Measuring visual opacity using digital imaging technology.

The U.S. Environmental Protection Agency (EPA) Reference Method 9 (Method 9) is the preferred enforcement approach for verifying facility compliance with federal visible opacity standards.

Evaluation of the digital opacity compliance system in high mountain desert environments.

The digital opacity compliance system (DOCS) has been proposed as an alternative to the U.S. Environmental Protection Agency Reference Method 9 (Visual Determination of the Opacity of Emissions for Stationary Sources).