Working of GPS | Why four satellites | How is time offset corrected.

Summary

In this video, we dive into how the Global Positioning System (GPS) works. GPS relies on satellites orbiting Earth, which transmit location and time data to your device. By measuring the signal's travel time, your device calculates its distance from the satellites. At least four satellites are needed to pinpoint your location accurately, compensating for device clock errors. The system's accuracy improves with more satellites, accounting for atmospheric interference. Additionally, relativistic time effects in satellites are considered to ensure precise readings. GPS is a vital, free tool for navigation, operating without the need for an internet connection.

Takeaways

• 😀 GPS (Global Positioning System) is made up of 31 satellites orbiting Earth at 20,200 km, providing location data to users worldwide.
• 🌍 The data from GPS satellites includes their precise location and the time the data was sent, which is used to calculate your position.
• 🔭 To find your location, a GPS receiver needs signals from at least 4 satellites. This allows for accurate triangulation and time correction.
• 🕰️ Your device's clock, being less accurate than the satellites' atomic clocks, is the main source of error in GPS calculations.
• 🔄 By using data from 4 satellites, your device can adjust for clock drift, ensuring accurate location determination.
• 📡 Each satellite's signal travels at the speed of light (300,000 km/sec), and by measuring the time it takes for a signal to reach your device, you can estimate your distance from the satellite.
• 🛰️ The intersection of multiple satellite signals creates spheres of possible locations, and the more satellites you have, the more accurate the result.
• 🌐 GPS doesn't require an internet connection, though additional data can be obtained through the internet to identify nearby landmarks or features.
• ⏳ Relativity plays a role in GPS, as the satellites' speed and gravity cause their clocks to run at a different rate compared to clocks on Earth.
• 💡 Without accounting for relativistic effects, errors in position could accumulate to 11.5 km per day, so the system compensates for these differences to maintain accuracy.
• ⚙️ The GPS system is owned by the U.S. but is available globally, with similar systems managed by other countries as well.

Q & A

What is the Global Positioning System (GPS)?

GPS is a constellation of 31 satellites orbiting 20,200 km above Earth, managed by the U.S. Department of Defense. It allows users to find their exact location anywhere on Earth using data sent from these satellites.

How does GPS work to determine your location?

GPS devices receive signals from satellites, which include the satellite's position and the time the data was sent. By measuring the time it takes for the signal to reach the device, the device can calculate the distance to each satellite and determine the user's location.

Why are at least 4 satellites required for accurate location determination?

You need data from 4 satellites to account for the drift in the device's clock. With three satellites, you would have an intersection of spheres, but the time discrepancy in the device's clock makes it impossible to find an accurate location. The fourth satellite helps to adjust the clock error, providing a more accurate position.

What happens when you receive data from more than 4 satellites?

The accuracy of your location improves further. With more satellites, the device can better minimize errors due to factors like signal refraction, speed variations, and other atmospheric influences.

How does relativistic time dilation affect GPS satellites?

Relativistic time dilation causes a difference in the passage of time due to relative speed and gravity. GPS satellites experience both factors, making their clocks run faster by 38 microseconds per day. If unaccounted for, this would induce an error of 11.5 km per day in positioning.

Why does a GPS device need to compensate for its clock's inaccuracies?

The clock in a GPS device is not as accurate as the atomic clocks in satellites. Even small discrepancies can lead to significant location errors. To address this, the device uses data from a fourth satellite to adjust its clock and improve accuracy.

What is the role of electromagnetic waves in GPS positioning?

GPS signals travel as electromagnetic waves at the speed of light (300,000 km/s). By measuring how long it takes for these waves to travel from a satellite to the device, the device can calculate the distance to each satellite and determine the user's position.

How does the atmosphere affect GPS signal accuracy?

The atmosphere, particularly the ionosphere, can refract GPS signals, causing slight errors in distance calculations. These errors are often minimized by using data from multiple satellites or by adding more satellites to the system.

What happens if there are only three satellites available for GPS positioning?

In rare cases, three satellites can be enough if the device already knows it's on Earth's surface. Earth itself acts as a sphere, and the data from the three satellites can pinpoint the location on the surface.

Can GPS work without an internet connection or mobile network?

Yes, GPS can work without an internet connection or mobile network. GPS relies solely on the satellite data, and no additional network is required. However, an internet connection or mobile network can enhance the experience by providing additional information about the surroundings.