Ship perturbation of irradiance measurements at sea 1: Monte Carlo simulations

Most in-water irradiance and radiance measurements at sea are carried out by suspending an instrument from a hydrocable located relatively close to the ship, the presence of which can severely perturb the in-water light field. This paper describes Monte Carlo techniques which have been developed specifically to assess such perturbations. Sample computations of the perturbation to the upward and downward irradiances due to the presence of the ship are presented for the case of a homogeneous ocean. The results reveal situations in which the downward irradiance, in the case of collimated illumination, is relatively unperturbed, while large effects are observed in the case of diffuse illumination. Conversely, the upwelled irradiance just beneath the surface is seen to be strongly influenced by the ship’s presence for both types of illumination.