Using reflectance to reduce solar angle effects on the scattering of far-red solar-induced chlorophyll fluorescence to better track the diurnal dynamics of gross primary productivity

IF 5.7 1区农林科学 Q1 AGRONOMY

Agricultural and Forest Meteorology Pub Date : 2025-08-18 DOI:10.1016/j.agrformet.2025.110794

Xuhui Lu , Peiqi Yang , Alasdair Mac Arthur , Christiaan van der Tol

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引用次数: 0

Abstract

Solar-induced chlorophyll fluorescence (SIF) is linked to photosynthesis and provides reliable estimation of Gross Primary Productivity (GPP). However, SIF observed (SIF_obs) at the top-of-canopy is theoretically less accurate in predicting GPP compared with the total emitted SIF (SIF_total). Converting remotely sensed SIF_obs to SIF_total is therefore crucial for improving GPP estimation. SIF_obs is a portion of SIF_total and their ratio is termed the fluorescence escape ratio (f_esc), describing the scattering and re-absorption processes. f_esc is affected by canopy structure and sun-observer geometry. Vegetation indices, such as the Fluorescence Correction Vegetation Index (FCVI) and the near-infrared reflectance of vegetation (NIR_v), have been developed to estimate f_esc and SIF_total with reasonable accuracy particularly under varying viewing angles scenarios. However, their performance in estimating f_esc and SIF_total has not been well-studied for a diurnal scale, in which solar angles vary. Solar angles affect both f_esc and SIF_total, while viewing angles affect f_esc but not SIF emission. In this study, we analyzed the solar angle effects on far-red SIF scattering and mitigated the effects by leveraging these indices to estimate f_esc, facilitating the derivation of SIF_total for improving GPP estimation. Numerical experiments were employed to support the use of FCVI and NIR_v for f_esc estimation under varying chlorophyll content (C_ab), leaf angle distribution (LAD) and leaf area index (LAI) conditions. SIF_total was derived to enhance the accuracy of GPP estimation at the diurnal scale in filed measurements. Our results indicated that both FCVI and NIR_v reliably estimated f_esc under varying solar angles. Moreover, SIF_total improved the SIF-GPP relationship, with R² increasing to 0.43 – 0.80, compared to SIF_obs (0.12 < R² <0.52), and its diurnal pattern was more consistent with that of GPP. Our study suggested that the use of FCVI and NIR_v for f_esc mitigates solar angle effects on SIF_obs and thus improves GPP estimation.

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利用反射率降低太阳角度对远红色太阳诱导叶绿素荧光散射的影响，更好地跟踪总初级生产力的日动态

太阳诱导的叶绿素荧光（SIF）与光合作用有关，并提供了对总初级生产力（GPP）的可靠估计。然而，与总排放SIF （SIFtotal）相比，在冠顶观测到的SIF （SIFobs）理论上对GPP的预测精度较低。因此，将遥感sifb转换为SIFtotal对于改进GPP估计至关重要。sifbs是SIFtotal的一部分，它们的比值被称为荧光逸出比（fesc），描述了散射和再吸收过程。Fesc受冠层结构和太阳观测器几何形状的影响。植被指数，如荧光校正植被指数（FCVI）和植被的近红外反射率（NIRv），已经开发出合理的精度估算fesc和SIFtotal，特别是在不同视角的情况下。然而，在太阳角度变化的日尺度下，它们在估算fesc和SIFtotal方面的性能尚未得到很好的研究。太阳角度影响fesc和SIF总量，而视角影响fesc但不影响SIF发射。在本研究中，我们分析了太阳角度对远红SIF散射的影响，并利用这些指标来估计fesc，从而减轻了SIF散射的影响，为提高GPP估计提供了方便。在不同叶绿素含量（Cab）、叶角分布（LAD）和叶面积指数（LAI）条件下，利用FCVI和NIRv进行fesc估算。为了提高田间测量在日尺度上估算GPP的精度，导出了SIFtotal。结果表明，在不同太阳角度下，FCVI和NIRv都能可靠地估计fesc。此外，SIFtotal改善了SIF-GPP的关系，其R²比SIFobs （0.12 < R2 <0.52）增加到0.43 - 0.80，其日变化规律与GPP更一致。我们的研究表明，使用FCVI和NIRv进行fesc减轻了太阳角度对sifob的影响，从而提高了GPP的估计。

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来源期刊

Agricultural and Forest Meteorology 农林科学-林学

CiteScore

10.30

自引率

9.70%

发文量

415

审稿时长

69 days

期刊介绍： Agricultural and Forest Meteorology is an international journal for the publication of original articles and reviews on the inter-relationship between meteorology, agriculture, forestry, and natural ecosystems. Emphasis is on basic and applied scientific research relevant to practical problems in the field of plant and soil sciences, ecology and biogeochemistry as affected by weather as well as climate variability and change. Theoretical models should be tested against experimental data. Articles must appeal to an international audience. Special issues devoted to single topics are also published. Typical topics include canopy micrometeorology (e.g. canopy radiation transfer, turbulence near the ground, evapotranspiration, energy balance, fluxes of trace gases), micrometeorological instrumentation (e.g., sensors for trace gases, flux measurement instruments, radiation measurement techniques), aerobiology (e.g. the dispersion of pollen, spores, insects and pesticides), biometeorology (e.g. the effect of weather and climate on plant distribution, crop yield, water-use efficiency, and plant phenology), forest-fire/weather interactions, and feedbacks from vegetation to weather and the climate system.