Home Articles The use of GPS and mobile mapping for decision-based precision agriculture

The use of GPS and mobile mapping for decision-based precision agriculture

Michael Rasher
Michael Rasher
National Cartography & Geospatial centre
FWFC, Bldg. 24, Room – 10,
Forth worth, TX. 76115
mras[email protected]

Precision Agriculture has evolved from a concept a half a decade ago into an emerging technology today. Precision Agriculture is often described as the next great evolution in agriculture. With an ever growing world population subject to famine, natural disasters, disease, and conflict, changes must be made in agriculture to meet world concerns while remaining committed to sustaining the natural resources need for future production. Precision agriculture may be the next great evolution in agriculture; provided that it is understood, easily applied, and produces results. The catalyst for the emergence of Precision agriculture has been satellite positioning and navigation. The combination of Global Positioning System (GPS) and mobile mapping provide the agriculturist with a new capability of gathering information for implementing decision-based Precision Agriculture.

The purpose of this paper is to (1) determine what precision agriculture is and to offer ideas on expanding the concept to a more useful solution, (2) to describe how Global Positioning System (GPS) and mobile mapping are integral components of decision-based precision agriculture and (3) provide sources for additional information.

What is Precision Agriculture?
Precision agriculture is relative new and lacks a recognized and useful definition. To better understand the need for an accurate definition of precision agriculture lets look at how precision agriculture is being considered. Precision agriculture is considered a concept, management strategy, and even a philosophy.

It is said, “Precision agriculture is a phrase that captures the imagination of many concerned with the production of food, feed, and fiber.” The concept of precision agriculture offers the promise of increasing productivity while decreasing production cost and minimizing environmental impacts. Precision agriculture conjures up images of farmers overcoming the elements with computerized machinery that is precisely controlled via satellites and local sensors and using planning software that accurately predicts crop development. This image has been called the future of agriculture.1

Management Strategy
Most management strategies for precision agriculture match resource applications and agronomic practices with soil properties and crop requirements as they vary across a site.

Sometimes referred to as site-specific or prescription application and generally includes:

  • Soil sampling – the ability to determine the physical characteristics and the variability of the soil in the field.
  • Variable rate application – the ability to precisely apply the required type and quantity of nutrient of chemical needed to specific areas of the field.
  • Yield monitoring – the ability to accurately measure the yield and simultaneously record the location in the field.

Each of these components is necessary, but alone or together does not constitute precision agriculture.

Precision agriculture is the ability to manage land by the square meter instead of the square mile.

Precision agriculture is changing the farmers and rancher’s relationship with the land.

“Through the ages agriculture production systems have benefited from the incorporation of technological advances primarily developed for other industries. The industrial age brought mechanization and synthesized fertilizers, the technological age offered genetic engineering and now the information age brings the potential for Precision Agriculture.”

What Precision Agriculture Should Be!
Precision agriculture is an information-based, decision-making agricultural System designed to improve the agricultural process by precisely managing each step to ensure maximum agricultural production and continued sustainability of the natural resources. Lets look at this definition more closely:

Information-based, decision-making system Farming and ranching have always been a gamble. There are so many variables, many of which the producer has no control over. Some of the variables can be reduced or eliminated when the producer has information, which enables them to make decisions, they were unable to before. Precision agricultural can provide the producer accurate and timely information for making decisions.

Designed to improve the agricultural process
Precision agriculture is technologically feasible as well as being economically and environmentally justifiable. Improving the agricultural process can maximizes financial return and increases the stewardship of land, water, and related natural resources.

Precisely managing each step to ensure maximum production
Most producers would admit that increasing yields is their number one goal. But increasing yields may have a negative effect on the financial return. Precision agriculture enables the producer to reduce production cost and increase the potential for greater yields.

Continue sustainability of natural resources
Production of food, feed, and fiber are dependent on the quantity and quality of soil, plant, water, and air. No matter what agricultural systems are used, without protecting the natural resources, yields will decrease until the point of no return.

The concept that precision agriculture is a system, (Webster: interrelated, interacting, independent elements forming a complex whole), provides a more useful foundation for understanding precision agriculture.

An Agricultural System that can be used for:

  • Land preparation
  • Seeding
  • Chemical application
  • Fertilizer application
  • Crop monitoring
  • Nutrient auditing
  • Soil & leaf testing
  • Pest management
  • Conservation practices; Operation & management
  • Gross margin analysis

Precision agriculture can be used for more than row crops. It can be as effective with specialty crops, hay production, pasture management, animal grazing, and many other not commonly thought of agricultural systems.

An Agricultural System that adapts to the variability in agriculture

  • Spatial – changes across a field.
  • Temporal – changes from season to season and from year to year.
  • Predictive – differences between predictions and actual results.

An Agricultural System with components Like any system, precision agriculture has components. These components add additional clarification to the idea of precision agriculture:

Observation- occurs throughout the year.

  • Soil mapping
  • Weed & pest mapping
  • Decease mapping
  • Crop growth
  • Rainfall
  • And other conditions

Analysis – developing and using Geographic Information System (GIS) to manage multi-layer geospatial information.

  • Maps
  • Photographs
  • Topography
  • Field observations
  • Testing results
  • Climatic data
  • Previous agronomic data

Timely & precise response to fine-scale variation using Variable Rate Technology (VRT)

  • Soil amendments
    • Nutrients (N.P.K, Macro & Micro
    • pH stabilizers
  • Herbicides
  • Pesticides
  • Plant nutrients – top dressing

Assessment – the ability to review all management decisions

  • harvest yield monitoring
  • Return in dollars/acre -vs.- total production cost.
  • One year -vs.- another

An Agricultural System with flexibility
Since precision agriculture’s initial acceptance was by larger agricultural producers benefiting from variable rate application and yield monitoring, it is often considered a “tool” for traditional crop production on very large fields. Actually many aspects of precision farming lend themselves to almost any type of agricultural operation and size.

Benefits of Precision Agriculture

  • Increase productivity and net profit
  • Provide better decision making ability
  • Improve soil productivity
  • Improve water quality
  • Improve wildlife habitat
  • Sustain natural resources for generations to come.

Precision Agriculture Summary
Precision agriculture is an agricultural system that has the potential of dramatically changing agriculture in this 21st century. Precision agriculture lends it self to most agricultural applications and can be implemented at whatever levels are required. Precision agriculture is based on information technology, which enables the producer to collect information and data for better decision making. Precision agriculture is a pro-active approach that reduces some of the risk and variables common to agriculture. Precision agriculture is more environmentally sound and is and integral part in sustaining natural resources.

Information Technology Behind Precision Agriculture
As indicated earlier, much of the ability to implement precision agriculture is based on information technologies; in particular, global positioning and navigation and geospatial mapping and analysis. From being to end, the cornerstone for precision agriculture is based on precise locations and time. Fortunately the Global Positioning System (GPS) provides positioning, velocity, and timing capability, and Geographic Information Systems (GIS) provide mapping and analysis capability.

Global Positioning System
The United States of America developed and initiated the NAVSTAR Global Positioning System (GPS) for the purpose of providing navigation and positioning capability anywhere on earth, anytime, under any and all conditions. GPS provides a Standard Positioning Service (SPS) which is available to anyone to use at no cost. SPS is governed by the Federal Radionavigation Plan, which specifies the level of accuracy and integrity that the service must provide.

The initial design of SPS included an introduced error know as Selective Availability (SA). With SA, the GPS-SPS provided horizontal positional accuracies on the order of 100 meters. This level of accuracy was useful for general navigation and positioning but not for precision agriculture.

On May 1, 2000, then President Clinton issued and Executive Order to eliminate SA. At midnight May 1, 2000, SA was permantely turned off.

The elimination of SA immediately improved the performance of GPS by almost 10 fold. Horizontal accuracies have been reported as good as 4-6 meters but generally closer to 10 meters. Currently, the 1999 Federal Radionavigation plan is being updated to reflect the changes in the GPS-Standard Positioning Service after the elimination of Selective Availability.

Even with the elimination of SA, some precision agriculture techniques require even better accuracy, generally on the order of 1- 2 meters. Fortunately, there is a method of improving GPS accuracy called Differential Global Positioning System (DGPS).

Differential Global Positioning System
DGPS is a technique that corrects for some of the natural and introduced errors common to normal GPS observations, thus improving GPS positions. DGPS corrections can be applied in two ways:

  • Post Processing – a technique that requires the GPS user to collect GPS data and then, using specialized software, process the GPS data with DGPS data, collected at the same time, from a known location like a base station or permanent reference station.
  • Real Time DGPS – Real time DGPS (R/T DGPS) allows the GPS user to immediately take advantage of differential corrections that are broadcast in real time from DGPS services. The obvious advantage is the immediate improved accuracy that allows for:
  • Single visit; Time is valuable and costly return trips can be avoided.
  • Increased Efficiency: R/T DGPS eliminates post processing and saves money, time and energy.
  • Better Results: R/T DGPS provides the capability for accurate mobile mapping.

R/T DGPS Services
R/T DGPS services are provided by Commercial DGPS services and by Government DGPS services. Both Commercial and Government provided DGPS services to the user by either satellite-based systems or land-based systems. These services are augmentations to GPS.

U.S. Government DGPS Augmentations
Until recently, GPS users who wanted to get differential corrections had to pay a subscription fee to a private company or maintain their own base station in order to acquire differential corrections. Today, there are U.S. Government R/T DGPS services that are available to anyone at no cost:

Wide Area Augmentation System (WAAS)
The Wide Area Augmentation System, known as WAAS, is a satellite-based system that is being developed to meet Federal Aviation Administration (FAA) requirements for a safety-critical navigation system. It is designed for aviation, providing improved accuracy, integrity, and availability of the basic GPS signals at 300 feet above ground. This system will allow GPS to be used as a primary means of navigation for enroute travel and non-precision approaches in the U.S., as well as for Category I approaches to selected airports throughout the nation.

WAAS is a relatively new system and is currently under development and testing prior to FAA certification for safety-of-flight applications. Initial testing began in August 2000. Currently, while testing, there are planned outages. Even though WAAS is available throughout the U.S. it is still difficult to rely on. As WAAS becomes more capable, GPS receivers that also have WAAS capability will be very useful.

Nationwide Differential GPS Service (NDGPS)
In 1990 the US Coast Guard (USCG) established a ground-based differential GPS, covering the coastal areas and navigable waterways. In 1994 a GPS Augmentation study was conducted and recommended that the Department of Transportation (DOT) expand the USCG’s maritime system to provide continues marine and land coverage for surface users. In 1997, Federal agencies began planning for a DGPS system to provide Nationwide coverage; the Nationwide Differential GPS (NDGPS).

Using the USCG’s existing DGPS radiobeacon network as a template, covering both coastlines, the Gulf of Mexico, the Great Lakes, and major inland waterways, the NDGPS program intends to densify the existing network with dual redundant terrestrial and waterway coverage, providing service to the remaining fifty-five percent of the continental US and Alaska. Under an exemplary cooperative effort, many government agencies are contributing to this program. A total of 53 Ground Wave Emergency Network (GWEN) sites located around the country are being converted from their old communications configurations to real-time GPS reference station installations. Differential corrections will be broadcast, at around 300 kHz, from 90-meter-tall GWEN transmission towers.

Once fully operational, the NDGPS will cover the nation with the most accurate and reliable navigation system that the country has ever had. GPS users, both civilian and government, will have free access to the NDGPS.

The NDGPS will augment the existing satellite system with ground-based radio transmitters, known as reference stations. The reference stations will broadcast a signal from a transmitter located at a known fixed location on the ground. Users who receive the ground-based signal in addition to the normal GPS satellite signals will be able to determine their position with greater accuracy.

Reasons for using NDGPS

Real Time Horizontal Accuracies of 1-5 meters.
The positional accuracy that is supported by the NDGPS system varies with the user’s distance from the reference station. Generally the horizontal accuracy is about 1 meter for each 100 meters from the reference tower.

Availability – 99.7%
Availability for a given broadcast is defined as the percentage of time in a one-month period during which a DGPS broadcast transmits healthy correction signals at the specified output level. The current NDGPS is designed for, and is operated to maintain a broadcast availability level, which exceeds 99.7%.


System Integrity is the ability of the system to provide timely warnings to users when it should not be used for navigation. NDGPS integrity is provided by dual integrity monitors at each site. The integrity monitors ensure the integrity of the broadcast pseudorange corrections and broadcast an alarm message to the user if the corrections fall outside preset limits.6 This provides additional security as to the positional quality of the signal.

NDGPS is free and easy to use

Accuracy Requirements for Soil Sampling
Soil Sampling is like the foundation of a house. No matter how much effort you put into building the house, the house is only as good as the foundation. The same principle applies to precision agriculture. Whether growing forage, feed, food, or fiber, plant growth depends on soil conditions and soil quality. To effectively manage soil-plant interrelationships, soils information is very important. Like the general rule says, the more important it is the more accurate it has to be.

There are two basic types of grid sampling used to collect soils data for precision agriculture

  • Area sampling (grid cell)
  • Point sampling with interpolation (grid point)

Grid sampling is used for precision agriculture because it is simple and does not require soil science mapping experience. Once the soil data has been collected, the data can be displayed and analyzed.

Determining and mapping the variations in soil characteristics across a field requires and accurate knowledge of the position that the samples were taken. Whichever grid sampling method is used the coordinate location of the soil sample should be accurate for developing a soils data layer and for navigating back to those locations for re-sampling.

This requires the use of a GPS receiver and a source of differential corrections so the producer can acquire an accurate (1- 2 meter) horizontal position that represents the soil sample location. Having acquired the coordinates, the position can be entered into a database while in the field.

After the soil sample location has been accurately acquired and entered into a database, all the physical soils data (texture, pH, nutrients, etc.) can be tagged to the coordinate location.

Geographic Information Systems
Geographic Information Systems (GIS) have evolved rapidly within production agriculture especially in the area of precision agriculture. GIS can provide the producer valuable insight into field variability, soil and plant interactions, and yield results. GIS is the most effective information tool the producer has to store, retrieve, map analyze, and manage agricultural data.

In many ways, agricultural producers have always been GIS users. Most producers use some type of map for planning what will be done for the coming year. Usually the maps have farm and field boundaries, along with any additional information that the producer might record for helping make decisions.

GIS is the link between the field and the office.

GIS allows the producer to

  • Compare different types of agricultural data
  • Query to find relationships within and between data sets, and
  • Produce maps and charts to visualize, interpret, and present the analysis results.

The degree of spatial variability present in a field will determine whether unique treatments are warranted for certain areas. Post harvest analysis of the variation in crop yield and the measured factors influencing crop yield will provide useful information for the next growing season. Each year, the producer is able to look back and benefit from previous year’s management decisions to help and guide in making current decisions.

The farm map is still the foundation of the farm GIS, but now it is a digital map instead of a sketch or lines drawn on and aerial photograph. Now the digital map includes other information and features, all associated with coordinates and time. All of this is linked in a computer database, able to be queried and analyzed.

The real reward to GIS as an information technology for making precision agriculture useful is the way GIS helps the producer to visualize the entire agricultural production system. GIS provides the producer a holistic view; beginning to end.

Mobile Mapping
Understanding how important information technologies are in precision agriculture, especially GPS and GIS, will provide a real appreciation for mobile mapping.

Mobile mapping is the ability to collect field data, with unique geospatial time tags and attributes, for integrating into or updating a GIS. Mobile mapping provides the freedom to collect data anytime, anywhere, in any manner. Mobile mapping is like a memory extension only better. It remembers what was recorded, when, and where.

Mobile mapping is more than a concept. Like precision agriculture, mobile mapping is a system with individual components:

Ruggedized Handheld Personal Computer (HPC)
Generally speaking, an HPC is a computing device that can be held in one hand and operated by the other. They come in various form factors: pad, clamshell or fold-over, and tablet form. Data entry occurs through touch screen – pen based entry, handwriting recognition, and/or attachable keyboard. Most HPCs can synchronize data with desktop PCs via serial or Universal Serial Bus (USB) ports. Some HPCs are able to communicate wirelessly, allowing Internet access on the go. Some preferable characteristics for HPCs are:

  • Small, lightweight, handheld.
  • Compatible with PC synchronization.
  • Sunlight readable displays and back lighting.
  • Survivable: Rugged, some degree of drop-proof capability.
  • Temperature tolerant.
  • Water-resistant & dust proof.
  • 8-10 hours of continuous operation
  • Quick and easy removal from vehicles for foot-mobile handheld use.

Durability, survivability, and sunlight viewing are essentials for mobile mapping. If you can’t see the screen or it won’t operate under outdoor conditions, then the HPC’s usefulness is severely limited.

HPCs – Pad Form Factor

HPC – “Clamshell” or “Fold-over”

HPC – Tablet Form Factor

HPC – with Keyboard

Application Software

Most HPCs include some onboard software, which enable the HPC to organize schedules, tasks, contacts, and notes. Most HPC software also has utilities like a clock and a calculator. Most of the HPC Operational Software also includes some business functions like spreadsheet and word processing.

In addition to these functions the HPC will need to operate specialized application software for data collection and mapping. For mobile mapping, here are some general requirements when considering application software:

  • Data Collection:
    • “Free Form” (notation)
    • “Choice List” selection, (predefined)
    • Editing existing attributes
  • Data Entry:
    • Pen stylist selection
    • Hand writing recognition
    • Voice recorder Import from other sources.
  • Expandable Memory and Storage
  • Modem Connectivity
  • Wireless Applications
    • Digital phone
    • Web based email
    • Web Browser

When considering application software, spend sufficient enough time itemizing your application requirements:

  • What do you want to do?
  • How do you want to do it?
  • What type of data do you want to capture?
  • What type of data do you want to import from an existing GIS database or other source?
  • How important is image data like maps and photographs?
  • Will the application software allow the import of digital camera images?
  • Will the application software allow import of GPS data?

Application software packages may be specifically designed for special applications or allow for use in all kinds of environments. Some application software provides image data capture capability with the use of digital cameras. This enables the user include image data captured at a site in the field or used as a source of information or cross reference for future data collection.

Some application software provides detailed maps that are made available from a database or from scanned aerial photographs, maps, or satellite image data.


Last but certainly not least is GPS
Mobile mapping is essentially useless without the GPS component. The GPS component not only provides the location for all data collected but also provides the time in which it was collected. GPS also enables the user to navigate back to any particular location anytime thereafter.

Once the field data has been collected using mobile mapping, the data can be downloaded into a desktop GIS. As described earlier, the GIS then provides the producer the ability to consider all the options for production. The producer can then use the positional data and the decisions that were made with the GIS to carry out the mechanized part of precision agriculture.

Placing the GPS antenna on top of the Tractor. Getting ready to use the data collected from mobile mapping and GIS to apply chemicals using variable rate application.

Additional Information

Precision Agriculture Resources

Precision Agriculture & Related Information Resources, University of Georgia,NESPAL,

National Environmentally Sound Production Agriculture laboratory, Univ. of GA https://nespal.cpes.peachnet.edu/

Oregon State University College of Agricultural Sciences,

Missouri Precision Agriculture Center https://www/fse.missouri.edu/mpac

Precision Farming Institute,

The Ag & Farm Search Engine,

PrecisionAg.Com, https://www.precisionag.com

Centre for Precision Farming, Cranfield University,

The University of Sydney, Australian Centre for Precision Agriculture, https://www.usyd.edu.au/su/agric/acpa/pag.htm


Precision Agriculture, The Learning Link, University of AZ

OSU Precision Agriculture Page, Oregon State University

Agriculture Online, Technology

“The Impact of Precision Agriculture”, Brett Whelan, Alex McBratney & Broughton Boydell,

“Precision Farming: A new Approach to Crop Management”, Stephen W. Searcy, The Texas A&M University >

“Sensors vs. Map-Based Precision Farming”, Mark T. Morgan, Purdue Agricultural and Biological Engineering Department, April 1995,

Variable Rate Technology
Variable Rate Technology, A State of the Art Review, University of Georgia,

Variable Rate Application Equipment for Precision Farming, R.L. Clark, R.L. McGuckin, Department of Biological & Agricultural Engineering, University of Georgia,

Table 1 – List of Equipment that has been used for Variable Rate Application, Department of Biological & Agricultural Engineering, University of Georgia,

Soil Sampling
Soil Sampling for Precision Farming, Precision Farming Links, Department of Biological & Agricultural Engineering, University of Georgia,

GPS Educational Resources
GPS Overview, University of Texas

GPS System Overview, University of California Santa Barbara https://www.ncgia.ucsb.edu/educatio…ula/gisc/units/u017/u017_toc.html

GPS Primer, The Aerospace Corporation https://www.aero.org/publications/GPSPRIMER/index.html

GPS Tutorial, Ashtech.com

GPS Tutorial, Javad.com

GPS Tutorial, Trimble.com https://www.trimble.com/gps/index.htm


GPS Update, Spacedaily https://www.spacedaily.com/gps.html

Professional Surveyor Magazine Online https://profsurv.com/home3c.htm

Spacenews.com https://www.spacenews.com/

GPS Surveying Resources
Plane Surveying Lecture Notes, University of Melborne

Timing Resources
Time service Department, U.S. Naval Observatory https://tycho.usno.navy.mil/

USNO GPS Timing Operations https://tycho.usno.navy.mil/gps.html

Mapping Resources
Coordinate Systems Overview, University of Texas https://www.utexas.edu/depts/grg/gcraft/notes/coordsys/coordsys.html

The Spheroid and Coordinate System, University of Buffalo https://www.civil.buffalo.edu/cie/cie303/lect1.html

Map Projections, University of Montana,

Map Projection Overview, University of Texas

Geodetic Datum Overview, University of Texas

Global Navigation Satellite Systems (GNSS)
European Space Agency

GLONASS – Russian Federation Ministry of Defense

GLONASS Updated Information Service, German Aerospace Center

American Congress on Surveying and Mapping, ACSM https://www.survmap.org/

Geospatial Information & Technology Association, GITA https://www.gita.org

The Institute of Navigation, ION https://www.ion.org

US Government REsources

U. S. Coast Guard
Navigation Center, NAVCEN https://www.navcen.uscg.gov/

Navigation Center – GPS

Navigation Center – DGPS

National Oceanic andAtmospheric Administration, NOAA

National Geodetic Survey, NOAA

Continuous Operating Reference Stations https://www.ngs.noaa.gov/CORS/

Federal Geodetic Control Subcommittee & GPS Interagency Advisory Council

U.S. Air Force
U.S. Space Command GPS Support Center, Air Force

NAVSTAR GPS Joint Program Office

National Aeronautic and Space Administration, NASA
GPS Applications Exchange, NASA

Shuttle Radar Topography Mission, STS-99

Department of Transportation DOT.gov https://www.dot.gov

Federal Aviation Administration, GPS Product Team


  • National Research Council, Board of Agriculture, Committee on Assessing, Crop Yield: Site-Specific Farming, Information Systems, and Research Opportunities, Precision Agriculture in the 21st Century, National Academy Press , Washington D.C. 1997
  • ATIS News, “Nationwide Differential GPS”,https://map.azfms.com/newsltr/vol3_1999/3ndgps.html
  • D.B. Wolfe, C.L. Judy, E.J. Haukkala, D.J. Godfrey, “Engineering the World’s Largest DGPS Network”, U. Coast Guard
  • R. L. Ketchum, J.J. Lemmon, J. R. Hoffman, Institute for Telecommunication Sciences, “Site Selection Plan and Installation Guidelines for A Nationwide Differential GPS Service” August 5, 1997
  • Pocknee, Stuart, Strategies-Soils-Grid Sampling, NESPAL, University of Georgia,