A mobile sensor for leaf area index estimation from canopy light transmittance in wheat crops

• A mobile canopy sensor was developed for estimating the leaf area index.
• The operating principle is based on light attenuation by the canopy.
• There is highly significant correlation with the reference LAI and biomass in wheat.
• Environmental conditions were of minor concern.

The leaf area index (LAI) is a key parameter describing the state and progress of crop canopies. Determination of LAI via proximal sensing supports decision-making processes in precision agriculture and improves biophysical modelling. Here we introduce the Canopy-Meter – a mobile sensor designed for determining LAI while driving over the field. The operating principle is based on the transmittance of sunlight passing through the plant canopy. This approach has not been previously applied to a proximal sensor. The sensor setup, its working principle, and the first field measurements are described. The setup of the Canopy-Meter consists of light sensors embedded in the upper and lower end of a tube. While positioned vertically in the plant canopy, the Canopy-Meter measures the above and below canopy irradiation flux. LAI is estimated from the ratio of above and below canopy irradiation through radiation transfer modelling. Spot measurements with the Canopy-Meter were conducted within three wheat fields during growth stages from 45 to 75 (Zadoks). Relationship between the SunScan SS1 LAI and Canopy-Meter LAI was linear for each measurement run (averaged R2 = 0.80) and pooled measurement points (R2 = 0.71). The relationships with biomass were linear and significant. Changing environmental conditions had a minor effect on the Canopy-Meter. The initial online measurements in wheat canopies exhibited a high correlation with the biomass densities observed in aerial photographs and with the reference LAI (R2 = 0.86). The results encourage further investigation on the Canopy-Meter as a new proximal sensor for precision agriculture.