St. Petersburg Coastal and Marine Science Center

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Florida Shelf Habitat (FLaSH) Map Project

Lidar Features

What can be seen in the National Coastal Mapping Project Lidar surveys?

The descriptions provided below are strictly for informational purposes and are not a key for feature classification. Under no circumstances are these lidar coverages to be used for navigation.

Lidar (Light Detection And Ranging) is a technology originally used to assess atmospheric conditions by gauging the amount of time required for a laser to reflect off airborne particles. Compact Hydrographic Airborne Rapid Total Survey (CHARTS), a suite of laser altimetry sensors and cameras developed by the U.S. Army Corps of Engineers, uses that basic technology to map the ground from an aircraft. Using two lasers, one of which reflects off the surface of the water, the distance to both the surface of the water and the underlying seafloor can be determined. Using several sets of lasers firing as many as a thousand times per second, enough dta can be collected to create a map of a region.

The color scheme of these datasets are semi-interpretive, in that depth classes have specific colors that (for the most part) relate to what they portray: blue and light green for features below sea level, beige for very low areas (ground), green for low altitude features (typically vegetation), and red-orange for higher altitude objects (typically human structures). Shapes and patterns are usually recognizable as specific natural and man-made features. When in doubt, aerial photography and road maps can be used to confirm the identification of features.

large buildings Tall buildings/structures
Tall buildings appear as large, rectangular, tall (red-orange) objects.
roadway Roads
Roads are visible as linear features lacking relief and are usually bordered by rectangular human structures that define the road's edges.
small trees Small Vegetation
Low vegetation appears as small, highly irregular, clumped points. Because of the color scheme, low vegetation usually appears green.
small buildings Low Buildings
Low buildings appear as small, regular, and usually closely-spaced points laid out in a grid. Because of the color scheme, smaller (lower) buildings such as single family homes often appear green.
large vegetation Large Vegetation
Tall vegetation is so tall it may appear on the map as red-orange. The irregular nature of the points contrasts with the more rectangular shape of manmade structures.
parking lot Parking Lots
Cars in parking lots appear as extremely small, low, very regular, closely-spaced objects.
pier Piers
Fishing piers are raised structures perpendicular to the shore and extend up to hundreds of meters offshore.
dunes Dunes
Dunes appear as long ridges parallel to the shore.
roadway Borrow Areas
Large, regularly-shaped deep patches some distance offshore are "borrow areas" where sand has ben dredged from the bottom for use in beach renourishment projects.
data holes Data Holes
During processing, unreliable data points are discarded. If a large number of data points in a region are not reliable, an overlay cannot be generated for that region. LiDAR equipment has trouble producing accurate readings whenever the water isn't clear. Heavy waves, for example, prevent accurate laser altimetry measurements, thus in many datasets there are frequent holes along the shoreline.
natural reefs Hardbottom/Natural Reef
Natural reef and hardbottom appears as irregular, high relief offshore features usually covering (continuously or discontinuously) a relatively large area.
artificial reefs Artificial Reef
Artificial reefs appear as irregular, high relief offshore features that usually cover a considerably smaller extent than natural reefs. There are relatively few artificial reefs in NCMP LiDAR coverages because larger artificial reefs (those that would be easily visible with LiDAR) are not permitted nearshore due to the navigational hazard they pose. Try downloading the artificial reef Google Earth dataset and then find them (if possible) in the NCMP coverages.
port channel Port Entrances
Well-defined, particularly deep channels are associated with ports for deep-draft ships.

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Page Last Modified: May 09, 2013 @ 12:54 PM (JSS)