This paper presents the results of satellite-image digital processing. The area of study covered Patos Lagoon (southern Brazil). Suspended matter distribution was used as conservative traces. Circulation patterns and their changes over time were also characterized. The process involved fitting an empirical relation function between digital intensity values for selected bands of the spectra (optical properties) and the values measured in situ corresponding to the satellite data. The 1999 and 2001 field campaigns involved measurements of suspended matter, water surface temperature and wind direction and velocity inside the lagoon. The lagoon covers nearly 10,360 km2. It is 250 km long along its NE-SW axis and 40 km wide. We applied algorithms widely used in remote sensing in our methodology. First, we generated maps of the spatial distribution of selected parameters. After that, we extracted the boundaries to define areas with constant reflectivity associated with the isoconcentration of suspended matter and zones of equal temperature (isothermal). We evaluated images with different hydrologic time series, including high, medium and low discharges from tributaries. This allowed us to identify the plumes of rivers, their size and changes over time, and the general circulation of different water masses inside Patos Lagoon.