Comparative analysis of red-edge hyperspectral indices Original Research Article

Using 3 nm bandwidth observations over the growth cycle of wheat in 680–820 nm range, the point of inflection was identified through differentiation and it was at 729 nm corresponding to peak observed at 64 days after sowing (DAS). To provide physical basis for various red edge hyperspectral indices reported in literature, the ratio indices (RI) corresponding to 1dB, 2dB, 3dB and half-power bandwidths around 729 nm were computed. These ratio indices had significant relationship with VOGa (after Vogelmann) = R740R720 and RESP (Red Edge Spectral Parameter) = R750R710. Here ‘Rλ’ refers to 3 nm bandwidth reflectance centered at wavelength λ. The λ used in GMI (Gitelson and Merzylak Index) = R750R700 and Inverse-Cartera Index (In-CI) = R760R695 wer found located at one-third and one fourth stage of the differential peak response at 64 DAS. The regression relationship between LAI and all the red-edge spectral indices (executed independently) was with r2 = 0.88 − 0.95 range for the decline phase of LAI while statistically significant relationship during growth phase of LAI was only for RESP, GMI, CI and RIhalf . The 3 nm bandwidth hyperspectral indices for ratio in 670–759 nm range to 673 nm had higher sensitivity as compared to corresponding normalized indices during peak vegetative and reproduction phenological stages.