Jin et al. (2026) Guiding VI selection for phenology monitoring: Differential sensitivity of vegetation indices to temporal dynamics in canopy leaf area and pigment

Identification

• Journal: Remote Sensing of Environment
• Year: 2026
• Authors: Jiaxin Jin, Xiaolong Cheng, Yulong Cai, Yuanwei Qin, Qiuan Zhu, Weifeng Wang, Peiqi Yang, Jianbo Qi, Feng Zhou, Guishan Yang, Jin Wu
• DOI: 10.1016/j.rse.2026.115296

Research Groups

• State Key Laboratory of Water Disaster Prevention, Hohai University, China.
• Jiangsu Key Laboratory of Soil and Water Processes in Watershed, College of Geography and Remote Sensing, Hohai University, China.
• School of Biological Sciences and Institute for Climate and Carbon Neutrality, The University of Hong Kong, China.
• State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, China.
• Faculty of Geographical Science, Beijing Normal University, China.
• College of Biology and the Environment, Nanjing Forestry University, China.

Short Summary

This study disentangles the influence of canopy structure (leaf area) and leaf biochemistry (pigments) on 21 vegetation indices used for phenology. It identifies that while most indices (e.g., NDII, EVI) track leaf area expansion, a specific subset (e.g., CVI, MTCI) is required to accurately monitor leaf chlorophyll maturation.

Objective

• To systematically evaluate the differential sensitivity of 21 common vegetation indices (VIs) to temporal dynamics in canopy leaf area index (LAI) versus leaf chlorophyll content (LCC).
• To determine which VIs best represent structural versus pigmental spring phenology (Start of Growing Season, SOS).

Study Configuration

• Spatial Scale: Northern Hemisphere deciduous broadleaf forests (DBF), including site-specific analysis at Harvard Forest (USA), De Inslag (Belgium), and New Forest National Park (UK), plus broad-scale validation across mid-to-high latitudes.
• Temporal Scale: Field observations from 1997, 2014, and 2016; satellite-based validation using MODIS data from 2001 to 2020.

Methodology and Data

• Models used: PROSAIL (coupling PROSPECT-5 and 4SAIL) for hyperspectral canopy reflectance simulation; LESS (3D radiative transfer model) for structural complexity validation.
• Data sources: Field-measured LAI (LAI-2000, hemispherical photography) and LCC (spectrophotometric analysis, SPAD-502); MODIS Nadir BRDF-Adjusted Reflectance (MCD43A4) and Land Cover (MCD12C1).
• Analysis: Perturbation experiments shifting LAI and LCC timelines by 1–10 days; five phenology extraction methods (10%, 20%, 50% thresholds, logistic inflection point, and maximum VI ratio).

Main Results

• VI Divergence: 14 VIs (including NDII, EVI, NIRv, and NDVI) primarily reflect canopy leaf area development. NDII showed the highest sensitivity to LAI expansion.
• Pigmental Tracking: 4 VIs (CVI, MTCI, GCVI, and CIre) specifically track pigment-related phenology (LCC). CVI was identified as the most sensitive indicator for pigmental onset.
• Mixed Sensitivity: 3 VIs (SR, NDRE, GNDVI) exhibited weak or mixed sensitivity to both drivers.
• Phenological Offset: Field and satellite data confirm that leaf area expansion (LAI-based SOS) precedes pigment maturation (LCC-based SOS) by approximately 15 to 31 days in deciduous broadleaf forests.
• Scale Effects: Several indices designed for leaf-level biochemistry (e.g., PRI, MCARI) function primarily as structural indicators at the canopy scale due to the dominance of multi-layer scattering.

Contributions

• Provides a mechanistic guide for selecting VIs based on specific research goals (structural vs. biochemical phenology).
• Resolves long-standing inconsistencies in VI-derived SOS estimates by attributing them to the fundamental spectral design and mathematical formulation of the indices.
• Recommends the explicit distinction between "leaf area" and "pigmental" phenophases in global change studies to improve ecological relevance.
• Identifies NDII and CVI as robust, unambiguous markers for leaf expansion and chlorophyll maturation, respectively.

Funding

• National Key Research and Development Program of China (2024YFF0808704).
• National Natural Science Foundation of China (41971374, 42571144).
• HKU Seed Funding for Strategic Interdisciplinary Research Scheme.
• Hong Kong Research Grant Council Collaborative Research Fund (#C5062-21GF).
• Innovation and Technology Fund (State Key Laboratory of Agrobiotechnology).
• Jiangsu Specially Appointed Professor Program.

Citation

@article{Jin2026Guiding,
  author = {Jin, Jiaxin and Cheng, Xiaolong and Cai, Yulong and Qin, Yuanwei and Zhu, Qiuan and Wang, Weifeng and Yang, Peiqi and Qi, Jianbo and Zhou, Feng and Yang, Guishan and Wu, Jin},
  title = {Guiding VI selection for phenology monitoring: Differential sensitivity of vegetation indices to temporal dynamics in canopy leaf area and pigment},
  journal = {Remote Sensing of Environment},
  year = {2026},
  doi = {10.1016/j.rse.2026.115296},
  url = {https://doi.org/10.1016/j.rse.2026.115296}
}

Generated by BiblioAssistant using gemini-3-flash-preview (Google API)