PROBLEM TO BE SOLVED: To enable accurate water content measurement of a target leaf even when the target leaf is located among a group of exuberant leaves by eliminating influence of scattered light (external light scattering) from surrounding leaves.SOLUTION: When evaluating water content of a plant, a white background board (background object) is placed to cover the back face of a leaf PT3 of the plant PT. A first projection light source irradiates the leaf PT3 with near-infrared light (reference light) having a wavelength of 905 nm, which is poorly absorbed by water. A second projection light source irradiates the leaf PT3 with near-infrared light (measurement light) having a wavelength of 1550 nm, which is easily absorbed by water. A threshold setting/water content index detection processor computes a water content index of one leaf as a sum ΣLn(I905/I1550) of reflection intensity ratios at all irradiated locations on the leaf PT3 based on reflections of the reference light and measurement light reflected at all the irradiation locations on the leaf PT3.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2017,JPO&INPIT【課題】多数の葉が生い茂った葉群の中にあっても、周辺の葉からの散乱光(外光散乱)による影響を排除し、測定対象の葉の水分量を正確に測定する。【解決手段】植物の水分量を評価する際、植物PTの葉PT3の背面を覆うように、白色背景板(背景物)を配置しておく。第1投射光源が、水分に吸収され難い特性を有する波長905nmの近赤外光(参照光)を葉PT3に向けて照射する。第2投射光源が、水分に吸収され易い特性を有する波長1550nmの近赤外光(測定光)を葉PT3に向けて照射する。閾値設定/水分指数検出処理部は、葉PT3の全照射位置において反射した、参照光の反射光と測定光の反射光とを基に、葉PT3の全照射位置における反射強度比の総和ΣLn(I905/I1550)である葉1枚の水分指数を算出する。【選択図】図1
