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Detection and Estimation of Damage Caused By Thrips Thrips tabaci (Lind) of Cotton Using Hyperspectral Radiometer

Ranjitha G, MR Srinivasan and Abburi Rajesh

Hyper spectral radiometry helps in assessing crop condition in ground based and satellite remote sensing. Use of remote sensing techniques for detection of crop stress due to pests and diseases is based on the assumption that stresses induced by them interfere with photosynthesis and physical structure of the plant, affect absorption of light energy and thus alter the reflectance spectrum of plants. Field experiments were conducted to detect and estimate damage caused by thrips in Surabi variety from 70 to 90 days after sowing using spectroradiometer, from which canopy reflectance was recorded and vegetation indices (VIs) were worked out. The reflectance was a decrease in near infrared (770-860 nm) while blue (450-520 nm), green (520-590 nm) and red (620-680 nm) reflectance increased compared to undamaged plants. Red band (at wavelengths 691 and 710 nm) and Green Red vegetative index (GRVI) were found to be more sensitive to thrips damage. The sensitivity curve shows single peak in blue region (at about 496 nm) which is characteristic of the thrips damage. There was a significant negative correlation between damage and VIs with significant R2 values of VIs indicating their capability to estimate damage. Linear regression equations were developed based on spectral indices and pest damage and a relationship between pest damage and VIs was established. Thus, it was found that detection and estimation of damage caused by cotton thrips can be done using hyper spectral radiometry.