Differences in Growth Estimation and Yield Prediction of Rice Crop Using Satellites Data Simulated from near Ground Hyperspectral Reflectance

Abstract

The simulated broadband data of satellites SPOT 5 and FORMOSAT-2 were mimicked from canopy high-resolution reflectance spectra measured near ground, by a field-portable spectroradiometer, and these spectral data were then used to compare the differences in growth estimation and yield prediction of rice crop relative to those of ground measurements. Reflectance of broadband sensors was acquired by using the mean value of reflectance averaging over the respective waveband regions of hyperspectral data. Results indicated that the calculated values of normalized difference vegetation index (NDVIs) from hyperspectral (i.e. NDVI(subscript NB)) and simulated satellites data (i.e., NDVI(subscript SPOT 5) and NDVI(subscript fORMOSAT-2)) were all nonlinearly distributed during the first and second cropping seasons of rice. The curves were nearly parallel to each other, but values of NDVI(subscript SPOT 5) and NDVI(subscript FORMOSAT-2) were lower than those of NDVI(subscript NB). The relationship between the measured leaf area index (LAI(subscript measured)) and NDVI(subscript NB) was best fitted to an exponential growth function, by which the estimated values of LAI(subscript NB), LAI(superscript SPOT 5) and LAI(subscript FORMOSAT-2) were obtained using the respective NDVIs as inputs. Values of LAI(subscript NB) were found higher than those of LAI(subscript SPOT 5) and LAI(subscript FORMOSAT-2) on the same sampling dates yet all the estimates were lower than the corresponding values of LAI(subscript measured) after ca. 55 days after transplanting. As the simulated satellites data obtained lower values of NDVI and LAI than those of NDVI(subscript NB) and LAI(subscript NB) counterparts, yields predicted from satellites data were less than yield predicted from ground-based hyperspectral data. These predicted yields were all lower than the measured yields.