COPY: Lecture 5 Global Positioning Systems

GPS requires four satellites to determine the user's 3D position, including altitude, using a process called trilateration.

The operational management of the GPS system and its satellites is overseen by the US Department of Defence.

Trilateration in GPS involves calculating distances from multiple satellites to a receiver, then finding the point where those distances intersect. This determines the receiver's position.

GPS is used in research projects to measure atmospheric parameters like water vapor content, temperature, and pressure.

The Master Control facility is located at Schriever AFB in Colorado Springs, Colorado, responsible for managing and controlling the GPS system.

A GPS receiver converts the satellite signals into position, velocity, and time estimates. It's the device that uses GPS information.

Four satellites are needed to accurately determine the user's position and time because one satellite provides the time reference and the other three contribute distance measurements for trilateration.

Trilateration is the process used in GPS to determine a user's position. It involves calculating distances to multiple satellites and finding the point where they intersect.

When trilateration is applied with distances to three satellites, often one point is discarded as it's impossible due to the geometric constraints of the calculation.

The User Segment of GPS includes things like receivers, antennas, and software, but not the satellites themselves.

The Master Control station uses ephemeris and clock data to enhance satellite performance and ensures accurate timing and orbits.

A common application for GPS receivers is navigating and positioning. They are used in cars, phones, and many other devices.

GPS is primarily designed for global positioning and navigation, providing location information to a variety of users around the world.

The Space Segment of GPS is responsible for sending signals from space. It consists of the constellation of GPS satellites.

The GPS constellation currently consists of 24 operational satellites, ensuring global coverage.

GPS satellites orbit the Earth at an altitude of 20,200 km, which allows them to provide coverage to almost the entire planet.

The Control Segment of GPS includes tracking stations around the world, responsible for monitoring and managing the satellites' performance.

The satellites' atomic clocks are a critical component of GPS as they provide the highly accurate timing necessary for precise position calculations.

GPS satellites emit specifically coded signals that allow receivers to calculate their position, velocity, and time.

Multiple satellites are visible from any point on Earth to ensure accurate position calculations in three dimensions.

The distance from a satellite to a receiver can be calculated by measuring the time it takes for the satellite's radio signal to reach the receiver. Distance = Velocity x Time.

Radio waves travel through space at the speed of light, which is approximately 186,000 miles per second.

The clocks of the satellite and receiver must be perfectly synchronized for GPS to determine accurate locations.

GPS uses iterative adjustments to correct for differences in time between the receiver and satellite, ensuring accurate position calculations.

The fourth satellite allows the receiver to synchronize its clock, as the first three provide distances but not time reference.

Accuracy in satellite timekeeping is crucial because it directly affects the calculation of travel time and distance, impacting the resulting position of the receiver.

A clock error in the GPS receiver can shift the calculated position to a wrong point, as the time difference impacts the distance measurements.

The receiver achieves precision by continuously iterating until it finds a unique intersection point where the distances from the satellites converge.