Automated field spectroscopy systems for collecting continuous measurements of radiance/reflectance in support of hyperspectral satellite missions

Continuous and long-term ground-based field spectroscopy measurements have a relevant role in support of future hyperspectral satellite missions. In this contribute we present two automated field spectroscopy systems (named Multiplexer Radiometer Irradiometer, and S-FluorBox) capable of collecting unattended, continuous, long-term (seasonal) hyperspectral measurements. These systems simultaneously collect high and ultra-high resolution spectra in the visible to near-infrared (VNIR) domain employing two spectrometers: (i) the first covers the spectral range 400–1000 nm with a 1.0 nm spectral resolution; (ii) the second provides a sub-nanometer spectral resolution within the 700–800 nm spectral range. The data collected by the first spectrometer allow retrieval of VNIR reflectance, while the higher spectral resolution data from the second device permit estimation of vegetation Sun-Induced Fluorescence (SIF) in the O2–A band (Cogliati et al., 2015). The automated field spectroscopy systems were mainly developed for vegetation studies and SIF retrieval from high-resolution data. However, they can be exploited for studying temporal dynamics of important geo-physical parameters useful for monitoring other land cover types. In particular, the instruments have been operated in several field campaigns with the aim to show: (i) the possibility of continuous and seasonal monitoring of plant growth and activity of an agricultural crop; (ii) the diverse and specific daily course patterns of different types of vegetation ecosystems; (iii) the capability of detecting intra- and inter-daily Chlorophyll-a concentration dynamics of a small fluvial lakes (Mantua lake, Italy). The studies conducted on land vegetation show that the spectral measurements collected for the entire growth cycle of a crop show the potential of such instruments in monitoring canopy temporal evolution. Part of the datasets were collected in collaboration with NASA/GSFC in the framework of dedicated airborne hyperspectral surveys. This allowed us to operate the MRI/S-FluorBox instruments in synergy with the multi-angular observations collected by the FUSION system (Corp et al., 2010). The case study related to the assessment of in-land water quality proved the possibility of retrieving Chlorophyll-a concentration, and to depict the intra- and inter-daily variability in the lake. The concentration values were correlated with meteo-climatic parameters, showing that solar radiance and wind speed are key factors regulating the daily phytoplankton growth and dynamics (Bresciani et al., 2013). The continuous measurements of down-welling irradiance could be further exploited to derive atmospheric properties. For this reason, the automated field spectroscopy system is currently running at the atmospheric-chemistry experimental site of the University of Milan-Bicocca. The preliminary comparison between optical and chemical/physical measurements will be shown.