers who would plot their course on a map, estimating their position based on the distance traveled, direction, and estimated speed.

To perform dead reckoning, one must first determine their starting position and their heading. This can be done using a compass, a sextant, or other navigational aids. Once the starting position and heading are determined, the navigator must track their progress by estimating the distance traveled and direction of travel.

Estimating distance and direction can be done in several ways. One method is to use the time it takes to travel a certain distance at a known speed. For example, if a ship is traveling at a speed of 10 knots and travels for 2 hours, it can be estimated that the ship has traveled 20 nautical miles. Another method is to use visual cues, such as landmarks or the stars, to estimate the direction of travel.

Dead reckoning is still used today in many different applications, including aviation, marine navigation, and wilderness exploration. The technique is particularly useful in situations where GPS signals may be disrupted or unavailable, such as in areas with heavy foliage or in underground tunnels.

In modern times, dead reckoning is used with some modifications and enhancements. The principles of dead reckoning are still relevant and useful, especially in situations where other navigational aids are unavailable or unreliable, such as in remote areas, underground tunnels, or when GPS signals are disrupted. A few such situations are:

  • One modern application of dead reckoning is in autonomous vehicles. Many self-driving cars, drones, and robots rely on dead reckoning to navigate their environment. They use sensors and cameras to estimate their position and direction of travel, based on their speed and direction, and adjust their course accordingly.
  • Another modern application of dead reckoning is in the military. Special Forces, for example, may use dead reckoning to navigate through enemy territory where GPS signals are disrupted or unavailable. They use maps, compasses, and other navigational aids to estimate their position and direction of travel and adjust their course accordingly.
  • In aviation, dead reckoning is still used as a backup to GPS and other navigational aids. Pilots are trained to use dead reckoning to estimate their position and direction of travel, based on their speed and heading, in case of GPS signal disruption or failure. This can be particularly useful in remote areas or during long-haul flights.

Errors in Dead Reckoning

It is important to note that dead reckoning is an estimation technique and is subject to errors. Factors such as wind, currents, and human error can all affect the accuracy of dead reckoning calculations.

For precise positional information, both speed and direction must be accurately known at all times during travel. Most notably, dead reckoning does not account for directional drift during travel through a fluid medium. These errors tend to compound themselves over greater distances, making dead reckoning a difficult method of navigation for longer journeys.

For example, if displacement is measured by the number of rotations of a wheel, any discrepancy between the actual and assumed traveled distance per rotation, due perhaps to slippage or surface irregularities, will be a source of error. As each estimate of position is relative to the previous one, errors are cumulative, or compounding, over time. For this reason, it is important to use other navigational aids, such as maps, GPS, or radio communications, whenever possible.

The accuracy of dead reckoning can be increased significantly by using other, more reliable methods to get a new fix part way through the journey. For example, if one was navigating on land in poor visibility, then dead reckoning could be used to get close enough to the known position of a landmark to be able to see it, before walking to the landmark itself - giving a precisely known starting point - and then setting off again.

In conclusion, dead reckoning is a valuable navigational technique that has been used for centuries. While it may not be as accurate as modern GPS technology, it is still useful in situations where other navigational aids are unavailable or disrupted. By understanding the principles of dead reckoning and practicing the techniques, navigators can become more confident and capable in their journeys.

Click here to learn about untethered dead reckoning.

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