Map-ல நம்ம Location ஏன் தப்பா காட்டுது?
10 Minutes
Learn how GPS works and why map locations show errors in this science guide for students on satellites and signal delays. A Tamil science lesson.
- How GPS satellites use trilateration to find your location
- Calculating distance with atomic clocks and the speed of light
- How the multipath effect and atmospheric delays cause GPS errors
What this lesson teaches
GPS location errors occur when radio signals travelling between satellites and a mobile phone are delayed or deflected, causing the phone to miscalculate its distance from the satellites and place the marker in the wrong spot on a map.
How GPS finds your location
Around 32 GPS satellites orbit roughly 20,000 kilometres above Earth, carrying atomic clocks that keep exceptionally precise time. These satellites continuously transmit their time data downward as radio signals. A smartphone receiver catches signals from three or four satellites and measures their travel time to calculate distance using the speed of light. By finding where these satellite distances intersect, a method known as trilateration, the phone pinpoints your location.
The multipath effect
- Satellite signals travel as radio waves that are meant to reach your phone directly in a straight line.
- In cities, these waves frequently hit tall concrete buildings, glass, and metal sheet surfaces.
- The waves bounce off these obstacles along zig-zag paths before finally reaching the phone receiver.
- This indirect journey takes longer, creating an unintended signal delay.
- Because the phone calculates distance from travel time, this delay inflates the calculated distance and shifts the pin on the map.
Atmospheric interference
Earth's atmosphere can also alter the travel time of satellite signals before they reach the ground. High levels of moisture and humidity in the air create resistance that slows the radio waves down. Furthermore, dry gases located within the troposphere, the lowest layer of the atmosphere, can also delay incoming waves. Because the speed of light is extremely high, a delay of even a tiny fraction of a second results in a noticeable error in the calculated distance.
Tips for better accuracy
- Standing directly beneath thick tree cover can weaken satellite signals and introduce errors.
- Narrow streets closely bordered by tall buildings increase multipath reflections.
- Moving out into an open space with an unobstructed view of the sky allows direct satellite communication and restores accurate positioning.