Wheat ear temperature estimation using a thermal radiometric camera

The temperature of the plant canopy is closely related with its transpirative status, and therefore, its stomatal conductance and cooling capacity. Ear and leaf temperature can provide useful information for monitoring crop water status, irrigation management and yield assessment. Previous studies have shown differences in temperature between ears and leaves, with higher ear temperatures than leaf temperatures observed. By employing a high resolution thermal radiometric camera for proximal imaging, temperature differences can be used for segmentation as well as for temperature estimation. This work uses thermal images taken from above the canopy at between 0.8 and 1m distance. Measurements were acquired after solar noon. The field trials were carried out in three experimental sites and two crop seasons in Spain: Aranjuez (2016/2017), Sevilla (2015/2016) and Valladolid (2016/2017). A set of 24 varieties of durum wheat in two growing conditions, irrigated and rainfed, were used to build the thermal imagery database. The algorithm uses a pipeline system to filter the low temperatures and enhance the local contrast in order to segment the ear regions in each thermal image. Finally, using the full thermal radiometric information, the algorithms provide the temperature for each ear automatically detected. The results show high correlation values between the ear temperatures manually measured (using the thermal camera software) and the ear temperatures automatically measured using an automatic image processing pipeline.