A method for quantifying freshwater discharge rates from satellite observations and Lagrangian numerical modeling of river plumes

Satellite remote sensing is an efficient tool for identifying buoyant river plumes in the coastal ocean that are formed by the interaction between river discharge and ambient seawater. A new method for reconstructing the volume rates of river discharge based on the shape, extent and orientation of plumes is described that combines the output from a Lagrangian numerical model and analyses of satellite imagery. At the first step in the procedure, a high resolution satellite image is used to identify the river plume. The spatial characteristics of the plume as seen in the image are not determined solely by the current river discharge rate, as they also depend on the hydrographic features in the sea and atmospheric forcing. A previously developed and validated hydrodynamic model for river plumes is run with a variety of forcing conditions to identify the discharge rate that provides the best match between modeled and observed plumes. The method can be applied to estimate indirectly discharge from small rivers and streams, many of which lack direct measurements. Here it has been applied and validated against in situ data for two rivers feeding the eastern part of the Black Sea.