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ABSTRACT: Digital Image Processing Techniques for Enhancement and Classification

Thomas Beckett Reed

The recent growth in the production rate of digital side-scan sonar images, coupled with the rapid expansion of systematic seafloor exploration programs, has created a need for fast and quantitative means of processing seafloor imagery. Regrettably, many synoptic imaging systems suffer noise degradation, produce distorted images, and provide imagery that is difficult for humans to interpret (i.e., an image of what the bottom sounds like). Computer-aided analytical techniques are presented to alleviate these problems and fill this need. A number of numerical techniques used to enhance and classify imagery produced by SeaMARC II, a long-range combination side-scan sonar and bathymetric seafloor mapping system, are documented. Most of the techniques are generalizable to alte nate imagery and bathymetry systems. Three categories of techniques are presented: (1) preprocessing corrections (radiometric and geometric), (2) feature extraction, and (3) image segmentation and classification. The correction routines produce images and maps that are faithful representations of the seafloor, free of system-induced errata. The feature extraction routines can be tailored to both detect known shapes and characterize geologic textures. The classifications routines, based on input from the feature extractions, yield thematic maps, which can be correlated with geologic samples to allow rapid areal subsea mapping. While significant correlation of the classification signatures with intrinsic geologic properties is pending, a strong correlation between image texture and surface roughness has been shown. These techniques are applied to SeaMARC II imagery from a variety of geologic environments, including lithified and nonlithified sedimentary formations, volcanic and sedimentary debris flows, and crystalline basaltic outcrops. Application of the above processing steps provided not only superior images for both subjective and quantitative analysis, but also the critical ability to discriminate between outcrops with radically distinct lithologies but similar image intensity.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990