The GPS Revolution
We???ve come a long way in our circumnavigation of our world. From using the stars to help us find our way to using space based satellites to pin point our location and destination. There is no need for a back seat driver with a modern GPS unit.
The United States first developed GPS for the military in the 1960s. In the beginning all four branches of the military had a different system. In the 1970s a single application was developed by the US government, which became NAVSTAR. The Reagan administration in the 1980s made it available for non-military applications such as commercial air transportation.
The first GPS satellite was launched in 1978 and has gradually grown to a full contingent of 24 in 1994. The 24 GPS satellites are solar powered and orbit approximately 12,000 miles high above the earth. In 2007 the constellation of GPS satellites has grown to 31. GPS satellites have a life span of about 10 years and are constantly being replaced as needed. The added satellites have helped to increase GPS accuracy, reliability, and availability. Russia, China and India are in the process of launching their own separate GPS satellite systems.
The Galileo global navigational system is being built by the European Space Agency and is scheduled to have it completed by 2013. That???s a lot of satellites up there.
A GPS unit needs four or more of the satellites to calculate your position. All GPS satellites run on atomic clocks which are very precise. The unit then takes the four different signals that each have the same time signatures and locations and transform the values of each into a user friendly form, such as longitude, latitude, altitude or a point on a map.
A GPS unit consists of an antenna which is tuned to the frequencies that the GPS satellites transmit, receiver processors that calculate the transmitted GPS signals. A highly stable clock is also included in the receiver that works in sync with the time signature that is transmitted by the multiple satellites. A typical GPS unit can display location, direction, time and speed information. A GPS unit also has channels. Each channel is a signal from a different satellite. You only need four signals or channels but most of the currents units now have 12 to 20 channels per receiver, making calculating your position very accurate
To calculate your position a GPS unit requires the current time, the position of the
satellite or satellites, and the measured delay of signal ??” (how long it takes for each
satellite signal to reach the receiver).
There are a few factors that may corrupt an
accurate reading. The first is that each signal being transmitted from a GPS satellite
must travel through the earth???s atmosphere. The speed of the signal may be affected as it passes through the ionosphere.
The location of the satellite is a variable in signal strength. You will get a more accurate reading from a satellite that is directly over head than you will from one that is on your horizon. Your location will also be a factor. When you and your GPS receiver change your position in altitude you change the measured signal delay from each satellite.
This is a simple error to correct, but there will be a small margin for error as the GPS estimates your current location and direction. Let???s not forget about humidity. A more localized atmospheric condition can also hamper signal delay. The topography of your surrounding terrain may cause signal inaccuracies.
The GPS satellites transmit signals 24/7 365 days a year so as long as your unit is powered up you should be able to receive and calculate your location. The accuracy of your GPS unit is controlled by the US Air Force who is in charge of monitoring the transmitted signal and its strength.
The Air Force also makes sure that each satellite stays in its correct orbital path so that your signal will be constant, current and optimized.
Since it???s inception by the military for targeting in the 1950???s GPS has become an application useful in every day life. The use of GPS in search and rescue and the creation of the most accurate maps possible are only two of the civilian applications that saw immediate benefits. With the flip of a switch or the touch of a screen you can use a GPS unit to calculate your exact position, your location according to your relative movement, and accurate time signature.
You can use a GPS unit to calculate your exact location in aviation, marine, and automotive applications. GPS is also fun for tracking your exercise regiment and duration or to keep you on track while hiking out on the trail. From portable handheld units to large sophisticated units used by airports or marine shipping to navigate the world GPS has arrived on main street and is constantly improving. Manufacturers of GPS units are battling each other to lead the field with new technologies and a steadily growing demand to increase accuracy and availability.
I think that it is safe to say that the use of GPS and all of it???s applications has a bright future. A general overview as it may be I hope that this article may bring a better understanding of the GPS unit and the constellation of satellites that are hard at work behind it that aid in any adventure you are involved in.
By peterc35
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