Measuring and mapping crop vigour using an active optical sensor in an ultra low-level aircraft

An ultra low-level aircraft carrying an active NIR/Red CropCircle™ sensor was successfully deployed at an altitude of 3-5 m over a 270 Ha field of skip-row sorghum (Sorghum bicolor) to record and subsequently map photosynthetically-active biomass (PAB) via the simple ratio (SR) index. The 2-D, ULLA-PAB map derived from 20 m transects was found to reproduce the gross patterns of spatial variability observed in a PAB map derived from a metre-resolution airborne digital multispectral image re-sampled to a similar spatial resolution. The fact that this type of sensor contains its own light source hence can be operated irrespective of ambient light conditions offers crop managers a viable alternative to conventional imaging technologies especially when they have day-to-day access to aircraft already conducting low-level operations, for example crop dusting and reconnaissance, over their agricultural fields.