Relationships of Spectral Vegetation Indices with Rice Biomass and Grain Yield at Different Sensor View Angles

Abstract

Changing sensor view angles can alter the proportion of water background in rice (Oryza sativa L.) canopy reflectance spectra. However, its impact on the reported interference of water background in rice fields and performance of spectral vegetation indices (SVI) derived from canopy reflectance as predictors of rice biomass and grain yield is unknown. The objective of this study was to evaluate the relationships of normalized difference vegetation index (NDVI) and simple ratio (SR), measured at different view angles using an active sensor, with rice biomass and grain yield. Sensor readings and biomass at panicle differentiation (PD) and 50% heading, and grain yield were collected from multiple variety × N rate trials established at different rice‐producing areas of the mid‐southern United States in 2009 and 2010. Three sensor view angles were evaluated: nadir 0°, and two off‐nadirs. The relationships of NDVI and SR with biomass and grain yield were exponential and linear (P < 0.05), respectively. At PD, the pattern and values of NDVI and SR with biomass were similar across sensing view angles. At 50% heading, the off‐nadir angles viewed more green vegetation scene from rice stems than the nadir which caused NDVI to approach saturation at a lower biomass level. In addition, there were a higher number of sites where the nadir‐acquired NDVI obtained better exponential relationships with biomass than the off‐nadir view angles. There were larger differences in coefficient of determination (r2) values across site years than view angles implying the larger influence of spatiotemporal variability on NDVI and SR.