What's in the water that changes ocean color (NOAA-21)

The Inherent Optical Properties (IOP) suite provides per-pixel inherent optical properties - quantities that describe how seawater and its constituents absorb and scatter light, independent of illumination or viewing geometry. IOPs are retrieved from spectral Remote Sensing Reflectance (Rrs) using the default configuration of the Generalized Inherent Optical Properties (GIOP) model framework. These products support water-type classification, water-clarity assessment, biogeochemical studies, and forward/adjoint radiative-transfer applications, and they enable more robust cross-sensor comparisons than purely apparent (AOP) products. Geophysical variables in this suite include: - a — Total absorption coefficient (sum of pure water + phytoplankton + CDOM/detritus, m⁻¹) - bb — Total backscattering coefficient (m⁻¹) - l2_flags — Level-2 processing flags (bitmask; see per-variable attributes for flag_masks and flag_meanings). - aph_445 — Phytoplankton absorption coefficient at 445 nm (m⁻¹) - aph_unc_445 — Uncertainty in absorption due to phytoplankton at 445 nm (m⁻¹) - adg_445 — Combined CDOM + non-algal detritus absorption coefficient at 445 nm; accompanied by adg_s (spectral slope, units nm⁻¹). - adg_unc_445 — Uncertainty in absorption due to gelbstoff and detrital material at 445 nm (m⁻¹). - bbp_445 — Particulate backscattering coefficient at 445 nm (m⁻¹); include bbp_s (power-law slope, unitless) describing spectral shape. - bbp_unc_445 — Uncertainty in particulate backscattering at 445 nm (m⁻¹). - rrsdiff — Fractional mean Rrs difference (reconstructed from inverted IOPs - input) (needs units).