The Challenge

Coastal pollution from sewage effluent is a major problem in southern California and other U.S. coastal regions. Inadequate containment may result in beach closings and long-term pollution with significant health and economic impacts. In southern California, beach closures during the tourist season result in the loss of millions of dollars of revenue to local businesses. In some cases, cities or their sanitation districts may be fined appreciable sums for lack of compliance. Monitoring discharges is essential for U.S. coastal sanitation districts that operate under the jurisdiction of an Environmental Protection Agency (EPA) permit process. Renewal of permits is dependent on evidence of compliance derived from regular field monitoring of physical and biological properties. Most sampling is done only on a weekly or monthly basis because of the high costs of field sampling. This schedule leaves large gaps when the sanitation districts and other agencies may lack information on the trajectories of wastewater plumes.

Remote Sensing Application

Incorporating satellite and aerial remote sensing into sewage outfall monitoring programs offers several advantages: (1) large areas can be sampled synoptically at high spatial and temporal resolution for costs significantly lower than those of traditional field surveys; (2) limited field data from key locations can be significantly extended by combining them with remotely sensed information that permits spatial interpolation to broad regional coverage; and (3) gaps in coverage from field sampling can be filled using remotely sensed data of improved frequency and regularity of coverage, and these data can serve as an early-warning system for undetected sewage effluent events. Ocean Imaging Corp. organized a feasibility study with the Orange County Sanitation District to develop new commercial applications for remote sensing of temperature, ocean color, and turbidity. The study used primarily time series of sea surface temperature data from the Advanced Very High Resolution Radiometer (AVHRR) sensor to compute upper-layer currents and estimates of turbidity derived from visible AVHRR data.