| AIRBORNE: Mapping the Everglades
The University of Georgia and the National Park Service construct a GIS database and associated vegetation maps to montor federally protected wetlands in South Florida.
By A. Victor Goodpasture In the Florida Everglades, the National Park Service is sponsoring a study to establish a database to measure and monitor the wetland environments threatened by urban expansion, agriculture, exotic plant invasion and hurricanes. The University of Georgia's Center for Remote Sensing and Mapping Science (CRMS) is working in conjunction with the National Park Service to construct a detailed GIS database and associated vegetation maps for a 6,000-square-mile area of federally protected wetlands in the Everglades.
"GIS is an integral component of natural resources monitoring and management," says Roy Welch, Ph.D., director of CRMS. "While it's useful for data storage, manipulation and map production, it's real strength is in spatial data analysis and predictive environmental modeling. By combining space-based satellite imagery with aerial photography, we can generate an excellent reference base for GIS data layers and up-to-date thematic information."
To know the exact grid coordinate of any point in the Everglades, the team first had to establish a network of ground control points using GPS survey techniques. CRMS then employed eight SPOT panchromatic images to construct a geocoded satellite image mosaic accurate to about 10 meters. The digital image mosaic was more than 200 megabytes in size.
"To get an accurate and detailed vegetation database, we needed images with enough resolution that we could identify plant species and the delineation of one-hectare or larger vegetation plots," Welch says. "And since the images had to have classification accuracies greater than 90 percent, we could not use Landsat or SPOT imagery."
Instead, CRMS purchased several hundred CIR aerial photographs from the U.S. Geological Survey (USGS) taken in 1994 and 1995 as part of the National Aerial Photography Program (NAPP). The aerial photographs were enlarged and compared to the SPOT images. Common features were annotated, numbered and their UTM (Universal Transverse Mercator) grid coordinates determined from the previously geocoded SPOT images. Now the actual interpretive work could begin.
Clear acetate overlays are placed over the enlarged USGS photographs and then the analysis begins. The NPS/CAMS team developed a classification system to identify major plant communities. Once completed, the acetate sheet is digitized, rectified, edited and added to the Everglades GIS database.
But to verify vegetation interpretations from the USGS aerial photography, the team conducted a series of helicopter surveys using a Trimble Pathfinder Pro XL GPS receiver, a 100 MHz Pentium laptop computer and a CIR Kodak Digital Science 420 GPS camera.
"We wanted to make sure that what we interpreted on the USGS aerial photos was indeed accurate," Welch says.
The laptop computer was linked to a GPS receiver, which had its antenna mounted on the forward hull of the helicopter. This allowed the laptop operator to display the satellite image mosaic and track the path of the helicopter in real time. The laptop operator could direct the helicopter to specific areas for detailed digital photography. The team even landed for identification and photography of plant species. About 300 digital images were taken. Additional information regarding the area such as major human disturbances or fires could also be entered into the computer and linked to a specific GPS coordinate.
"Helicopter operation is very expensive, costing us about $650 an hour," Welch says. "By using GPS in real time, we spent our time wisely by going directly to where we needed to go. It was never a 'fishing' expedition."
The CIR digital images were easily tracked and linked to specific geographic points because of the camera's GPS interface. Not only were the CIR images used as a vegetation index, but they also added to the GIS database. A user can click on a specific area and view any of the ground photography taken there.
"Not only are we developing a GIS database, but we have proved the value of digital imaging and GPS to gather and verify data," Welch continues. "Once we had established a standard ground coordinate system with a high degree of positional accuracy, the aerial photographs provided source information for the derivation/revision of thematic data layers such as vegetation and land use."
With the geocoded SPOT image mosaic, resource managers can quickly find areas of interest and develop image subsets for further investigation. And with the GIS database of the Everglades almost completed, updates in the coming years will provide valuable data that can be used to better assess the damage being done by human encroachment, non-native plants and hurricanes.
"The methodologies we employed: using SPOT imagery to construct a geocoded satellite image mosaic; interpreting USGS CIR photography; and using GPS, digital cameras and helicopter and ground survey techniques to verify photo interpretation can all be used in other remote areas to create valuable GIS databases," Welch says. "The technology is available. All we have to do is use it." About the Author:
Writer/photographer A. Victor Goodpasture is based in Carlsbad, Calif. Back |
