With sensors, a more accurate map of the Chesapeake Bay's forested wetlands

Two USDA scientists used two types of sensors to create more accurate maps of the Chesapeake Bay watershed. The advancement impacts agriculture and conservation.
Written by Andrew Nusca, Contributor on

Two U.S. Department of Agriculture scientists have created new, more accurate maps of the Chesapeake Bay's forested wetlands with the help of sensors.

The new maps are about 30 percent more accurate than existing versions.

Wetlands are vital to the health of bodies of water like the Chesapeake Bay, but many are forested, making them difficult to survey using aerial photography and thus inaccurate.

Using software and models, Agricultural Research Service soil scientist Greg McCarty and USDA Forest Service ecologist Megan Lang combined the data from two remote sensing devices -- an airborne LiDAR ("Light Detection And Ranging") laser sensor and a SAR ("Synthetic Aperture Radar") satellite sensor -- to get a better look.

Their objective? To see whether water flows without filtration into the bay, or whether it flows first through a forested wetland that may filter out pollutants.

Both SAR and LiDAR are active sensors, meaning they transmit their own energy (for SAR, that comes in the form of long-wavelength microwave energy; for LiDAR, shorter wavelength laser energy). Both sensors detect the time it takes for signals to travel to the wetlands and the strength of the returning signal to help detect the presence and quantity of water.

  • SAR sensors are usually mounted on satellites, allowing for frequent image collections over large areas. They are best for spotting short-term changes in water levels (e.g. flooding) and are not restricted by inclement weather.
  • LiDAR sensors are usually mounted on airplanes, allowing for greater spatial resolution. They are best for visualizing flooding and understanding the surface-water flow paths and how they change over longer periods of time.

The researchers compared the maps for relationships between low and higher elevations on one map and wet and drier spots on the other. What they found in the new maps were never-before-seen features, including connection between some wetlands, drainage ditches, intermittent streams and ponds, farming and weather.

That's important because forested wetlands have been thought to be isolated from each other and the bay, and thus they were not afforded regulatory protection under the Clean Water Act.

The maps can also be used to predict flooding and the effects of climate change, and help inform cleanup efforts and conservation discussions moving forward.

"The combined sensors can greatly improve understanding of ecological services that wetlands provide and will likely have bearing on the management and conservation of wetland ecosystems in agricultural landscapes nationally," McCarty said in a statement.

Their research was published in the journal Wetlands.

Photos: Peggy Greb/USDA ARS

This post was originally published on Smartplanet.com

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