Estimating Biomass and Nitrogen Amount of Barley and Grass Using UAV and Aircraft Based Spectral and Photogrammetric 3D Features. - Roope Näsi; Niko Viljanen; Jere Kaivosoja; Katja Alhonoja; Teemu Hakala; Lauri Markelin; Eija Honkavaara (Remote. Sens., 2018)