The Global Positioning System (GPS) consists of 27 satellites that orbit the earth. Using receivers on earth, these satellites are used to obtain a wide variety of information for several applications today. Military usage of this technology were one of the first fields to take advantage of the benefits of this system. Bringing advancements in tracking , communication, and mapping, the GPS technology allowed the military to ultilize its troops more efficiently. In Civilian usage, this system has allowed drivers to navigate more accurately and efficiently. The GPS technology has also served as tracking devices in monitoring vehicles and people in real time, assisting the police force in decreasing crime and violent activity. This instrument has also been a key tool in measuring tectonic motions in earthquake studies. The size of the earthquake can also be more accurately obtained using the GPS system. Engineering fields have also used this technology to expand their knowledge and resources in field surveying, mapping, structural deformation analysis, data inventory, etc. The GPS technology is a crucial tool in the development and advancement of various fields of study in society today.
GPS-10 Group Members
- Brian Sherman: Responsible for describing the alternatives to GPS and performing the GPS experiment
- Jose Rodriguez: Responsible for describing how the GPS system works and performing the GPS experiment
- Sam Agresta: Responsible for describing the military applications of GPS systems
- Jason Caperilla: Responsible for describing the civilian applications of GPS systems
- Danielle Salmon: Responsible for describing the use of GPS systems in Earthquake Studies
- Tharu George: Responsible for describing the use of GPS systems in Engineering applications and Executive Summary
How GPS Systems Work
The Global Positioning System, better knows as "GPS", is a system of 27 satellites that orbit the earth. There are 24 in operation at any given time and three additional satellites in case one fails. It was the U.S. military developed a network for military navigation purposes. Each satellite rotates over the earth at about 12,000 miles and completes two rotations per day. The GPS receivers here on earth locate as many of these satellites as possible at least three are needed however. Using geometry and the mathematical principal of trilateration it can locate the GPS receiver. This video provides a quick one minute briefing on how GPS works. The video was provided by HowStuffWorks, Inc. http://videos.howstuffworks.com/nasa/2191-how-gps-works-video.htm
This unit is made of mostly a plastic shell with a rubber coating back probably for an increase friction factor when the device is placed down. The screw on back can tightly seal water or moisture out of the electronics inside giving it a resistance to water, but by no means is the device waterproof. There is a screen on the front of the device which is difficult to read if there is not adequate light.
GPS in Earthquake Studies
Global positioning systems are used in many different applications including the analysis of earthquakes to measure tectonic motions during and in between sesimic waves. GPS ground-based receivers allows signals to be detected and used in order to determine the receivers' positions (latitude, longitude, height.) The radio signals are sent at two different L-band frequencies (between 390 and 1550 MHz) comprised of a coded sequence. By comparing the received sequence with the original sequence, scientists can determine how long it takes for the signal to reach the Earth from the satellite. The signal delay is useful in learning about the Ionosphere and the Troposphere, two atmospheric layers that surround the Earth's surface.
Additionally, scientists are currently using GPS systems to measure the size of an earthquake by examining the final amount that a station has been displaced in an event.This is done by examining the total distance that a station has moved in an earthquake by comparing its position prior to the event with its position following the event. It has been concluded that there is a relationship between the amount of displacement caused by an earthquake and its magnitude. It is by using this relationship between slip and magnitude that scientists can measure the relative size of an earthquake using GPS.The global positioning system is not used to measure the actual shaking of the ground because of the way in which the actual data is collected. Data is sampled at a certain rate, called a sample rate, which means that the receiver records the information being sent to it from the satellites at a certain interval of time all day long. As a result, data can be processed and a daily solution is determined, which means that the change in position of the receiver is calculated for one day at a time by combining the data collected throughout the day. The data can also be processed at another solution interval. This is the reason why GPS is not used to directly measure the ground shaking during an earthquake. Seismometers are much better equipped to accurately record that sort of high-frequency motion than GPS. So, earthquake size is determined instead by measuring the final displacement of the stations and using the slip versus magnitude relationship.
GPS systems are also being used to provide early earthquake warnings. Currently in California, geophysicists are developing a new network of 250 Global Positioning System stations that will provide rapid early warnings of major earthquakes. The alerts could provide enough warning to automatically shut down gas lines, slow or stop trains, warn doctors performing surgery or even prevent a nuclear reactor melt down.The network will work by detecting movement between GPS stations on opposite sides of the fault. The stations are capable of relaying their position once a second and can detect the first five centimeters of movement within 10 seconds.Seismic waves travel at about five kilometers per second, so cities more than 50km from the epicenter could receive a warning before any shaking starts.
The technology exhibited by GPS systems can also be used to determine whether an earthquake is big enough to generate an ocean-wide tsunami, and in turn provide faster tsunami warnings.The method entails measuring the time that radio signals from GPS satellites arrive at ground stations located within a few kilometers of an earthquake. By calculating how far the stations moved because of the earthquake, scientists could derive an earthquake model as well as its true size or "moment magnitude," which is connected to rather a quake would generate into a tsunami.
Global positioning systems can also be used to monitor structures. It provides the absolute motion of the structure in ways that are not easily achieved with other techniques.The difference between the motion of a GPS receiver on the roof of a building and one at mid level, and one at ground level can help seismologists understand how to increase the building's resistance to earthquakes.
The above figure shows a network of broad-band seismometers that is designed to rapidly localize the earthquake and determine its strength. The monitoring of the deformation takes place at the same time via the GPS network with high resolution in order to gather as much information as possible on the earthquake.
An Earthquake Monitoring Network with GPS
Edited by: Danielle Salmon
On the back cover of the receiver the chamber in which the batteries are located will be found. This cover is secured with two screws on opposite sides. To remove the cover no tools are necessary just unscrew them by hand. Inside this chamber two "AA" batteries are found which power the unit. If the batteries are removed a memory card is found in which the receiver can store information.
Disassembly of the actual GPS receiver unit is slightly more complicated. On the back of the unit there are ten screws securing the two halves of the unit together. To dissemble the unit a small philips screw driver will be necessary. Removing the back of the unit will expose the main circuit board. This process should be done carefully because the back half is connected to the front through wiring which if not a professional should not be disconnected. Below is a picture of the circuit board and the two parts of the GPS receiver.
The different components that make up the device can be found in the image below along with a table organizing what each part does for the GPS unit. Taking the unit apart is not difficult it is help together with screws. It was purposely designed this way so that if the unit needs to be serviced the owner or technician can easily repair it. The only tools that were needed to dissasemble the device was a screw drivere.
The Global Positioning System (GPS) was originally developed by the military for multiple purposes. The original attempt at such as system was the GEE system developed by the British during WWII to aid with guiding bombs. The system worked by sending out radio waves in two directions and timing how long the waves took to return. Once both waves required equal amount of time to return the pilot had reached a halfway point. The system was accurate up to 160 yards, however, GEE was difficult to use and took too much time to interpret data. The next attempt at such as system was in the 1960’s by the United States Navy. The system was called TRANSIT. TRANSIT was used the help guide ships. However, TRANSIT was short lived because it was difficult to use. In the 1970’s a new positioning system had entered the arena known as LORAN. Like the British GEE system, LORAN also worked from radio wave transmission. The radio waves would be sent out to slave station to create a signal chain. Next, the data would be received and a series of circles would be plotted on a map. LORAN also proved to be difficult to use. As computers progressed, however, the system became more manageable and even appeared on a few civilian boats in the 1980’s. The emergence of GPS quickly made such system obsolete.
Originally there were two types of GPS signals. The first the slightly inaccurate signal used for civilian use. The second was a more accurate signal known as Selective Availability. Selective Availability (SA) was the most accurate version of the GPS system because it accounted for correction factors. Until May of 2000 the SA system was only able to be used for military purposes. That year President Clinton signed into effect that all civilian units will work off the L1 signal which uses the SA correction factors. Placed into effect September of 2007 the Department of Defense started the GPS III system which has no error factor.
The emergence of GPS system aided military navigation greatly. GPS allows military camps to move into areas that are not mapped or have outdated maps. As a result the military can set up camps in remote areas with much less trouble. In the Army, the movement of ground troops became much easier with the advancement of GPS. In the desert there are no recognizable land marks. With the aid of a GPS system a soldier can lock on series of location and return to an exact point. Also, the troops can move though intense sandstorm when vision is extremely low with the aid of GPS. These devices helped greatly during Desert Strom in the 1990’s. During the Gulf War there were about 1000 GPS units in operation, therefore, there were many soldiers without a GPS unit. This lead to soldiers purchasing the own civilian units which lacked the Selective Availability features, yet other country’s troops had these capabilities. In the battle field the CSEL (Combat Survivor Endeavor Locator) system has been employed. This system integrates GPS capabilities with communication radio. CSEL helps to located downed crews and lost crew members. These capabilities have greatly improved response times and survival rates.
The US Navy also employs a version of GPS. They combine GPS capabilities with acoustic sound transmission to aid with sea floor mapping. Such mapping helps with the navigation of ships through shallow waters and considers the effects of tidal flows with the seasons. This system is known as WGS (World Geodetic System) and it produces highly accurate data of +/- 3 meters. Since the emergence of WGS the Navy has been able to navigate through water ways that were previously were unable to be traveled.
Targeting an object with GPS capabilities requires the highest level of accuracy. As a result, the military developed the DGPS (Differential Global Positioning System). DGPS has accuracy up the a few millimeters. In conjunction with DGPS, the military uses the MLRS (Multi Launch Rocket System) to navigate their missile attacks. The MLRS is capable of aiming the missile and locking on to a target in a short period of time. The reduced aiming time prevents detection and counter attacks.
Edited by: Samuel Agresta
Initially designed for the military, GPS systems were not cleared for civilian use until the 1980’s. Once the early restrictions on the satellite signals were lifted, the civilian GPS became ten times more accurate and found its place in modern society. Newer GPS systems have the ability to use WAAS (Wide Area Augmentation System) which uses satellites and ground stations to give GPS corrections and increase accuracy. Signals can also be corrected by DGPS (Differential GPS), however this requires a differential beacon receiver and beacon antenna in addition to the standard GPS device.
The most common civilian applications for the GPS system revolve around its abilities for calculating absolute position, speed and orientation. The GPS can track the user’s position to within three meters, making it an infinitely valuable tool in surveying and navigation. Using a detailed map, the GPS unit can find a route between two points or continually find the best route in real time. GPS units are already used by millions of drivers and the navigation aid is making itself more commonplace on mobile phones as well. Aside from using a mobile phone for navigation purposes, advertisers are looking into ways to make GPS-compatible phones receive text messages when they enter a certain proximity to a retailer. GPS devices are also an important tool for hikers, and essential gear for marine vessels. Ships equipped with a GPS device can easily steer away from danger by constantly being able to locate other ships and objects in the vicinity despite bad weather or poor visibility. Another use for the civilian GPS is the high-tech game of treasure hunting called geocaching. Geocachers seek out hidden treasures by following the GPS coordinates provided online by those hiding the cache.
Another common use of the GPS system is as a tracking device. Tracking devices can be used to log data or send it to a central location. Data loggers intermittently record the position of the device to be reviewed later. Data pushers are devices that send the location of the device to a central server at regular intervals, and data pullers constantly send out the position of the device to be viewed at any time. Tracking systems can be especially useful to companies that need to track several vehicles or people at once. Using GPS tracking devices, they can monitor the position of everyone in real time and make adjustments or service alerts accordingly. Tracking devices can also be used to locate stolen vehicles and allow police to keep tabs on those under house arrest.
GPS technoloy is being used in several fields of engineering, such as kinematic and static surveying, structural deformation analysis, and topographic mapping. As an alternative to more conventional and traditional methods that have been used previously, the GPS system is allowing for more accurate and reliable results that can be more effectively used in real time.
In civil engineering, this particular technology has allowed engineers to measure the displacement response of high-rise buildings, bridges, industrial chimneys, TV towers, etc. to factors such as wind, temperature, and earthquakes. The basic procedure of such a study consists of taking a fixed reference point at a certain elevation and attaching the unit at another location on the structure itself. The GPS system then produces the data results allowing one to see the pattern of response movement of the structure itself against the wind velocity, temperature change, etc. This a valuable tool for civil engineers to use today in the design and construction of high-rise structures. The data provided from the GPS system will allow engineers to develop an overall structure-failure prevention or alarm system, allowing them to set a scale for possible deformation or failure of high-rise structures when faced with certain factors. It will also allow engineers to have a more accurate and reliable displacement reading over a long-period of time in comparison to the traditional method of using accelerometers.
Field Surveying and Transportation
Another application of GPS technology within Engineering is the use of the system in inventory and data collection of roadways in Field Surveying. With this system, roadway signs and features can be logged throughout a given site to assist in the planning and designing phases for engineers. With this information, as-build road geometry can be created to produce more accurate results using corrected GPS data in real time. Since 1994 Real time Kinematic surveying has allowed engineers to locate field points and stake points using GPS technology. This system has furthered design capabilities for surveys, mapping, boundaries, as well as construction staking.
GPS sensors have also been a useful tool for gathering and logging data when scoping and analyzing the environmental conditions of various regions. Playing the role of an electronic field notebook, this system has allowed engineers to keep an accurate inventory of field tests. Once the field tests are logged, the GPS system is also used for computation purposes in order to derive more accurate and precise results. Through the use of this technology, data and results can also be sent to other field engineers as a more efficient way of communication.
Alternatives to GPS
GPS is the only fully functional global navigation service available, but many others technologies are being created. Google is working on a technology that maps where you are using your cell phone. When using Google Maps Mobile, you can have Google approximate where you are by it determining your proximity to cell phone towers using their cell ID. It can tell by the number of cell IDs it picks up and use their known coordinates. If a phone has GPS when it uses this new feature, it also sends Google the GPS coordinates. Google is developing a database of cell IDs at known coordinates which will help improve the systems accuracy over time.
The point of this technology, compared to GPS is that it does not require maintaining the million dollar GPS system. It simply uses what is already on the ground. When eventually Google’s database is published and stored on devices, it will be a lot faster than sending signals all the way up to satellites, which enough errors arise just from this.
This technology is still young and relatively inaccurate. It approximates where you are using a circle; the larger the circle the more inaccurate, because the area is larger that you could be.
Apple’s iPhone has this new technology programmed into it, so as an experiment, the GPS was taken out along with an iPhone to various locations in the city to compare the accuracy. The area it guessed was as wide as a few miles in some cases or as accurate as a city block. Sometimes it even changed its accuracy when remapped from the same location.
Here are a few pictures to show how accurate it was. Sometimes it calculated where we were much more accurately, with our location (drawn with a red circle) in the center of its guess (shown in a blue circle). In one case it missed the location entirely. The location was not even in the circle. It seemed it was stuck on the previous mapping and did not move forward when the location was remapped.
Every time the GPS device was accurate. Google still lists its Maps Mobile technology in beta, so they know it is not entirely reliable yet. To get this system as accurate as GPS’s it must be used much more and Google's database needs to expand.
1998 Smithsonian Institute http://www.nasm.si.edu/exhibitions/gps/work.html
1998 Alonso, Johny HowStuffWorks, Inc. http://videos.howstuffworks.com/nasa/2191-how-gps-works-video.htm
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2002 GPS may provide early earthquake warning http://www.newscientist.com/article/dn3157-gps-may-provide-early-earthquake-warning.html