Testing the robustness of the Plant Phenology Index to changes in temperature

Abstract: Traditional vegetation indices have long encountered a problem of saturating at high biomass levels. A newly formulated vegetation index, the Plant Phenology Index (PPI), which has a near linear relationship with canopy green leaf area index (LAI) is tested in this study against temperature at 12 sites across Sweden. For comparison, the performance of the Normal Difference Vegetation Index (NDVI) and Enhanced Vegetation Index 2 (EVI2) are also tested. This study aim was robustness of PPI, and to see how well PPI correlates to temperature. PPI was shown to correlate very well with temperature for 11 out of the 12 sites, and also demonstrated a much more linear relationship to temperature than NDVI and EVI2. These results were replicated in a test of the vegetation indices against Growing Degree Days, a measure of accumulated heat, with high correlation coefficients for PPI. This indicated that PPI was more sensitive to changes in temperature than NDVI and EVI2 and is thus an efficient tool to show the phenological stages of vegetation.