Mitigating the effect of optical back-scatter in multispectral underwater imaging

Spectral information of an underwater scene, which can be found from a set of underwater multispectral images, is a very useful technique for extracting information from underwater world. But, underwater imaging is problematic even in multispectral image format. The main problem is the effect of optical back-scatter, which changes the scene reflectance value in each spectral band and this causes inaccuracy in the spectral information. In this work, a filter is used to detect the level of optical back-scatter in each spectral band from a set of multispectral images. Extraction of an underwater object spectra can be done by subtracting the estimated level of optical back-scatter and scaling the remainder in each spectral band from the captured image in the corresponding band. An experiment is designed to show the performance of the proposed filter for correcting the set of multispectral underwater images and recovering the pixel spectra. The multispectral images are captured in 33 bands in clear and different levels of turbid water. The results of processing experimental images in turbid water show that the effect of optical back-scatter can be mitigated in the image of each spectral band and as a result the spectra of the object can be recovered. However, for very high level of turbid water the recovery is limited because of the effect of extinction.