Is it relevant to consider remote sensing information for targeted plant monitoring?

An experiment was carried out to test the relevance of using satellite images (NDVI) to define locations of plant monitoring systems. The experiment took place over a 200 ha commercial vineyard located in Navarra (Spain). Airborne images of 30 cm. resolution were processed to compute a biomass index (NDVI). Images were segmented in four classes according to the NDVI pixel values. Each of the zones was assigned a linguistic label: low, medium, high, very high. For each of these zones, punctual information related to plant vigour and plant water deficit were collected during the vine growing period. Plant monitoring systems (dendrometer) and soil monitoring systems (C-probe) were positioned according to NDVI zones. Parameters like Daily growth (DG) and maximum daily shrinkage (MDS) were derived from dendrometers for each NDVI zone. Similarly, soil moisture provided by soil sensors was associated to NDVI zones. Finally, harvest quality was measured.
Data were analysed on a NDVI zone basis. Results confirmed the relevance of NDVI information to highlight zones of different vigour and yield which corresponded, in our conditions, to zones with different water restriction. Results highlighted the difficulty to use NDVI information as a surrogate for harvest quality. This experiment also pointed out the lack of coherence between NDVI zones and information provided by plant and soil monitoring systems. This weak relation may be explained by problems of high variability due to the choice of the plant or the soil location and difficulty to compare values provided by different sensors at the same time.