Remote sensing of coastal fronts and their effects on oil dispersion

Abstract

Most estuarine chemistry and pollution studies are based on classical notions of estuarine circulation, in which diluted sea water moving up the bottom of the estuary is mixed and advected upward into an upper layer of relatively fresh water moving downstream. Circulation is assumed to be two-dimensional ( axial and vertical) and salinity variations and flows in the transverse direction are dealt with as minor perturbations on the basic two-dimensional model. Satellite, aircraft and boat observations of estuarine circulation, however, are disclosing numerous fronts which represent regions of discontinuity and high gradients in physical parameters, the most important being the water velocity and density fields. Fronts are formed when a denser fluid under-rides a lighter fluid giving rise to an inclined interface with convergence zones which capture oil slicks and strongly influence the dispersion of surface pollutants. The capture of oil by fronts was observed by airborne remote sensors tracking oil slicks in Delaware Bay as part of a field verification of an oil drift and dispersion model. The model was able to predict oil slick movement over a practical range of wind and current conditions, except when the oil was captured by fronts. To incorporate frontal information into the model, 36 Landsat images were used to prepare 12 maps charting the location of several types of fronts during 12 1-hour segments of the tidal cycle.