A novel optical shadow edge imaging method based fast in-situ measuring portable device for droplet deposition

Accurate and rapid measurement of droplet deposition on the spray target provides feedback data on spray quality to optimise application parameters and confirm crop protection efficacy. However, simultaneously meeting the requirements for field measurement remains a challenge. In this paper, a novel Optical Droplet Edge Imaging (ODEI) method based on a portable droplet deposition and distribution measurement device is proposed to enable in-situ reusable sampling and on-line automatic digitisation for field spraying. First, the principle of the ODEI method is presented to realise the sampling state closer to droplet deposited on the leaves. Then, a low-cost portable in-situ droplet deposition measurement device is designed and the optimal light field parameters of the device are determined. Finally, the simultaneous acquisition of the top and bottom side of the droplet deposition image of the collector is obtained and its image processing algorithm is presented to obtain the performance indexes of droplet deposition, such as individual droplet size and distribution, total droplet number, volume median diameter, droplet density and the ratio of droplet amount between the top and bottom side of the collector. The relationship between droplet volume and image area is calibrated with an average deviation of 3.22 %. Experimental results show that the VMD deviation between the device and the WSP image measured by same image processing method is 15.34 μm. Due to the difference in deposition state between the device and the water sensitive paper (WSP), the droplet deposition area conversion from this device to the WSP was also calibrated. The absolute deviation between the WSP moving average coverage rate and the converted collector coverage rate of this device is 1.21 %. The measurement result of the spray experiment shows that this device has the same measurement capability as the WSP, as the droplet diameter distribution is very consistent with the WSP distribution. This in-situ and automatic measurement method is a promising and useful addition to the spray performance monitoring tool for field droplet deposition.