The variable area display o£ seismic data has achieved practically universal acceptance by geophysicists for easy interpretation. In the past, survey recorders aboard ship displayed seismic data in a variable density mode using depth sounder instruments. This report describes a recorder capable of plotting offshore seismic data with rapid access to the recorded data and the visual benefits of variable area recording displays.
The recorder uses a new technique to permit slave operation from the energy source to initiate the display sweep. This permits variable cycle timing of the energy input without concern for the recorder mechanism.
The plot is made by galvanometers on direct write type oscillograph paper for viewing the section as the survey progresses. From one to four galvanometers can be used to record the seismic data. Timing lines are added coincidentally by a xenon flash lamp with .1 second and emphasized 1 second intervals beginning at TØ A crystal oscillator provides the stable time base for the timing line generation and synchronous motor drive as well. A magazine is provided for receiving the exposed section and is always used when film sections are made.
The plot is made on 10 inch wide paper using 9 inches of the surface for the data. Typical plotting speed is 2 inches/second for 4.5 seconds of data. The paper advances automatically at the end of the sweep and the mechanism resets in less than 3 seconds to await another input.
Field results of offshore data are displayed to show typical output of the recorder.
One of the least documented subjects in the field of seismic exploration is that of data display. Volumes of material are written on the theory, the sources, processing techniques and results, but very little on the actual display of the information gathered. The man/machine interface is the ultimate result of all the effort and its importance should not be underestimated. The device to be described, is a variable area recorder for displaying offshore data in the form of a section plot that is accessable as the work actually progresses.
Rieber, in 1936, described a system for field recording using variable density photographic techniques adopted from sound-on-film work.1 This recording method did not receive wide spread adoption but was well known in the industry. A continuous profile of seismic data made from oscillograph film strips placed in sequence was described by Prescott in 1951.2. He remarks that a variable density or variable area oscillograph field record could be used but his displays were all of wiggle trace recordings. A step further in seismic section display was described by Palmer.3 This apparatus used variable density form of presentation from data recorded in the field on 70 mm film strips by variable density tracks. Time corrections were made to the data in plotting the variable density section and the results were of good quality. The use of film recording in the field was not widely adopted due to the emergence of magnetic tape recording techniques.
