The technique is described to isolate the diffuse component of the sea water reflectance by measuring the S and P polarization components of the upwelling radiation. This technique far extends capabilities of remote shipborne measurement of the chlorophyll A concentration from the ocean color and enhances their accuracy. In particular, it allows measurements at rough sea, overcast conditions, and at different sighting angles. Examples of applying this technique to field measurements of the chlorophyll A concentration are presented.