Diffuse reflectance of oceanic shallow waters Influence of water depth and bottom albedo.pdf

Limnol. Oceanogr., 39(7), 1994, 1689-1703
0 1994, by the American Society of Limnology and
Diffise reflectance of oceanic shallow waters: Influence of
water depth and bottom albedo
Stgphane Maritorena
Laboratoire d’Ecologie Marine, Universid Francaise du Pacifique, BP 6570-Faaa/Aeroport, Tahiti, French Polynesia
Andre Morel and Bernard Gentili
Laboratoire de Physique et Chimie Marines, Universite Pierre et Marie Curie RS, BP 8, 06230 Villefranche-
sur-Mer, France
Abstract
We used simplifying assumptions to derive analytical formulae expressing the reflectance of shallow
waters as a function of observation depth and of bottom depth and albedo. These formulae also involve
two apparent optical properties of the water body: a mean diffise attenuation coefficient and a hypothetical
reflectance which would be observed if the bottom was infinitely deep. The validity of these approximate
formulae was tested paring their outputs with accurate solutions of the radiative transfer obtained
under the same boundary conditions by Monte Carlo simulations. These approximations were also checked
paring the reflectance spectra for varying bottom depths positions determined in coastal
lagoons with those predicted by the formulae. These predictions were based on separate determinations
of the spectral albedos of typical materials covering the floor, such as coral sand and various green or
brown algae. The simple analytical expressions are accurate enough for most practical applications and
also allow quantitative discussion of the limitations of remote-sensing techniques for bottom recognition
and bathymetry.
As early as 1944, Duntley used a spectro- designed for optically shallow waters (Philpot
graph mounted in a glass-bottomed boat or 1987); this model was thereafter used to ex-
flown in an airplane to analyze radiances plore the feasibility of mapping bathymetry
emerging from the ocean and shallow waters. with r