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jothirnadh/Basics of GPS and GNSS.md

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Show and Tell about GPS and GNSS
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Basics of GPS and GNSS.md

Let's have an overview of Basics of Remote Sensing

History of GPS (Global Positioning System)

  • Started by US military in 1973
  • Three main objective: 1. Determining position, speed and time, whether in motion or at rest. 2. Contineous global 3 dimentional position irrespective to weather. 3. Useful for civilian needs

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Functioning of GPS

  • Space Segment
  • Control Segment
  • User Segment

gps segments

How GPS satellites communicate:

  • It uses Codes (binary, zeros and ones, language of computers)
  • To travel longer distances we use high energy carrier waves (L band of electromagnetic spetrum (microave region))

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  • C/A (Coarse Acquisition) code
  • P-code (Precise - Military)
  • Navigation Message/code

Types of Global Positioning Systems

constellationgps

  • GLONAS: Russia, military, fully working, will be modernized GLObal NAvigation Satellite System with 24 functioning satellites.
  • [GALILEO] (https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)): Europe, civil, being built up, Expected to be completely operational by the end of 2020 with 30 satellites (24 operrational and 6 active spares).
  • There are also other Regional positioning systems developed by India, China and Japan.

Errors in data collection and its rectification

  • The quality of the data depends on the distribution of 4 satellites.
  • Multipath errors

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GPS vs GNSS (Global Navigation Satellite System)

GNSS = GPS + other positioning systems (GALILEO, GLONAS, GAGAN, etc.,)

DGPS

  • Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that provides improved location accuracy
  • Accuracy Improvement: from 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations.
  • By applying differential correction to code, positions can be obtained to an accuracy of 0.5 m. -Accuracy: depends upon distance between base and rover stations

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GAGAN & IRNSS

  • GPS Aided Geo Augmented Navigation-GAGAN
  • GSAT-8 & GSAT-10; GSAT-15 scheduled for launch this year
  • GAGAN is the first SBAS system in the world to serve the equatorial region
  • India has become the third country in the world to have such precision approach capabilities.
  • IRNSS, the Indian Regional Navigation Satellite System
  • The system is designed with a constellation of 7 spacecraft and a vast network of ground systems operating.
  • The first three satellites (IRNSS-1A, 1B &1C) were launched in 2013-14.
  • IRNSS-1D, the fourth satellite of IRNSS constellation was successfully launched on March 28, 2015 on board PSLV-C27
  • The unique Geostationary Earth Orbit (GEO) /Geo Synchronous Orbit (GSO) constellation design provides a position accuracy of better than 15 metre for longer duration of 20 hours in a day even with 4 satellites

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