This parameter describes several different types of absorption: Absorbed radiation by phytoplankton (ARP) This parameter is critical for calculation of fluorescence efficiency, and determining photosynthetic rate of growth of phytoplankton and primary ocean production. Downwelling irradiance is needed as an input to the chlorophyll a algorithm and it is used to convert the normalized water-leaving radiance values into remote-sensing reflectance values. Gelbstoff absorption coefficient It is operationally defined as the absorption coefficient of the material that can fit through a 0.2 micron filter. It is also known as yellow substance or colored dissolved organic material (CDOM) absorption. Chlorophyll a absorption The chlorophyll a absorption coefficient is that part of the absorption coefficient attributable to chlorophyll a. Total absorption This includes includes absorption due to water, phytoplankton, detritus and gelbstoff.