We use spectral measurements for learning about the spectral response of ground materials and land vegetation phenology as a reference for satellite measurements. We are establishing a network of spectral sites for continuous monitoring of vegetation close to carbon flux towers. The aim of these measurements is to obtain calibration and validation data and to better understand satellite measurements. Currently, we are measuring at a number of locations across Fennoscandia and in Greenland (see map below). We also operate sites in the Sudan. More about the network is given in Eklundh et al. (2011).
We have installed spectral instruments on towers above the canopies, and tilted the instrument in order to measure within the footprint areas of current flux towers. These instruments measure incoming and reflected radiation in the green, red and near-infrared (NIR) wavelengths, for estimation of vegetation indices like the normalized vegetation index (NDVI), the photochemical reflectance index (PRI), and our newly formulated plant phenology index (PPI; Jin and Eklundh, 2014a). We also measure incoming, reflected and intercepted broad-band photosynthetically active radiation (PAR) for estimation of the fraction of incoming photosynthetically active radiation absorbed by vegetation (FAPAR). Most of our sensors are produced by SKYE Instruments Inc. We also carry out field campaigns in selected study areas, measuring with handheld spectroradiometers produced by ASD Inc. and PP Systems.
To maintain accurate long-term measurements we have developed an in-situ method for calibrating radiation instruments (Jin and Eklundh 2014b).
Our spectral measurements are part of the following international networks: