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| Contour line map of the Puna Ridge showing the locations of planned rock sampling sites. |
As scientists, we make many observations, so many that we would get totally confused if we didn't have an organized way of archiving, displaying, and finally analyzing our data.
Visual displays of how one parameter varies against another, and maps which show the locations of geologic features, what the topography of the seafloor looks like, or where we collected our data samples, are ways in which we convey information to everyone.
When we study the ocean floor, our most important map is a bathymetry map, which gives water depth in areas where water covers the earth's surface; it is the submarine analog of topographic maps on land (which have air covering them).
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| Shaded relief map of the Puna Ridge. Different colors are used to indicate seafloor depth and relief is shown by illuminating the ridge from the southeast. We use bathymetry maps to help us navigate the ship along the rift axis. |
Bathymetric maps are usually contour maps of the seafloor, but water depth can also be presented through shaded relief maps, which illuminate the topography to depict roughness, two-dimensional profile maps, which show seafloor depth along a line between two points, or a three dimensional map, in which a mesh grid is draped over the topography to provide relief. The bathymetric maps aid us in navigation, and help us to find our way around the seafloor.
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| Side scan sonar image of the East Pacific Rise rift axis. |
The types of maps that we'll be using and making during our Puna Ridge scientific study include bathymetric, side scan sonar, sample location, and geological interpretation maps. We will use existing bathymetry maps as guides to tell us where to collect our high-resolution data set. Using the DSL-120 instrument to collect side scan sonar images and bathymetry of the Puna Ridge. We will then analyze the features, identify the different sonar textures, and create a geological seafloor map which shows the distribution of volcanic cones, craters, pillow lavas, fissures and faults along the rift axis.
These maps will be used to select interesting sites for rock sampling using a wax core sampler and a rock dredge. We will also collect photographic data of the seafloor so that we can determine which sonar textures and reflectivity intensities correspond to which types of volcanism or tectonism. Marine geologists call this 'ground truthing', or correlating the remotely-sensed data (e.g., side sonar data) with landforms that are actually observed. Ground-truthing is usually done on a small diagnostic data set, and once established for an area, can be used to geologically interpret a large study region.
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| Photos of Serocki volcano on the Mid-Atlantic Ridge are used to establish (or ground truth) that the grainy sonar texture corresponds to low-relief pillow lavas. | |
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