Motion-specialized deep convolutional descriptor for plant water stress estimation

Abstract

Mechanical water stress assessment is needed in agriculture to mechanically cultivate high-sugar-content crops. Although previous methods estimate water stress accurately, no method has been practically applied yet due to the high cost of equipment. Thus, the previous methods have a trade-off relationship between cost and estimation accuracy. In this paper, we propose a method for estimating water stress on the basis of plant images and sensor data collected from inexpensive equipment. Specifically, a motion-specialized deep convolutional descriptor (MDCD), which is a novel image descriptor that extracts motion features among multiple sequential images without considering appearance in each image, expresses plant wilt strongly related to water stress. Implicit exclusion of appearance enables extraction of general features of plant wilt, which is insulated from the effect of differences in shapes and colors of places and individual plants. We evaluated the performance of the proposed method using enormous agricultural data collected from a greenhouse. Accordingly, the proposed method reduced the error of mean absolute error (MAE) by approximately 25% compared with a naive convolutional neural network (CNN) using original images. The results show that the MDCD enhances temporal information, while reducing spatial information, and expresses the features of plant wilt appropriately.