PACE OCI Level-3 Global Mapped Apparent Optical Properties Data, version 3.2

Users apply AVW for water-type classification, algorithm selection/blending (e.g., guiding chlorophyll retrievals), regional change detection, and as context alongside chlor_a, Kd_490, IOPs, and PAR. Fluorescence Line Height (FLH) quantifies the red chlorophyll-a fluorescence (~678-683 nm) emitted by phytoplankton, computed as the height of the measured water-leaving radiance above a spectrally interpolated baseline. FLH is widely used for HAB detection and tracking, identifying productive waters, and assessing phytoplankton physiology; values tend to be elevated in active blooms and can be reduced in complex waters.

Aerosol Optical Thickness (AOT) represents the column-integrated aerosol loading in the atmosphere, describing the attenuation of light due to scattering and absorption by aerosols. AOT is a key parameter in atmospheric correction and is also used to study aerosol transport, air quality, and aerosol-ocean interactions. Remote Sensing Reflectance (Rrs) provides the remote sensing reflectance at wavelength λ (nm) - the ratio of water-leaving radiance to downwelling irradiance just above the surface (units sr^-1).

Variables are named by their band center (e.g., Rrs_412, Rrs_443). Rrs_λ is the foundational observable used to retrieve products such as chlor_a, Kd_490, IOPs, and to support algorithm development, validation, water-quality, and ecosystem applications. Users should review per-file quality flags (e.g., land, cloud, sun glint, high aerosol) and mission documentation - especially in optically complex coastal/inland waters.

As with all ocean-color retrievals, uncertainties increase in optically complex coastal/inland waters or under high aerosol/glint; users should refer to per-mission algorithm notes and quality flags before analysis. Usage notes: - Rrs and Rrs_unc are stored as scaled integers; use the scale_factor and add_offset attributes to obtain physical values. - Quality control should use l2_flags per the flag_meanings attribute to mask clouds, land, high glint, and other conditions.

Geophysical variables in this suite include: - Rrs - Remote sensing reflectance (sr^-1) - aot_865 - Aerosol optical thickness at 865 nm (unitless) - angstrom - Aerosol Angstrom exponent, 443-865 nm (unitless) - avw - Apparent Visible Wavelength (nm) - nflh - Normalized Fluorescence Line Height (W m^-2 um^-1 sr^-1)