ODM2 Variable Name Controlled Vocabulary ODM2 Working Group A vocabulary for describing the name of Variables. Photosynthetic photon flux density (PPFD) The number of photons per unit time and per unit area in the wavelength band 400 to 700 nm Wikipedia https://en.wikipedia.org/wiki/Photosynthetically_active_radiation Added to support Critical Zone Observatory (CZO) data use cases.