Water turbidity and perpendicular vegetation indices for paddy rice flood damage analyses

Reflectance factors were obtained for paddy rice at two sites in calibrated TM scenes acquired on two dates for the Kanto district of Japan-1 day after a typhoon inundated the paddies (6 August 1986, when the rice was at boot stage of development) and a month later (7 September 1986, during grain filling). A water turbidity index (WTI), analogous to soil brightness, and the perpendicular vegetation index (PVI) were computed for these data as WTI = 0.91RED + 0.43NIR and PVI = - 0.43RED + 0.91NIR, respectively. Rice yield measured for the inundation-damaged paddies and experimental nondamaged paddies at Tsukuba, Japan, were pooled and related to the PVI calculated from the respective TM scene and ground-measured reflectance factors. The ground and TM data coincided well, and the regression relation YIELD (t/ha) = 0.26PVI - 3.0 for the pooled data. The relation between flood water turbidity at boot stage and yield was also examined for the two test sites; the more turbid the flood water, the greater the damage to the crop. The results demonstrate the possibility of spectrally assessing flood damage to rice and other crops.