Introduction to GNSS Outline GNSS Basics Common Uses
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 (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 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 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 GPS can be, mathematical models are used by GPS 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 DGPS Site
RTK Differential Correction Receiver Radio/Cell DGPS 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 2007 -2009 Integrated Applications GPS guidance ties location and machine controls for integrated business applications
Precision Agriculture – Brief History 2010 - 2011 Autonomous applications Digital Convergence Focus on “on-farm” Connectivity 2011 - 2012 Autonomy Actionable Information Combining agronomic data and machine info to increase yields Assisting Operators Removing Operators System Worksite
Reasons for Adoption – NA/LA/EU Land n More efficient and productive use of equipment Lewis, P. , et al (1998), Issues, Indicators & Ideas, Longman, South Melbourne. Input Costs n Reduce in field and end field overlap 2009 USDA– NASS - August Labor n More efficiency with lower skilled level of labor 2008 Eurostat – Agriculture statistics Main Results 2006 -2007 Gov’t Reg n Manage business for better compliance Sugar cane burning in Brazil
Reasons for Adoption Land Map out land soil productivity Water Determine optimum drainage and leveling Point B Point A Crop Access to Market Information based upon Location Gov’t Policy Real time knowledge of crop conditions and potential yield impact
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
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