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Coastal Monitoring: More Than a Day at the Beach
By Harold Hough When Allison, the first hurricane of the 1995 season hit the Florida coast, remote sensing experts were already gearing up for any potential disaster. Although the damage was minimal this time, people like John Jenson of the University of South Carolina were prepared for major storm damage if it had occurred.
"We would have had SPOT take a sideways image later today when the sky cleared so we could compare it with older imagery," he noted. "We would have also looked a couple of weeks later when the dead vegetation would have been more noticeable."
Although Jenson and other hurricane specialists didn't need satellite imagery this time, they and others are regularly using imagery to monitor the coastline and protect it from other emergencies like major hurricanes and oil spills. They are also monitoring more subtle degradation caused by ocean side construction and pollution. Oil Spills
Next to hurricanes, oil spills are one of the biggest threats to the coastline. According to Hattie Davis of Chevron, the final damage often depends on the type of coastline that the oil washes upon. For instance, an oil slick will often slide off a rocky wall and continue to float along with the current. Other shorelines like sand will absorb the oil.
Yet, with hundreds of thousands of miles of shoreline near oil tanker shipping lanes, it's difficult to use traditional methods to discover the type of shoreline and the potential environmental threat. That's where satellite imagery comes to the rescue. With SPOT's and Landsat's multispectral capability, analysts can differentiate rocky shore, sand beaches, mangrove swamps, and mudflats and then enter it into a geographic information system (GIS). Then, according to Davis, if a spill occurs, all the operator has to do is enter the wind and weather information into the computer, and the system will tell how far the oil spill will travel and where it will wash ashore.
An added benefit of satellite imagery is the logistical data it provides. In addition to showing the coastline, it also provides information that spill response teams can use to respond to the emergency. The imagery shows roads and airstrips where spill equipment can be moved. It also identifies fishing villages and habitats that require greater attention during an emergency. In the case of the California Fish and Wildlife agency, their portable spill response GIS system also includes additional data like phone numbers and available resources. "It covers the whole array of what we need," notes Fish and Wildlife Official John Ellison. Plumbing The Depths
Satellite imagery is especially useful in coastal monitoring because multispectral sensors can detect different types of light which penetrate different depths of water. For instance, while near infrared light can't see underwater, red light can see objects as deep as 10 meters and green light can penetrate up to 30 meters of water. This means that multispectral imagery of a seashore can differentiate between land, water no deeper than 10 meters, water between 10 and 30 meters deep, and water that is deeper than 30 meters.
This ability to see depths is important to the South Florida Water District, according to Tom Lo. As part of their inventory of water resources in South Florida, they are looking at coastlines and determining depth and bottom cover. With satellite imagery, they can separate mud flats from sea grass or sandy bottom.
Part of the water district's coastal monitoring responsibility is ensuring that the salt water doesn't enter the fresh water wells of South Florida, a serious problem as more people move to the Sunshine State and place a greater demand on its water resources. "Basically the whole of South Florida is wetland," notes Lo, who says that it's very easy for coastal salt water to flow inland and upset the natural balance. Already, cities like Palm Beach and Sarasota have experienced salt water intrusions.
With satellite imagery, Lo and others can determine where the line between salt and fresh water is by looking at vegetation like mangroves and sawgrass which only grow around salt water. Although this program is only in the research stage, it promises to become a tool for maintaining the natural balance, especially as Florida's population grows.
This natural balance along the coastline is critical because the coastal areas are also important as breeding grounds for fish. According to Richard Lacy, remote sensing manager for the Land Resources and Conservation Districts of the South Carolina Department of Natural Resources, South Carolina's, "coastal marshes are the nursery for a $100 million recreational and commercial fishing industry." The Marine Resources Division is currently planning to start a program this year where they will use satellite imagery to study non-point source pollution from golf courses and farms. According to Lacy, many golf courses use treated effluent to water and fertilize their fairways. Although this makes the sewage disposal problem for municipalities easier, the runoff flows into the marshes along the coast and pollutes the hatching areas for several types of fish.
With satellite imagery, South Carolina can locate golf courses near the coastal wetlands and estimate how much effluent is draining from them into the wetlands. They will also monitor the water flow through rice farms, which often block the natural flow of water into the ocean, according to Andy Bury of the Marine Resources Division. This may stem the recent decline in commercial fish that has ruined many state fishing industries.
South Carolina isn't using satellite imagery just to monitor its current coast. It's also looking at what are called Carolina Bays, remnants of the seashore that were surrounded by land as the coastline moved eastward. Although these bays evolved into freshwater lakes and wetlands over the years, they are still important as a home to many species. According to Lacy, 90 percent of the bays have been destroyed by agriculture and the state is trying to find and protect the remainder through an awareness program. "SPOT is particularly useful in finding them," Lacy notes, "because with the SPOT multispectral data we can see the state in tenth of an acre parcels. With the imagery, they can detect the water and the sand rims that are all that remains of the former Atlantic coast.
However, today man alters the coastline more than nature. In Florida, the Army Corps of Engineers is beginning to use satellite imagery to monitor shoreline changes caused by "man's intrusion" according to Coastal Design Section Branch Chief Roy Hilton. They are currently looking at Dade County and noting the shoreline changes as well as the depth of the waterways. Protecting Coastal Species
Protecting the shoreline also includes protecting the species that rely on it. South Carolina is protecting endangered species that live along the coast and are often dependent on habitats that are threatened or nourished by the coastline. With the Species At Risk Program, scientists are using maps of known animal colonies, and identifying the type of habitat they prefer. Using multispectral imagery, they look for other possible habitats and send specialists to see if other colonies can be found there. According to Lacy, identifying land in tenth of an acre parcels, "can find prime habitats and save you fieldwork. Maybe a species could be reduced from endangered to threatened with this method."
In one case, the threat to a species wasn't from man, but Mother Nature. When Hurricane Hugo smashed into the Carolina Coast, it threatened the habitat of the Red-Cockaded woodpecker. The endangered bird prefers to live in sparse coniferous forests and makes its home in the hollows of dead trees. "The problem is that these trees are brittle and liable to blow over or shear off at the top where the homes are," Lacy said. With imagery taken before and after the storm, they were able to monitor the damage to the woodpecker's habitat and determine that its existence wasn't threatened.
Although Allison's damage was so small that satellite imagery wasn't needed by the professionals who monitor the health of the coastline, there is some comfort that when they need it a satellite is often only hours away from acquiring the imagery they need to get back to normal. "Satellites save you a bunch of time," Lacy notes. That leaves more time to do what they were hired to do, monitor and protect the coastline. About the Author:
Harold Hough is a freelance writer specializing in satellite remote sensing. He may be reached at 602-578-1934.
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