About Benthic Mapper Layers and Maps
Using Benthic Mapper
About Layers and Maps
This page provides a brief description of what you can expect to see on each of Benthic Mapper's data and interpretive layer maps. It does not go into the details of what you can learn by combining multiple layers - that will be for you to explore - but it does suggest a few combinations of layers that you may find interesting.
Layers are selected by checking boxes in the Layers menu (Data Layers, Interpretive Layers, Reference Layers) on the lower right hand side of the Benthic Mapper Viewer. A layer is made active for use of the Identify tool by selecting the layer in the Active Layer pull-down menu on the upper right hand side of the Viewer.
If you have questions or comments about Benthic Mapper, the data or the Viewer, you can send email to: email@example.com.
Understanding Data Layer Maps
Data Layers show actual measurements made of the river's sedimentary floor. The data layers are described below in the order in which they appear on the Layers menu.
Selecting the Bathymetric Contours layer will apply blue contour (elevation) lines to the riverbed. Each contour line represents a two meter change in depth.
N/S and E/W Ship Tracks
The two Ship Tracks layers display the actual paths of the ship taking sidescan sonar and subbottom profile measurements. East/West paths are drawn horizontally in red, while North/South lines are drawn vertically in green. N/S lines are labeled with their line identification (id) numbers; to see line id's and latitudinal and longitudinal ranges for each line, use the identify tool.
When you view a Color Bathymetry map, the river is filled with a spectrum of colors. Dark blue represents the deeper areas of water, with pink denoting the shallowest areas. Each color represents a two meter increment of depth (located between two bathymetric contour lines if you view the two layers together). This data layer can be used as a backdrop or base map for other data layers of point data (cores, grabs, sediment profile imagery - SPI) or line data (bathymetric contours, ship tracks). You cannot combine this map with either of the Side Scan Imagery maps or the River Bottom Morphology map.
N/S and E/W Side Scan Imagery
At first glance, you may notice that the Side Scan Imagery layers look as though someone tried to color in the river with a pencil, then erased some of the pencilling. This pattern is caused by the data collection process, in which the ship travelled along a track and collected data to either side of the track. The image was then made by piecing together the strips of data.
To understand sidescan images, try to ignore the striping and pay attention to the areas that are darker than other areas. Essentially, the darker the "pencilling" looks, the harder or sandier (more reflective) the bottom is at that spot, while lighter or brighter areas indicate a silty, clayey base (less reflective). The N/S and E/W tracks were developed separately due to the 90-degree difference in the direction of the ships movement. When there are natural lineations on the estuary floor, sensors at different orientations (traveling in different directions) will "see" these lineations differently, causing slight variations between the maps.
You can use the N/S or E/W Side Scan images as a backdrop for other data layers of point data (cores, grabs, SPI) or line data (bathymetric contours, ship tracks). These maps cannot, however, be viewed in combination with each other (N/S data will dominate E/W), or with Color Bathymetry or River Bottom Morphology maps.
Sediment Profile Imagery (SPI)
The Sediment Profile Imagery data layer displays triangles in various colors, each representing a different type of sediment on the estuary floor at the spot where a photographic image was taken.
The Core Samples map displays circles on the river map wherever core samples were taken: light-green for core samples with photos and dark-green for samples without photos. if you activate the Identify tool and click on a circle, the sample's composition will appear at the bottom of the map. If a photo was taken for a particular sample (light-green circle), a link to the image will appear at the far right of the soil composition box (scroll to the right side of the composition box to find the link).
The Grab Samples layer displays plus-marks on the river map wherever grab samples were taken. If you activate the Identify tool and select a plus-mark, the composition of the sample taken at that location will be displayed below the map.
Understanding Interpretive Layer Maps
Interpretive layers contain features of the river bottom revealed by expert interpretation of the Benthic Mapper data.
River Bottom Morphology
The shape, or morphology, of the river bottom generally governs the strength and direction of currents, and therefore on the rate and location of sediment settling. With the River Bottom Morphology layer active, the river area is filled with four colors representing channel areas, channel margins, margin flats, and margin tributary areas.
While you can use the River Bottom Morphology map as a backdrop or base map for other data layers that are composed of point data (cores, grabs, SPI) or line data (bathymetric contours, ship tracks), it is not compatible with all layers. The present implementation of Benthic Mapper does not permit you to combine the River Bottom Morphology layer with the other interpretive layers (bedforms, grain size or anthropogenic deposits), the Side Scan Imagery layers or the Color Bathymetry layer.
When you select the Anthropogenic Deposits layer, you will see patches of diagonal stripes within the mapped portions of the river. The lines are drawn in different colors, each representing a different feature of the estuary bottom (anchor drag marks, yellow; piers, red; debris fields, grey, and mooring fields, brown). You might want to combine The Anthropogenic Deposits layer with a sidescan image layer to see how these deposits appear in the acoustic remote sensing data.
Naturally Occurring Bedforms
Naturally occurring bedforms (sediment waves, submerged aquatic vegetation root masses, and obstruction scour and deposits, dominate the estuary floor. These bedforms are represented by areas of grid squares, with different colored grid lines. You might want to combine the Bedforms layer with a sidescan image to compare the expression of bedforms in the two maps. The boundaries of the bedform fields were mapped from the sidescan images.
Sediment Grain Size
The Sediment Grain Size map, uses color filled grid squares to indicate exposed bedrock and three primary grain size classifications of sediment (coarse, sand, and fine). Boundaries between areas of different grain sizes were determined by experienced marine geologists, based on the sidescan images and the core and grab sample data. Users might find it interesting to view the grain size layer in combination with a sidescan image or with core and grab location layers.