Comparison of Sun-Induced Chlorophyll Fluorescence Estimates Obtained from Four Portable Field Spectroradiometers

Abstract

Remote Sensing of Sun-Induced Chlorophyll Fluorescence (SIF) is a research field of growing interest because it offers the potential to quantify actual photosynthesis and to monitor plant status. New satellite missions from the European Space Agency, such as the Earth Explorer 8 FLuorescence EXplorer (FLEX) mission-scheduled to launch in 2022 and aiming at SIF mapping-and from the National Aeronautics and Space Administration (NASA) such as the Orbiting Carbon Observatory-2 (OCO-2) sampling mission launched in July 2014, provide the capability to estimate SIF from space. The detection of the SIF signal from airborne and satellite platform is difficult and reliable ground level data are needed for calibration/validation. Several commercially available spectroradiometers are currently used to retrieve SIF in the field. This study presents a comparison exercise for evaluating the capability of four spectroradiometers to retrieve SIF. The results show that an accurate far-red SIF estimation can be achieved using spectroradiometers with an ultrafine resolution (less than 1 nm), while the red SIF estimation requires even higher spectral resolution (less than 0.5 nm). Moreover, it is shown that the Signal to Noise Ratio (SNR) plays a significant role in the precision of the far-red SIF measurements.

Surface Reflectance and Sun-Induced Fluorescence Spectroscopy Measurements Using a Small Hyperspectral UAS

“…The residual error is lower than a few-tenths of mW m −2 sr −1 nm −1 , and it is probably caused either by slight changes of the reference irradiance spectrum or errors introduced from the 3FLD method. The SIF values retrieved for vegetated targets are higher and fall in the range of values obtained by field spectroscopy measurements reported in the literature [9,[48][49][50]65,72,73]. The obtained results strongly agree with the findings of Rossini et al [73].…”

“…In particular, we computed the far-red fluorescence comparing L inc (λ) and L ref (λ) spectral radiance inside and outside the O 2 -A band, according to the widely-used 3FLD (Fraunhofer Line Depth) approach [8,63]. We limited our analysis to the O 2 -A band because the spectral resolution offered by the USB4000 spectrometer can still provide meaningful results at this broader spectral feature [8,65]; conversely, it is not suitable for retrieving fluorescence at the narrower O 2 -B band. Although the HyUAS measurement approach is very similar to the typical field spectroscopy method, we carried out radiative transfer simulations to assess the impact of atmospheric effects in the limited path length between the target surface and the HyUAS sensor (typically 10 m).…”

Deriving diurnal variations in sun-induced chlorophyll-a fluorescence in winter wheat canopies and maize leaves from ground-based hyperspectral measurements

“…However, it is important to note that our ASD FieldSpec ® 4 Standard-Res Spectroradiometer measurements might overestimate true SIF values due to the relative width of the sensor FWHM and that of the O 2 -A absorption line as has been demonstrated by Julitta et al (2016).…”

Analysis of Red and Far-Red Sun-Induced Chlorophyll Fluorescence and Their Ratio in Different Canopies Based on Observed and Modeled Data

“…Variations in fluorescence emission values related to measurement techniques, type of instrument and setups are not negligible [14]. Damm et al [15] showed how the accuracy of fluorescence retrievals is affected by the spectral and radiometric resolution of the instruments used.…”