可視・近赤外カメラによる茶葉摘採時期の決定および樹勢判定

摘要

生育中の茶葉のテアニン，タンニン，繊維等の成分を計測し，摘採時期を決定することは当該成分を確認したうえで茶葉を摘むことにより，品質が保証できることから極めて重要である。衛星搭載可視近赤外放射計データを用いて茶葉成分の計測が可能であるが，この際，空間分解能もさることながら観測頻度が問題となる。観測頻度は衛星の回帰日数，クロストラックポインティングによる観測頻度の向上を考慮しても，なおかつ晴天率に依存する。%Method for determination of tealeaves harvest timing with ground based visible and near infrared cameras is proposed together with tea tree vitality assessment. Off-nadir viewing cameras acquire not only tealeaves but also shadow and shaded portions of tealeaves as well as soil surface which depend on illumination conditions of the sun, soil surfaces and winds. In order to avoid these influences on determination of tealeaves harvesting timing, a method to extract tealeaf surfaces of which the tealeaf surfaces are pointing to zenith direction. Relations between Near Infrared: NIR data which is acquired with the proposed ground based NIR camera and nitrogen and fiber contents in tealeaves as well as harvest amount of tealeaves are clarified. Meanwhile, tea tree vitality is defined as nitrogen contents in harvested tealeaves multiplied by harvesting amount per unit area. A method for tea tree vitality estimation with satellite remote sensing visible to near infrared radiometer data which are acquired in February time frame is also attempted. The proposed method is validated with ground truth data of nitrogen and fiber contents in tealeaves and harvest amount of tealeaves. The estimation results of tea tree vitality are displayed on Geographic Information System: GIS together with satellite imagery data and ground truth data. Thus leaf tea producing process can be controlled with the GIS derived information by tea fields.