Automated agricultural vehicles can help alleviate labor intensity concerns, reduce the cost of inputs, and improve the profitability. Significant progress has been made in automatic guidance for agricultural vehicles during the last two decades. More recently, research and development are focused on achieving more autonomy, with the ultimate goal to develop autonomous vehicles or field robots for agricultural operations. This paper gives a review of recent development in autonomous vehicles, including localization, navigation control, mission planning, perception and safeguarding, and implement control. Trends and future directions in autonomous vehicle development are discussed.

In the process of agricultural sustainable development, diseases and insect pests have always been the focus of attention. Due to the flexibility and convenience, unmanned aerial vehicle (UAV) spray has attracted wide attention in the field of plant protection, and new progress has been made in prevention and control of diseases and insect pests. However, there are still some problems in the UAV spray technology, such as droplet drift and pesticide waste. The deposition effect of droplets is the greatest concern in the UAV spray operation. This paper summarized the characteristics of droplet deposition distribution and the influence factors on droplet deposition and its distribution. Besides, new methods of detecting droplet deposition were listed. The research showed that the deposition effect was influenced by many factors such as flight parameters, natural factors and spray equipment and modes, which should be integrated together in the UAV application, and the wind field
below the UAV should be especially included. Moreover, it is quite necessary to develop new types of nozzles and droplet deposition detection technology to provide a guarantee for improving the deposition effect of droplet.

Unmanned aerial vehicle (UAV) has the characteristics of flexibility, not easily affected by weathercondition, and can acquire high-esolution images when used to monitor crop growth status with mounted sensors. Thus, the UAV is of great significance to assist precision agriculture. In addition, the UAV can also be equippedwith agricultural machinery to make field management, which can improve working efficiency and reduce disturbance to crop growth. In recent years, the application of UAV in agriculture has become a hot spot, and a series of studies have been conducted. However, in general, research in this area is still at its beginning phase. Therefore, we need to systematically summarize the application status of UAV and analyze existing problems, which can promote its better application in agriculture. This paper concluded the hardware equipment of agricultural UAV and its application status in some aspects, including plant growth monitoring, yield forecasting, nitrogen nutrition diagnosing, pests and diseases detecting and field management, and then put forward some development directions, in order to provide references for further research in related fields.

In order to study the wettability of droplets on the leaves during aerial spraying and its influencing factors, orthogonal test and single factor test were applied to analyze the change of contact angle, which was affected by the location of leaf, foliar fertilizer type and concentration, adjuvant concentration, droplet size and instantaneous velocity. The results showed that the wettability of foliar fertilizer was effectively improved by adding adjuvants and ensuring the instantaneous velocity of the droplet at least 1.55 m/s. Liquid type and concentration, and droplet size had a certain influence on the wettability of foliar fertilizer, while the location of the leaf had no significant influence on the
wettability of foliar fertilizer. The contact angle can reach 8.5° by applying the optimal combination, that is, spraying the reverse side of leaves, high concentration of Jiaduobao foliar fertilizer, 1% adjuvant and small droplets. This study can provide references for improving the effect of agricultural aerial spraying.

For the purpose of practical application of farmland navigation, we constructed a system of real time kinematic (RTK) to study its positioning accuracy mainly based on Piksi positioning module of Swift Company in the United States. The results showed that single Piksi module point positioning accuracy [root mean square error by two folds (2DRMSE), with 95% degree of confidence] was about 8 m, and the RTK static accuracy (2DRMSE, 95%) was about 1.5 cm. The design of dynamic dual-track experiment verified the feasibility of using line fitting method for dynamic linear accuracy: When the flow station was linearly moving at an average speed of 0.4 m/s to 2.3 m/s, the positioning accuracy obtained by fitting was about 1.5 cm. According to the difference between the distance of measured point to the fitting center and the fitting radius, we evaluated the positioning accuracy of the circular motion, and found the accuracy of linear motion at 0.4-1.6 m/s was also about 1.5 cm. Considering the point- to- point problem in the actual application process, the measurement error obtained by the fitting analysis
was small and the true dynamic accuracy of Piksi RTK was about 3-5 cm after a preliminary judgment. It is suggested that the low cost RTK-GPS can meet the actual needs of agriculture.

Due to high dimensional characteristics of unmanned aerial vehicle (UAV) hyperspectral remote sensing data, we proposed a dimension reduction method based on main base analysis. The 400-1 000 nm bands which are sensitive to chlorophyll, were selected to be subjected to Gram_Schmidt transform. After finding the projection space, the main base of concentrated band information was constructed, and the least square regression model was established to estimate the chlorophyll content in rice canopy leaves. The results showed that the modeling coefficient of determination (R²) was 0.689, with the root mean square error (RMSE) of 2.20, and the RMSE of validation model was 1.20. Compared with the prediction accuracy of the same model established by three vegetation indexes PRI, RD2 and MCARI, the modeling R² was greatly improved, while the RMSE of verification model was greatly reduced. It is proved that the proposed method is effective, and it is significance for estimating chlorophyll content of plant leaves.

To avoid hitting the edge of paddy field or moving obstacle in the paddy field when global position system signal was weak or was influenced by the strong wind, we proposed a laser sensor- based collision avoidance system. This collision avoidance system was based on Otsu method to find out the optimum position of edge point between the edge ground class and paddy field area class for determining the distance from the airboat to the edge. The dynamic experiment results showed that the root mean square error was 0.18 m for referring to the 3 m between the airboat and one edge of paddy field. For moving obstacle, a rectangular danger zone was set at the front of the airboat. A structure array was set up to record the obstacle information including obstacle number and distance between airboat and obstacle. The results showed that when the obstacle intruded the danger zone, the airboat would brake until the obstacle moved out, which would avoid the collision.

To solve the problems of pulse width modulation (PWM) proportional solenoid valve control mode, such as large current ripple and low control precision, a method of dual PWM was adopted to control the proportional solenoid valve. Here, the dual PWM meant a second modulation was added in one PWM period. The results showed that this dual PWM can improve the control precision of the proportional solenoid valve, reduce the current ripple of proportional electromagnet, thus reducing the impulse of the proportional solenoid valve. As a result, it increased the life of solenoid valve, reduced the maintenance and replacement cost of product parts, and decreased the current fluctuation of the non-road mechanical products by nearly 1/3 in the shift, effectively slowing down the velocity jump caused by shifting and eliminating the sense of shift and frustration.

Ophiopogon japonicus, a kind of local herbal remedies in Zhejiang, is usually grown on rectangular pieces of land. In harvesting season of O. japonicus when a tractor accidentally falls into any furrows, mechanical parts of the tuber harvester hitched behind are prone to break. To solve this problem, an automated leveling system, consisted of a field computer, an electronic control unit (ECU), a dual-antenna GPS receiver, a rope-type sensor, a cylinder, and a hydraulic valve, was developed and tested so that the harvester remained level. The computer got rolling angle of the tractor and displacement of the cylinder in sequence, and then deduced rolling angle of the harvester. The system employed a proportion integration differentiation (PID) algorithm to calculate control quantity of the valve. The experimental results conducted in the fields of O. japonicus showed that the average elevation difference of the left and right points was 1.04 cm, and the standard deviation was 2.39 cm. Therefore, the harvester could remain horizontal all the time, and its mechanical fracture would not happen again.

To shorten research and development cycle and reduce cost, an air conveying system in the air assisted sprayer was designed and optimized by computer fluid dynamics (CFD) technology. Based on the principle of minimizing the energy loss and vortex of airflow and maximizing the uniformity of flow distribution, we determined the optimal structure and specific parameters of the bellows. In addition, to adapt to different growth periods and different types of orchards by adjusting the height and inclination of the system according to the canopy shape, we explored the influence of air velocity and installation angle on air-flow field using CFD simulation calculation and test, and simulated the distribution of flow field in the sprayer. Then we established the linear model between spray height and nozzle inclination after obtaining the relationship between airflow distance and airflow velocity (as the wind transmission distance increased, the wind speed gradually decreased, and the decreasing amplitude also decreased). The results showed that when the nozzle inclination was greater than 85° or less than 40°, there was little effect on the change of airflow field; when the nozzle inclination was 40°-85°, the spraying height was basically linear with the nozzle inclination with the increase of nozzle inclination. This study provides a theoretical basis for the automation of simulation spray.

In order to improve the automation and processing efficiency of log sawing equipment and ensure the output rate of log sawing, an automatic sawing and turning concept prototype was designed based on infrared detection. Algorithms of sawing strategy and sawing angle were analyzed, and the test platform for log outline detection device was applied to verify the proposed algorithms. The log outline detection device adopted an infrared distance measuring sensor to detect the eight-position parameters uniformly distributed on the outer contour of an arbitrary cross-section of the log. The polygon composed of eight points could approximately represent the outer contour of the log cross- section. Approximate octagonal profiles with different axial crosssections were clipped with the Weiler-Atherton algorithm, and the least square method was used to fit the clipped polygon into elliptical effective regions. The result showed the ellipse fit well with the profile of the cross-section of the log small-end. It is suggested that the sawing strategy and sawing angle calculation method based on the fitted ellipse are feasible for the sawing analysis of logs with less curvature and taper.

This study focuses on exploring the damage susceptibility and the realistic representation of time dependent nonlinear mechanical behaviour of maize kernel under various impact cases with threshing unit. A reverse engineering approach based on three dimensional (3D) scanning technology, finite element method (FEM)-based explicit dynamics simulations and response surface method (RSM) were utilized to investigate contact force, Von Mises stress and displacement characteristics, determine critical velocity of maize kernel. Five
moisture contents (11.78%, 17.63%, 23.45%, 29.31% and 34.73%) and five impact velocities (4, 6, 8, 10 and 12 m/s) were considered in the impact simulation scenarios. Useful numerical data and deformation visuals were obtained from the simulation results. These results showed that when impacting, the stress concentrated in the small contact area and spread around and decreased gradually. The maximum contact force, maximum Von Mises stress decreased while maximum displacement increased as the moisture content increased, and the critical velocities of maize kernels with moisture contents of 11.78% , 17.63% , 23.45% , 29.31% and 34.73% were determined as 5.51, 6.75, 8.15, 9.36, 10.57 m/s, respectively. In addition, prediction models were successfully established with reasonable coefficient of determination (R2) values. The best parameter combination was obtained through multi-objective optimizing as moisture content of 26.99% with impact velocity of 5.17 m/s, and the corresponding contact force, Von Mises stress and displacement were calculated as 19.30 N, 40.64 MPa and 0.73 mm, respectively. Verification checks of the prediction models also indicated that the relative errors between the results of simulation and the empirical model were less than 8%. The above results suggest that these models are reliable to describe the damage susceptibility of the maize kernel for various impact cases.

Aimed at lack of automated assembly line in the domestic vegetable seedling production field, combined with the seeding process of domestic vegetable seeds, the air-aspiration drum type tray precision seeding streamline was designed. The assembly line included an unpowered pressure hole device, a drum-inlaid convex suction nozzle, and a seeding machine for conveying and drum synchronous transmission. The data of air-aspiration drum type tray precision seeding steamline was showed as follows: seeding precision of 98%, seeding cavity rate of 0.6%, productivity of 580 disks/h, seeding amount of 145 disks/(kW·h), and seed breakage rate of 0.4%. The above data shows that the technical indicators of the streamline meet the standards, and the design is reasonable and reliable, which can satisfy
the needs of the actual use of the streamline.

Header losses are the most serious part of grain loss which affects the quality and efficiency of rapeseed harvesting operations. In order to solve this problem, we chose the reel’s horizontal position, reel’s vertical position and reel’s rotation speed as the main parameters, and took the header loss rate as the main objective. At the same time, we used the total feeding amount as an auxiliary target considering the harvester’s operation efficiency. First, single-factor test was performed on the three main parameters, and the effects of different factors on the loss rate and feed amount were analyzed. On the basis of single factor, a response surface test was conducted on the three main parameters according to the Box-Benhnken center combination design theory. Then, a regression model was established to determine the factors affecting significance. The experimental results showed that the loss rate was affected by the reel’s horizontal position, reel’s vertical position and reel’s rotation speed, while the total feeding amount was only affected by the reel’s rotation speed. The result of response surface experiment was consistent with the results of single factor experiment; the significant order of influence is reel’s vertical position, reel’s rotation speed and reel’s horizontal position through the analysis of impact effects. The optimum working parameter combination of the rapeseed harvester’s header with high efficiency and low loss rate as constraints was that the horizontal position of the reel was 50 mm, the vertical position of the reel was 1 056 mm, and the rotation speed of the reel was 30 r/min. Under the optimized conditions, the header loss rate was 0.97%, the feed amount was 8.35 kg/s, and the experimental value was 1.01% for the header loss rate, 8.48 kg/s for the feed amount with the relative error of less than 5%. The above results can provide a reference for optimization design of the header structure of rape combine harvester and optimization of operating parameters.

A pattern recognition method based on computer vision was developed for the identification of Daiqu large yellow croaker. First, 24 morphological parameters of Daiqu large yellow croaker were measured for both F₂ and F₃ generations by computer vision technology. Then principal component analysis (PCA) and successive projections algorithm (SPA) were respectively applied to extract and select the measured morphological parameters, and then obtained three groups of different characteristic variable sets, which were PCA transformed feature, PCA selected feature, SPA selected feature, respectively. Finally, respectively. Finally, sparse representation (SR) models were built for identificating the F₂ and F₃ generations of Daiqu large yellow croaker by using the extracted morphological features. The results indicated that the main morphological features for the identification of Daiqu large yellow croaker were total length/body length, total length/head length, total length/caudal peduncle length, body length/head length and caudal peduncle length/caudal peduncle height. The results of SR models showed that the three groups of characteristic variable can effectively identify the F₂ and F₃ generations of Daiqu large yellow croaker, with the average recognition accuracy of 88.3%, 79.0% and 80.5%; among them, the best SR model with PCA transformed feature achieved an average accuracy of 88.3% for the identification of Daiqu large yellow croaker. This study provides an effective way to establish shape index and carry out shape evaluation research of Daiqu large yellow croaker.

In order to overcome the time-consuming and laborious problems of artificial observation, we proposed an automatic detection method of abnormal behavior of fish school under low dissolved oxygen stress based on image processing and compressed sensing algorithm. Taking Cyprinus carpio as the research object, by obtaining the video images of fish school behaviors under two conditions of normoxia and hypoxia, we used the image processing technology to get the location histogram of fish school, of which the average, variance, skewness, kurtosis and energy were extracted to form the fish movement characteristic parameters of each image. On this basis, the data dictionary matrix was constructed, and the abnormal behavior detection of fish school under low dissolved oxygen stress was implemented by compressed sensing classification. The results showed that the detection method can effectively detect the abnormal behavior of fish school under the low dissolved oxygen stress, with the detection accuracy rate of 98.50%.

Conventional seed dehulling methods are unable to separate caryopses from intact cupules of eastern gamagrass as the cupules are thick and rigid, and the seeds are irregular-shaped. To put forward a feasible method of mechanical dehulling, we investigated and analysed the physical and mechanical characteristics of intact seeds, cupules and caryopses, and then evaluated the characterics that can be applied in mechanical dehulling. The testing results indicated that the tertraploid cultivar Meadowcrest had a larger seed size and a heavier seed mass than diploid Pete. The mean caryopsis mass was approximately 1/3 and 1/4 of the intact seed mass for Pete and Meadowcrest, respectively. The intact cupule was approximately twice as long as the caryopsis for all three seed lots measured. The moisture content of the cupules was significantly lower than that of the caryopses. The rupture force of the intact cupules was 1/2-2/3 of the caryopses for Pete and Meadowcrest when pressed longitudinally, respectively. Seed size, moisture content and rupture force codetermined that longitudinal seed pressing might be an effective method to remove the cupules without harming the caryopses.