COMPARING ACTIVE OPTICAL AND AIRBORNE MEASUREMENTS OF GRAPE CANOPIES
We used airborne imagery to map the canopy vigor in vineyards, enabling selective harvest of wine grapes, which in turn enables higher quality grapes to be processed separately into higher quality wines. We extended this research to evaluate the use of ground-based active optical sensors. The Greenseeker (GS) uses pulses of red and near infrared light to determine the Normalized Difference Vegetation Index (NDVI). In contrast with airborne imagery, this active optical approach is independent of sky conditions and offers side-views of the canopy. We collected both GS data and airborne imagery during the 2006 through 2007 growing seasons on two research juice grape blocks and a commercial wine grape vineyard all located in south-central Washington State. Overall, the imagery-based NDVI values were higher than the side-viewing GS in both juice grapes and wine grapes; the age of the leaves doesnt explain this result. The analysis to date demonstrates that (1) accurate (sub-meter) GPS locations are critical for research in trellised perennial crops such as grapes, and (2) additional analysis is needed to determine the best approaches for spatial interpolation of the GS data.
Perry, E.M., Pierce, F.J., Davenport, J.R. and Smithyman, J. (2009). COMPARING ACTIVE OPTICAL AND AIRBORNE MEASUREMENTS OF GRAPE CANOPIES . Acta Hortic. 824, 75-84
remote sensing, NDVI, airborne imagery, leaf reflectance