Navigation From Dead Reckoning to Global Positioning

Navigation

From Dead Reckoning to Global Positioning

Early Navigation

From the time of the Thales (circa 640-546 B.C.), who first postulated that the earth was a sphere, until 1760 when John Harrison developed his first workable chronometers, the technologies of navigation left much to chance.

Early Navigation

Ancient navigation relied mostly upon staying close enough to shore and familiar landmarks to get from one port to another.Dead (from deduced) reckoning was a widely used navigation technique.

In dead reckoning, ships would start off on course and continue on it until they arrived at their destination.

Early Navigation

The speed of a ship was calculated by throwing knotted lines overboard and counting how many knots passed through a sailor’s hands in a minute.

This technique worked well for voyages across the Mediterranean, but voyages across oceans were often disastrous.

Early Navigation

From the fourteenth through sixteenth centuries, technological innovations enabled sailors to explore all the corners of the earth.

Who were some of the famous navigators of this time period?

• Ferdinand Magellan, Vasco da Gama, De Soto, Ponce de Leon, and Christopher Columbus. (Spanish explorers)

• Sir Frances Drake (English.)

Navigation Technologies

What navigation systems (technologies) replaced dead reckoning and promoted this Age of Exploration?

celestial navigation,



astrolabe,

Navigation TechnologiesWhat navigation systems (technologies) replaced dead reckoning and promoted this Age of Exploration?

quadrant,


sextant,



astronomical charts,


magnetic compass.

Global Positioning System

The Global Positioning System (GPS) is a worldwide telecommunications system formed from a constellation of 24 satellites and their ground stations.

GPS uses these “man-made stars” as reference points to calculate positions accurate to a matter of meters.In fact, with advanced forms of GPS, measurements can be made to better than a centimeter.


GPS was developed by the Defense Department primarily for military purposes.

Global Positioning SystemGPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. That makes the technology accessible to virtually everyone.

These days GPS is finding its way into cars, boats, planes, construction equipment, moviemaking gear, farm machinery, and even laptop computers.Soon GPS will become almost as basic as the telephone.


GPS uses satellites in space as reference points for locations here on earth.

By very, very accurately measuring our distance from three satellites we can “triangulate” our position anywhere on earth.


Suppose we measure our distance from a satellite and find it to be 11,000 miles.

Knowing that we’re 11,000 miles from a particular satellite narrows down all the possible locations where we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 11,000 miles.

Somewhere on the Sphere


We measure our distance to a second satellite and find out that it’s 12,000 miles away.

That tells us that we’re not only on the first sphere but we’re also on a sphere that’s 12,000miles from the second satellite. Or, in other words, we’re somewhere on the circle where these two spheres intersect.

2 Intersecting Spheres

http://www.womenoceanographers.org/Content/Profiles/KathrynKelly/images/LearnMore7.jpg


We then make a measurement from a third satellite and find that we’re 13,000 miles from that one,

that narrows our position down even further, to the two points where the 13,000 mile sphere cuts through the circle that’s the intersection of the first two spheres.

3 Intersecting Spheres

http://mail.colonial.net/~abeckwith/images/spheres.gif


By ranging from three satellites we can narrow our position to just two points in space.Usually one of the two points is a ridiculous answer

(either too far from Earth or moving at an impossible velocity) and can be rejected without a measurement

Sort of Like This

Imagine that you are somewhere in the United States and you are totally lost—for whatever reason, you have absolutely no clue where you are.

Sort of Like This

You find a friendly local and ask, “Where am I?” He says, “You are 625 miles from Boise, Idaho.”

Sort of Like This

You ask somebody else where you are, and she says, “You are 690 miles from Minneapolis, Minnesota.” Now you’re getting somewhere. If you combine this information with the Boise information, you have two circles that intersect.

Sort of Like This

You now know that you must be at one of these two intersection points if you are 625 miles from Boise and 690 miles from Minneapolis.

Sort of Like This

If a third person tells you that you are 615 miles from Tucson, Arizona, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points.

Sort of Like This

You now know exactly where you are—Denver, Colorado.

GPS Navigation

GPS Satellite

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Navigation From Dead Reckoning to Global Positioning