UAV borne spectrometers for high resolution soil and crop monitoring
The UAVSOIL project aims at testing the potential of air- and UAV- borne spectrometers (hyperspectral cameras) to produce parameters for explaining yield variations through input of up-to-date and high resolution soil variables with a perspective to improve yield prediction and optimization. The variability of soil properties can be considerable within single fields and are complex as management and land consolidation have changed over time and left patterns that are difficult to reconstruct. Fertilization advice models take soil parameters into account, but due to the cost of obtaining up-to-date and high resolution data, are often constrained to use regional means or default values. Requacarto in the Walloon region and the tool developed by INAGRO in the Flemish region are instruments that enable differentiated soil sampling within fields based on the soil series of the Belgian soil map. Results of ongoing Stereo III projects (PROSOIL, iPot, BELCAM) and the VISA project (CRA-w) have demonstrated that high resolution (hyperspectral) remote sensing is able to produce detailed maps of soil properties (such as SOC) and crop parameters (sequentially throughout the growing season). Nevertheless, spatial correlations between crop and soil parameter maps have not yet been exploited and challenges still remain: i) UAV platforms are already used for crop monitoring and could also be used for retrieving soil properties, although spectral coverage and resolution of their sensors is still somewhat limited, ii) UAVs have been shown to produce detailed soil maps, but extensive soil analysis for calibration during each flight is still required, iii) routine application of UAV sensors would only be possible if a prior and stable calibration could be developed using e.g. spectral transfer techniques on a pan European spectral library (LUCAS), iv) narrowband indices related to crop vigor have not yet been applied on UAV borne sensors.
Outputs of UAVSOIL are a quantification of the intra-field heterogeneity in crop performance and its correlation to soil properties in the form of high resolution maps. These will subsequently allow the definition of areas with different yield potentials within a field for which management variable zones (MVZ) specific application of N fertilizers can be suggested.