Optical characteristics of small surface targets, measured in the False Bay, South Africa; June 2007

During the False Bay trial (June 2007), the performance of a set of three optical sensors was tested against several small surface targets in a coastal area: a hyperspectral camera, a camera with a rotating polarization filter and a high resolution camera. One objective was the validation of a contrast and clutter model for the visual spectral band in this type of scenarios. Another issue was to test the benefit of using a polarisation filter and a hyperspectral unit in front of standard TV cameras. Finally the loss in identification capability of a high resolution camera at long range due to atmospheric blur was investigated. Data were collected of targets in near-sun direction at ranges up to seven kilometers, in all cases for down looking angles (targets below the horizon). Environmental parameters such as solar irradiance and windspeed were measured as input for the contrast and clutter models. Spatial, spectral and temporal effects of the target contrast and of the background clutter behaviour in the visual spectral band were determined as function of range and compared with model predictions. Samples of data and predictions are presented in this paper. The spatial and temporal target characteristics are of key importance for the development of algorithms for target detection, classification and tracking. Finally, rules of thumb, based on the measurements and model predictions, on the detection and identification range performances of specific optical sensors against small surface targets in a maritime environment are presented.