Optical and Radar Fusion: Mapping Coastal Marsh Dieback

Science Center Objects

With the help of remote sensing, USGS maps the progression of marsh dieback along the Louisiana coast.

 

Map of coastal marsh dieback study
Map of coastal marsh dieback study

Science Issue and Relevance: Spartina alterniflora marshes that dominate regularly flooded salt marshes of the Atlantic and Gulf coasts of the United States have experienced scattered and irregularly timed periods of browning (chlorotic), leading in many cases to marsh loss, since the 1960’s. Many drivers of the sudden dieback have been suggested; however, causes remain uncertain because of the inability to capture the dieback near onset. That changed in 2008 when a USGS remote sensing project directly related the Louisiana coastal-wide dieback to surges from Hurricanes Gustav and Ike.

The progression of marsh condition
The progression of marsh condition

Methods for Addressing the Issue: The 2008 mapping success set the stage for the USGS and NASA remote sensing project illustrated above. That project, utilizing satellite radar and optical images and ground measurements, captured a large dieback in 2011 that was unnoticed by all other monitoring methods. Although the dieback cause is uncertain, the coincident pre- to post-data collections uncovered what biophysical changes accompanied the dieback onset and recovery and projected these to specific and recognizable changes in the optical and radar image data. The biophysical changes provided project researchers with knowledge of what to look for.

Future Steps: The remote sensing technology used for dieback onset and progression mapping was implemented following Hurricane Sandy to determine whether surge flooding detrimentally impacted the New Jersey coastal marshes. This study advanced previous studies by utilizing a progressive sequence of postsurge radar images to provide new information concerning surge persistence and its relation to marsh resilience. While the methodology is being peer reviewed, work continues to identify support for transferring uniquely effective mapping methods to bimonthly and rapid-response operations. 

Map of 2011 Radar Dieback in White
Map of 2011 radar dieback in white
Map of 2011 Optical Dieback in Red
Map of 2011 optical dieback in red