Introduction to Global Navigation Satellite System (GNSS)

Introduction to Global Navigation
Satellite System (GNSS)

Global Navigation Satellite System

Introduction to GIS

 GNSS are satellite-based technologies that give precise positional information, day or
night, in most weather and terrain conditions.

 GNSS are very important for field data collection in GIS.

GNSS

 US: NAVSTAR GPS

 Russia: GLONASS

 China: BeiDou

 Europe: Galileo

Global Positioning System

 Sometimes used synonymously for GNSS

 More specifically refers to the US developed satellite navigation system - first developed
and deployed globally

Characteristics of GPS

 Free

 Accurate

 Reliable

 Worldwide

 Unlimited User Capacity

GPS Components

 Space Segment

,  Control Segment

 User Segment

Space Segment

 24+ satellites

 Altitude 20,200 km (12,600 miles)

 About eight satellites visible from any point on Earth

GPS Constellation

 Each satellite constantly broadcasts: the Time message was sent, the Ephemeris (precise
orbital information), the Almanac (general system health)

Control Segment

 Determine satellite orbits

 Transmit orbital data to satellites

 Daily adjustment to orbit (if necessary)

User Segment

 GPS antennas & receiver/processors

 Position

 Velocity

 Precise timing

 Used by: Aircraft, Ground vehicles, Ships, Individuals

How does GPS work?

 GNSS positioning is based primarily on range distances. A range distance, or range, is a
distance between two objects.

 GNSS signals travel approximately at the speed of light. The range distance from the
receiver to each satellite: Range = speed of light * travel time

Need 3 satellites for 2D position

 Gives precise Latitude – Longitude

Minimum 4 satellites for 3D position