GPS Basics - Forestry Natural Resources and Wildlife - Lecture Slides, Slides of Wildlife Ecology

Download GPS Basics - Forestry Natural Resources and Wildlife - Lecture Slides and more Slides Wildlife Ecology in PDF only on Docsity! GPS Basics Docsity.com Locating a Given Position using GPS Locating Your Position using GPS Uses of GPS in Agriculture How GPS Works MAIN Docsity.com NEXT The GPS receiver knows which satellite it has received a signal from, and it knows that satellite’s position in orbit. It now has to determine the distance to the satellite in order for it to triangulate it’s position on Earth. The satellites contain four atomic clocks each. These atomic clocks can maintain extremely accurately time, down to less than a millisecond, for a very long period of time. The codes are different for each satellite but they are the exact same length. Kind of like a different song for each satellite but the songs are all the exact same length and the GPS receiver knows all of these songs by heart. Docsity.com The GPS receiver knows all of the codes and when they are transmitted. Since these codes all travel at the speed of light approx 186,000 miles a second, the GPS receiver can determine the distance to the satellite by comparing when the code was transmitted to when it was received. The GPS receiver compares this time gap and can determine the distance to the satellite based on the length of this time gap. Length of Time gap is .07sec 186,000 X .07 = 13,020miles Speed X time = distance NEXT Time code is received Time code is transmitted Docsity.com NEXT Ok, we know the satellite we received the code from, we know where the satellite is on its orbital path above the earth and we know the distance to the satellite. So, we must know exactly where we are right? ……WRONG! Actually we need more that one satellite to tell us our exact location. This is because the Earth is a sphere, and there would be more than one position on the earth that had the same distance to the satellite. You could actually draw a circle on the Earth, and all the points along that circle would be the same distance from the satellite, and you would be somewhere on that circle. You could be Here Docsity.com YOUR ARE DEFFINATELY RIGHT HERE NEXT It is best if you identify and have distances to at least four satellites in order for your location to be accurately measured. Some GPS receivers will not give you a location at all, unless you have at least four satellites. Docsity.com By having a distance from a fourth satellite it increases the accuracy of your location and can also give you an accurate altitude as well. Because of how the 24 satellites are arranged in orbit there will be between 5 and 8 satellites above you no matter where you are on Earth. Most GPS receiver can handle as many as 12 satellite contacts at a time, so you shouldn’t worry about receiving too many satellite signals at any one time. NEXT Docsity.com In short, a GPS receiver works by receiving and identifying signals from at least four satellites. By measuring the time lag in the signals it can determine the distance to each satellite. Once the receiver has determined the distance from the four satellites it can then determine its Latitude, Longitude, and altitude above sea level. G C F A NEXT Docsity.com Uses For GPS GPS was primarily designed to be used by the military. However, many industries have found it to very useful including Agriculture. BACK NEXT Docsity.com Farming Farmers can use GPS to help them plow very straight rows to enable them use their land more efficiently. NEXT Docsity.com Agriculture Farmers can use GPS to help mark areas for pesticide or fertilizer application. Thus reducing waste. NEXT Docsity.com How to Locate Your Position cont.. Once you have pressed “ENTER” The status screen will appear. This screen displays the GPS satellite’s current locations, and which satellites are currently visible to the the unit. In the image to the right the positions are noted, but none are currently visible to the unit. When satellites become visible to the unit, small vertical lines will appear below the locations. These are the satellites locations Currently no satellites are visible to the unit. NEXT Docsity.com How to Locate Your Position cont.. Once the unit begins to receive signals from the satellites it will display the strength of the signals on the screen. When the unit has received good signals from at least 4 satellites the screen will change to the “POSITION” screen. NEXT Signal strength Docsity.com How to Locate Your Position cont.. The position screen will display your: • Latitude • Longitude • Elevation (altitude above sea level) • Speed you are traveling if you are moving. • Distance traveled since last position mark. • If you are moving it will also display the direction you are heading. POSITION SCREEN NEXT Docsity.com How to Locate A Given Position First we need to be at the POSITION screen. If you are not at this screen hit the NAV button until the POSITION screen is in view. From the POSITION screen press the MENU button. NEXT Docsity.com How to Locate A Given Position Cont.. Scroll down to PROJECTION using the down arrow. Once PROJECTION has been highlighted hit ENTER. This will bring up the PROJECTION screen where we will enter in our Lat. and Long. NEXT Docsity.com How to Locate A Given Position Cont.. When you arrive at the PROJECTION screen the first number next to BRG will be highlighted. You will need to hit ENTER 3 times. This will highlight BRG and DST. Next we will hit the down arrow one time. NEXT Docsity.com How to Locate A Given Position Cont.. Be sure to note the landmark number given by the unit, especially if you will be trying to navigate to more than one location. You now need to hit the down arrow and highlight SAVE LMK, and hit ENTER. NEXT Docsity.com How to Locate A Given Position Cont.. Now hit the GOTO button. Then select USER. This will bring up a list of landmarks that the user has entered. Scroll down and highlight the landmark you just entered. NEXT Docsity.com How to Locate A Given Position Cont.. Once you have hit enter it will bring up the POSITION screen again. But this time it will have a small arrow above the compass. This arrow will point in the direction you will need to turn to find your given location. An easier screen to work with when navigating can be found by hitting the NAV button twice. NEXT Docsity.com