Precision Agriculture Terminology

The following list of terms is provided to help practicioners of precision agriculture reduce or eliminate the frustration associated with devloping a working knowledge of the technology. While significant effort has gone into the devlopment of this glossary, we invite comments and suggestions to improve the use of this tool. Comments should be addressed to the webmaster at shearer@bae.uky.edu.

aerial photography - photograph of a field or section taken by an airplane or satellite (remote sensing).

algorithm - a mathematical formula that may be used to control variable rate applications.

anti-spoofing - process of encrypting the L2 signal to prevent unauthorized transmissions of false GPS signals.

ASCII - widely used computer code for identifying numbers, letters and special characters (American Standard Code for Information Interchange).

base map - a simple map that shows the boundaries of a field or section and information about any unique feature (sinkholes, or streams).

contour map - yield map that combines dots of the same intensity/yield level by interpolating (or kriging).

carrier frequency - frequency at which radio signals are encoded and transmitted.

contour line - a line used to represent the same value of an attribute (elevation or yield).

contouring - interpolation method used to distinguish between different levels of an attribute (elevation, fertility, yield).

control segment - the network of tracking stations that monitor and control GPS satellites.

controller - a microprocessor used to adjust application rates according to field location.

coarse acquisition (C/A) Code - a unique code for each GPS satellite or the standard code used by civilian receivers.

database - a collection of different pieces of georeferenced information (yield, soil type, fertility) that can be manipulated (layered) in a GIS model.

dead reckoning - a method of estimating field position based on forward speed, time of operation, implement width and number of passes.

Department of Defense (DoD) - the U.S. government organization responsible for the creation and control of the Global Positioning System.

dielectric - a material that can sustain an electric field but does not conduct electric current.

differential correction - correction of a GPS signal that is used to improve its accuracy (to less than 100 m/~330 ft) big using a stationary GPS receiver whose location is know. AThe second receiver computes the error in signal by comparing the true distance from the satellites to the GPS measured distance.

differential global positioning system (DGPS) - a method of using GPS which attains the position accuracy needed for precision farming through differential correction.

dot map - yield map that represents one dot for each data point collected by the yield monitor (usually every one or three second intervals). Each dot is color coded to identify the yield level observed for that particular location.

end of pass delay - a delay that allows any grain that passes by a flow sensor to be included in yield calculations after the combine header has been raised.

Federal Communications Commission (FCC) - government agency responsible for enforcing communication standards and frequency band usage.

flow sensor - a sensor that measures the amount of flow through an enclosure (tube, pipe or housing) per unit of time.

frequency modulation (FM) - a method of transmitting information on radio waves by encoding the information as a change in frequency or number of cycles per second.

geographic data - data that contains information about the spatial location (position) and the attribute being monitored (yield, seed population, etc.)... a.k.a. spatial data.

geographic information system (GIS) - a computer based system used to input, store, retrieve, and analyze geographic data sets. The GIS is usually composed of map-like spatial representations called layers which contain information on a number of attributes such as elevation, land ownership and use, crop yield and soil nutrient levels.

geometric dilution of precision (GDOP) - an intentional error controlled by the DOD to reduce the accuracy of GPS receivers. This inaccuracy requires the use of differential correction to achieve the level of precision required for the site-specific management.

georeferenced data - geographic/spatial data that identifies a specific location on earth. or Aterm that quantifies the effect of satellite geometry (relative positions of several satellites) on the magnitude of error in a GPS position measurement.

georeferencing - the process of adding geographic data to yield data or other field attributes either in real-time (on-the-go) or by post-processing or the process of associating data points with specific locations on the earth’s surface.

geo-stationary satellite - an orbital path of a satellite that is synchronized with the earth’s orbit or space vehicles in an orbit which keeps them over the same location on the earth at all times.

global positioning system (GPS) - a radionavigation facility which consists of a network of satellites and earth stations that are controlled by the DoD to determine a radio receiver’s position in latitude, longitude and altitude.

GLONASS (GLObal naya NAvigatsionnaya Sputnikovaya Sistema) - the Russian global navigation satellite system.

grid center method - soil sampling method in which samples are taken from the center of a grid cell of a few acres...aka grid point sampling or point sampling.

grid sampling - soil sampling method which divides fields into square units (grids) of a few acres.

ground control points - stationary objects/areas on the earth’s surface that provide georeferenced points in a remote sensing image/aerial photograph.

ground truthing - site based verification of a field investigation that occurs simultaneously with remote sensing.

interpolation - mathematical procedure for estimating unknown values from neighboring known data.

inverse distance weighting - an interpolation method that gives more weight to known data that is near the point of estimation than those that are farther away.

ionosphere - atmospheric layer that exists from 50 to 250 miles above the earth=s surface and contains electrically charged particles.

Kriging - an interpolation method for obtaining stastically unbiased estimates for field attributes (yield, nutrients, elevation) from a set of neighboring points.

L-band - the segment of the radio spectrum that ranges in frequency from 1000 to 20000 megahertz (MHz).

lag - the horizontal distance between two geographic data points. Used to create a semi-variogram.

LANDSAT (LAND SATellite) - a series of U.S. satellites used to study the earth=s surface using remote sensing techniques.

latitude - a global standard coordinate used to identify a position on earth given in degrees, minutes and seconds, indicates the north/south position above/below the equator, positive is in the northern hemisphere and negative is in the southern hemisphere.

land cell - a device that uses strain gauges to convert a force or weight to an electrical signal that can be read directly and/or recorded in a data set.

local average - interpolation method which computes the simple average of known values near the desired location to estimate an unknown value.

local coordinate system - a coordinate system in which the coordinates are referenced to a known location in the immediate area. Two local coordinate systems may not always line up on the same map.

longitude - a global standard coordinate used to identify a position on earth given in degrees, minutes and seconds, indicates the east/west position around the globe from a reference point which overlays Greenwich, England, negative values are east of Greenwich and positive values are west.

NAVSTAR (NAVigation by Satellite Timing And Ranging) - the U.S. based global navigation satellite system that was funded by taxpayers and controlled by the DOD.

PCMCIA card - data collection, storage and retrieval device that is approximately the size of a credit card that is used by most yield monitors.

pixel (picture element) - the smallest unit or area of an image map.

positioning system - general term to identify and record the location of an object on the earth=s surface.

post-processing - method of applying differential correction of GPS data after it has been collected in the field and stored on a microprocessor or PCMCIA card.

potentiometer - a device that changes electrical resistance with the relative position of its components.

precise (P) code - a unique pseudorandom noise code transmitted by each GPS satellite in the system (reserved mainly for military-grade receivers).

precise positioning system (PPS) - military-grade GPS receivers that provide full accuracy (within an inch) with a single mobile receiver (no differential correction needed). AIt includes access to the P-code and the removal of selective availability effects.

precision farming - managing crop production inputs (seed, fertilizer, lime, pesticides, etc.) on a site-specific basis to increase profits, reduce waste and maintain environmental quality.

pseudorange - an estimate of the true distance (range) from a GPS receiver to a satellite. The estimate contains some error due to atmospheric perturbations and the offset between the receivers clock and the satellite clock.

RADAR (RAdio Detection And Ranging) - a method of estimating the distance or travel speed of an object by bouncing high frequency signals off the object and measuring the reflected signal.

raster format - format for storing GIS spatial data in which the data is stored in cells which are addressed by rows and columns of the cells.

real-time correction - correction of a GPS signal by simultaneously transmitting the differential correction information to a mobile receiver.

real-time kinetic (RTK) - procedure whereby carrier-phase corrections are transmitted in real time from a reference receiver to the user’s receiver.

remote sensing - the act of monitoring an object without direct contact between the sensor and object.

RTCM (Radio Technical Commission for Marine Services) - NMEA subcommittee 104 of the RTCM developed standard message formats for GPS signals.

satellite ranging - a method of determining position by measuring distances from several different satellites.

selective availability (SA) - intentional pseudorange error in GPS signals created by the DOD as a measure of national security to prevent Anon-military receivers from obtaining high accuracy position information.

semi-variance - a measure of the difference between two neighboring data points (defined as 1/2 the square of the difference between two values).

semi-variogram - line fit to the data in a plot of semi-variance versus lag.

serial port - computer connector used to communicate to other serial devices such as a modem, the most common of which is an RS-232.

site-specific crop management (SSCM) - the use of yield maps, grid sampling and other precision tools to manage the variability of soil and crop parameters and aid decisions on production inputs.

site-specific yield map - a map that indicates differences in crop yield within a field. Data is usually collected by a yield monitor on a combine over one to three second intervals.

soil map - a map that indicates differences in soil properties (texture, fertility, organic matter, pH, etc.) within a field.

soil texture - the physical structure of a soil determined by the relative amounts of sand, silt and clay.

soil type - a general term used to distinguish between combinations of the primary constituents of a soil, i.e. silty clay loam, fine sand, heavy clay, etc.

space segment - GPS component made up of 24 NAVSTAR satellites that orbit the earth in six paths at an altitude of 10,900 miles.

space vehicle (SV) - GPS or communication satellite.

spatial data - synonymous with geographic data.

spatial resolution - the size of the smallest unit that can be identified by a remote sensing observation.

spatial variability - differences in observed attribute(s) that are noted between locations in a field.

spectral resolution - the ability of sensing system to differentiate between electromagnetic radiation of different wavelengths.

speed sensors - sensors that measure the rotational speed of a shaft or the reflection of radio or sound waves off the ground to determine forward speed.

spherical error probable (SEP) - a measure of accuracy of a three dimensional position estimate produced by a GPS receiver.

standard deviation - a measure of the variation of measurements around their average value, defined as the square root of the sum of squared differences between the average value and all observed values.

standard positioning services (SPS) - the positioning service using a single receiver which is available to any user on a continuous, world-wide basis -- this system uses only the C/A code transmitted via the satellites and the horizontal position accuracy can be degraded by SA.

strain gage - an electronic device whose resistance changes as it is deformed, used in land cells to convert force or weight to an electrical signal.

start of pass delay - a delay that allows the initial flow of grain to be ignored in yield calculations when starting a pass before the full flow of grain is achieved.

state plane coordinates (SPC) - a coordinate system similar to UTM (with units of feet) using the NAD27 datum. Each state may have a different coordinate system in order to minimize distortion.

static random access memory (SRAM) - electronic data storage device that can be randomly accessed, such as PCMCIA card (as opposed to sequentially accessed). Static refers to its ability to retain the data as long as power is supplied to the device either by a battery or a computer.

universal transverse mercator (UTM) - a metric coordinate system commonly used for mapping at scales of 1:50,000 or larger. Satellite imagery is usually supplied in UTM coordinates because it provides georeferencing at high levels of accuracy for the entire grid.

user segment - the position of GPS consisting of receivers used by civilians and the military for determining the position of an object.

variable-rate application (VRA) - adjustment of the amount of crop input such as seed, fertilizer, lime or pesticides to match conditions (yield potential) in a field.

variable-rate technology (VRT) - system of sensors, controllers and agricultural machinery used to perform variable-rate applications of crop production inputs.

vector format - a format for storing and displaying GIS spatial data that is stored as points, lines or areas to create a map object. By using a nearly continuous coordinate system, vector data can be more accurately georeferenced than raster data.

vaporware - description of software/features that is/are not currently available but may never be available.

yield monitor - electronic device that continuously measures and records crop yields and moisture on-the-go.

This list of terminoloy was compiled by Samuel G. McNeill, an Extension Specialist with the
University of Kentucky Princeton Research and Education Center at Princeton, Kentucky.