Detection of organic tea farms based on the density of spider webs using aerial photography with an unmanned aerial vehicle (UAV)

Abstract

Organic tea farms promote biodiversity and perform important ecological functions that benefit the environment and supply safe and secure products to consumers. The study of organic farming requires field study to identify and collect species on site. I proposed the use of aerial photography obtained by an unmanned aerial vehicle (UAV) to identify tea farms that provided a habitat for spiders. In this study, two locations were selected in tea farms near the town of Wazuka, in Kyoto Prefecture, Japan. Aerial photographs were taken after confirming conditions on the ground were right for maximum contrast because the spider webs appearing white when the right atmospheric conditions highlight fine water droplets adhering to the strands in the webs. This occurs when the temperature and humidity combine in such a way as to cause moisture to condense from the atmosphere, also known as the dew point. When this occurs, the webs appear white in daylight and are easily identified by visual orthomosaic images obtained from the UAV. The spatial distribution of spider webs varied as a function of farming method used in different sections of the farms. The results of the visual analysis showed that the density of spider webs correlates with the type of farming method. Sections in which organic farming methods were practiced showed the highest density of webs, followed by sections of conventional farming (extensive cultivation), and lastly, sections using conventional farming methods had the lowest density of webs. The density was easily estimated from orthomosaic images constructed from aerial photographs and demonstrated that organic tea farms can be distinguished from farms employing conventional farming methods based on this criterion.