GPS & GIS in Agriculture

Global Positioning Systems (GPS) were developed to provide for navigation in three dimensions. They are used by aircraft, ships, ground vehicles and hand carried by individuals. A GPS may used alone to provide "ballpark" positioning and navigational data. The coordinates provided by standalone units are accurate only to 0 to 100 meters but are accurate enough to put a plane within sight of the airport, for example, and as such are invaluable. The new GPS units have increased receiver capabilities that track up to eight satellites (versus four in the older receivers). This provides more accurate readings. Precise positioning is provided by using a GPS unit in conjunction with a ground station at a known reference location. The GPS compares its relative position with the ground station and is then able to make corrections to its readings. This is called differential correction and is accurate to 0 to 5 meters. Differential correction is valuable to us for collecting data to describe points, lines and areas. Accurate descriptions of agricultural fields allow us to calculate acreage, overlay the fields onto road maps, etc.

Another valuable new feature of GPS units is internal recording of the latitude / longitude coordinates coupled with the ability to download directly to a computer. This eliminates manual data recording and entry thus saving time and reducing errors.

Requirements

An understanding of the implementation process. Knowledge of GIS, GPS and database technologies. An appropriate level of expertise about the hardware, software and the way in which the system will be used. Willing participants at all levels, from field to administration. An adequate budget and sufficient allocation of time (Somers 1996).

Basic Steps to Implementation

Planning - Clarify overall goals for the project, describe resources (time, money, labor, data), establish a schedule or timetable. Analysis - Analyze the resources you have (data, knowledge, skills, equipment) then examine your needs, for example, you may need answers to questions that have geographic components in order to make an optimal decision and take action to solve a problem. Design - Determine what type of GIS will suit your particular situation. Design choices depend on needs and resources. Acquisition, development and training - After selecting appropriate equipment and software, these components must be put together into a working unit. Then the GIS work begins. This work includes data acquisition, application development and user training. Operation, maintenance and upgrade - decisions include who will use the GIS and keep the data current. Routine maintenance is required as with any other system.

The Value of Having Good Maps

We need to track various parameters (insect counts, plowdown, etc) for the agricultural fields for which we are responsible. For that reason, the Arizona Cotton Research and Protection Council, State of Arizona hand drew, in MapInfo, the boundaries of each field. They began this project in the late 1980’s (as part of the Boll Weevil Eradication Project). As references, they used the streets and physical boundaries already available in MapInfo as well as field maps hand drawn by their field personnel. They provided us with a copy of these maps and the maps were very valuable.

However, we realized we required far more precision in the maps in order to make management and regulatory decisions. We examined the options available at the time. Keep in mind that the technology is dynamic and standards change rapidly. We are fortunate in that the current technology is very powerful, accurate and much more affordable than it was years ago. We compared current GPS technology to aerial photos and compared ArcInfo to MapInfo.

We subsequently purchased GPS units, trained our personnel and have been collecting GPS data. We continue to examine and consider other compatible technologies in a constant effort to get the best data for the time and money spent.

Our Current GPS Equipment and Its Use

We are now using hand held, differentially correctable GPS units made by Corvallis Microtechnology in Corvallis, Oregon. These units, pictured above, have a full keypad for descriptive data entry. They are programmed to record the specific types of points, lines and areas in which we are interested. Programming is done on a regular computer and downloaded to each GPS unit.

The feature file for our units is:

The person operating the GPS unit collects latitude/longitude data at each feature site, as the situation requires. The unit stores the raw data for the entries day’s work.

The data is downloaded to a desktop or laptop computer at the end of the day or work period.

Meanwhile, the base station is continuously collecting lat/long data. The base station collects lat/long data once per minute and compares the reading to its own, known (surveyed to within millimeters) position. It then builds a “correction” file.

When the field data comes in, it is differentially corrected by calculating the differences between what the base station recorded, at say 8:01 a. m., to what the base station knows to its exact position. The base station’s reading at 8:01 a. m. may be 1 meter north of what the base station knows to be true so the field data that was collected at 8:01 am is corrected by that amount, in the proper direction. The result is a “differentially corrected” file that is highly accurate.

The corrected data is then imported into a GIS and appended to a larger map of the region. We use the GIS MapInfo to query the database for to create thematic maps, customize, display and print maps. Maps can be exported to other programs, such as this presentation software. Maps are used to support regulatory, administrative and scientific decision making, and are also used operationally for planning and job assignment.