Weed Sensing - Where Are We?

Recognition of the potential benefits of being able to variably apply herbicides based on the sensing of weeds has led to much research and development activity. The purpose of this paper is to survey what work has been done already with a view of formulating future research and development directions with a goal of the development of practical weed sensing technology. Two approaches have typically been used for weed detection. The first is the photo-detection approach, which measures the average reflected light from the field of view of the detector. Light-detecting (photo) diodes or resistors have been used in this low resolution approach meaning that the area sensed by one sensor is large. The other approach is the machine vision approach. In this approach, digital images of the field scene are acquired with some type of camera, and the information contained in these images is processed by a computer to retrieve knowledge or understanding of the scene. Examples of both of these approaches will be discussed in this paper

Open and Closed Loop System Characteristics of a Tractor and an Implement Dynamic Model

Accurate guidance of towed implements is important for performing agricultural field operations and for gaining the ultimate benefit from an agricultural automatic guidance system. The study of open and closed loop system responses can be helpful in the design of practical guidance controllers. A dynamic model of a tractor and a towed implement system was developed. Open loop analysis of the kinematic and dynamic models revealed that the dynamic model was essential for capturing the higher order dynamics of the tractor and implement system at higher operating velocities. In addition, a higher fidelity dynamic model was also developed by incorporating steering dynamics and tire relaxation length dynamics. Closed loop system characteristics were studied by using a linear quadratic regulator (LQR) controller. The tractor position and heading and implement heading states along with respective rate states were fed back to close the loop. The higher fidelity closed loop system used a practical range of steering angles and rates to keep the response within nominal off-road vehicle guidance controller design specifications in the forward velocity range of 0.5 m/s to 10 m/s (1.8 km/h to 36 km/h). These simulation studies provided understanding about the characteristics of the tractor and towed implement system and showed promise in assisting in the development of automatic guidance controllers

Targeted Sampling of Elevation Data Based on Spatial Uncertainty of Prior Measurements

An efficient sampling strategy should address knowledge gaps, rather than exhaustively collect redundant data. In this study, spatial uncertainty in DEM estimates was used to locate targeted sampling areas in the field. An agricultural vehicle equipped with RTK-DGPS was driven across a 2.3 ha field area to measure the field elevation. Data were collected at 3.05 m (10 ft) intervals in a continuous fashion at a speed of 9.6 mph. A geostatistical simulation technique was used to simulate field DEMs with different measurement pass intervals and to quantitatively assess the spatial uncertainty of the DEM estimates. The high uncertainty areas for each DEMs were classified using image segmentation methods and targeted sampling was performed on those areas. The resulting DEMs were compared with each other to evaluate the effect of including targeted measurement on DEM accuracy. The addition of targeted measurements significantly reduced the time dedicated for the re-sampling effort and resulted in DEMs with lower RMSE. For the widest interval between sampling passes, the RMSE of 0.46 m of the DEM was reduced to 0.25 m after adding the targeted measurements which was close to the 0.22 m RMSE of DEM with whole field re-sampling. The results show that spatial uncertainty models are useful to design targeted sampling for field mapping. The method is not limited to map elevation data but can be extended for mapping other spatial data

Modeling the Raven SCS-700 Chemical Injection System with Carrier Control with Sprayer Simulation

Mathematical models of the chemical and carrier control sub-systems of the Raven SCS-700 chemical injection system were developed. The step responses of both control sub-systems were predictable using the models. From this process of model development, it was observed that the voltage saturation effect limited the response speed of the carrier valve motor and the resulting speed at which changes could be made to the carrier flow rate. The rate at which flow rate measurements were available limited the extent to which valve motor speed could be increased without causing instability. The performance of three different types of sprayers was simulated using these models. Simulations were performed with and without carrier control. Sprayers using carrier control misapplied to smaller areas than those without carrier control. Differences between the response of the chemical and carrier sub-system controllers produced concentration variations that contributed to application error. These errors, however, were small relative to the errors caused by response times of both systems and the ground speed sampling rate

Topographic Mapping Through Measurement of Vehicle Attitude

A self-propelled agricultural sprayer was equipped with four RTK DGPS receivers, and an Inertial Measurement Unit (IMU) to measure vehicle attitude and field elevation as the vehicle was driven across a field. Data was collected in a stop-and-go fashion at 3.05 m (10 ft) intervals, as well as in a continuous fashion at three different speed levels. Using ordinary kriging, surface grids were interpolated using only elevation measurement, as well as combinations of elevation and vehicle attitude measurements. The resulting surfaces were compared to each other to evaluate the effect of including attitude measurement on DEM (Digital Elevation Model) accuracy. At the widest row spacing, the DEMs generated with attitude measurements had lower RMSE than those DEMs generated without attitude measurements. Vehicle speed also affected DEM accuracy. Vehicle attitude measurements have the potential to improve DEM accuracy for larger swath widths in ordinary field operations