The results were published in 1969 as H.O. Pub. 1301, Bathymetric Atlas of the North Pacific Ocean.
MAPPING THE NORTH PACIFIC OCEAN SEA FLOOR
T. E. Chase, Associate Specialist in Marine Geology
S. M. Smith, Associate Specialist in Submarine Geology
Scripps Institution of Oceanography
Abstract: A series of sea floor topographic and physiographic charts of the North Pacific Ocean are being prepared for the Under-sea Surveillance Oceanographic Center (NAVOCEANO). In addition, reliable bathymetric and magnetic data throughout the Pacific are being put into digital storage.
Divided into three areas, the coverage consists of 160 topographic charts originally prepared at approximately 1:1,000,000 scale, then reduced to about 1:2,500,000 for printing into three atlases; 10 composite contour charts, and 10 physiographic diagrams will be prepared for distribution throughout the scientific and naval communities. 49 charts between latitudes 0° to 60°N and longitudes 100°E to 160°E are completed and published in an atlas form. Three composite charts covering the area are also completed and undergoing color separation and printing.
Computer programs have been developed to aid in processing data, and to date 392,000 miles of bathymetry and 206,000 miles of magnetics plus navigational tracks have been digitized.
On July 1, 1967, the Scripps Institution of Oceanography began a contract with the Undersea Surveillance Oceanographic Center of NAVOCEANO to prepare a series of charts and a digital tape of bathymetric soundings of the North Pacific Ocean.
The purposes of these efforts are many, and two are of immediate importance.
Increased studies of the origin and history of the Pacific basin are important to the fields of Marine Geology and Geophysics. Detailed bathymetric sea floor charts are critically needed in such studies.
Within many research organizations, studies of sound trans-mission in water along selected paths are often interrupted by topographic features. Here, reliable charts are also important. The majority of existing sea-floor contour charts, however, have been found to be of a smaller scale, contour interval, or too old to aid in these studies.
Four series of charts are being produced: physiographic charts (10 sheets); bathymetric contour charts (10 sheets); bathymetric contour charts at approximately 1:1,000,000 scale (160 sheets); and 3 atlases of bathymetric contour charts.
The charts are a compilation and interpretation of the best bathymetric contours and sounding data available, and they present a complete series of topographic and physiographic charts for ease in referencing the floor of the North Pacific Ocean. They are designed for use by interested persons or groups working in the marine sciences as a quick reference to bathymetric contours and physiographic provinces.
Figure 1 shows the distribution of and numbering system for location of the charts. The heavy borders are small-scale regional contour and physiographic charts. Areas I, II, and III are boundaries of the three atlases. Area I is contoured, and 49 charts are published in the Bathymetric Atlas of the Northwestern Pacific Ocean. Figure 2 shows a page from that atlas. (H. O. Pub. 1301.)
The atlas of area I contains 49 bathymetric charts covering nearly 7-1/2 million square miles of the North Pacific Ocean between 4°S and 60°N latitude and between 100°E and 160°E longi-tude, including the South and East China, Yellow, Japan and Okhotsk Seas.
SOURCES OF DATA
Figure 3 shows the different sources of data used. The most useful were original echograms or soundings with high navigational quality.
J. C. Sylvester, Bathymetry Division (NAVOCEANO), supplied random soundings for each chart plus microfilm copies of original echograms and ships' navigational tracks.
Marine Geophysical Surveys, NAVOCEANO, supplied original echo-grams of detailed cruises in the North Philippine Sea. The ASW/USW Project, NAVOCEANO, under Mr. W. T. Hammond, supplied soundings of extensive surveys in the Sea of Japan. Published charts from the Maritime Safety Agency, Japan and the USSR gave detail in areas where soundings were sparse.
Echo sounding equipment used to gather data for the charts included the Edo Corporation Sonar Sounding Set AN/UQN-1B, Westrex Corporation Mark V, X, and XV Precision Depth Recorders (PDR), Thomas Gifft Company Depth Recorder (GDR), Alden Electronic and Impulse Recording Equipment Company, Inc., Precision Graphic Recorder (PGR), Alpine Geophysical Associates, Inc., Precision Echo Sounder Recorder (PESR), and Kelvin-Hughes Echo Sounder.
EVALUATION OF DATA
All data was evaluated for its importance in preparing the contour charts and for digitizing into the data bank. Unfortu-nately, many of the random soundings were of value in predicting topographic trends but lacked enough orecise navigational information to warrant inclusion in the digital data collection.
A large segment of the data was shown on charts and sounding sheets contoured in meters, both corrected and uncorrected for sound velocity. These were converted to "uncorrected" fathoms by use of Matthew's Tables of the Velocity of Sound in Pure Water and Sea Water.
Initially, efforts were made to use digital (computer) output for the chart preparation. However, the random spacing of pre-cision sounding information with precise navigation was insuffi-cient. Therefore, it was necessary to prepare a data tape separately and to develop the charts by visual interpretation and manual cartographic methods with extensive use of stable base materials.
DIGITIZING OPERATION
Data from smoothed navigation plots were digitized onto IBM cards using the Benson-Lehner OSCAR 5-2 XY Reader. After the cards are run through data checking programs and errors removed, they are input to a program which produces a magnetic tape containing time in accumulated minutes and positions at these times. A parallel series of operations are carried out on the echograms and magnetic records, using a CALMA 480 in addition to the B-L OSCAR, the final product being another magnetic tape having time in accumulated minutes and the depth or magnetic field values at these times. Most of the depth data were digitized on the OSCAR at 3 to 5 minute intervals of ship time (1/2 to 1 mile apart), the remainder being done on the CALMA at 1 minute intervals. The interval for magnetic data was 6 minutes. The navigation and depth on magnetic value tapes are used in turn as input to another pro-gram which merges the navigation and depth or navigation and magnetics onto another tape that becomes the primary storage for the expedition. The merged data can then be used for profiles at various scales and vertical exaggerations (Figure 4), sounding plots of single expeditions, sounding compilations of many cruises within a given area (Figure 5), statistical analyses, and trans-mission to other agencies. Additional programs are being developed for producing computer plotted index track charts of digitized data as well as bathymetric and magnetic profiles plotted along tracks on Mercator projection. As of March 1969, 392,000 miles of bathymetry and 206,000 miles of magnetics have been processed.
CONCLUSIONS
The efforts expended during the chart preoaration has resulted in contours of many previously uncharted seamounts, trend determinations of other primary structural features like trenches and ridges, plus limits of large physiographic provinces.
Basic knowledge of structural and tectonic conditions were used throughout the chart preparations. Where sounding data was not sufficient to give detailed portrayal, interpolation was ex-tended to gain the most accurate configuration.
The charts presented here do not represent the final configuration of the sea floor, for many precise and detailed surveys are needed to give complete coverage. It is felt, however, that the different scales, contour interval, and physiographic interpretation used is sufficient to give as complete a sea-floor portrayal as possible with the present data available and knowledge of geologic features.
(Note: Figure 1 is not shown here but may be seen along with the entire report on the web at: usnavysymposiumo669usna.pdf, pages 345-53.)
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| One of the illustrations included shows the ocean bottom contours of the Mariana Trench, part of which is six miles deep. Click for larger image. |
