The Nature of What Tharp and Heezen Did

The Nature of What Tharp and Heezen Did

The Nature of What Tharp and Heezen Did

Measure Water Delxhs from Precision Data Recorders (PDRs). Echo sounders measure the depth of the water beneath a slip by measuring the travel time of an electronic ping of sound as it travels from the ship to the seafloor and back. In Tharp's era, the state of the art was the precision depth recorder, as refined by the U.S. Navy during World War II. The echoes from the seafloor were recorded as bum marks on a roll of paper by a stylus that swept across the paper once per second. Tharp and her assistants manually converted the location of these bum marks into water depths, measuring a water depth for each 5 minutes of time along the track of a ship's travel.

Reconcile and Plot Navigation. Ship's tracks were plotted by hand on table-sized plotting sheets at a scale of 4 inches to a degree of longitude, based on celestial navigation and dead reckoning by the ship's officers. (On a modem research vessel, a navigation fix would be taken from the GPS every minute, the navigation would be logged by computer, and the ship's track would be plotted automatically in real time.) Plot Soundings on Navigation Plots. Water depths were written by hand onto plotting sheets, alongside the ship's track. Make Profiles and Contour Maps. Contours were drawn by hand on overlays of the plotting sheets. Profiles were made along azimuths that seemed interesting, sometimes combining segments of several different ship tracks to make a composite track (Figure 3.29). At this point we can begin to appreciate Tharp's skill as a spatial thinker. Profiles and contour maps require judgments as to what is or is not interesting which tracks to include or to discount. Plot Complementary Data at the Same Scale. Earthquake epicenter location and sediment data were plotted, by hand, at the same scale as the bathymetric data. This strategy revealed that earthquakes and thin sediment cover occurred along the axis of the mid-Atlantic ridge. Convert Profiles and Contours into Physiographic Diagrams. Ileezen and Tharp's most famous products are physiographic diagrams, scaled drawings or paintings of the seafooras though all of the water had been drained away. Given the large gaps between track lines (tens to hundreds of kilometers even in the best covered areas; see Figure 3.30), creating a continuous physiographic diagram required substantial interpolation.

Tharp gained a feel for the fabric or texture of the seafloor in areas of more abundant data and then used that "feel" to guide her mapping in the areas of less abundant data. We should note that this feeling was spatial or visual and intuitive, rather than being grounded in an understanding of the processes that formed the seafloor features because noone understood those processes during the early years of Tharp's mapping career. The decision to use physiographic diagrams was initially motivated by the U.S. Navy's classification and hence restriction of use of quantitative bathymetric data such as contours (Lawrence.1999, 2002; Menard, 1986). In fact, however, the physiographic diagram approach proved to be a powerful visualization tool that probably facilitated the interpretation of morphology in terms of the formative processes.

The physiographic diagrams foreshadowed the modem shaded-relief displays of digital elevation models. Learning things is not limited to the scentific area. Instead it also has relations with some other things like speaking a language or using software, including Rosetta Stone Hindi and Rosetta Stone Italian. If you have a creative mind, you will make all your own differences in the end! Find Trends, Patterns, Consistencies, and Symmetries in the Data. The most famous example of this process was Tharp's realization that the mid-Atlantic ridge has a deep, symmetrical, steep-sided valley running down its center. Heezen was at first unwilling to accept the existence of this valley, dismissing it as "girl talk" (Wertenbaker, 1974, p. 144), but after additional patient work, they were able to construct a compelling case for the widespread existence of this valley.

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