Paul D. Ayers

Environmental damage from tracked vehicle operation

Abstract Soil surface forces resulting from traffic tracked vehicles can cause environmental damage by decreasing plant development and increasing erosion. This paper investigates the soil surface disturbance from tracked vehicle operation. Sharp turns (lower turning radius) from M113 operation produce increased disturbed widths and more severe vegetation damage. The pad-load ratio for the M113 track shoe was determined at various loads. The soil rut produced from tracked vehicle operation was determined at various driving models (straight, smooth turn, sharp turn). The width and depth of track rut and height of soil piled increased when the tracked vehicle negotiated a sharp turn. The results of this study indicate for the soil conditions tested, the width of disturbance is dependent on the operating characteristics of the vehicle. A vehicle conducting sharp turns will disturb a larger width of soil than a vehicle travelling straight or conducting smooth turns.

INTEGRATING GIS AND GPS INTO A SPATIALLY VARIABLE RATE HERBICIDE APPLICATION SYSTEM

A spatially variable rate herbicide application system was developed and a site-specific evaluation of its field performance and accuracy was conducted. A 4.2-ha (10.4-ac) field was sampled on an 18.3-m (60-ft) grid for soil type and organic matter percent (OM%). A herbicide management table was used to determine the appropriate active ingredient (AI) application rate for each area of the field depending on spatial variation of field parameter data (soil type and OM%). Application rate of AI varied from 3510 mL/ha (1.5 qt/ac) up to 5260 mL/ha (2.25 qt/ac). Using geographical information system (GIS) software, a georeferenced map (management map) of field application rates was produced. A direct nozzle injection field sprayer was equipped with a real-time differentially corrected global positioning system (DGPS). A program was developed to receive on-the-go the sprayer position data (latitude and longitude) and retrieve the desired application rate from the GIS map at the current sprayer field position. A datalogger was used to change on-the-go the AI flow rate (water was used as a substitute for the AI) to correspond with the desired application rate at a specific sprayer ground speed and field position. To evaluate the system accuracy in reproducing the management map, data was collected from the DGPS to determine its field accuracy. DGPS data and datalogger output (data produced by sprayer monitoring sensors) along with the GIS map were utilized to reveal the spatial accuracy of the application system. Control system reaction time and accuracy were investigated using data from the datalogger program output. Results revealed that the DGPS maintained an accuracy of at least 1 m (3.3 ft). Spatial analysis showed that the application system reproduced the application rate management map. On the average, the greatest reaction time of the control system was 2.2 s. For the four application rates used in the study, the highest average application rate error was 2.0%.

Perspectives on delineating management zones for variable rate irrigation

Up to 40% of soil available water content variance was explained by pie shape zoning.Dynamic zoning strategy may be needed if soil spatial arrangement varies by depth.Soil ECa and satellite images were useful attributes for irrigation zone delineation. This study aimed at investigating the performance of multiple irrigation zoning scenarios on a 73ha irrigated field located in west Tennessee along the Mississippi river. Different clustering methods, including k-means, ISODATA and Gaussian Mixture, were selected. In addition, a new zoning method, based on integer linear programming, was designed and evaluated for center pivot irrigation systems with limited speed control capability. The soil available water content was used as the main attribute for zoning while soil apparent electrical conductivity (ECa), space-borne satellite images and yield data were required as ancillary data. A good agreement was observed among delineated zones by different clustering methods. The new zoning method explained up to 40% of available water content variance underneath center pivot irrigation systems. The ECa achieved the highest Kappa coefficient (=0.79) among ancillary attributes, hence exhibited a considerable potential for irrigation zoning.

Evaluation and Refinement of the Nitrogen Reflectance Index (NRI) for Site-Specific Fertilizer Management

Environmental and economic concerns have collectively created a demand for more efficient agricultural fertilizer application. Remote sensing of plant parameters has recently shown the potential to improve fertilizer application efficiency by showing corn (Zea mays L.) producers when and where to apply fertilizers based on crop needs. Previous studies have indicated that a normalized near-infrared over green (nir/green) waveband reflectance ratio, called the Nitrogen Reflectance Index (NRI), could be used to assess in-season corn N status (CNS) in small plots. This study evaluated the NRI using small plot data and then tested possible index improvements in a larger area. Data from four small plot site years indicated that the NRI explained > 70% of the variability occurring with in-season CNS for canopies with Leaf Area Index (LAI) ³ 2. These results led to the development of an early-season feasibility indicator (ESFI) – a non-invasive method of assessing LAI. This created a simplistic guideline for appropriate use of the NRI based on minimum ground-cover. The ESFI, calculated by subtracting the green and red reflectance, utilized a minimum threshold level of 0.01 to remove measurements where LAI < 2. Another proposed improvement to the NRI illustrated that the cumulative density function of the nir/green ratio could be used to develop N variability maps and improve fertilizer management. Further testing within a 22.5 ha area was used to determine platform compatibility and performance comparisons of the NRI versus other indices. After filtering with the ESFI, results showed strong compatibility between aerial imagery and ground-based radiometer measurements. Comparing the NRI to the NDVI, Green NDVI, SAVI, and MSAVI showed that all of these indices accurately assessed N variability based on total N uptake measurements collected.

Off-road Vehicle Rollover and Field Testing of Stability Index

Off-road vehicles are often operated in unstable situations and on rough terrain where operators may be subjected to high-risk conditions. Tractor stability and the reduction of injuries related to tractor rollovers are areas that need to be addressed. This article presents typical tractor rollover tests and analyzes tractor stability in terms of the stability index developed by authors. Three radio-controlled tractors were used to complete the tests. Tractors? dynamic state variables, such as roll and pitch angles, roll and pitch velocities, and ground speed, were recorded by the measuring system of tractor stability developed by authors, concurrently the image from videotape was used to identify the stability status of the tractors. The effect of velocity, ramp height, slope, and turning radius on tractor stability was studied. Rotation velocities can also significantly contribute to tractor rollover. The results indicate the validity of the stability index model. Language: en

A Physics-Based Vehicle/Terrain Interaction Model for Soft Soil Off- Road Vehicle Simulations

In the context of off-road vehicle simulations, deformable terrain models mostly fall into three categories: simple visualization of an assumed terrain deformation, use of empirical relationships for the deformation, or finite/discrete element approaches for the terrain. A real-time vehicle dynamics simulation with a physics-based tire model (brush, beam-based or Finite Element models) requires a terrain model that accurately reflects the deformation and response of the soil to all possible inputs of the tire in order to correctly simulate the response of the vehicle. The real-time requirement makes complex finite/discrete element approaches unfeasible, and the use of a ring or beam -based tire model excludes purely empirical terrain models. We present the development of a three-dimensional vehicle/terrain interaction model which is comprised of a tire and deformable terrain model to be used with a real-time vehicle dynamics simulator. The governing equations of both models are physics-based, rather than utilizing popular terramechanics models that are empirical. The tire draws on a lumped-mass model based on a radial spring-damper-mass distribution. The terrain model utilizes Boussinesq and Cerruti soil mechanics equations to determine the pressure distribution and deformation of a volume of soil as a function of normal and tangent forces applied at the soil surface by the tire. The soil volume that describes the terrain is discretized as a set of vertical columns of soil, and the deformation of each is modeled using visco-elasto-plastic compressibility relationships that relate subsoil pressures to a change in bulk density of the soil, which in turn produces soil displacements. Different loading combinations applied by a tire passing over a column of soil will be reflected in the state of each volume of soil contained in the column, rather than treating the column of soil as homogeneous in the vertical direction and only associating one set of parameters with the entire column, e.g. a Bekker type model. Furthermore, the time-dependent elastic and plastic response of the soil to repetitive compression/rebound tire loads is also taken into account. Horizontal soil force/displacement produced by tractive and turning forces will also be incorporated into the model. Both the vertical and horizontal force/displacement relationships allow the calculation of total energy and power required to deform the terrain. These physics-based models will be integrated into a real-time vehicle dynamics simulator and is anticipated to lead to a realistic vehicle dynamic response when driving on off-road, deformable terrain conditions, especially when repeated loading occurs or non-homogeneous soil conditions are present. Additionally, the changes in soil states can be used to directly compute the energy and power required to deform the terrain. In order to retain the ability to run real-time simulations, a GPU-accelerated approach is considered to leverage the inherently parallel nature of performing multiple independent terrain geometry queries and soil-mechanics calculations. Numerical experiments include a single soil volume node under a known load and a simplified tire model applying normal forces on the surface of the terrain. Results are given for the vertical plastic soil deformation, and for the power and energy required to perform the deformations.

Evaluation of Deposition and Application Accuracy of A Pulse Width Modulation Variable Rate Field Sprayer

Due to over applications of agricultural chemicals, concerns of chemical costs and environmental contamination continue to increase. From these concerns, there has been a great deal of devotion to the development of accurate variable rate technologies to increase spraying efficiency. The type of variable rate technology that is discussed in this paper is pulse width modulation. This is a technology that controls the length of a nozzle valve pulse duration (i.e., pulse width) used on field sprayers. This paper discusses the performance of this technology and its effectiveness on weed control from herbicide applications. Performance analysis of the sprayer technology indicated that nozzle flow rate variation along the boom was acceptable with a coefficient of variation less than 2%. Changes in nozzle flow rate were approximately proportional to the duty cycle setting with an average error of 4% from the theoretical. In addition, the spray pattern uniformity along the length of the boom was tested at various duty cycle settings. A desirable spray pattern was found with a coefficient of variation less than 10%. This suggests that intermittent spray clouds had no effect on spray pattern along the boom. Although nozzle pulsing had no effect on the spray pattern along the boom, uniformity of spray pattern in the direction of travel was studied. It was found that the coefficient of variation varied from 65% to less than 10% at duty cycle settings ranging from 25% to 100%. Due to this large variation in spray pattern along the direction of travel, an efficacy evaluation of post and pre-emergence herbicide application were performed using pigweed as the indicator species. The weed control varied from 65% to 100% at duty cycle settings of 25% to 100% for the postemergence herbicide application. Weed control for pre-emergence herbicide application was found to be nearly 100% for all duty cycle settings. This shows that the longitudinal uniformity at certain low pulse widths have an effect on resulting weed control from postemergence herbicide applications; however, it has little to no effect on weed control from pre-emergence herbicide applications.

Application of a Tractor Stability Index for Protective Structure Deployment

The reduction of injuries related to tractor rollovers is important to the agricultural industry. ROPS (Roll-Over Protective Structures) and seat belts have been installed on many tractors, though many are still without this protective equipment. The existing hazard of tractor rollover is still impacting operators and encourages scientists to develop more effective control technologies and protective equipment. The purpose of this article is to present the application of a stability index model for the rapid deployment of protective structures during a field upset. A preliminary deployment model was developed, and mainly consists of a measuring system of a stability index, a deployment strategy, and simulated control actuation. Results generated during upset tests of radio-controlled full-size tractors, equipped with a measuring system and deployment model, are presented. Video technology was used to validate the operation of the preliminary deployment model.

Monitoring Controller-based Field Sprayer Performance

This study investigated the performance and accuracy of a ground-driven boom sprayer in applying liquids when operated with and without an electronic sprayer control system. The sprayer was instrumented to monitor ground speed, boom flow rate, and nozzle pressure. Also, the sprayer was equipped with a pressure-based sprayer control system. Using a data acquisition system, flow rate, and ground speed measurements were acquired and utilized to determine errors in application rates.

INFLUENCE OF TRAVEL DIRECTION ON GPS ACCURACY FOR VEHICLE TRACKING

The influence of travel direction on GPS dynamic accuracy for vehicle tracking is discussed in two sections. The first section investigates the influence of travel direction on GPS accuracy due to the GPS satellite sky distribution. GPS dilution of precision (DOP) was calculated based on GPS satellite geometry at a variety of locations and different mask angle settings. Results show a significant difference between north DOP and east DOP in a mid-latitude area. A clear trend of the 24 h average ratio of the north DOP to the east DOP was found related to latitudes and mask angle settings. Cross-track dilution of precision (XDOP) is defined as the GPS DOP perpendicular to the travel direction. The influence of the GPS satellite geometry on GPS accuracy was mapped into the vehicle platform frame to derive the XDOP, and accordingly to derive the influence of travel direction on the GPS dynamic accuracy. Results showed that the XDOP increased as the course over ground (COG) changed from 0° to 90°. Considering that a regression line fitting through GPS data may be referenced as the true path for calculating GPS errors, the second section reviews methods for fitting linear models. The most commonly used approach for linear fitting is least-square regression that minimizes the sum square of vertical offsets, rather than perpendicular offsets. This approach can result in a potential model fitting error, which was found to be dependent on the direction of travel and the dynamic accuracy of the tested GPS receiver when this approach was used to generate the referenced true path for calculating GPS cross-track errors. Our results showed that the fitting error reached its maximum when the tested vehicle was traveling in the N-S (or S-N) direction and decreased when the travel direction moved away from the N-S direction.