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Solar induced chlorophyll fluorescence has been shown to be increasingly an useful proxy for the estimation of gross primary productivity (GPP), at a range of spatial scales. Here, we explore the seasonality in a continuous time series of canopy solar induced fluorescence (hereafter SiF) and its relation to canopy gross primary production (GPP), canopy light use efficiency (LUE), and direct estimates of leaf level photochemical efficiency in an evergreen canopy. SiF was calculated using infilling in two bands from the incoming and reflected radiance using a pair of Ocean Optics USB2000+ spectrometers operated in a dual field of view mode, sampling at a 30 min time step using custom written automated software, from early spring through until autumn in 2011. The optical system was mounted on a tower of 18 m height adjacent to an eddy covariance system, to observe a boreal forest ecosystem dominated by Scots pine. (Pinus sylvestris) A Walz MONITORING-PAM, multi fluorimeter system, was simultaneously mounted within the canopy adjacent to the footprint sampled by the optical system. Following correction of the SiF data for O2 and structural effects, SiF, SiF yield, LUE, the photochemicsl reflectance index (PRI), and the normalized difference vegetation index (NDVI) exhibited a seasonal pattern that followed GPP sampled by the eddy covariance system. Due to the complexities of solar azimuth and zenith angle (SZA) over the season on the SiF signal, correlations between SiF, SiF yield, GPP, and LUE were assessed on SZA <50° and under strictly clear sky conditions. Correlations found, even under these screened scenarios, resulted around ~r2 = 0.3. The diurnal responses of SiF, SiF yield, PAM estimates of effective quantum yield (ΔF/Fm′), and meteorological parameters demonstrated some agreement over the diurnal cycle. The challenges inherent in SiF retrievals in boreal evergreen ecosystems are discussed.

Accurately determining the field-of-view (FOV) is a basic requirement in photogrammetry and imaging spectroscopy but has rarely been considered in detail in field spectroscopy where the specifications for different spectroradiometers generally lack clarity or detail. The issue can be further compounded with full spectral systems (0.4 to 2.5µm) which include multiple spectrometers; in these systems the size and alignment of the viewing optics may cause significant spectral non-uniformity across the theoretical measurement area. When recording spectra from heterogeneous targets it is important to have the FOV accurately defined because distinct reflecting surfaces may be present in varying proportions. We assessed the FOVs of the Analytical Spectral Devices Field Spec Pro FR and Spectra Vista Corporation GER 3700 spectroradiometers. The resulting directional response functions are plotted, highlighting several areas of concern.