GPS stands for Global Positioning System, a satellite navigation system with twenty-four satellites in orbit. These satellites were put in place by the United States Department of Defense for military uses, and were called NAVSTAR. The first satellite was launched in 1978 and the twenty-fourth and last satellite was finally in place in 1994. In 1980 NAVSTAR was made available to the general public for commercial use.
GPS works 24 hours a day in any weather. The satellites orbit the earth twice a day in a specific orbit that is about 12,000 miles above us. In orbit, the satellites travel as fast as 7,000 miles an hour. As they are orbiting, they transmit information to receivers on earth. The receivers use this information to calculate the user’s location. This calculation is made by determining the difference between the time a transmission was made and when the receiver received it. This is then used to calculate the distance and the position is displayed on the receiver.
For a receiver to calculate a latitude and longitude position is to receive information from three satellites. To calculate latitude, longitude and altitude a receiver must be able to receive information from four or more satellites. After position is known the GPS can then tell the user information about speed, trip distance, the distance to a desired destination, sunrise and sunset times, bearing and other information.
While in orbit, the satellites are powered by solar energy. They also have backup batteries that are used in the event of no solar power such as an eclipse. The energy is used to power small rockets on the satellites that keep them in the proper orbit. At any one time only about 50 watts of power or less is used to transmit information. The satellites are designed to last about ten years, and the U.S. Department of Defense is constantly making and launching replacement satellites. Each satellite is about 2,000 pounds and seventeen feet across when the solar panels are out.
GPS receivers are generally accurate within 15 meters. Other than investing in a receiver there are no fees or other equipment required to access the GPS signal. If very accurate readings are needed, Differential Global Position Systems (DGPS) will provide accuracy within three to five meters. The United States Coast Guard operates the most popular DGPS.
Two power signals are transmitted and are referred to as L1 and L2. The L1 frequency is used for civilian purposes. These signals are relatively low power signals and travel by line of sight, so they can go through clouds, glass, and plastic, but not solid objects like buildings or mountains. In every transmission the satellite sends three types of information, its pseudorandom code, ephemeris data and almanac data. The pseudorandom code is an I.S. code that identifies which satellite the information is being sent from. Ephemeris data tells the receiver where the satellite should be at any time of the day, and almanac data sends information about the status of the satellite, the current date and the time. The almanac data is the part that is essential for determining the user’s position.
By: Chris Simons
Posts Tagged ‘Satellites’
Handheld GPS Hunting – Never Lose Your Trophy Kill Again
January 3rd, 2010
There are handheld GPS receivers for just about any sport out there today, hiking, biking and now fishing and hunting. Several manufacturers of GPS units are making handheld receivers for hunters complete with camouflage and compasses. Many of these personal GPS receivers have up to 12 satellites calculating your position. Some have a built in calendar helping you to chart the best time to go hunting. Most weigh between six and 10 ounces and won’t weigh you down, but have so many capabilities. Features include being able to store 500 to 2,000 waypoints – which are location you can navigate to later – both with graphics and names and the track log stores up to 10 to 50 retraceable paths. The trip computer indicates such things as sunrise and sunset times, speeds, distance and much more.
Some hunters think the handheld GPS receiver units are great when out wondering in the woods. One reason is because they don’t have to pay close attention to where they are going and can pretty much wonder freely and still be able to find their way back to their vehicle or campsite with the GPS trackers. Since you have marked your waypoints, you can easily find you way back to camp or your vehicle by turning around and placing the GPS on directional or compass screen and when the arrow points left, go left and when the arrow point right, go right and you will soon be where you want to be.
One of the most popular handheld GPS hunting receivers is one that has multiple receivers for hunting dogs as well as the hunter. You attach a GPS tracking unit to each of your dogs and then you can track there whereabouts with your GPS handheld unit. There are two screens in which to do this. One is a compass and if you have more than one dog, will show you which direction each dog is going, if they are running or on point (pointing to a bird or other wildlife) and do it in different colors so you can tell the dogs apart on the screen. The other way to track the dogs is on the dog info screen which give you individual dog information, such as where they are located, if they are running or on point, how much battery life their GPS unit has left and average distance and speed they have traveled over a predetermined amount of time. There is a dog screen for each dog you have, it even shows if one or more are back at the camp in their crates, not just out in the field.
There is additional software available for the handheld GPS hunting units to upload topographical maps and public hunting area maps. These are very useful to hunters who do not own or know someone with private property to hunt on. This upgraded system also comes with a memory card and personalizable software so you can create your own maps to use year after year.
By: Charlie Lee
