Automatic Optical and Infrared Image Registration for Plant Water Stress Sensing

Abstract

In many countries around the world, about 70% of water resource will be used to for agriculture irrigation each year. Precisely control irrigation can significantly reduce the waste of irrigation water while increasing plant productivity. Automated sensing of plant water status via non-destructive, automatic techniques plays a central role in such irrigation control system development. Plant canopy temperature acts as a good indicator of the plant water status. When plants experience water stress, their temperature increases. A novel approach to irrigation scheduling and thus, potential water savings, is to monitor plant temperature and relate to the plants water status. To say further, if we want to know the plant water status, we need to know the canopy temperature at first. Recent research in agriculture indicates that plant water status may be monitored if the canopy temperature distribution of the plant is known (Jones, 1999a,b; Jones and Leinonen, 2003; Guilioni, et al., 2008; Grant, et al., 2007; Wheaton et al., 2007). Plant water status information can be obtained via the computation of the crop water stress index (CWSI) (Jones, 1999a). This index offers great potential to generate an automated irrigation control system where plant canopy temperature distribution is acquired via thermal imaging. Such a system is expected to be able to optimize irrigation water usage and the potential to maintain plant health in real time, thus increasing the productivity of limited water resources. Typically, measurement data of the infrared (IR) thermography sensing system consists of a reference optical image and an IR image. The optical image is obtained by using a normal digital camera and is taken at the same location as the IR image to provide a true view of the IR image scene, one may identify the area of interest (e.g., plant leaves other than ground or sky) from the optical image. The optical image allows the underlying plant canopy of interest to be flawlessly identified. To quantify plant water stress, the value of CWSI is calculated based on the canopy temperature, and temperatures of a dry and wet reference surface. These temperatures can be estimated once the temperature distribution of the