Introduction to GNSS ABE 459 What is GNSS

Introduction to GNSS ABE 459

What is GNSS? • GNSS (Global Navigation Satellite System) – Satellite navigation System – Accurately and precisely locate a point on Earth – US – GPS (Functional) – Russian – GLONASS (Functional) – European – Galileo (Non Functional) – Chinese – COMPASS (Bei. Dou-2) (Non Functional) – Indian Regional Navigation Satellite System – IRNSS (Non Functional)

How does it Work? Each GPS satellite transmits data that indicates its location and the current time Satellites can be used if they are in the sight of a receiver as long as they are 25⁰ or greater above the horizon GPS receivers require unobstructed view of the sky and they only receive data, don’t transmit it

How does it Find Location? Trilateration: The process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles or spheres • Can be accomplished using information from 3 separate satellites

How GNSS Works Okay, you’re lost, you have amnesia, and you have absolutely no idea where you are. You go up to someone, and like a good amnesiac you ask, “Where Am I? ” This person tells you that you are 180 miles from Chicago. You say, sarcastically, “Wow, that’s some great information. Thanks Buddy. ” Chicago

We’re Getting Closer You still have absolutely no idea where you are, so once again you go up to someone and ask, “Where Am I? ” This person tells you that you’re 170 miles from Indianapolis. You just scratch your head, but then you start to remember what you learned in GPS class, and, with the US map in your pocket to guide you, you proceed. Chicago Indianapolis

Now We Know! You see a another smiling face and ask “where am I” one more time. This time you get the reply “you are 150 miles from Quincy. The light pops on in your brain. It’s all clear now. You draw three circles extending in the radii of 180 miles from Chicago, 170 from Indianapolis, and 150 miles from Quincy. The circles intersect in Decatur! Aren’t you glad that you took this class? Chicago Indianapolis Decatur Springfield

2 D Trilateration Procedure 1. You know the location of 3 satellites 2. Given the distance you are from those 3 satellites 3. Draw a circle, center is the location of the satellite, radius is distance from satellite 4. Repeat for all satellites 5. Your location is where the 3 circles intersect

Trilateration (continued) • In 3 -D you can use 4 satellites (using spheres opposed to circles) to locate a precise location and include elevation • The more satellites that are in range the more accurate GNSS can be, mathematical models are used by GNSS units to determine best accuracy.

Differential Correction • Raw GNSS is accurate only ~ 5 -10 Meters • Differential Corrections adjust for errors. – Satellite Based • WAAS/EGNOS • Purchased – Ground Based • Real Time Kinematics

Satellite Differential Correction Receiver DGNSS Site

RTK Differential Correction Receiver Radio/Cell DGNSS Site

Signal Interference Earth’s Atmosphere Solid Structures Metal Electro-magnetic Fields

Common GNSS Uses • • • Military (Weapons precision) Navigation (Civilian or Commercial) Surveying Drainage Design Topography Measurements Precision Agriculture

Precision Agriculture – Brief History 1983 1991 - 1999 Finding the market - (20 years) “Wandering in the Wilderness” 1999 -2004 2005 -2007 Guidance adoption balloons Satellite based guidance show payback Reagan announces GPS will be free for civilian use Customers begin Yield Mapping Guidance Prices Decline and Expand Platforms; increasing ROI Disabling of Selective Availability 2007 -2015 Integrated Applications GPS guidance ties location and machine controls for integrated business applications

Other GNSS Facts • GNSS time is theoretically accurate to about 14 nanoseconds • GNSS systems have settled disputes between land owners • GNSS data has revealed that Mt. Everest is getting taller!