Radiative transfer modelling for sun glint correction in marine satellite imagery
Kay, Susan Barbara
Thesis or dissertation
University of Exeter
Remote sensing is a powerful tool for studying the marine environment; however, many images are contaminated by sun glint, the specular reﬂection of light from the water surface. Improved radiative transfer modelling could lead to better methods for estimating and correcting sunglint. This thesis explores the eﬀect of using detailed numerical models of the sea surface when investigating the transfer of light through the atmosphere-ocean system. New numerical realisations that model both the shape and slope of the sea surface have been created; these contrast with existing radiative transfer models, where the air-water interface has slope but not elevation. Surface realisations including features on a scale from 3 mm to 200 m were created by a Fourier synthesis method, using up to date spectra of the wind-blown sea surface. The surfaces had mean square slopes and elevation variances in line with those of observed seas, for wind speeds up to 15 m/s. Ray-tracing using the new surfaces gave estimates of reﬂected radiance that were similar to those made using slope statistics methods, but signiﬁcantly diﬀerent in 41% of cases tested. The mean diﬀerence in the reﬂected radiance at these points was 19%, median 7%. Elevation-based surfaces give increased sideways scattering and reduced forward scattering of light incident on the sea surface. The elevation-based models have been applied to estimate pixel-pixel variation in ocean colour imagery and to simulate scenes viewed by three types of sensor. The simulations correctly estimated the size and position of the glint zone. Simulations of two ocean colour images gave a lower peak reﬂectance than the original values, but higher reﬂectance at the edge of the glint zone. The use of the simulation to test glint correction methods has been demonstrated, as have global Monte Carlo techniques for investigating sensitivity and uncertainty in sun glint correction. This work has shown that elevation-based sea surface models can be created and tested using readily-available computer hardware. The new model can be used to simulate glint in a variety of situations, giving a tool for testing glint correction methods. It could also be used for glint correction directly, by predicting the level of sun glint in a given set of conditions.
Great Western Research; ARGANS Ltd
Kay, S.; Hedley, J.D.; Lavender, S. Sun Glint Correction of High and Low Spatial Resolution Images of Aquatic Scenes: a Review of Methods for Visible and Near-Infrared Wavelengths. Remote Sens. 2009, 1, 697-730.
Susan Kay, John Hedley, Samantha Lavender, and Alex Nimmo-Smith, "Light transfer at the ocean surface modeled using high resolution sea surface realizations," Opt. Express 19, 6493-6504 (2011) http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-7-6493
S Lavender et al., Applying uncertainties to ocean colour data. Metrologia 2012, 49, S17, doi:10.1088/0026-1394/49/2/S17
PhD in Biological Sciences