Application technical GNSS applications for agricultural practices by Guy Blanchard Ikokou, University of Cape Town

Global positioning systems are relatively new technologies when it comes to applications in agriculture. Applications in tractor guidance, variable rate supply of chemical inputs and field monitoring of crop yield were recently tested using GPS. This article studies the basic concepts of GPS as they apply to agricultural production and provides a detailed analysis of the recent developments in this area with a focus on functionality and efficiency.

ver the past 30 years satellites are maintained within 24 information worldwide and provides agricultural machinery has circular orbital planes inclined 55° with support to military, civil and commercial Oreached high technical respect to the equator plane [1]. The applications. standards in order to improve system currently provides two user A total of 24 GLONASS satellites are agriculture production. Precision services: (i) the Standard Positioning actually operational with the latest agriculture or satellite agriculture is a Service (SPS), open to civil users is satellite placed into space on 26 April highly effective farming management available for civil applications such as 2013 with an inclination of 64,8° method that focuses on intra-field agricultural practice and farming, and and an altitude of 19 100 km [3]. variation in order to optimise (ii) the Precision Positioning Service, The system broadcasts two types of agriculture returns while conserving restricted to authorised users such navigation signals: (i) the standard environmental resources. It relies on as the United States military and accuracy signal mainly available to civil new technologies such as the Global their allies. The first GPS accuracy for users worldwide which is generated Positioning System, global navigation civil users was 13 m for horizontal using a 0,511 MHz chipping rate and satellite systems, augmentation positioning and 22 m for vertical (ii) the high accuracy signal restricted systems, and geospatial tools such as positioning [1]. This precision did not to the Russian Ministry of Defence and GNSS receivers. Satellite technology include errors due to atmosphere, multi authorised entities which has a signal and augmentation systems, such as path or user equipment. The ground of 5,11 MHz chipping rate. On 18 May the European Geostationary Navigation network that controls, monitors and 2007, Russian president, Vladimir Putin Overlay Service (EGNOS), have made commands GPS satellites is called the signed a decree reiterating the offer to a major contribution in improving control segment (CS) and comprises provide GLONASS civil signals free of agriculture productivity. Satellite a master control station (MCS), a direct users fees, to the world [2]. The tracking, ploughing monitoring, global set of monitoring stations and GLONASS system comprises a ground harvesting, distribution of fertiliser, ground antennas.This control segment control segment with ten monitoring herbicide and water irrigation are recently went through two important stations distributed through Russia and some of the applications of positioning improvements with the addition of a additional facilities to command and technologies in agriculture to improve number of new monitoring stations, control the satellites. productivity. Tested in several taking the total number of 6 to 14 countries, this practice revealed [2] and the upgrading of the master The European Galileo system important economic and environmental control station completed in 2007 benefits. The Galileo system is the European that transformed the system from navigation system designed for civil and Evolution from GPS system to the IBM mainframe computer system commercial applications. The Galileo global navigation satellite system to a more modern system based system is interoperable with the other upon a distributed Sun Workstation navigation systems. This interoperability The US GPS system. Configuration. attribute offers to all users the benefits The global navigation satellite of more satellite availability for system (GNSS) is the worldwide The Russian GLONASS system redundancy and high accuracy. The satellite constellation, supported Completed about twelve years after constellation of the Galileo system is by several augmentation systems the American GPS system, in October currently four satellites placed in three and user equipment [1]. The GPS 1982, the Russian GLONASS satellite Medium Earth Orbital (MEO) planes satellite system is the first global system was only used by the Russian inclined at 56° to the equator at about navigation satellite system, developed military for years and was only opened 23 000 km altitude. Each plane has one by the United States of America in to civilians in 2007 [3]. Comparable active spare of satellite to cover in case early 1970 [2]. From the 57 GPS to the American Global Positioning of any failed satellite in that plane. The satellites placed in orbit (including System, the Russian navigation system European system offers horizontal and spare satellites in case of failure), is a radio-based vertical measurements within 1 m 31 are currently operational. These system providing location and time precision. The system is supported

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Fig. 2: An illustration of a satellite-based augmentation system. The GNSS signal is received from the satellite by worldwide reference stations that transmit the signal to the master station. The master station corrects the signal before sending it to connection stations.

consists of two separate satellite for entities authorised by the Chinese constellations. The first constellation government such as the Chinese Fig. 1: The ground anatenna receives GNSS signals and transmits the corrections called Beidou1 is a limited test military. The Compass Navigation to GNSS receivers directly or via a system of four satellites that has been Satellite System is a CDMA-based geostationary satellite. operating since 2000.The first satellite, system with DSS signals on four BeiDou-1A, was launched on 30 carrier frequencies: the 1207,14 MHz October 2000, followed by BeiDou-1B frequency shared with Galileo E5b, by two Galileo Control centres, five on 20 December 2000. The third the 1268,52 MHz frequency shared monitoring and control stations and five satellite, BeiDou-1C was put into orbit with Galileo E6, the 1561,098 MHz uplink stations (ULSs) to enable global on 25 May 2003. In February 2007, frequency (E2) and the 1589,742 MHz coverage without interruptions. The the fourth and also the last satellite frequency (E1). The receiver power Galileo Control centres comprise two of BeiDou-1 system, the BeiDou-1D level of Compass navigation satellite separate types of facilities: a ground was launched into space. From 2008 system was reported stronger than the control segment (GCS) and a ground the Chinese government decided to typical received GPS power level [1]. mission segment (GMS). The ground offer the BeiDou1 service to civil users The international cooperation between control segment uses a global network with an accuracy of 10 m. The second China and the European Union with of nominally five tracking, telemetry and constellation called Beidou2 or Compass regards to global navigation satellite control stations to communicate with navigation system is a constellation technologies materialised in October each satellite [1]. The Galileo navigation of seven satellites operating since 2004 with the signing of an agreement system transmits signals in four 2007. In April 2007, the first BeiDou-2 for the Galileo project. China invested frequency bands namely E5a, E5b, E6 satellite called the Compass-M1 was €230-million in the European Galileo and E1. These frequencies interoperate placed into orbit. The second satellite project. By April 2006, eleven with other navigation systems by either Compass-G2 was launched on cooperation projects within the Galileo overlapping or continuous to frequencies 15 April 2009. On 17 January 2010, framework were signed between China used by GPS and GLONASS systems. In the constellation’s third satellite and the European Union. addition, Galileo provides an exceptional Compass-G1 was placed into orbit. On global search and rescue (SAR) function. 2 June 2010, the fourth satellite was GNSS augmentation systems In fact Galileo satellites are equipped successfully put into space. The fifth Augmentation systems are used with a transponder which relays distress satellite was launched into space from to increase the accuracy of the signals from the user's transmitter to Xichang Satellite Launch Centre by basic GNSS signals by transmitting the Rescue Co-ordination Centre, which an LM-3I carrier rocket on 1 August corrections to the GNSS receivers then initiate the rescue operation. At 2010. On 1 November 2010, the sixth either via satellite or terrestrial radio. the same time, the system provides a satellite was sent into orbit by the For instance, instead of a normal GPS signal to the users, informing them that LM-3C carrier rocket. Another satellite, accuracy of 4,5 m, an augmented their situation has been detected and the Compass IGSO-5 satellite, was system can pinpoint this location that help is on the way. This function launched from the Xichang Satellite measure to an accuracy of 0,6 m. is considered a major upgrade in the Launch Centre by a Long March-3A GNSS constellation compared to the carrier rocket on 1 December 2011. Ground-based augmentation systems existing GPS, GLONASS and COMPASS The system also provides low-rate A ground-based augmentation system navigation systems, which do not bidirectional communications and (GBAS) uses radio towers to transmit provide feedback to the users. differential GPS/GLONASS services. corrections to the GNSS receivers. The Compass system offers two There are hundreds of ground-based The Chinese Compass system services to users: An open service augmentation systems around the The Beidou Navigation System is the providing an accuracy of 10 m and world transmitting signals in a wide first Chinese navigation system which an authorised service, only intended variety of frequencies ranging from

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Fig. 3: A semi-automated soil sampler equipped with a GNSS receiver. Each soil sample is associated with its geographical location.

162,5 KHz to 2,95 MHz. In the United States of America, the Nationwide Differential GPS (NDGPS) system is an example of an augmentation Fig. 4: Examples of field traffic patterns that a vehicle equipped system. Ground-based augmentation with GNSS can follow [7]. Each pattern is characterised by an systems receive signals from the allignment of points with known geographical coordinates. GNSS constellation and compare the received values with their accurately surveyed locations and the differences States Wide Area Augmentation agriculture vehicles. Auto guidance are used to calculate corrections of System and the Japanese Multifunction is the guidance of vehicles using the GNSS signals. The corrections are transport Satellite system MTSat. Fig. 2 satellite-based positioning equipment then conveyed either to the GNSS shows an illustration of the concept of a as illustrated in Fig. 3. This technique receivers via geostationary satellites satellite-based augmentation system. reduces skips and overlaps, lower or terrestrial radio. An illustration of a Three other satellite augmentation operator fatigue and enhances the ground based augmentation system is systems are at different stages of ability to work in poor visibility shown in Fig. 1. construction including the Nigerian conditions. Communication Satellite (NIGCOMSAT), An important feature of GNSS is the Satellite-based augmentation systems the Chinese Satellite Navigation ability to accurately follow particular A Satellite-based augmentation system Augmentation System (SNAS) and traffic patterns and provide effective provides differential corrections, the Indian GPS/GLONASS and GEO feedback so that the operator or integrity parameters and ionospheric augmented Navigation (GAGAN) auto-steer system can appropriately data over a given region. This system (Groves, 2008). respond. Most systems can effectively consists of a ground network of perform straight-line patterns (linear monitoring stations that collect GNSS Applications of GNSS in swathing), and many can follow measurements. The receivers in the agriculture. contours and other field features as ground network for the case of the US Decision making is an important step illustrated in Fig. 4. GPS system are capable of tracking in the management of agricultural the GPS L1 and L2 C/A and L2 P(Y) production. GNSS can be a useful Management of crop health code signals in order to determine the support system for tactical decision Remote sensing devices are devices electron content of the ionosphere making to enable the farmer to that are able to collect data from integrated along the signal path from evaluate a multitude of different distances. This is achived by light the visible satellites. Semi codeless scenarios based on all the variables reflectance collected by instruments processing techniques are used to track influencing his agricultural activities in airplanes, orbiting satellites or the encrypted P(Y) code signals [4]. [5]. The use of yield sensors developed Some satellite based-augmentation from the new technologies, combined hand-held devices. Remotely sensed systems ground networks are capable with GNSS receivers, has been gaining data provide a valuable tool for of monitoring GPS and GLONASS ground ever since [6]. This practice evaluating crop health. Overhead L1 signals. Error corrections and allows, for example, farmers to vary images are useful to detect plant integrity data are then computed by the rate of fertilisers across the field stress related to moisture, nutrients a centralised facility. This information according to the need identified on as well as crop disease. The real time is then broadcast to the end users GNSS guided maps. information provided by these sensors through a geostationary satellite link. is valuable for making management Only three satellite augmentation Agricultural vehicles guidance decisions in order to improve systems are actually operational: The In addition to location based agriculture profits. Fig. 5 shows an European Geostationary Navigation information, GNSS technologies example of an affected area on an Overlay Service (EGNOS), the United make possible the auto guidance of image provided by GNSS satellites.

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Fig. 5: A satellite image showing an agriculture sub-field affected by either crop disease or soil poor fertility. The knowledge of the exact location of the problem enables the farmer to apply an appropriate Fig. 6: A mobile sensor platform collecting soil samples in order to targeted solution. study the acidity levels of the agricultural field [8].

Fertilisers and soil management (MSP) with mounted GNSS receiver example, one would plant fewer Global navigation satellite systems to study soil pH, as illustrated in seeds in sandy soil than in silt loam can be used to determine in which Fig. 6, can enable the identification soils areas because of less available precise part of an agricultural field of field areas with acidic soils. The moisture [8]. Since soils vary even a tractor has collected soil samples measurements collected can be used across an individual agricultural field, the ability to change seeding rates as for fertility analysis. Resulting to evaluate the amount of fertiliser one goes across the field allows the information about the variability of needed to raise the soil pH to a farmer to maximise this seeding rate soil fertility within a field is essential suitable level for a specific type of according to the soil conditions. for decision support. Soil information crops. The mounted GNSS receiver can be obtained by physically can also provide elevation data of the Benefits of satellite agriculture obtaining samples throughout fields area and enable the identification of Traditional sampling techniques such and analysing these samples at a field areas with spatially variable soil laboratory or through the use of water-holding capacity. as whole-field sampling to assess the on-the-go-soil sensors mounted In addition, maps of soil mechanical fertility levels have shown limits on a tractor [8]. The application resistance can expose field areas as they do not always guarantee of chemicals and fertilisers in not potentially appropriate for crop a perfect representation of fertility appropriate proportions is of economic growth [8]. Both soil compaction and variation across the field [8]. In and environmental concern to the low moisture content theoretically contrast, regularly-spaced grid farmers as a consequence, results cause high soil strength. Using precise soil sampling provides data that of soil analysis in combination with location information associated with better characterises the variability information about the agricultural different soil types would lead to of soil fertility. The technique has returns can form the foundation higher yields as a consequence of shown promising results in terms for planning future fertilisers better management of agriculture of reduction of pollution from resources, involving low production management for specific types of agricultural chemicals [8]. This is cost. Fig. 7 illustrates a prototype crops. Using a GNSS positioning possible by linking each fertility zone integrated soil physical properties receiver along with crop health to respective geographical location to mapping system used to study soil information identified on satellite facilitate application of fertilisers more resistance. imagery, a farmer is able to apply efficiently as illustrated in Fig. 8. pesticides in a safer manner. In Effective seed management On-the-go agricultural mapping, fact, the spraying equipment can be Certain agricultural seeds perform semi-automated agricultural vehicle pre-programmed to automatically turn best when placed at spacing that guidance have revealed great economic off when it reaches a certain location allows the plants to benefit at benefits around the world. In Texas on the agricultural field. Additionally, maximum from the sunlight and soil for example, the technique resulted farmers can pre-program the rate of moisture. A computerised soil map in higher cotton yields and higher fertilisers to be applied at specific of a field on a computer fitted on the net returns compared to traditional locations of the field so that only the tractor along with a GNSS receivers agricultural methods. Moreover, the amount determined by the soil studies can inform farmers where they are application of GNSS in agricultural is applied at a variable rate from one in the field, allowing the adjustment practice has resulted in a better area to the other. This saves money of seeding according to suitable management of pesticides and higher and allows for safer use of farming spacing. Combining positional data cotton yields in Georgia, United resources and minimises environment with soil texture, organic matter, and States of America. In Colorado, the pollution. soil moisture information can enable technique led to better management of More over, the use of technologies the farmer to vary the seeding rate nitrogen in corn agriculture compared such as the Mobil Sensor Platform according to the soil condition. For to traditional practice. In Nebraska,

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Fig. 8: An illustration of a fertility map serving as a decision support for the application of targeted soil fertilisation.

Fig. 7: A prototype integrated soil physical properties mapping system (ISPPMS).The instrument analyses soil structure and identifies suitable areas for agriculture practice that can be mapped using GNSS receivers.

studies during 2004 – 2005 by the University of Nebraska showed savings in production cost of US$9,54 per acre when integrating GNSS in agriculture compared to traditional methods. With improvement in the quality of positioning technologies the saving increased up to US$26,38 per acre Fig. 9: Comparison of soil pH maps obtained from the on-the-go when the study was repeated in 2008. mapping using a GNSS receiver and the traditional 2,5 acre grid Similarly, the integration of positioning sampling technique. Mapping using a GNSS receiver on the right, shows a better delineation of soil pH distribution [8]. technologies in agriculture results in more accurate soil pH mapping [8]. Tested on a Kansas agricultural field, the agriculture practice and provided risks because it enables the study approach produced a very accurate pH an analysis of some of the recent of soil resistance and moisture that map compared to the conventional 2,5 developments in this area with a focus can reveal areas with high risk of soil acre grid sampling technique. In fact on functionality and efficiency. The the traditional 2,5 acre grid sampling erosion. Precision agriculture also produced inaccurate mapping results use of GNSS in agriculture enables enables a more reasonable use of water in which some areas with neutral a more effective use of agricultural resources as irrigation farming is the and acid pH could not accurately be resources including crops, pesticides, largest consumer of water resources geographically located as illustrated in fertilisers, irrigation water as well as worldwide. Concentrating on efficient Fig. 9. a good management of soil through use of water for agricultural purposes tillage and soil fertility analysis. More A study of the benefits of integrating is very important. Precision agriculture effective use of agricultural resources GNSS technologies in agriculture enables farmers to reduce their means greater crop return while undertaken by Bowman [9], revealed consumption of water by identifying minimising environmental impacts a 68% increase in farm gross areas in agricultural fields characterised of chemicals. Precision agriculture margins resulting from a better by high soil moisture that would need management of agriculture resources, addresses economic and environmental less irrigation water. In Australia, 67% reduction in farm labour costs issues that affect agriculture practice precision agriculture has reduced as a consequence of automation of today. The technique increases the carbon emission in recent years [11]. agriculture vehicles guidance, 90% economic margins of crop production Precision agriculture enables farmers to reduction in soil erosion caused by by improving yield and reducing input identify problems in their fields that are agriculture practice, 93% reduction costs [10]. The integration of GNSS difficult to identify by using traditional in nitrogen loss through runoff and technologies in agricultural practice methods. reduces manpower and as a result 52% reduction in CO2 emissions, in comparison to traditional techniques enhances productivity due to automatic References agriculture vehicle guidance. Application employed in previous years. [1] C Hegarty and E Chatre: “Evolution of of GNSS in agriculture enables targeted the GNSS,” Proc. IEEE, vol. 96, no. 12, Conclusion application of fertilisers and pesticides pp. 1902 – 1917, Dec, 2008. This article presented the basic reducing the risks of pollution from [2] B Parkinson and S Gilbert: Bnavstar: concepts of global navigation agro-chemicals [10]. Moreover, “Global positioning system -Ten years satellite systems as they apply to precision agriculture reduces erosion later”,[ Proc. IEEE, Oct.1983.

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[3] SG Revnivykh: “Glonass Status, [6] N Zhang, M Wang, and N Wang: Traffic Farming”, Proc. 6th Australian Development and Application”, “Precision agriculture-a worldwide Controlled Traffic Farming Conference, International Committee on Global review. Computers & Electronics in dubbo, NSW. P.61-69. ACTFA., 2008. Navigation Satellite System (ICG) Agriculture 36, 113–132, 2002 [10] RJ Godwin, TE Richards, GA Wood, JP Second meeting , Bangalore, India. [7] R Grisso, M Alley and G Groover: Welsh, SK Knight: An economic analysis September 4 – 7, 2007 “Precision Farming Tools: GPS of the potential for precision farming [4] KT Woo: ”Optimum semi codeless Navigation”, Virginia Cooperative in UK cerealproduction. Bio systems processing of GPS L2”, Navigation: J. Extension, Publication 441-501, 2009. Engineering (SpecialIssue on Precision Agriculture), 84(4), 2003. Inst. Navig., vol. 47, no. 2, pp. 82 – [8] VI Adamchuk, JW, Hummel, MT Morgan 99, summer, 2000 and SK Upadhyaya: “On-the-go soil [11] C Helm: “Precision farming in South Africa. In: Farm Tech. Proceedings. p. 76 [5] J Hendriks: “An analysis of precision sensors for precision agriculture”, – 80, 2005. agriculture in the South African Computers and Electronics in Agriculture Summer grain producing areas”. 44, 71–91.2004. Contact Guy Blanchard Ikokou, Masters thesis, North West University, [9] K Bowman:”Economic and Environmental University of Cape Town, South Africa.2011 Analysis of Converting to Controlled [email protected]

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