Ultra low level aircraft (ULLA) as a platform for active optical sensing of crop biomass

Crop producers requiring crop biomass maps to support timely application of in-season fertilisers, pesticides or growth regulators rely on either on-ground active sensors or airborne/satellite imagery. Active crop sensing (for example using Yara N-Sensor™, Greenseeker™ or CropCircle™) can only be used when the crop is accessible by person of vehicle, and extensive, high-resolution coverage is time consuming. On the other hand, airborne or satellite imaging is often hampered by cloud, either in the sensor-image path or by associated non-uniform illumination of ground targets. We have combined the desirable attributes of active optical sensing with the fast, synoptic coverage afforded by aircraft platforms. An ultra low-level aircraft (ULLA) system 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 measure and map crop vigour via the simple ratio (SR) index.