Estimating the Impact of Air Movement on Golf Greens Using Spectral Reflectance Mapping.

The installation of turf fans along the perimeter of golf putting greens has become a common practice to alleviate heat stress and poor air circulation. Scientific validation of the impact of incremental increases in air movement is lacking from the literature. Linear sampling across putting greens has demonstrated the distal benefits of decreasing root-zone temperature and increasing rooting depth as surface wind speed increases. However, individualized sampling is time consuming and does not accurately depict benefits across an entire putting green. Researchers have adopted spectral reflectance indices as viable options for objective turfgrass quality measurements, though these data are seldom linked to direct measureable turfgrass attributes. Geo-referenced reflectance data has been utilized to generate turf quality maps across a variety of turf surfaces. The objective of the current study was to demonstrate the utility of using the near-infrared index to predict relative root zone temperatures and root length at unsampled locations on putting greens where fans are utilized. Ground truth samples of root zone temperatures and root length were collected along three 21 m arcs in 3 m increments and marked using an OmniStar corrected GPS.  Reflectance data were collected using a Holland Scientific ACS470 in the red (670nm) red-edge (730nm) and near-infrared NIR (760nm) and transformed using the ratio vegetation index (RVI:  NIR/Red). These data were correlated with root zone temperatures and root length, with a random subset of ground truth samples retained for accuracy assessments.  Preliminary results indicate a strong negative correlation exists between RVI and root zone temperatures (r = -0.91- -0.93) and moderate relationship exists between RVI and root length (r = 0.58 – 0.62).  Regression results explained from 59-86% of the variability in root zone temperatures and approximately 34% of the variability in rooting depth.  Results were used to create surface maps of root length and root zone temperatures for entire greens with a minimum of 15 ground truth samples collected per green.