Global Positioning SystemGlobal Positioning System

Applications in AgricultureApplications in Agriculture

INTRODUCTION

Agriculture is a changing industry. As technology makes agriculture more efficient, these systems have become commonplace in our industry. The goal of the Global Positioning System: Applications in Agriculture instructional materials is to introduce precision agriculture into the Agricultural Education curriculum.

General instruction of Global Positioning Systems will be presented, as well as technical information and hands on applications on using the Garmin III+ and Garmin 12 handheld units. It is our hope that this curriculum will give both instructors and students a comprehensive understanding of Global Positioning Systems, regardless of the make and model of equipment that is available.

Global Positioning System: Applications in Agriculture was prepared by Paul Oehlke, Agriculture Department Chair and instructor at the North Dakota State College of Science, and Tony Boehm, Agricultural Education instructor at the Richland County Vocational Center. This project was made possible by a United State Department of Agriculture grant received by NDSCS and RCVT, titled Implementing Precision Agriculture into the NDSCS and RCVT curriculums.

Unit 1 – Introduction to Unit 1 – Introduction to Global Positioning SystemsGlobal Positioning Systems

I – What is GPS

1 – Global Positioning Systems – a network of satellites that makes it possible to precisely identify a location on earth

2 – U.S. Dept. of Defense satellites transmit signals while orbiting the Earth in a precise pattern

3 – System comprised of:

a - at least 24 satellites

• 1 – in a distinct pattern • 2 – approximately 12,000 miles above

the earth• 3 – contain atomic clocks accurate to 1

second of error every 1 million years

b - ground control stations• 1 – uplinks corrected orbital and clock

information• 2 – 5 stations worldwide

c – receivers• 1 – handheld GPS receivers• 2 – mounted on farm implements,

vehicles, planes, boats, ect

II – How does GPS work

1 – Each satellite sends a data message to the receiver including

a – satellite locationb – clock corrections c – rough information about other satellites in the constellation

2 – The time it takes the signal to reach the receiver allows the receiver to calculate the distance to the satellite

3 – Using 3 satellites, latitude and longitude can be identified

4 – Altitude can be identified with a fourth satellite

5 – Differential GPS (DGPS) – uses known beacon locations to correct satellite within inches

III – History 1 – The U.S. Dept. of Defense (DOD) designed and implemented the system for military applications

2 – This system was referred to as NAVSTAR, or the Navigation Satellite Timing and Ranging by the DOD

3 – The first satellite was launched in 1978

4 – A full constellation of 24 satellites was completed in 1994

5 – GPS was to become available to civilians by an executive decree in the 1980’s and in May 1, 2000 GPS became fully available when the Selective Availability, or intentional clock noise, was turned off

IV – Uses and Careers

1 – Engineering

a – city planningb – city information systemsc – construction site restoration

2 – Military

a – troop deploymentb – navigationc – artillery fire

3 – Outdoor Recreation

a – hiking and campingb – finding specific recreation location

4 – Automotive/Aviation

a – navigate to specific locationb – identify location if lost, stolen, or in need of repairc – locate and track fleet vehicles

5 – Agriculture

a – Field Guidance • 1 – reduce skips and overlap • 2 – mark locations

– a – insect and weed infestations– b – low yield– c – soil characteristics

• 3 – create and follow accurate rows• 4 – advantages over foam

– a – drive 20% faster with light bar in cab than foam 30 feet away

– b – can be seen at night– c – foams can freeze

• 5 – custom application of correct locations

• 6 – variable rate application of fertilizers and seed

b – Field Information Management • 1 – measure acreage accurately • 2 – keep records

– a – yield– b – application rates– c – infestations

• 3 – map fields for drainage • 4 – create topographical maps for

variable rate application

V – Terminology

1 – Control segment - A world-wide network of GPS monitor and control stations that ensure the accuracy of satellite positions and their clocks

2 – Atomic Clock - A very precise clock that operates using the elements cesium or rubidium with an error of one second per million years; GPS satellites contain multiple atomic clocks

3 – Beacon – Land based transmitter that emits signals in all directions, broadcasting correction data to nearby GPS receivers for greater accuracy

4 – Differential GPS (DGPS) - GPS system that uses beacons to correct GPS receivers; DGPS reduces the effect of selective availability, weather, buildings, etc. and can improve position accuracy to within feet

5 – Waypoints - Locations or landmarks worth recording and storing in your GPS

6 – Bearing - The compass direction to a waypoint measured to the nearest degree; also call an azimuth

7 – Track (TRK) - Your current direction of travel relative to a ground position; Course Over Ground

8 – Coordinate - A set of latitude/longitude numbers that describes your location on or above the earth

9 – Prime Meridian - The zero meridian, used as a reference line from which longitude east and west is measured; runs from the north to south pole and passes through Greenwich, England

10 – Greenwich Mean Time (GMT)- The mean solar time for the meridian at Greenwich, England; still the standard time zone for the prime meridian

11 – Coordinated Universal Time (UTC) - Replaced GMT as the world standard for time in 1986 and is based on atomic measurements rather than the rotation of the earth

12 – Latitude - A position's distance north or south of the equator measured by degrees from zero to 90; one minute of latitude equals one nautical mile

13 – Longitude - The distance east or west of the prime meridian

14 – Nautical Mile - Used in sea and air navigation and based on the length of one minute of latitude/longitude; equal to 1,852 meters (about 6,076 feet)

15 – Statute Mile – Equal to 5,280 feet or 1,760 yards (1,609 meters)

16 – Triangulation - A method of determining the location of an unknown point by using the laws of plane trigonometry

17 – Dilution of Precision (DOP) - A measure of the GPS receiver-satellite geometry; a low DOP value indicates better relative geometry and correspondingly higher accuracy

18 – Geographic Information Systems (GIS) - A computer system or software capable of assembling, storing, manipulating and displaying location information

19 – Magnetic North - Represents the direction of the north magnetic pole from the observer’s position, or the direction a compass points; may not be accurate

20 – True North - The true direction of the north pole

21 – 2D Operating Mode - A two-dimensional GPS position fix that includes only horizontal coordinates; requires a minimum of three visible satellites

22 – 3D Operating Mode - A three-dimensional GPS position fix that includes horizontal and elevation coordinates; requires a minimum of four visible satellites

23 – Wide Area Augmentation System (WAAS) – a DGPS system used by the Federal Aviation Administration

  Unit 2 - How to Use Unit 2 - How to Use the the Garmin III+Garmin III+