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

Milton Hom,Micol Rossini,Elizabeth Middleton,Andreas Burkart,Uwe Rascher,Neville Davies,Lawrence Corp,Roberto Colombo,Sergio Cogliati,Anke Schickling,Tommaso Julitta,Alasdair Mac Arthur

doi:10.3390/rs8020122

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.

Highlights

Active chlorophyll-a fluorescence measurements have been used, both in laboratory and in the field, to better describe physiological processes of plants, such as photosynthesis, carbon fixation and stress [1]
The graph reports the mean values of the 60 solar radiance spectra measured with the different spectroradiometers in the spectral range (670–800 nm) covered by all of the spectrometers
This study shows an empirical inter-comparison between spectroradiometers with different performance characteristics and their impacts on Sun-Induced Chlorophyll Fluorescence (SIF) retrievals

Summary

Introduction

Active chlorophyll-a fluorescence measurements have been used, both in laboratory and in the field, to better describe physiological processes of plants, such as photosynthesis, carbon fixation and stress [1]. Fluorescence (SIF) from remote sensing platforms have been developed, opening unprecedented opportunity to monitor canopy fluorescence at the ecosystem scale. This will lead to a better understanding of the significance of spatial variability in the SIF signal and will facilitate the up-scaling from the canopy to the landscape levels [2]. SIF is an electromagnetic signal emitted throughout the red and near-infrared (NIR) spectrum by chlorophyll-a, the primary photosynthetic pigment in green vegetation, in response to the absorption of photosynthetically active radiation from the sun. The global estimation of SIF from space is relevant due to its potential for improving our ability to accurately quantify terrestrial photosynthesis and to monitor plant functional status of ecosystems

Methods

Results

Conclusion