Preserving amplitude in high-resolution marine geophysical profiles

High-resolution seismic and side-scan sonar images built up by stacking density-modulated line traces can properly represent signal amplitude in terms of image density. Faithful representation is possible only if signal amplitude is maintained at all steps in processing, including compensation for spherical spreading loss and conversion of the amplified signal to image density on the electrically or photographically sensitive paper or film. Copying may degrade the original recordings, especially the dark portions representing high noise level or full-wave-detected strong signal. Microfilm copies from the original can retain amplitude information better than paper copies, and can be reproduced inexpensively by contact printing. Quality control test objects incorporated in any form of copying can be a gauge of quality of intermediate copying as well as of the end product. Original recordings well suited to copying can be made with fiber-optic cathode ray tube (CRT) recorders directly on photographic film. Calibration of amplitude and test patterns could be incorporated in a microfilm image made directly from the CRT. Contact prints of this original would be the cheapest form for disseminating copies of better quality than forms generally used now. Negative microfilm developed for low contrast and exposed for maximum density 2 can be successfully enlarged to make good quality work prints.