rOPTRAM: An R package for satellite-derived soil moisture in rangelands using the OPTRAM model

Considerable research has been conducted to assess soil moisture (SM) of the upper soil layer by earth observation systems. Previous efforts have contributed to monitoring vegetation growth, status, and yield, which depend on SM. A more recent remote sensing-based model, the OPtical TRapezoid Model (OPTRAM), has been developed and validated. Unlike earlier thermal-based models, the current relies only on the commonly available visible and shortwave infrared spectral bands. The current paper presents an implementation of the OPTRAM model in the R programming language for assessing and mapping soil water content in rangelands worldwide. The new rOPTRAM package includes several innovations compared to early applications of the model. These new features include automated acquisition and pre-processing of Sentinel-2 imagery, programmatic delineation of trapezoid edges, and multiple curves (e.g., linear, exponential, and polynomial) fitting options for those edges. • This work implements the OPTRAM model in R. • Trapezoid boundaries are determined programmatically. • Multiple curve fitting functions are presented to determine trapezoid edges.