Coastal Classification Atlas

Mapping Methods

A coastal storm-hazard assessment involves two different activities. The first is classification of ground conditions, and the second is translation of that information into a storm-hazard vulnerability index. Present ground morphology and any man-made alterations of the land were first interpreted in the laboratory, using three independent visual sources:

1. airborne color video surveys,
2. 35-mm aerial color slides, and
3. Digital Orthophoto Quarter Quadrangles (DOQQs) obtained from the U.S. Geological Survey EROS Data Center in Sioux Falls, South Dakota (http://edc.usgs.gov/).

The video tapes and slides are oblique low-altitude photographs of the beach obtained during helicopter surveys with horizontal positions determined by a Global Positioning System (GPS). Dates of the various surveys are presented in Table 1.

Table 1. Types of imagery used for mapping and the dates they were acquired. Type of Imagery Date Aerial Oblique Video Survey July 1996 Digital Orthophoto Quarter Quadrangle February 1995 Lidar Survey August 2000 Map Verification January 2006

The video surveys, slides, and DOQQs were used to prepare the coastal classification units (Fig. 2) and to interpret the geomorphological and urban attributes of each coastal segment. Elevations of the land surface adjacent to the barren backbeach were obtained by processing lidar (light detection and ranging) data. The highest elevations of the foredunes or beach crest (where dunes are absent) are shown as a series of dots. Each dot is color coded to represent a narrow range of elevations. The units of elevation are decimeters, or tenths of meters.

In some local areas, there may be differences between the backbeach position observed on the DOQQs and those observed on the lidar surveys. These differences are attributed generally to coastal dynamics and specifically to beach erosion, spit accretion, or inlet migration. The dates of the surveys (Table 1) indicate which beach position is most recent. In all areas, the lidar survey is more recent than the DOQQ survey.

continue to: Coastal Classifications

U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubsdata.usgs.gov/pubs/of/2006/1133/methods.html
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