SPECTROMETER FOR FAST MEASUREMENTS OF IN-VIVO REFLECTANCE, ABSORPTANCE, AND FLUORESCENCE IN THE VISIBLE AND NEAR-INFRARED

A new type of VIRAF spectrometer (Visible Infrared Reflectance Absorptance Fluorescence), the VIRAF II, is presented The VIRAF spectrometer has been developed and constructed for ground truthing of remote sensing of terrestrial vegetation and for other types of ecophysiological measurements. It is a multipurpose instrument with the capability to measure reflectance, absorptance, and fluorescence in the visible and near-infrared (400-910 nm). The Position of the sample is unchanged throughout the measurements, which guarantees a good comparison between the different types of spectra. since leaf samples can be left intact and attached to the plant, real in vivo measurements as well as long-term and repetitive studies using different addition techniques can be carried out. In contrast to conventional spectrometers, the sample is illuminated with strong white (or blue) light and only a narrow angle of the reflected, transmitted or emitted light is detected. This mimics the outdoor situation in remote sensing Furthermore, the strong light maintains the physiological activity of the leaf sample. The new VIRAF II described here has a diode array detector and a shutter which enables to measure within 20 ms. This opens the possibility for studies of kinetic changes in the range of seconds or minutes. Results are presented from a comparison of light green leaves of an Aurea mutant and dark green leaves of a wildtype tobacco plant (Nicotiana tabacum L.). The data are interpreted in terms of difference in chlorophyll concentration, leaf tissue structure, epidermis structure, and photosynthetic activity. Slight differences between the 20-ms reflectance spectra of a dark-adapted leaf taken directly after onset of illumination and after 60 s or 180 s of continuous illumination (decrease between 650 nm and 800 nm and increase between 400 nm and 600 nm) may be attributed to changes of the chlorohyll fluorescence and to chloroplast movements, respectively, reflecting physiological activity of the sample.