SIFSpec: Measuring Solar-Induced Chlorophyll Fluorescence Observations for Remote Sensing of Photosynthesis

Abstract

Solar-induced chlorophyll fluorescence (SIF) is regarded as a proxy for photosynthesis in terrestrial vegetation. Tower-based long-term observations of SIF are very important for gaining further insight into the ecosystem-specific seasonal dynamics of photosynthetic activity, including gross primary production (GPP). Here, we present the design and operation of the tower-based automated SIF measurement (SIFSpec) system. This system was developed with the aim of obtaining synchronous SIF observations and flux measurements across different terrestrial ecosystems, as well as to validate the increasing number of satellite SIF products using in situ measurements. Details of the system components, instrument installation, calibration, data collection, and processing are introduced. Atmospheric correction is also included in the data processing chain, which is important, but usually ignored for tower-based SIF measurements. Continuous measurements made across two growing cycles over maize at a Daman (DM) flux site (in Gansu province, China) demonstrate the reliable performance of SIF as an indicator for tracking the diurnal variations in photosynthetically active radiation (PAR) and seasonal variations in GPP. For the O2–A band in particular, a high correlation coefficient value of 0.81 is found between the SIF and seasonal variations of GPP. It is thus concluded that, in coordination with continuous eddy covariance (EC) flux measurements, automated and continuous SIF observations can provide a reliable approach for understanding the photosynthetic activity of the terrestrial ecosystem, and are also able to bridge the link between ground-based optical measurements and airborne or satellite remote sensing data.

Comparison of Bi-Hemispherical and Hemispherical-Conical Configurations for In Situ Measurements of Solar-Induced Chlorophyll Fluorescence

“…Several types of ground-based systems have been employed for continuously monitor vegetation SIF during the past few years. Up to now, the most acceptable construction of this kind of system (e.g., FLoX, FluoSpec2, Photospec and FAME) integrates spectrometers from Ocean Optics Inc.: FLAME/HR2000+, QEPro, with splitters fiber and inline TTL for sequentially measuring and switching between solar irradiance and vegetation radiance [18,23,27]. Our new built SIFprism was derived from a prism system developed by Ari Kornfeld and Joe Berry (Department of Global Ecology, Carnegie Institution for Science), and the part of splitter fiber and inline TTL was replaced with a rotary prism box.…”

“…During the past few years, many kinds of instruments were employed for continuous vegetation canopy spectra observation and were usually set up at flux tower sites [20]. Based on prototypes (e.g., TriFLEX, MRI, SFLUOR box, SIF-system) [12,21,22], many improved systems (e.g., FluoSpec, SIFSpec, PhotoSpec) [13,18,23,24] were developed in addition to existing commercial products such as FLoX (JB Hyperspectral Devices UG, Düsseldorf, Germany) and Piccolo Doppio (University of Edinburgh, Edinburgh, UK) [14]. Thus far, the widely accepted spectrometer for SIF measurement is QEPro (Ocean Optics Inc., Dunedin, FL, USA), which has a typical signal to noise ratio (SNR) of 1000 and can be customized with red and far-red regions (mostly 730-780 nm or 650-800 nm) granting the full width half maximum less than 0.3 nm.…”

“…Thus far, it seems that the hemi-con configuration was used more in the field than it's counterpart [20,23] although each of them have their own merits. The upwelling sensor of the hemi-con configuration can be installed at the nadir or off-nadir point at any places of interests but is strongly influenced by the sun-target-viewer geometry, which needs to be considered at either a diurnal or seasonal scale [16,[38][39][40].…”

Advances in Quantitative Earth Remote Sensing: Past, Present and Future

“…The fourth paper, by Du et al [4], is focused on development, test and evaluation of a sensor for in situ measurements of sun-induced fluorescence (SIF), which is used widely in the study of terrestrial ecosystems gross primary production and their contribution to the cycling of carbon in the Earth system. SIF is considered as a proxy for photosynthesis in terrestrial vegetation.…”

A Spectral Fitting Algorithm to Retrieve the Fluorescence Spectrum from Canopy Radiance

“…Joiner et al, (2016) [10] and Wolanin et al, (2015) [11] were the only attempts to retrieve red F from GOSAT and SCIAMACHY, respectively. Conversely, studies based on measurements collected by field spectrometers [12][13][14][15][16] and airborne high-resolution imaging spectroscopy [17][18][19][20][21][22] more frequently considered both the red and far-red F.…”