The development of a hyper spectral imager for forest monitoring

The hyper-spectral reflectance factor over the forest canopy is expected to obtain the information, related to the health condition, leaf biochemical contents ratio and photosynthetic activity. A hyper spectral imaging system was developed in order to take the hyper-spectral images of the forest canopy in the daytime automatically. This paper describes the outline of this imaging system and initial result of acquired images of Tomakomai Flux research site. A spectroscope and the 2-dimensional CCD camera constitute this imager and cover the wavelength range from approximately 500nm to 980nm with a spectral resolution of 5nm. This imager has been installed at the top of the CO 2 flux measurement tower of the 25m heights which was built in the forest of Japanese larch (Larix Kaempferi). The perpendicular viewing angle is 25 degrees, and the horizontal scan is performed by rotation of the computer-controlled stage. The maximum horizontal rotation angle is 340 degrees. The data acquisition is carried out from 8 a.m. to 6 p.m. in the 2-hour interval. In 2003, the observation was carried out between June to the end of November. In advance observation period, this imager was calibrated by using standard lamp and integrating sphere to transform the observed value of each pixel into radiance or reflectance. By using these images, narrow waveband NDVI (normalized difference vegetation index) which has correlation in the vegetation biomass and PRI (photochemical reflectance index)are calculated. When seasonal change of NDVI was obtained according to the individual trees, having a different seasonal change pattern was observed with larch, the broadleaf trees, and the grass of a background. Furthermore, PRI of larch canopy changes with the photosysthetically photon flux density (PPFD) was found.