From Hyperspectral Indices to Global Fluorescence: PACE Vegetation Indices as Predictors of Terrestrial Photosynthesis

Solar-induced chlorophyll fluorescence (SIF) serves as a direct remotely sensed indicator of photosynthetic activity, making it a valuable tool for assessing terrestrial productivity. However, the practical application of satellite-derived SIF is hindered by spatial resolution limitations and data gaps. The NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission presents an opportunity to overcome these challenges through its hyperspectral Ocean Color Instrument and globally distributed Land Vegetation Index (LANDVI) product suite. This study's primary contribution lies in demonstrating that PACE vegetation indices alone can reliably predict SIF from global retrievals obtained using data from the Copernicus Sentinel-5P Tropospheric Monitoring Instrument (TROPOMI), even in the absence of PACE BRDF and albedo products (and their associated corrections). Using 8-day global composites from 2024, we establish a temporal and spatial correlation between PACE indices and TROPOMI SIF (TROPOSIF) across fifteen biome-stratified study regions, including forests, grasslands, agricultural systems, and xeric landscapes. Simple univariate linear models reveal that the Enhanced Vegetation Index (EVI) and the Chlorophyll Index Red Edge (CIRE) are the most reliable global predictors of SIF, accounting for 80% and 77% of the variance, respectively. Notably, the stability of the EVI-SIF and CIRE-SIF relationships across seasons further emphasizes the significant role of canopy structure and chlorophyll information captured by these two indices in explaining global SIF variability. Seasonal analyses indicate that while EVI and CIRE are most effective in most forests and agricultural systems, moisture-sensitive indices and pigment indices perform better during dry seasons and transitional periods in water-limited ecosystems. Spatial residual analyses suggest minimal global bias but systematic underestimation in boreal forests and selected tropical regions, which aligns with established effects of canopy architecture and fluorescence escape probability. Considering that EVI, in particular, is available even from moderate-resolution Earth resource satellite missions such as Sentinel-2 and Landsat, there is substantial potential for SIF downscaling to management and policy-relevant scales.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Forestry

Department dc:contributor.department

Forest Resources and Environmental Conservation

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2026

Author dc:creator

• Harmon, Caleb Sloan

Chairs dc:contributor.committeechair

• Wynne, Randolph H.
• Thomas, Valerie Anne

Committee member dc:contributor.committeemember

• Huemmrich, Karl Fred

• Solar-induced chlorophyll fluorescence
• PACE mission
• Ocean Color Instrument
• Hyperspectral vegetation indices
• Enhanced Vegetation Index
• Chlorophyll Index Red Edge
• Gross Primary Productivity
• Global terrestrial ecosystems
• Carbon cycle monitoring

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:45384

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/140839