BIDIRECTIONAL REFLECTANCE OF OCEANIC WATERS - A COMPARISON OF MODELEDAND MEASURED UPWARD RADIANCE FIELDS

The bidirectional reflectance of oceanic waters is conveniently descri bed in a normalized way by forming the ratio of the upwelling irradian ce E(u) to any upwelling radiance L(u)(theta', phi). This ratio, Q[the ta', theta(0), (phi(0) - phi)], where theta', phi are the nadir and az imuth angles for the upward radiance and theta(0), phi(0) are the zeni th and azimuth angles of the Sun, has been determined from measurement s at sea and computed via Monte Carlo simulations using the inherent o ptical properties measured in the field and appropriate boundary condi tions (clear sky, no wind, varying Sun angle). Experimental and comput ed Q values are in excellent agreement. This successful comparison con firms the importance of the bidirectional character of ocean reflectan ce, already pointed out from a purely numerical approach without field validation, and corroborates the extended range of the Q variations. The later point is of importance when interpreting the marine signals detected by an ocean color satellite-borne sensor. The validation is e xtended by considering the historical data for the radiance distributi ons in Lake Pend Oreille determined at various depths. The closure iss ue in ocean optics is examined by solving the direct problem of radiat ive transfer and through a model-data comparison in terms of radiance field.