Abstract
During recent decades, solar-induced chlorophyll fluorescence (SIF) has shown to be a good proxy for gross primary production (GPP), promoting the development of ground-based SIF observation systems and supporting a greater understanding of the relationship between SIF and GPP. However, it is unclear whether such SIF-oriented observation systems built from different materials and of different configurations are able to acquire consistent SIF signals from the same target. In this study, we used four different observation systems to measure the same targets together in order to investigate whether SIF from different systems is comparable. Integration time (IT), reflectance, and SIF retrieved from different systems with hemispherical-conical (hemi-con) and bi-hemispherical (bi-hemi) configurations were also evaluated. A newly built prism system (SIFprism, using prism to collect both solar and target radiation) has the shortest IT and highest signal to noise ratio (SNR). Reflectance collected from the different systems showed small differences, and the diurnal patterns of both red and far-red SIF derived from different systems showed a marginal difference when measuring the homogeneous vegetation canopy (grassland). However, when the target is heterogeneous, e.g., the Epipremnum aureum canopy, the values and diurnal pattern of far-red SIF derived from systems with a bi-hemi configuration were obviously different with those derived from the system with hemi-con configuration. These results demonstrate that different SIF systems are able to acquire consistent SIF for landscapes with a homogeneous canopy. However, SIF retrieved from bi-hemi and hemi-con configurations may be distinctive when the target is a heterogeneous (or discontinuous) canopy due to the different fields of view and viewing geometries. Our findings suggest that the bi-hemi configuration has an advantage to measure heterogeneous canopies due to the large field of view for upwelling sensors being representative for the footprint of the eddy covariance flux measurements.
Highlights
Remote sensing methods have long been used for monitoring vegetation, usually using reflectance-based vegetation indices (VIs) and other vegetation parameters derived from spectral measurements [1]
We conducted a field experiment for solar-induced chlorophyll fluorescence (SIF) measurements from four different observation systems (SI and SIII built from existing construction, system II (SII) newly built and SIV bought as a commercial product) together to find out whether SIF from different systems are comparable
We investigated the impacts of different field of view (FOV) on the SIF observations
Summary
Remote sensing methods have long been used for monitoring vegetation, usually using reflectance-based vegetation indices (VIs) and other vegetation parameters derived from spectral measurements [1]. These VIs may fail to detect short-term changes in plant function as most of them do not have a direct connection with the photosynthetic functioning of the plants [2]. To collect high-precision data, spectrometers are usually embedded in temperature-controlled box, keeping away from humidity and fluctuation of temperature, which may cause reduces of SNR Such automatic and long-term mounted systems are able to collect temporally continuous data and to monitor diurnal and seasonal dynamics of SIF, especially to analyze SIF with concurrently measured bioclimatic parameters and carbon flux [18,25–28]
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