Repeated and missed spraying are common problems during the working of boom sprayers, especially in the breakpoint continuous process. Therefore, the present study investigated a breakpoint continuous spraying system for automatic-guidance boom sprayers based on a hysteresis compensation algorithm for spraying. An operational breakpoint identification algorithm, which combines a real-time kinematic global navigation satellite system (RTK-GNSS) and wheel odometer, was proposed; a pre-adjusted proportional-integral-derivative (PID) control algorithm for the opening degree of the proportional control valve was designed in thus study. Tests were conducted to establish equations correlating the opening degree of the proportional control valve, pump output flow rate, and main pipeline flow rate, with an R² ≥ 0.9525. The time to adjust to the target flow rate was experimentally tested. The breakpoint identification accuracy of the RTK-GNSS and RTK-GNSS + wheel odometer was experimentally assessed. A field spraying deposition variation experiment was conducted. According to the results, the system effectively eliminated missed spraying, with a maximum repeated spraying distance of ≤3.3 m, and it achieved a flow control error within 3%. This system also reduced the repeated spraying area and enhanced the pesticide spraying quality of breakpoint continuous spraying for automatic-guidance boom sprayers.

Ultrasonic feedback energy is affected by the variety, planting, and growth state of crops; therefore, it is difficult to find applications for this energy in precision agriculture systems. To this end, an ultrasonic sensor was mounted in a spray boom height detection system. Winter wheat was used as the test object to obtain feedback energy values for the spray boom height from the top of the wheat in the field during six critical growth stages: the standing stage, the jointing stage, the booting stage, the heading stage, the filling stage, and the maturity stage. The relationship between the actual value of the height from the spray boom at the top of the wheat (H_abw) and the detected value of the height from the spray boom at the top of the wheat (H_dbw) was analyzed. A spray boom height detection model based on the ultrasonic sensor during the full growth cycle of wheat was determined. Field validation tests showed that the applicability of the spray boom height detection distance (D_d) of the spray boom height detection model proposed in the present study was 450~950 mm. Within the applicable D_d range, the detection error of the detection model was ≤50 mm during the full growth cycle. This study provides a method for constructing a boom height detection model based on the whole growth cycle of wheat, which improves the reliability and accuracy of ultrasonic boom height detection for different wheat growth stages. The proposed method solves the problem of low accuracy of repeated detection of low-cost ultrasonic sensors in different environments and can provide technical support for improving field applications of the boom height control system based on ultrasonic sensors.

Ultrasonic feedback energy is affected by the variety, planting and growth state of crops, it is difficult to fine application in precision agriculture systems. To this end, an ultrasonic sensor was mounted in a spray boom height detection system. Winter wheat was used as the test object to obtain feedback energy values for the spray boom height from the top of the wheat in the field during six critical growth stages: the standing stage, jointing stage, booting stage, heading stage, filling stage and maturity stage. The relationship between the actual value of the height from the spray boom to the top of wheat (Habw) and the detected value of the height from the spray boom to the top of wheat (Hdbw) was analyzed. A spray boom height detection model based on the ultrasonic sensor during the full growth cycle of wheat was determined. Field validation tests showed that the applicability of the spray boom height detection distance (Dd) of the spray boom height detection model proposed in the present study was 450 mm~950 mm. Within the applicable Dd range, the detection error of the detection model was ≤5 cm during the full growth cycle. This study provides an ultrasonic detection model construction method, which improves the reliability and accuracy of ultrasonic boom height detection for different wheat growth stages.

View-dependent canopy gap fraction is a directional descriptor of canopy openness that provides structural information for characterizing fruit-tree canopy heterogeneity. However, existing LiDAR-based canopy characterization methods are limited in their stability for characterizing zone-specific variations in canopy occlusion. This study proposes a LiDAR point-cloud column projection method for estimating zone-specific view-dependent canopy gap fraction of fruit tree canopies. A flash LiDAR sensor and an RGB camera were used to acquire paired point-cloud and image data from a simulated fruit tree and real peach trees under matched viewing directions and consistent region-of-interest constraints. Image-derived canopy gap fraction, calculated from the blue-cloth background area in each 3 × 3 subregion, was used as the reference value. The proposed column projection method was compared with a regional volumetric occupancy method and a regional two-dimensional projection coverage method. Under the indoor method-development conditions, using 88 paired frames, the proposed method achieved a mean absolute error of 8.59%, a Pearson correlation coefficient of 0.925, and a Spearman rank correlation coefficient of 0.914 relative to the image-derived reference values. In the preliminary semi-controlled outdoor evaluation using eight paired real-tree samples, the method achieved a mean absolute error of 10.48% and showed lower numerical errors and systematic bias than the two baseline methods. These results indicate that the proposed method can provide zone-specific view-dependent canopy gap fraction estimates that are more consistent with image-derived reference values under the tested conditions.