Spectral-based vegetation indices (VI) have been shown to be good proxies of grapevine stem water potential (Ψstem), assisting in irrigation decision-making for commercial vineyards. However, VI-Ψstem correlations are mostly reported at the leaf or canopy scales, using proximal canopy-based sensors or very-high-spatial resolution images derived from sensors mounted on small airplanes or drones. Here, for the first time, we take advantage of high-spatial resolution (3-m) near-daily images acquired from Planet's nano-satellite constellation to derive VI-Ψstem correlations at the vineyard scale. Weekly Ψstem was measured along the growing season of 2017 in six vines each in 81 commercial vineyards and in 60 pairs of grapevines in a 2.4 ha experimental vineyard in Israel. The Clip application programming interface (API), provided by Planet, and the Google Earth Engine platform were used to derive spatially continuous time series of four VIs-GNDVI, NDVI, EVI and SAVI-in the 82 vineyards. Results show that per-week multivariable linear models using variables extracted from VI time series successfully tracked spatial variations in Ψstem across the experimental vineyard (Pearson's-r = 0.45-0.84; N = 60). A simple linear regression model enabled monitoring seasonal changes in Ψstem along the growing season in the vineyard (r = 0.80-0.82). Planet VIs and seasonal Ψstem data from the 82 vineyards were used to derive a 'global' model for in-season monitoring of Ψstem at the vineyard-level (r = 0.78; RMSE = 18.5%; N = 970). The 'global' model, which requires only a few VI variables extracted from Planet images, may be used for real-time weekly assessment of Ψstem in Mediterranean vineyards, substantially improving the efficiency of conventional in-field monitoring efforts.
Bibliographical noteFunding Information:
The authors thank Itamar Lensky for fruitful discussions, Yaron Michael and Shilo Shif for assisting with GEE Java script and Planet's Clip API, and Planet Labs for providing API tools and images, as part of Planet's Education and Research Program. We also thank Ben Hazut, for assistance in the field and laboratory, Yair Hayat from BarkenWinery, Shlomo Zsadok and Tamar Sokolsky from Golan HeightsWinery, David Twito and Dror Dotan from Carmel wineries for agro-technical assistance. This research was supported by the Chief Scientist Fund of the Ministry of Agriculture and Rural Development in Israel (Grant No. 20-12-0030). This research was funded by the Chief Scientist Fund of the Ministry of Agriculture and Rural Development in Israel, grant number [20-12-0030].
© 2018 by the authors.
- Google Earth Engine
- Stem water potential
- Time series