Dei'ah veDibur - Information & Insight
  

A Window into the Chareidi World

9 Iyar 5761 - May 2, 2001 | Mordecai Plaut, director Published Weekly
NEWS

OPINION
& COMMENT

HOME
& FAMILY

IN-DEPTH
FEATURES

VAAD HORABBONIM HAOLAMI LEINYONEI GIYUR

TOPICS IN THE NEWS

HOMEPAGE

 

Produced and housed by
Shema Yisrael Torah Network
Shema Yisrael Torah Network

 

 

 

 

 

 

 

 

 

 

NEWS
Global Positioning System: Knowing Where It's At
by Yated Ne'eman Staff

In the early 1970s, the Defense Department needed a navigational tool that troops on the move could use to pinpoint their location. As a result, they created the Global Positioning System, or G.P.S., a hi-tech system of two dozen satellites, atomic clocks, microwave radio transmitters and some heavy-duty number-crunching hardware.

The G.P.S. is now used by millions for fun and profit. Any time you take a plane trip, receive goods from a commercial shipping agency or drive a car with a NeverLost or OnStar navigation system, you are benefiting from G.P.S. technology.

A receiver on the ground or in the air uses time signals from four satellites to calculate its position. The calculation itself is based on a kind of triangulation -- a math technique used to locate an object based on its distance from three points. So signals from three satellites are necessary, although in practice a signal from a fourth satellite is used to improve the accuracy of the other three signals.

To calculate these distances, the system uses another basic high school math equation: distance is equal to the speed of travel multiplied by the time.

In addition to the time, a signal from a G.P.S. satellite also includes information about the satellite's exact location, which is known, tracked and kept accurate by ground control stations. The time signal is also very accurate, because each satellite contains several atomic clocks. These rely on the natural, and very regular, oscillation frequencies of atoms to keep time.

The end result is that a G.P.S. receiver -- such as a dashboard navigation system in a car -- can produce highly accurate coordinates of latitude, longitude and altitude. This kind of system was used in a recent report in Yated that discussed the boundaries of Eretz Yisroel as being north of the 30th parallel of latitude.

Software developers in the commercial sector took care of the final step, placing your location on a map and providing directions. Companies provide consumer products that combine a G.P.S. receiver with map programs that can provide turn-by- turn directions for drivers. From longitude and latitude readings that update every second, these programs can determine the speed and direction, information that enables them to superimpose a "you are here" arrow on the display of a road map.

This navigation technology also has implications for the trucking industry, which has begun to automate its fleet management systems with customized G.P.S. equipment. In addition to receiving G.P.S. satellite signals and calculating location, they also transmit location information to a central computer that handles route planning for multiple deliveries. This enables new delivery and pickup points to be added to a driver's route without requiring any data entry by the driver.

The G.P.S. does have some blind spots, however, if the receiver is behind trees, tunnels, power lines and tall buildings which can block satellite signals.

Another problem is the orbits of the satellites, since not all parts of the earth have the minimum four satellites within range at all times.

A greater source of error is atmospheric conditions, which can ever-so- slightly slow down the radio signals from the satellites, introducing errors into the system.

To help improve accuracy, an enhancement, called differential G.P.S., uses stationary ground-based receivers to monitor the signals from the constellation of G.P.S. satellites. Differential G.P.S. can provide accuracy down to a meter or so.

 

All material on this site is copyrighted and its use is restricted.
Click here for conditions of use.