Use of Unmanned Aircraft for Applying Crop Protection Chemicals

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1 Tarım Makinaları Bilimi Dergisi (Journal of Agricultural Machinery Science) 2014, 10 (2), Use of Unmanned Aircraft for Applying Crop Protection Chemicals Durham K. GILES, Ryan BILLING Department of Biological and Agricultural Engineering, University of California, Davis, CA UNITED STATES Received (Geliş Tarihi): Accepted (Kabul Tarihi): Abstract: The objective of this study was to deploy and evaluate the suitability and performance of unmanned, remotely-piloted aerial vehicles for applying crop input materials to specialty crops such as vineyards and nut orchards. A small, commercially-produced helicopter was used to spray grapes in a commercial production area in Northern California, USA. Depending on the spray method deployed, specifically, the swath width used and the flight pattern in the vineyard, the unmanned aircraft-based spray application could achieve 2.0 to 4.5 ha/hr work rates while applying volume rates of 14.0 to 39.0 l/ha. Spray deposition was comparable to that from conventional manned aircraft. Key words: Unmanned aerial systems, UAS, spray deposition, grape, specialty crop, helicopter, remote control, precision agriculture INTRODUCTION Unmanned aircraft systems (UAS), which include unmanned aerial vehicles (UAV s), are aircraft that are operated remotely either by telemetry, where the operator maintains visual contact with the aircraft or autonomously along preprogrammed paths using GPS and inertial guidance. The initial uses in agriculture have been for remote sensing, primarily visual inspection of crop conditions, soil and field areas and for monitoring assets such as machinery, workers or crop products. UAS technology has utility in agriculture, forestry and vector control for not only observation and sensing but also for application of agrochemicals. The application of crop inputs such as fertilizers and pesticides by UAV s presents an engineering design challenge different from their use as an inspection platform. The payload and power demands from a spraying or granular applicator are significantly greater than those of low-mass, low-power cameras or sensors. Increases in the payload mass that can be carried on-board and dispensed leads to increased flight endurance and improved economic return from use of the technology. Previous work has addressed the design of agricultural spray systems for small UAV s (Huang, et al., 2009) including specialized electrostatic rotary atomizers (Ru et al., 2011). In these works, the requirement for low volume application, in consideration of limited payload capacity, was emphasized. Other work has investigated the use of multiple UAV s flying in coordinated fleets for spray application (Zhigang, et al, 2013) and the development of on-board monitoring systems to aid the ground-based operator s situational awareness of the UAV s status (Sugiura et al., 2005). The potential ease of deployment, reduction in operator exposure to chemicals and the improved ability to apply chemicals in a timely and highly spatially resolved manner make UAS spray application an attractive endeavor from a technical viewpoint. However, there are concerns and limitations due to flight and chemical safety, potential environmental contamination, vehicle cost, flight endurance, payload constraints and regulatory treatment by aviation and agrochemical agencies. In order to analyze the technical and economic feasibility of UAV deployment in agricultural spray applications, it is necessary to have spray deposition, vehicle suitability and work rate data (Giles and Billing, 2014). This project addressed the initial assessment of a small (100 kg) 139

2 Use of Unmanned Aircraft for Applying Crop Protection Chemicals UAV for spray applications in specialty crops (vineyards and orchards) in California. A commercial UAV was used to spray crops and the work rate and spray deposition measured for a number of spray techniques and spray volume application rates. The objectives of this work were to: 1) deploy an unmanned aerial vehicle for spraying a semicommercial scale vineyard; 2) develop, within the payload and range limitations of the UAV, a series of spray techniques to apply a range of liquid volume rates; and, 3) assess the resulting spray deposition and work rate of the UAV spray application. qualified, tested pilots for manned aircraft and also hold an FAA Class II Medical Certificate. Flights were limited to a radius of 1.8 from an established vineyard test site ( N, W) and all flights were limited to areas greater than 9.1 km from any airports; operations were limited to daylight hours and in Visual Flight Rules (VFR) conditions. All flights were conducted in Class G airspace, as defined by the International Civil Aviation Organization (ICAO). MATERIALS and METHOD The UAS used in this project was a commercial UAV and associated ground control station. The aircraft was a gasoline-powered helicopter (RMAX, Yamaha Motor Co. USA, Cypress, CA USA) developed for spraying of rice in Japan (Figure 1). The primary characteristics of the aircraft are: Vehicle mass = 100 kg; Rotor diameter = 3.1 m; vehicle length = 3.6 m and vehicle height = 1.1 m. The aircraft power plant is a two-stroke, 250 cm 3 displacement, liquid cooled, 13.6 kw engine. Control of the aircraft is through a radio linked, 60 mw, dual joystick handheld transmitter operating in the 72 MHz band. The model used in this project did not have provisions for autonomous operation; operation of the aircraft was limited to a 400 m line-of-sight range. The manufacturer s operational requirements and the U.S. Federal Aviation Administration specified that all operations be conducted with an observer positioned to monitor the location and movement of the aircraft at all times. Therefore, both the operator and the observer maintained visual contact with the aircraft during all testing. The flights and testing of the UAV were conducted under a Certificate of Authorization or Wavier (COA) issued by the United States Federal Aviation Administration (FAA). Currently, there are no provisions for legal commercial flights of UAV s in the United States. COA s are also issued for research and development use; the COA for this project was issued to the University of California for agricultural spraying. The terms of each COA specify and limit the aircraft that can be flown, the geographic areas in which the aircraft can operate and the conditions under which the aircraft could be operated. Current rules on COA s also require that the pilot and the observer be Figure 1. The remotely-piloted aircraft used in the field testing project. The COA under which this research was conducted stipulated that no active chemical or tracer could be discharged from the aircraft; only water could be used as a test fluid. Therefore, the only method available for measurement of spray deposition was the use of water sensitive paper (provided by Spraying Systems Co., Wheaton, IL USA and produced by Ciba Geigy, Basel, CH). While water sensitive paper has limited sensitivity and linearity for deposit measurement;for this research application, given the limitations of the COA, it was an acceptable method for spray deposition assessment. Before spraying, water sensitive paper cards were positioned on grapes leaves and affixed to the vines in vertical and horizontal planes at thirteen sample locations throughout the canopy. After spraying cards were reclaimed and saved in sealed plastic bags. Cards were analyzed optically for spray deposition using DropVision AG (Leading Edge Associates, Waynesville, NC USA). Spray testing was conducted under dormant conditions (November), mid season (May) and late 140

3 Durham K. GILES, Ryan BILLING season (August) conditions. However, due to an industry-standard canopy thinning programs, there was little difference in the actual canopy from the mid-season to late season testing. Results presented in this paper are limited to the May mid-season spray. The overall spray deposition results were pooled for all sample locations. The spray system on the aircraft consisted of an electrically-powered diaphragm pump supplying liquid to two flat fan nozzles (TeeJet XR11002) at a flow rate of 1.3 to 2 l min -1. The nozzle and pressure combination produced droplets in the fine to mediumfine category. The spray tanks were two (side saddle mounted) detachable tanks of 8 l capacity. The primary test area for spray deposition and performance assessment was a 0.61 ha block of Cabernet Sauvignon vine grapes located at the University of California Oakville Field Station in Napa County, CA USA. The block was configured as rows 61 m long with a spacing of 2.4 m; there were 42 rows in the block. To determine the spray application rate (in l ha -1 ) and the sprayer productivity or work rate (in ha hr -1 ), the aircraft was deployed to spray the test field in a typical manner that would be used to treat the field commercially. During the spray process, the time and motion of the aircraft was monitored and recorded by visual monitoring and through on-board two video cameras with time stamped records. The time spent spraying each pass, repositioning the aircraft at the end of each pass, ferrying the aircraft from the loading site to the test field and the time spent refilling the aircraft were all recorded. During the spray tests, the water sensitive paper was positioned in the test block. The refilling site was approximately 50 m from the corner of the test block. Refilling of the aircraft was done by filling the spray tanks. The tanks provide a quick connect and refilling option; in commercial deployment, a back-up set of tanks could be used to speed reloading. Application height above the top of the vines was approximately 3 m; during ferrying for refill over the test field, the aircraft was flown at 5-6 m above the vines. The standard flight pattern, as specified by the manufacturer and used by the operator in this test, was for the operator to be positioned at one end of the field and fly the aircraft down the rows, away from the operator, while observing the alignment of the aircraft over the centreline of the swath. At the end of the row, the operator would move the aircraft perpendicularly to the length of the rows and reposition the aircraft at the centreline of the next pass. The operator would then fly the aircraft backward, toward the operator, and spray the next pass as the aircraft returned. The observer, in radio contact with the operator, would inform the operator as the aircraft approached and reached the end of the row. During all application, the aircraft was headed away from the operator; this maintained a constant orientation which aided remote control ability. Ground speed control was achieved through operator experience and was supplemented by a warning light if aircraft speed exceeded a setpoint. Future deployments of the aircraft will likely include autonomous flight operation so that demands for operator skill can be reduced. For this initial testing, no modifications to the liquid handling and spraying system were permitted; the sprayer was required to be operated in one standard configuration with constant flowrate. Similarly, the ground speed was desired to remain constant at km/hr. Therefore the only method by which the application rate (l ha -1 ) could be changed was to adjust the effective swath width, that is, the distance between parallel passes down the rows and the number of times each swath was sprayed. Four spray flight patterns, producing a range of application rates were tested. The flight patterns tested were: a) one pass covering two grape rows for an effective swath width of 4.8 m; b) two passes, that is, spraying down and back over the same 4.8 m swath; c) one pass covering three grape rows for an effective swath width of 7.2 m; and, d) two passes, that is, spraying down and back over the same 7.2 m swath. RESULTS and DISCUSSION The most basic observed result was the actual achieved application rate from the aircraft using the four spray patterns. The application rate was determined directly by volumetrically measuring the actual liquid discharged from the aircraft while the spraying the known land area of the test vineyard. The results are shown in Table

4 Use of Unmanned Aircraft for Applying Crop Protection Chemicals Table 1. Achieved spray application rates for flight patterns in test vineyard. Resulting application rate (l ha -1 ) 2 (4.8) (4.8) (7.2) (7.2) As expected, spray work rate, or productivity, decreased as application rate increased, due to more time spent flying the aircraft within the field and more time spent ferrying and refilling the aircraft. During testing, over the 0.61 ha field, 1-2 spray loads were required. The achieved work rates, for the four flight patterns, are shown in Table 2. Table 2. Achieved spray application work rates for flight patterns in test vineyard. Resulting work rate (ha hr -1 ) Table 3. Achieved spray deposition rates on water sensitive paper for flight patterns in test vineyard. Resulting deposition rate (l ha -1 ) average and std dev 2 (4.8) (34.89) 2 (4.8) (10.66) 3 (7.2) ( 18.57) 3 (7.2) (1.77) The results can also be expressed in more useful manner in which the resulting spray deposition is shown in relation to the achieved work rate (Figure 2). In this manner, a potential user of the aircraft could, based on experience or knowledge of requisite spray deposition rates for effective pest control, determine the optimal flight patterns to achieve the needed deposition and the greatest work rate. It is notable to observe the almost linear trend between reduced spray deposition rate and increased operational work rate. 2 (4.8) (4.8) (7.2) (7.2) Spray deposition was expressed as l ha -1 based on the optical scanning of the water sensitive paper and all located within the vineyard were pooled and averaged. The achieved deposition rates, for the four flight patterns, are shown in Table 3. There was, as is often the case in field spray deposition measurements, significant variability in the spray deposit observed. However, the visual assessment of the cards in the field before removal revealed no apparent consistent trends in the variability, that is, no recurring areas of lower or higher deposition. The turbulent rotorwash of the aircraft appeared to well mix the spray; nonetheless, individual cards showed variability from location to location and replication to replication. Figure 2. Relationship between field work rate, i.e., productivity, and resulting spray deposition. CONCLUSIONS The experimental results observed and presented in this paper support the following conclusions: 1) Unmanned aircraft systems can be successfully deployed in specialty crop spraying conditions. 2) Spray application rates on the order of 10 to 40 l ha -1 can be achieved through manipulation of the flight patterns and effective swath width. 3) Effective spray work rates of 2-5 ha hr -1 can be achieved, even considering the limited payload and range of the aircraft. 142

5 Durham K. GILES, Ryan BILLING 4) Spray deposition rates of 10 to 40 l ha -1 can be achieved; however significant variability in deposition can be present. 5) Operator skill is required for unmanned aircraft spraying; however, use of on-board vehicle stabilization systems and aided by autonomous operation, can reduce operator work load and required skill. The results from this study provide an initial insight into the potential commercial deployment of unmanned vehicles for specialty crop spraying in a high value crop environment. Spray application rates and resulting deposition rates were comparable to those typically observed in manned aerial spraying. Sprayer work rates achieved were in excess of those typical with ground-based vehicle spraying in grape production. Therefore, in the tested conditions, UAV spraying could provide hybrid performance that includes beneficial aspects of both manned aerial spraying (high work rates) and ground-based spraying (ease of deployment). ACKNOWLEDGEMENTS This work was supported by Yamaha Motor Company USA of Cypress, CA USA and the Agricultural Experiment Station, University of California, Davis, CA. Appreciation is expressed to Steve Pearson of Spraying Systems for the donation of water sensitive paper, Bill Reynolds of Leading Edge Associates for use of Drop Vision AG and to Mike Anderson of the Oakville Field Station. REFERENCES Giles, D.K., R. Billing Unmanned Aerial Platforms for Spraying: Deployment and Performance. Aspects of Applied Biology, 122: Huang Y., W.C. Hoffmann, Y. Lan, W. Wu, B.K. Fritz, Development of a Spray System for an Unmanned Aerial Vehicle Platform. Applied Engineering in Agriculture, 25: Ru Y., H. Zhou, Q. Fan, X. Wu, Design and Investigation of Ultra-low Volume Centrifugal Spraying System on Aerial Plant Protection. Paper No , american Society of Agricultural and Biological Engineers. Presented at Louisville, KY USA. Sugiura R, K. Ishii, N. Noguchi Development of Monitoring System to Support Operations of an Unmanned Helicopter. Paper No , American Society of Agricultural and Biological Engineers. Presented at Tampa, FL USA. Wang Z, Y. Lan, W. C. Hoffmann, Y. Wang, Y. Zheng, Low Altitude and Multiple Helicopter Formation in Precision Agriculture. Paper No , American Society of Agricultural and Biological Engineers. Presented at Kansas City, MO, USA. 143