Use Of Polarization Methods In Earth Resources Investigations

Relatively little attention has been paid to the potential of polarization techniques to provide additional information for the mapping of earth resources, compared to the published work concerning other active and passive remote sensing systems. Recently, a substantial number of polarized light images of a variety of terrestrial scenes have been obtained from the Space Shuttle. A boresighted pair of Hasselblad cameras was used, in which polarization filters were fitted. The polarization directions were perpendicular to each other for the two cameras. Image pairs were acquired with one image being of maximum intensity, and the other showing minimum intensity. Selected pairs of images, obtained using black and white films, were digitized. The images were registered and compared, using digital image analysis techniques. Differences due to polarization were observed, these included intensity and contrast differences, together with differences in the spatial frequency, orientation and population of observable contrast boundaries. It was found empirically that some digital image analysis techniques enhanced the differences. A comparison of the enhanced difference images, obtained from the polarization pairs, with the intensity data that would have been obtained without the aid of polarization filters, confirms that a considerable degree of new, useful information may be obtained by the use of polarization techniques. This new information was most helpful in better defining the observed ground features in the cases studied. This is because the better definition of contrast boundaries, improvement of contrast across boundaries, improvement of shadow detail and reduction of noise level increases the useful information in an image, and improves its interpretability.