Influence of Synthetic Pigment Light Absorption on Plant Reflectance Measurements.

The use of synthetic pigment products on golf playing surfaces has increased dramatically by golf course superintendents to provide added green color and improve stress tolerance. Most turf colorants are synthesized from various phthalocyanine pigments, which share visible spectral properties with healthy turf. Vegetation indices, such as normalized difference (NDVI) and simple ratio (RVI), are commonly used by researchers to quantify plant health or turf quality. Research reports have indicated that turf canopy reflectance is sometimes positively and sometimes negatively impacted by synthetic pigments. The specific spectral wavelength utilized for vegetation indices varies by sensor type, which may explain these inconsistencies. A greater understanding of light absorption characteristics of synthetic pigments is needed. Therefore, the research objectives were to determine the spectral signature of synthetic pigments alone and to quantify their influence on light reflectance of treated turfgrass canopies. Narrow bandwidth (<3nm) reflectance was collected from across the visible and near infrared regions of the electromagnetic spectrum using a handheld field radiometer (PSR-1100, Spectral Evolution, Inc., Lawrence, MA) to develop spectral signatures of pigments alone, healthy turf, and healthy turf treated with pigments. Results of this research indicate that synthetic pigments have a strong influence on light reflectance of certain wavelengths of near infrared light. The vegetation index should be carefully selected for objective turf measurements when synthetic pigments are applied.