The MobilLas mobile canopy sensor was initially developed for variable rate fertilisation and plant protection. Because of the several canopy variables sensed the sensor has wider application in crop and soil variability studies, detailed crop water balance studies, spatial modelling of photosynthesis as part of carbon dioxide flux studies, etc.
The current version of the MobilLas sensor includes three integrated measurement systems:
- Near-infrared laser range finder, AccuRange 4000 (Acuity Research Inc., CA, USA)
- Two-band radiometer, Crop Circle ASC-210 (Holland Scientific Inc., NE, USA)
- Global positioning system, GPS 16 (Garmin International Inc., KS, USA)
The MobilLas sensor frame and electronics are placed at the front of a farm tractor.
The Crop Circle ASC-210 is an active canopy sensor providing its own illumination. Measurement rate 20 Hz. From reflectance measurements made at near-infrared (NIR) and visible (amber) wavelengths the spectral index, RVI, is calculated as the ratio (NIR/amber) of the reflectance values.
Laser range measurements are made at a 50 deg. off nadir angle. Canopy height and leaf area index (LAI) are calculated from 1024 range measurements made within 1 s.
The GPS position is received at a rate of 1 Hz and a full measurement is recorded approximately every 1.6 s. Selected measured and derived data are displayed in real time on the system monitor placed in the tractor cab.
The driving speed is variable but typically between 4 and 6 km/h resulting in a full measurement being recorded for every 2 to 3 m travelled.
During 2009 MobilLas measurements were made in a small (1.2 ha) winter wheat (Triticum aestivum var. Ambition) field fertilised at four nitrogen (N) levels: 40, 80, 120, and 160 kg/ha. The 2009 data are used to show the measuring capabilities of the sensor. The use of the sensor for precision N fertilisation is also introduced.
