Global Positioning Systems

INTRODUCTION

Agriculture and Engineering are changing industries. New technologies have made it possible to increases the accuracy of certain tasks. The goal of the Global Positioning Systems unit is to introduce precision agriculture and engineering into the curriculum.

General instruction of Global Positioning Systems will be presented, as well as technical information and technical applications using the Garmin Dakota 20 handheld units. It is our hope that this curriculum will give both instructors and students a comprehensive understanding of Global Positioning Systems, applicable to a wide variety of careers.

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

For example: You are lost and someone tells you that you are 625 miles from Boise, Idaho.

You ask someone else where you are and they tell you that you are 690 miles from Minneapolis.

You could be at one of two points where the circles intersect.

You ask a third person and they tell you that you are 615 miles from Tucson, Arizona.

Which means that you are in Denver, Colorado according to where the circles intersect.

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 – marking and 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 – Precision Agriculture – management of the farming operation in order to maximize production and profitability• 1 – Includes cropping systems, livestock

production, waste management, the protection of the environment and the enhancement of biological diversity (PAIT, Iowa State University).

• 2 - The goal is to increase the efficiency of the farming system by making site-specific decisions rather then a whole system need

b – 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 used at night– c – foams can freeze

• 5 – custom application of specific locations

• 6 – variable rate application of fertilizers and seed

c – 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 – Atomic Clock - very precise clock that uses elements cesium or rubidium with error of one second per million years; GPS satellites contain multiple atomic clocks

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

3 – 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

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

5 – Bearing - The compass direction to a waypoint measured to the nearest degree

6 – Course - Your actual current direction of travel (Course Over Ground or Track)

7 – Heading – Direction of travel relative to the 3600 of a compass

8 – Prime Meridian – A reference line from which longitude is measured, run between poles and passes through Greenwich, England; divides the east and west hemisphere

9 – Equator – A reference line from which latitude is measured; divides the north and south hemispheres

10 – Latitude - Position north/south of the equator measured by degrees from zero to 90

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

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

A – Divided into hours, minutes, seconds and fractions thereof • 1 – Latitude

– One hour = 60 degrees– One degree = 60 minutes– One minute = 60 seconds

• 2 – Longitude – One hour averages 15 degrees as longitudinal

lines get narrower toward the poles (24 hour day/360 degrees)

B – One minute = one nautical mile

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

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 – Triangulation - Method of determining the location of an unknown point by using bearings from two known points

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

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

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

19 – 2D Operating Mode - A two-dimensional GPS position fix that includes only lat./long.; requires a minimum of three visible satellites

20 – 3D Operating Mode - A three-dimensional GPS position fix that includes lat./long. and altitude; requires a minimum of four visible satellites

VI – Operating Garmin Dakota 20

18 Main Menu icons

MapWhere To?Trip ComputerActive RouteRoute PlannerSetup

Main Menu icons continued

Mark Waypoint GeocachesCompass Elevation PlotShare Wirelessly Waypoint ManagerProfile Change CalendarTrack Manager CalculatorSun and Moon Stopwatch

Global Positioning Systems