Introduction to GNSS

Outline• GNSS Basics

• Common Uses

• Precision Agriculture – Brief History NA/LA/EU

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 (BeiDou-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?

• Can be accomplished using information from 3 separate satellites

Trilateration: The process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles or spheres

How GPS WorksOkay, 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

Springfield

Decatur

2D Trilateration Procedure

1. You know the location of 3 satellites2. Given the distance you are from those 3

satellites3. Draw a circle, center is the location of the

satellite, radius is distance from satellite4. Repeat for all satellites5. 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 GPS can be, mathematical models are used by GPS units to determine best accuracy

Differential Correction

• Raw GNSS is accurate only ~ 5-10Meters

• Differential Corrections adjust for errors.– Satellite Based

• WAAS/EGNOS• Purchased

– Ground Based• Real Time Kinematics

Satellite Differential Correction

DGPS SiteReceiver

RTK Differential Correction

DGPS SiteRadio/CellReceiver

Earth’s Atmosphere

Solid Structures

Metal Electro-magnetic Fields

Signal Interference

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

Precision Agriculture – Brief History

Integrated Applications

Guidance adoption balloonsFinding the market - (20 years)“Wandering in the Wilderness”

1991 - 1999

Reagan announces GPS will be free for

civilian use

1983

Customers begin Yield Mapping

1999-2004

Satellite based guidance show payback

Guidance Prices Decline and Expand

Platforms; increasing ROI

2005-2007 2007-2009

GPS guidance ties location and machine controls for integrated business applications

Autonomous applicationsDigital Convergence

2010 - 2011

Focus on “on-farm” Connectivity

System Worksite

Assisting Operators

Removing Operators

Combining agronomic data and machine info

to increase yields

Autonomy Actionable Information

2011 - 2012

Precision Agriculture – Brief History

Reasons for Adoption – NA/LA/EU

Sugar cane burning in Brazil

2008 Eurostat – Agriculture statistics Main Results 2006-2007Lewis, P., et al (1998), Issues, Indicators & Ideas, Longman, South Melbourne.

2009 USDA– NASS - August

Land Labor

Gov’t RegInput Costs

More efficient and productive use of equipment More efficiency with lower skilled level of labor

Manage business for better compliance Reduce in field and end field overlap

Reasons for Adoption

Access to Market Information based upon Location

Land Water

Gov’t PolicyCrop

Map out land and soil productivity

Determine optimum drainage and leveling

Real time knowledge of crop conditions and potential yield impact

Point B

Point A

Other GPS Facts• GPS time is theoretically accurate to

about 14 nanoseconds• GPS systems have settled disputes

between land owners• GPS data has revealed that Mt. Everest

is getting taller!

Thank You