Transcript Slide 1
Introduction to GNSS
Outline
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GNSS Basics
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Common Uses
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Precision Agriculture – Brief History NA/LA/EU
What is GNSS?
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GNSS (Global Navigation Satellite System)
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Satellite navigation System
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Accurately and precisely locate a point on Earth
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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?
Trilateration: The process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles or spheres
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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 Decatur Springfield Indianapolis
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)
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In 3-D you can use 4 satellites (using spheres opposed to circles) to locate a precise location and include elevation
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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
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Raw GNSS is accurate only ~ 5-10Meters
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Differential Corrections adjust for errors.
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Satellite Based
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WAAS/EGNOS Purchased
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Ground Based
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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
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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 2007-2009 Integrated Applications Reagan announces GPS will be free for civilian use 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
Precision Agriculture – Brief History Autonomous applications Convergence 2010 - 2011 Autonomy 2011 - 2012 Actionable Information Focus on “on-farm” Connectivity System Worksite Assisting Operators Removing Operators Combining agronomic data and machine info to increase yields
Reasons for Adoption – NA/LA/EU Land
More efficient and productive use of equipment
Labor
More efficiency with lower skilled level of labor
Lewis, P., et al (1998), Issues, Indicators & Ideas, Longman, South Melbourne.
Input Costs
Reduce in field and end field overlap
2008 Eurostat – Agriculture statistics Main Results 2006-2007
Gov’t Reg
Manage business for better compliance
2009 USDA – NASS - August Sugar cane burning in Brazil
Reasons for Adoption Land
Map out land and soil productivity
Water
Determine optimum drainage and leveling
Point B Crop
Access to Market Information based upon Location
Point A Gov’t Policy
Real time knowledge of crop conditions and potential yield impact
Other GPS Facts
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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!