Brownout Cloud Characterization Using the Modulation Transfer Function

The paper describes how to extract the modulation transfer function (MTF) of a brownout cloud from video recordings of specific optical patterns. The MTF is a measure of the loss of contrast and resolution caused by the cloud and can be used as the basis for a quantitative metric of brownout severity. The application of two MTF calculation methods to actual flight test data is described. One requires the use of specially designed targets, such as a Siemens star, the other relies on simple dark/light visual edges. The results show that MTF extraction can be successfully performed with a standard consumer-level video equipment and appropriate postprocessing. Also, MTF extraction can be automated using suitable image-processing techniques. The results rigorously quantify the intuitively known facts that the visual degradation caused by brownout is a space- and time-dependent phenomenon and that high spatial frequency features, i.e., fine-grained detail, are obscured before low spatial frequency features, i.e., large objects.