U.S. Department of the Interior
U.S. Geological Survey
FS-162-96
The major issues facing ecosystem restoration and management in south Florida are centered on the availability and distribution of clean, fresh water. Surface water flow modeling studies are an important aspect of the scientific information needs of the ecosystem restoration initiative. Hydrologic models provide much needed predictive capabilities for evaluating options for management of parks, refuges, and lands planned for acquisition, as well as for understanding the impacts of land management practices in surrounding areas. Models must account for the expansive and extremely low relief terrain of south Florida, where surface waters of the natural system are transported by sheet flow from Lake Okeechobee through the Everglades to Florida Bay and the Gulf of Mexico. To model sheet flows, highly accurate elevation data that define the surface topography are required as the most critical input parameter to the Natural Systems Model and other hydrologic models. These data are necessary for calculating water surface slope, depth, velocity, and direction of flow. Hydrologists have stated vertical accuracy requirements of between 3 and 15 centimeters. These accuracy requirements are so stringent, because of the extremely flat terrain, that any standard or other currently available data products would not suffice for this modeling application.
The role of the U.S. Geological Survey
(USGS) is to design, develop, and implement plans for collecting
high-accuracy elevation data that define surface topography for
very large areas. Use of traditional methods for collecting these
data is not possible because of the high costs and difficulty of
working in a challenging environment such as the Everglades.
Therefore, it was hypothesized that emerging Global Positioning
System (GPS) techniques could provide a cost-effective method for
surveying elevation data while meeting the stringent vertical
accuracy requirements. To test this hypothesis, an interagency
proof-of-concept pilot project was designed and conducted during
fiscal year 1995. The USGS, the U.S. Army Topographic Engineering
Center, and the National Oceanic and Atmospheric Administration
(NOAA) formed partnerships to leverage equipment and expertise
(for example, dual-frequency GPS receivers, field scientists,
computers, air boats, and so on). An interagency team of more
than a dozen scientists and engineers was formed for planning the
project, performing field work, and postprocessing data to
effectively execute the project. The results of the pilot project
were highly successful. The average variance to known reference
control points was 1.4 centimeters. These results and the
methodology developed during the pilot project proved that new
GPS techniques provided a feasible, cost-effective solution to a
very difficult problem. Planned Approach As a result of the
successful pilot project, efforts were expanded to collect
high-accuracy elevation data covering much broader areas. A
requirements letter soliciting elevation needs was distributed to
agencies involved with the restoration initiative. As a result,
forty-eight 7.5-minute quadrangle maps, or approximately 8,100
square kilometers, were identified as priority area
requirements. Because of the scope of these require-ments, work
to collect these data in areas that lend themselves to the
developed methodology and are accessible by air, boat or truck is
being contracted to the private sector. The vertical accuracy of
these data is about 15 centimeters, and data points are being
collected approximately every 400 meters in a grid
fashion. Significant features that influence sheet flow, such as
cross-sections of roads and levies, are being surveyed as well (fig. 1). In areas not accessible by
these surface transportation modes, such as in heavily vegetated
mangrove stands along the Buttonwood Embankment, a
helicopter-based system is being designed to collect elevation
data as accurately as possible. A new pilot project is now being
developed to experiment with this approach for data collection
and accuracy assessment.
For more information contact:
For more information on other USGS products and services:
The EARTHFAX fax-on-demand system Related information:
U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
Figure 1. Plot of representative elevation data.
(Click on image for larger picture.)
Charles Henkle or Greg Desmond
U.S. Geological Survey
MS 521, National Center
Reston, VA 20192
call 1-800-USA-MAPS,
e-mail esicmail@usgs.gov, or
fax 703-648-5548.
is available 24 hours a day at 703-648-4888.
SOFIA Project: High Accuracy Elevation Data Collection
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Last updated: 11 October, 2002 @ 09:31 PM
(KP)