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 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 Springfield Decatur

2D 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 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 Site Receiver

RTK Differential Correction DGPS Site Radio/Cell Receiver

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 balloons Finding the market - (20 years) “Wandering in the Wilderness” Reagan announces GPS will be free for civilian use 1983 Customers begin Yield Mapping Satellite based guidance show payback Guidance Prices Decline and Expand Platforms; increasing ROI GPS guidance ties location and machine controls for integrated business applications

Autonomous applications Digital Convergence Focus on “on-farm” Connectivity System Worksite Assisting Operators Removing Operators Combining agronomic data and machine info to increase yields Autonomy Actionable Information Precision Agriculture – Brief History

Reasons for Adoption – NA/LA/EU Sugar cane burning in Brazil 2008 Eurostat – Agriculture statistics Main Results Lewis, P., et al (1998), Issues, Indicators & Ideas, Longman, South Melbourne USDA– NASS - August Land Labor Gov’t Reg Input 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 Policy Crop 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