We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Systematic Assessment of Retrieval Methods for Canopy Far‐Red Solar‐Induced Chlorophyll Fluorescence Using High‐Frequency Automated Field Spectroscopy.
- Authors
Chang, Christine Y.; Guanter, Luis; Frankenberg, Christian; Köhler, Philipp; Gu, Lianhong; Magney, Troy S.; Grossmann, Katja; Sun, Ying
- Abstract
Remote sensing of solar‐induced chlorophyll fluorescence (SIF) offers potential to infer photosynthesis across scales and biomes. Many retrieval methods have been developed to estimate top‐of‐canopy SIF using ground‐based spectroscopy. However, inconsistencies among methods may confound interpretation of SIF dynamics, eco‐physiological/environmental drivers, and its relationship with photosynthesis. Using high temporal‐ and spectral resolution ground‐based spectroscopy, we aimed to (1) evaluate performance of SIF retrieval methods under diverse sky conditions using continuous field measurements; (2) assess method sensitivity to fluctuating light, reflectance, and fluorescence emission spectra; and (3) inform users for optimal ground‐based SIF retrieval. Analysis included field measurements from bi‐hemispherical and hemispherical‐conical systems and synthetic upwelling radiance constructed from measured downwelling radiance, simulated reflectance, and simulated fluorescence for benchmarking. Fraunhofer‐based differential optical absorption spectroscopy (DOAS) and singular vector decomposition (SVD) retrievals exhibit convergent SIF‐PAR relationships and diurnal consistency across different sky conditions, while O2A‐based spectral fitting method (SFM), SVD, and modified Fraunhofer line discrimination (3FLD) exhibit divergent SIF‐PAR relationships across sky conditions. Such behavior holds across system configurations, though hemispherical‐conical systems diverge less across sky conditions. O2A retrieval accuracy, influenced by atmospheric distortion, improves with a narrower fitting window and when training SVD with temporally local spectra. This may impact SIF‐photosynthesis relationships interpreted by previous studies using O2A‐based retrievals with standard (759–767.76 nm) fitting windows. Fraunhofer‐based retrievals resist atmospheric impacts but are noisier and more sensitive to assumed SIF spectral shape than O2A‐based retrievals. We recommend SVD or SFM using reduced fitting window (759.5–761.5 nm) for robust far‐red SIF retrievals across sky conditions. Plain Language Summary: Solar‐induced chlorophyll fluorescence (SIF) is light energy emitted by photosynthetic machinery which contains information about photosynthetic activity. SIF retrieval accuracy is crucial for properly interpreting SIF dynamics and understanding its relationships with photosynthesis. Different methods have been developed to retrieve SIF from ground‐based systems, but to date their consistency has not been evaluated under all sky conditions using field measurements. Here we use a combination of continuous field measurements and synthetic data to evaluate the sensitivity of commonly used SIF retrieval methods to variable atmospheric conditions, measurement noise, and changes in canopy structure and biochemistry. We offer recommendations for optimal retrieval method configurations that can be used by SIF ground systems. Key Points: Across sky conditions, SIF‐PAR relationships converge for Fraunhofer‐based but diverge for O2A‐based retrievals, even under clear skiesThe robustness of O2A‐based retrievals under cloudy conditions can be improved by using a narrower fitting windowThese conclusions hold for both bi‐hemispherical and hemispherical‐conical systems; the latter are less sensitive to atmospheric impacts
- Subjects
CHLOROPHYLL spectra; PHOTOSYNTHESIS; REMOTE sensing; REFLECTANCE; BIOCHEMISTRY
- Publication
Journal of Geophysical Research. Biogeosciences, 2020, Vol 125, Issue 7, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2019JG005533