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Digital tools such as Geographic Information Systems and Global Positioning Systems allow very precise mapping of agricultural areas. These technologies, combined with soil mapping and yield monitors have led to the production methods referred to as "Precision Agriculture" (sometimes also called Prescription Agriculture). The basis of Precision Agriculture is applying agrochemicals only where necessary. The point of Integrated Pest Management is to apply pesticide only when it's necessary. By using these technologies in IPM, we can develop "Precision IPM", only applying pesticides where and when it is necessary. This chapter will provide an overview of some aspects of GIS and Global Positioning Systems (GPS) and provide some suggestions as to their possible use in IPM. Some additional readings and links to other WWW sites which can provide further information are also included in the text. What are Geographic Information Systems (GIS)??Geographic Information Systems are essentially relational databases. The relationship between items in the database are their locations, either in real-earth coordinates (e.g. UTM, or longitude/latitude), or on a grid (i.e. X,Y coordinates). GIS combine digital mapping, database functions, and spatial analysis. Basically, GIS are computer software packages that are capable of assembling, storing, manipulating, and displaying geographically referenced information. The system itself includes the operator. As with any computer program, a GIS cannot confirm the quality of the data being input or interpret the output. These two tasks require an operator familiar with the field for which the digital tool is being used. The difference between a GIS and standard database software is the ability for GIS to
conduct spatial analyses on the data. For example, in table 1 below, the percentage of
wheat crop damaged by the Russian wheat aphid (RWA), Diuraphis noxia, at any one
site location is a simple, a spatial query. Because the geographic location of the sites
is also known (and linked to the site numbers), a GIS can also describe the relationship
of % of crop damaged and latitude (the more northerly the site, the lower the percentage
of the crop damaged by D. noxia). This is a spatial query. This is a relatively
simple example, but given the computational power of today's desk top systems, very large
datasets can be examined in a similar fashion. Table 1. Completely fictional data on the percentage of wheat crop damaged by the Russian wheat aphid, D. noxia, in eastern Colorado.
Another useful feature of GIS is the ability to link databases whose items have locations associated with them. If we have other data that is associated with a geographic position, we can combine it with the existing database and examine trends of RWA damage across an entire area. We can combine datasets by using exact-matching spatial data (e.g. if we have the coordinates of other sample sites outside Colorado, we can simply add these to our map and extend its boundaries); or by hierarchical-matching spatial data (e.g. if we have estimates from other counties, but not the specific sample site locations, we can estimate and compare damage levels within counties), or even by fuzzy-matching spatial data (e.g. if we have estimates for RWA damage to wheat crops and to barley crops, we can combine these two different types of maps and get an estimate for the total damage to all crops by RWA). In this manner, GIS facilitates the examination of population dynamics on very large geographical scales.
There are two different categories of data features in a GIS, spatial data and attribute data. Spatial data is data that describes the geographic shape and position of features in the database. Spatial data is represented as either points, lines, or polygons. Attribute data describes spatial data. For example. A fence post is spatially a point. It may have the attributes of being constructed of wood or metal, or of being a corner post. The entire fence is spatially a line. It may have the attributes of height, direction, and type of fence (e.g. barbed wire, split rail, etc). The field bounded by the entire fence line is a polygon and may have the attributes of being rangeland or a cropping system, dryland or irrigated. Biological data can be considered attribute data of a sample site. Data input can be accomplished via a number of methods. Standard planar maps can be entered using a digitizing table. Digitizing is creating a digital data file from a non-digital format. Similarly, photographs and other images (including printed maps) can be digitized using a scanner. Importing these digital images into a GIS involve assigning them real-world location coordinates. Not every point on the image need be individually assigned a location; if several reference points are assigned, the GIS software can then calculate any other location on the image. This process is referred to as georectifying or registering an image. GIS software packages vary greatly in price and abilities. They are available for almost all operating systems (i.e. UNIX, DOS, MAC, Window '95 & Windows NT). The price of a GIS is generally directly related to the abilities of the software. Some packages are oriented more for digital mapping and have only weak spatial analysis capabilities. Others are very complex programs that incorporate sophisticated statistical procedures, require considerable training and have steep learning curves. Choosing the right GIS for a job requires evaluating what is expected from the software and choosing a package with the appropriate features. GIS software is available from approximately $300 and runs into the thousands. The power behind using a GIS as a database for biological data lies in locational reference. There are several ways of associating sample sites with their real earth location. For example, sample sites can be located on a map and the site coordinates extrapolated or surveying tools can be utilized from a set bench mark. However, the easiest method is probably using a Global Positioning System (GPS). Some suggested reading on GIS:
Some GIS sources on the WWW (many of these point to lots of other GIS sites):
Global Positioning Systems (GPS)
Obviously, if GPS is used for surveying, the accuracies discussed above are unsatisfactory. There are ultra-precise techniques which enable non-military GPS units to achieve centimeter accuracy. One of these methods is called 'Differential Correction'. There are several different methods of differential correction, but all basically involve the same theory. A GPS receiver (the base station) is be placed on a known location on the ground (i.e. a benchmark) and calculates the error in the satellite signal. An error correction is calculated and transmited via FM radio to the unit being used to calculate actual locations (the rover). The correction signal is called 'differential correction'. Differential correction signals have a standarized format which is called RTCM 104. Other methods of obtaining differntial correction signal include a commercial satellite system and a number of companies offer differntial correction signal broadcast on FM bands to which you must pay a subscriber fee. Using differntial correction, it is possible to obtain sub-meter accuracy receiving only the C/A code. Many of the lower cost hand-held GPS receivers are now differential-ready (can accept differential correction signal). Some survey quality GPS receivers can recieve the P code. These systems, however, are very expensive.
Which GIS/GPS Should I Use?Choosing the appropriate GIS and GPS for a project is analogous to choosing the right tool for any other job. There is a wide variance in price and associated abilities and functions in both of these technologies. A project's needs should be evaluated and the appropriate equipment selected. There are some features which are helpful to have in these technologies regardless of the project. A Geographic Information System should have methods of editing both spatial and attribute data in the database; approximately 80 percent of any GIS project involves making the spatial data useable. Importation of data should be well supported and filters for various data sources supplied. In addition, a GIS should have the ability to manipulate different map layers in at least the following ways: merging different layers from the same geographical area to form a new layer which incorporates all of the features of the original layers, merging different layers from the same geographical area into a new layer which incorporates only the features in common of the original layers, building a buffer area of a given size around any feature on a layer, and joining layers from different geographical areas. A GIS should also have the ability to query all features of it's database, including Boolean searches (e.g. Standard Query Language, SQL). The spatial analyses available should include methods of interpolation between sample points, estimating dispersal and aggregation of point patterns is useful ability, and performing tabular analyses of the database. Finally, a GIS must present the results of the process in a clear and understandable format. Graphics characteristics should include support for full color, a variety of symbols, fonts, line styles and fill patterns, and support for common color printers and plotters. The cost of a Global Positioning System receiver is principally dependent on the accuracy required. Models start at under $200 and range in price to tens of thousands of dollars. Earlier considerations when purchasing a GPS involved tradeoffs between power consumption and accuracy, these have been resolved. All GPS receivers must receive signal transmission from at least 4 satellites to calculate an accurate position. Basically, the more satellites a GPS unit can receive, the more accurate will be it's calculated location. Even very inexpensive GPS receivers now track 8-12 satellites simultaneously, so this should not be an issue unless purchasing an older, second-hand unit. In addition, newer units also are multi-channel receivers, allowing a greater signal to noise ratio, allowing the unit to lock onto satellite signal under more adverse conditions and to track satellites which are almost on the horizon. These receivers also receive satellite signal continuously, allowing them to calculate position and velocity instantaneously. Some newer models still utilize an older technology called multi-plexing, meaning they use a single (or sometimes several) channels that rapidly switch from one satellite to the next. Multi-plexing receivers are generally not as accurate or as flexible as multi-channel receivers. The recent decreases in price and accompanying increases in performance in GPS receivers means that excellent field units are quite affordable. A field GPS receiver should be able to store and later download data. In addition, download capability should also follow the standard format (i.e. NMEA 0183 is a standardized download code for GPS). A field GPS receiver should also be 'differential ready', meaning it comes equipped to receive standardized differential correction signal (i.e. RTCM 104 format). In the U.S., the Department of Transportation is considering making differential correction signal available on a no-fee basis across the country. In addition, congress has recently been pressuring the military to remove the encoded error in the C/A code. Using GIS and GPS in IPMThrough these two technologies we are now able to very accurately locate and map fields, crop production, and pest populations. These abilities offer advantages in both IPM research and implementation. Scouting and monitoring pest populations, predicting pest outbreaks and movement, identifying and categorizing patterns of damage, assessing the success and refining the application of control tactics can all benefit from GIS/GPS technology. Many of these applications are compatible with remote sensing methods. The ability to import and georectify digitized images makes GIS a useful partner with remote sensing. Indeed, GIS is an excellent tool to facilitate the analyses of remotely sensed data. Although the extent of weed infestations frequently are assessed by remote sensing techniques, insect and plant pathogen populations are generally too small to sense remotely and patterns of damage are generally used as indicators. Satellite imagery, aerial photography, and radar have all been used to estimate insect populations remotely. Scouting, Monitoring & Mapping Pest Populations - Scouting and monitoring pest populations and making control decisions based on those population estimates is one of the bases for IPM. The ability to accurately and precisely map the density and location of pest populations has obvious advantages, especially in regard to application of control tactics. Monitoring programs can now digitally map the location of sample sites (taken in the field with a GPS) and the resulting GIS layers can then be used to interpolate the pest population over the sampled area. This is not a new technique; interpolative techniques, without GIS, have been used to estimate populations. However, a GIS layer will not only estimate populations but can be linked to other similar layers throughout a region, resulting in regional maps which estimate pest populations. This technique is used when constructing state or region wide estimates of pest populations or crop damage. Typically, sampling has been done on a field level but this might not accurately reflect the driving influences behind a pest population outbreak. Populations tend to function on much larger scales and immigration from population sources can greatly impact the pest population in a field. Temporal series of GIS map layers of the same area, each layer representing the same type of data from a different sample period, can show not only changes in pest populations but, when combined with biological and ecological knowledge of the pest, indicate if this is a reproductive response or movement. If the boundaries of the monitored area are wide enough, source populations responsible for subsequent re-infestations of fields can be identified. Precision Application of Agrochemicals - Using GIS & GPS to map the populations of weeds and plant pathogens offer some very tangible practical applications. Weeds especially are likely to re-occur in the same o neighboring area in a field. Consequently, mapping weed beds in a field during harvest and using this map to direct application of pre-emergent herbicide the following year can lower the amount of herbicide used in a production system. This technique is being incorporated into many brands of agricultural machinery. Pest populations and crop yields are mapped for particular fields and appropriate agrochemicals (pesticides and fertilizers) can then be applied only to the spot within a field that require them. GIS software is linked to the application equipment and is used to activate and stop spray nozzles. Using a computer to analyze a variety of inputs from environmental sensors, the system can compensate for many influencing factors (e.g. decrease drift and overspray resulting from wind). This is the process of precision agriculture. Although the original outlay in the cost of the technology can be high, many high value cropping systems are already incorporating both GIS & GPS. There is considerable data indicating that such technology can provide improved control of pests using significantly less chemical. Using GIS to apply insecticides is possible but perhaps less cost-effective than its use with either herbicides or fungicides. Insects are much more vagile and within field distribution may vary year to year. However, certain trends in insect population distribution can be easily demonstrated using GIS. Certain insect pests track patterns in resource availability or are regularly reintroduced after localized extinction because of prevailing weather patterns. The factors responsible for both of these situations can also be incorporated into GIS databases and because the software can examine spatial relationships between items in the database, it can be used to develop predictive models. For example, the species composition of grasshopper complexes in the interface of dryland, irrigated and rangeland agroecosystems vary over the growing season. Different species occupy the different cropping systems at different times through the year. Preliminary data suggest this is because the different species are tracking various resources through the summer and into the fall (see example). The situation in the example was clarified from examining GIS maps of the temporal distribution of individual grasshopper species present in each of the neighboring agricultural systems. From the GIS database and resulting maps, we are able to see when and where both monitoring and control applications must occur to be effective. ConclusionGIS and GPS can provide us with the ability to very accurately map a production area
and everything in it, including pest populations. The software can be linked to
agrochemical application equipment to precisely apply pesticides and fertilizers only
where such chemicals are needed. This can not only decrease the chemical load in the
environment but can also result in better pest control at lower overall costs. In
addition, this technology can be used to refine understanding about the distribution of
pest populations and therefore target both monitoring and control tactics. The usefulness
of these technologies in IPM, both in combination and alone, increases with proficiency in
their use. The investment in adopting these systems, in purchase costs and time invested
overcoming the significant learning curve of some packages, means they should not be taken
on lightly. Like any other tool, GIS and GPS can offer unique solutions to certain types
of problems but can cause others. In the case of using GIS in research, for example, it
should be realized that GIS is an excellent tool for defining hypotheses, but deriving
conclusions from any existing database without validation from a separate data source I
considered data-mining. However, once adopted and in place, they can be used for much more
than simply monitoring populations and control applications. They can be used to analyze
the most efficient travel paths for machinery and delivery of products, the offer some
obvious benefits to evaluating crop varieties by location, and they have tremendous
potential in land management. There are other uses which have not been mentioned, and new
uses will continue to evolve the more widely used these systems become. Return to Radcliffe's IPM World Textbook Home Page The University of Minnesota is an equal opportunity educator and employer. Privacy Policy Last modified Friday, 23 January, 1998 © Regents of the University of Minnesota, 1998
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The latter two types of combining data are, perhaps, GIS software's
most powerful attributes. GIS software can combine and contrast spatial data like this by
treating each different data type as a separate 
When the
acetate is laid down over the map of the island and the corners are aligned, the roads
appear to be in the correct location on the island. Now peel the roads acetate off of the
map. Imagine the rivers are drawn in the same manner and peel them off of the map. Now the
towns and now the forests, peeling back each type of data until all that is left is an
outline of the island with no features. This is how GIS 'thinks' about data. Not only
geographical data is treated this way; layers can be created which would represent the
density and distribution of particular species on the island. Any data point that is tied
to a real location on the face of the planet - including things which may seem transitory
like animal movement (e.g. the number of Canada Geese passed over a given area of land per
migration season) can be databased with a GIS. Different layers can be merged, combining
all of their features, or intercepted, combining only the features common to both layers.
The same can be done with complete maps (composed of many different layers). It is easy to
see how such a tool can be used to investigate population dynamics on a very large scale.
referred to as a GPS unit) measures the distance from a satellite
using the time it takes for a radio signal, sent from the satellite, to arrive at the GPS
unit. The system is designed so that the location of the satellites in the sky is known
and very accurate atomic clocks in the satellite transmit a time code as part of the
signal. GPS receivers also contain a self-correcting clock which synchronizes to the
satellites and compare the time coded in the signal to that indicated by their own clock
and the difference is the length of time the signal took to be received. It is then a
simple calculation to conclude the distance to the satellite. Theoretically, with signals
from 2 satellites (whose location in the sky we know), we can find our location on the
earth through triangulation. However, given the potential for the receiver clock to be of,
three satellites are the minimum for calculating accurate locations (this invovles the
self-correction mechanism in the receiver). Receiving 3 (or preferably more) satellites
will correct for many of the error sources. Four satellites are required for 3 dimensional
locations (i.e. locations including altitude). Even the lowest priced GPS units are
capable of receiving at least 5 satellites.
