What does it mean when the absorption proportion of aph_443_qaa + adg_443_qaa + aw (POPE & FRY, 1997) related to a_443_qaa does not make 100%? May I understand there is something else absorbing light (fishes or floating bodies) or is it some kind of error inherent to the method (sensor or algorithm accuracy)? 

I found out some images where aph_443_qaa + adg_443_qaa + aw are much greater than 100% and some other images (more usual) where the result is less than 100% related to a_443_qaa. How can I explain that? Specially the first case