Wold-Crosby 1970 Seismic Survey of Flathead Lake
Slides of 1970 field operations provided by Richard Wold and scanned by Bob Lankston in summer 2006
Images of 2006 tape transcription provided by Richard Hess.
The captions for the following images are based on various sources including discussions with Richard Wold and various people familiar with seismic surveying in lakes in the late 1960's and early 1970's. Notations on extant sections from the survey on file at the University of Montana Department of Geosciences yielded some details. Richard Hess of Vignettes Media in Toronto provided details on the field tape recorder and the instrumentation and methods employed for the 2006 recovery of data from an archive tape long stored in the US Geological Survey library at Woods Hole, MA.
Feedback that could improve the captions is welcome. Names of anyone pictured would be most appreciated. Click on any image for a larger view. The larger view will be most useful in seeing details of the hardware. Use your back button to return to this page.
The survey was conducted in August of 1970 and used the University of Montana research station at Yellow Bay as a base of operations. This is an aerial view of Yellow Bay. The main facilities of the research station are in the window glare in the upper right of the image.
The principal investigators were Richard (Dick) Wold of the University of Wisconsin-Madison (UW-M) and Gary Crosby of the University of Montana (UM). This image shows Dr. Crosby standing on the left. The person sitting cross-legged on the deck is believed to be Sidney Prahl, a graduate student at UM. The man sitting on the bow is Ron Friedel, the UW-M technician who, along with Dick Wold, designed and constructed the seismic system. The student standing behind Ron is Carl Brzozowy, a graduate student at UW-M. The name of the person on the left standing on the boat is not known. Dick Wold, being the photographer, is not in any of the pictures
Some members of the survey party apparently had their families with them.
Dr. Crosby (left) and Ron Friedel appear to be working on the air gun source. The yellow object in the foreground is a float from which the air gun was suspended to maintain a constant depth. The suspension frame can be seen around the yellow “bird”.
This view of the stern of the survey boat shows what appear to be two gasoline powered generators (yellow tops) and a gasoline powered air compressor (gray). A pressure gauge can be seen on the deck on a hose extending from the compressor.
The dark rectangle in the bottom center of the image is the power conditioning unit seen in a later image. It is believed that the output from one generator was routed through the power conditioner to the tape recorder and the output from the other generator powered the chart recorder.
Ron Friedel working on the air compressor or air gun.
Student working on one of the gas powered generators. The yellow object hanging on the boom over the stern is the bird that supported the air gun assembly.
This view shows the air gun support bird that was towed. The air gun can be seen on the port side step at the end of the support harness.
The bird in the water with the survey boat underway. View is to the northeast from the Bird Island area.
This is a view of the port side of the stern. This is believed to show the deployment of the hydrophone. Hydrophone cable is coiled on the roof of the boat's cabin being secured with a rope tied to the hand rail. The cable extends to the red end of the boom and then just above the surface of the water to a white splash in the water.
The Wold 1982 USGS paper (MF 1433) states that boat positions were determined from paired theodolite readings from the shore. The exact process employed is not known. For example, were the two theodolite stations on opposite sides of the lake during a seismic traverse?
The Wold paper shows the positions of the lines on his basemap, but only a few of the lines are labeled. The existing seismic sections at the University of Montana Department of Geosciences show the times of “sextant” readings, but no actual surveyor's notes are in the file. The seismic sections have line labels, e.g., Line E, and notations indicating approximate locations of line ends, e.g., Blue Bay. This information is being captured an integrated with the Wold paper and the recently digitized data.
This appears to be a frequency regulated power supply, i.e., the label left of the meter can be read when the original scanned slide is enlarged. This unit probably stabilized the power that was used for the tape recorder. Stable power levels and alternating current frequency would have been more important for the tape recorder than for the paper recorder.
This is the tape recorder that was used during the survey. It was a readily available, economy, studio-grade instrument in the late 1960’s and early 1970’s. This particular model is a Magnecord 1024. As with the power conditioner, the label can be read in an enlarged image. The recorder used ¼ in tape on 7 in reels. This recorder, as arranged, appears to be capable of recording four channels simultaneously. In concept, one channel on the tape recorded the seismic data, and another channel recorded a timing pulse. With no surviving field tape, the actual recording scheme is not known. Although the stock recorders usually ran at 3.75 and 7.5 in/s (known then as i.p.s.) some versions could be special-ordered that included an 1.88 (1-7/8) in/s speed. These recorders would have low frequency response to 20 Hz or below, especially at the lower speeds, but did not go to DC. Low-frequency anomalies are always present in "direct" recording on magnetic tape as a result of head contour effects. This Magnecord is essentially an audio recorder. The copy of the USGS archive tape that was recently digitized was made as an FM tape on an instrumentation recorder, i.e., the archive tape is some sort of transcription of the field tape(s).
The tape recorder was the heart of the seismograph system, which was designed and assembled at the University of Wisconsin-Madison.
This is a view of the paper chart recorder. Whether or not the paper recordings that have survived at the University of Montana Department of Geosciences were made in real time is not known, but real time recordings probably were made for acquisition QC if nothing else. Because the data were on tape, they could have been played back on shore to make paper sections for interpretation. The 1982 USGS paper by Wold references post-acquisition processing by Sidney Prahl. Whether the sections preserved by the University of Montana Department of Geosciences are original field recording or playbacks of the data is not known.
This is the same section in the previous image just rotated into a more vertical perspective. The lake bottom reflection is clearly evident in this section. The base of the lake and basin fill sediments might be interpreted as the base of the generally featureless zone. In the water section, the ringing of the air gun source is obvious, and this source signature is imprinted on the actual geologic signal, e.g, an image of the water bottom reflection is obvious. Modern digital processing should be able to sharpen the source signature and to collapse the diffraction arcs. The timing lines on the section are believed to be 25 ms. Time zero on the section is not clear. The travel time to the lake floor reflection in the center of the section is either (approximately) 125 or 150 ms, depending on how time zero is defined, or between 300 and 375 ft, i.e., this section crosses a very deep part of the lake. This section may correlate to the east-most south-north line in the Wold 1982 paper. That line crosses Skidoo Bay and ends near Yellow Bay. To date (January 2007), this section has not been recognized in the data that were recovered from the USGS archive tape. Based on the duration of the recording on the archive tape and comparison of sections made from the digitized data, only 1/3 of the data from the survey was copied to the archive tape.
The original sections were made by placing a dot on the paper along the respective traces at discrete times whenever the signal amplitude was in excess of some threshold value. Individual dots are discernible in the original sections. This is a small portion of one of the sections that has been preserved by the University of Montana Department of Geosciences. This image, provided by recent University of Montana Ph.D. graduate Michael Hofmann, covers about 1.5 mi in the center of the lake on Wold's Line D, which extends approximately from Angel Point on the west to Woods Bay on the east. West is to the left in this image. The pale line that tracks the apparent water bottom reflection is on the paper section. This interpretation of the water bottom possibly tracks some diffraction arcs thereby missing the locations of sharp reflecting points that may indicate normal faulting or glacially faceted basement rocks.
As part of the 2006 data recovery project, Bob Lankston added some interpretation suggestions to the section above to indicate the importance of modern processing. The green line is interpreted to be the lake bottom reflection and differs somewhat from the pencil line referenced in the previous frame. In the central part of the section, the lake bottom reflection could be essentially horizontal in the vicinity of the yellow line but is being obscured by source noise. However, the strong event indicated by the green line is probably the lake bottom reflection. Attenuation of the source noise should resolve questions like this. The blue lines could indicate the base of lake sediments or the base of Tertiary basin fill. The red lines are interpreted normal faults based on the crests of the diffraction arcs. The timing line interval is 25 ms. The brown wavy line is a suggestion of what the actual waveform might be, but determining amplitudes from this sort of display is not possible.
This is the same section in the previous two images after digitization of analog data on the archive tape in the USGS library at Woods Hole. The data have been presented in variable area format using the program gnuplot. No bandpass filtering, agc, or other processing has been applied to the data. The main features of the previous image can be recognized, though they appear slightly later in this image than in the original section above. This is a result of parameters that were set in the program that extracted the traces from the digital file. The position of time zero will be adjusted as part of the planned processing. Processing using modern algorithms to filter, deconvolve, and migrate the data is in progress with the hope of enhancing reflections within the basin fill section and of better defining the basin bounding structures.
Dick Wold left the University of Wisconsin-Madison and then worked for the USGS for a number of years in the late 1970’s and early 1980’s. Gary Crosby left the University of Montana in 1973 and worked for a major petroleum company. Both scientists are engaged in consulting pursuits now.
When interest in the Wold-Crosby survey surfaced in early 2006, Bob Lankston learned that the USGS library in Woods Hole, MA, had an analog tape of the data. Nancy Soderberg, the USGS archivist had very little information about the tape. However, she checked the tape out to Bob so that he could attempt to recover the analog data and convert them to a modern seismic format. In a modern format, the data could be deconvolved to sharpen the source signature and reduce multiples and migrated to collapse the diffraction arcs.
Because the seismic system was built outside of the conventional seismic industry, no petroleum industry seismic lab in Houston, New Orleans, or Wales (UK) was able to read the tape. After considerable internet research, Bob found a service company in suburban Toronto that specializes in recovering data from old analog audio recordings, which the USGS archive tape seemed to be. Analysis of the archive tape and conversion of the analog signals to digital .wav files was done by Richard Hess of Vignettes Media.
Because so little was known about the tape, the first thing that Richard Hess did was “develop” the tape. This is a process of applying a solution of “iron filings” to the tape and seeing how they align. This image shows the results of such a test on the USGS archive tape. Even before this test was done, however, it was clear that the archive tape was not a field tape. The Magnecord 1024 used ¼ in tape on 7 in reels. The archive tape was ½ in wide, as can be seen in this image, and on a 10 in reel. Therefore, the archive tape had to be a transcription of the original field tape or tapes. The number of tracks on the tape was not known. Various tape head standards exist for ½ in tape, including 2, 4, 7, 8, and more tracks. Richard determined that this tape was recorded with the IRIG format. IRIG (Inter-Range Instrumentation Group) was developed for missle-range work and is embodied in many versions of IRIG Standard 106. It is now considered obsolete.
This tape was recorded on a machine with a two part head assembly with 7 interleaved tracks, i.e., 3 heads on one part of the assembly intercalated with 4 heads on the other part of the assembly. Fortunately, the data were on tracks 2 and 4, which were both on one of the two head assemblies and are indicated by the light gray stripes in the right half of the tape. While the field recorder was most likely a common audio deck, the transcribed archive tape was made with an instrumentation recorder, not an audio recorder. Audio and instrumentation are similar, but are not identical. Also, how the tape was wound on the reel was not known, i.e., did it need to be rewound to get to the beginning. Richard was able to resolve these and many other issues in order to read the tape in analog form and then to digitize the analog signals.
The USGS archive tape is on the right spindle on Richard Hess’ playback machine. While this Sony machine is essentially an audio recorder, Richard has a set of IRIG Standard 106 7-track heads specially mounted on a spare head block so that he can handle this obsolete format. The heads themselves were from a Racal Store 7DS instrumentation recorder that a colleague was coincidentally converting to an audio transport. Unfortunately, the Racal Store 7DS does not take the size reel that the Flathead Lake tape came on.
This is a screen capture from Richard Hess’ early tape analysis efforts. The vertical red bars in the second track from the top, track 2 in the developed tape image above, are the high energy burst at the start of each seismic trace. They occur at approximately 4 s intervals. Other periodic energy bursts at 10-12 s intervals were interpreted to be residual noise from a previous tape erasure episode.
Direct playback and digitization of the analog tape yielded the upper trace. This did not have the appearance of seismic signals. Richard Hess did additional analysis of the digitized signals and research on the equipment of the 1970’s and deduced that the data on the USGS archive tape were FM. The lower trace is the result of demodulating the upper trace. This looks more like a seismic trace. The timing lines are 50 ms making this image a little more than 300 ms.
Richard Hess digitized the two tracks on the USGS archive tape and delivered .wav files that were images of each track. He also decimated the standard 44 kHz sampling of the .wav files to 1 kHz sampling and 8 kHz sampling. Bill Menger, manager of seismic processing at ConocoPhillips, set about converting the seismic data in the 1 kHz and 8 kHz .wav files to SEG-Y format. At the same time, Bob Lankston took a slightly different approach which led to a series of images of the data on the tape such as the variable area section above. Bob used an open source program called sox to convert the .wav file to tabular ASCII. The ASCII file was reformatted for input to Excel using gawk. Excel was chosen for extracting the individual traces because of its ready plotting capability. The files did not seem to have any indication of trace starts. Therefore, a scheme had to be developed to recognize the high energy of the direct arrival at the hydrophone. A scheme was developed in Excel, and approximately 5000 traces were recovered from the file for one of the two tracks. The scheme was not perfect, and as much as 5% of the traces was not recovered. Work is ongoing to see if the missing traces can be extracted from the file. Bill faced the same difficulty and undertook developing the trace start recognition scheme in C. Ideally, both schemes should deliver the same results. Bill's provided a regular set of 4 s traces, but gaps and misalignments exist in the SEG-Y files also. To date, extracting the discrete traces from the continuous stream of traces has been the most difficult problem in dealing with the digital data.
Excel was satisfactory for developing the trace start scheme, but it was not suitable for plotting large numbers of traces. The open source program gnuplot was used to plot the more or less 5000 traces. The table below contains links to images of 16 sections. The horizontal axis in the sections is time in seconds on the archive tape divided by 100. The maximum time indicated on the final section is 215, which is 21500 s of playback time. Shots were approximately 4 s apart which gives 25 traces between the horizontal index lines on the sections. Traces are approximately 10 m apart.
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The 2007 Data Processing Experiments
The University of Montana Department of Geosciences has digitally scanned all of the sections, handwritten notes, and interpretation sketches that have survived in their files for over 35 years, and the department is making a digital archive from which copies of the old sections can be readily made. Discrete traces have been extracted from the .wav files into various formats for modern processing.
gnuplot was an improvement over Excel for plotting variable area sections. However, for processing the data and to make use of more sophisticated data display tools, another major step up was needed. The Seismic Unix (SU) package developed by the Center for Wave Phenomena (CWP) at the Colorado School of Mines was installed on a dual boot PC and is being used for processing the digital traces. Early tests show promise that images more detailed than the original sections can be generated. Examples of processed sections will be posted here when they become available.