Exploring the applicability of field measurements of mid-infrared reflectance using a portable band-pass filter type radiometer to assess paddy rice yields

Abstract

There are few case studies concerning field radiometric measurements in the mid-infrared (MIR) wavelengths for crop plants. This article describes radiometric experiments measuring reflectance in the MIR bands (3.425 ± 0.1 and 3.9 ± 0.1 μm) to evaluate the number of panicles (NP, m−2) of ripening paddy rice using a portable band-pass filter type spectroradiometer. First, laboratory experiments were conducted using containers filled with rice grains of various 1000-grain weights and fresh and dry slashed rice culms plus leaf sheaths, leaf blades and panicles. The intensity of light from the sun or electric bulbs reflected from the grains or plant organs was measured in the MIR, visible (VIS), near-infrared (NIR) and short-wave infrared (SIR) bands. Heavier grains and dense panicles reflected less in the MIR bands than lighter grains and the same occurred in the SIR bands. Field measurements were conducted for several plots of ripening rice where the panicles were partly plucked beforehand. The trial showed that the instrumentation and the method for measuring MIR band reflectance factors were usable for investigating the possibility of MIR measurements for NP.