# Folia-authored index — not present in Awesome Spectral Indices at pinned SHA.
# Spec: docs/spec/SPECTRAL_INDICES.md
# Lifecycle: registry/indices/folia/README.md
slug: pri
name: Photochemical Reflectance Index
short_name: PRI
formula: (R531 - R570) / (R531 + R570)
bands:
  - R531
  - R570
domain: vegetation
theme: vegetation
concepts:
  - light-use-efficiency
  - vegetation-stress
rank: null
display:
  colormap: rdylgn
  range: [-0.2, 0.2]
references:
  - url: https://doi.org/10.1016/0034-4257(92)90059-S
date_of_addition: '2026-06-07'
contributor: https://github.com/folia-org
platforms:
  - PRISMA
  - EnMAP
  - DESIS
  - AVIRIS
  - Sentinel-2  # approximate via B3 (G ~560nm) + B6 (RE1 ~740nm); narrow-band ideal
source:
  authority: folia
  upstream_id: null
  url: https://doi.org/10.1016/0034-4257(92)90059-S
  note: |
    Not in Awesome Spectral Indices at pinned commit 7f28d3fe. Genuine gap
    in ASI upstream — PRI is a well-cited narrow-band physiology index
    (Gamon et al. 1992; ~7k Scholar citations as of 2026). Hand-curated by
    Folia. Upstream PR pending. Migrate to ASI-synced lifecycle when
    accepted upstream.
match_tags:
  - light-use-efficiency
  - photosynthesis
  - pigment
  - pri
  - r531
  - r570
  - reflectance
  - vegetation
  - xanthophyll
status: experimental