Leaf area index (LAI) is a key biophysical parameter used to determine\nfoliage cover and crop growth in environmental studies. Smartphones are\nnowadays ubiquitous sensor devices with high computational power, moderate\ncost, and high-quality sensors. A smartphone app, called PocketLAI, was\nrecently presented and tested for acquiring ground LAI estimates. In this\nletter, we explore the use of state-of-the-art nonlinear Gaussian process\nregression (GPR) to derive spatially explicit LAI estimates over rice using…