Automated Scar Extraction and Kernal Density Analysis

Texas Parks and Wildlife Department

Seagrass beds are an important nursery habitat for many fish and shrimp species in Texas' coastal waters. Boaters often cause damage in these shallow areas by scarring seagrass beds with their propellers, leaving long "scars" or bare areas.

Due to the sensitive nature of this precious resource, the Texas Parks and Wildlife Department (TPWD) monitors seagrass health carefully. In 2005, the Texas Parks and Wildlife Commission passed a law prohibiting the uprooting of seagrass in Redfish Bay, and TPWD Coastal Fisheries staff began an intensive study of seagrass scarring trends. To observe scarring behavior, TPWD acquired high-resolution imagery (0.1m) in 2007 intending to make comparisons with imagery in 2008 and 2009.

This map represents phase 1 of the assessment in which automated feature detection software was employed to quickly identify scarred areas. A data mining tool was then used to remove commission errors from the Feature Analyst output. (This methodology was developed by Kass Green, Mark Tukman, and Mark Finkbeiner in the 2008 Redfish Bay Texas Airborne Sensor Comparison and Propeller Scar Mapping Final Report.) Parameters were changed to suit the needs of this project.

Using the ArcGIS Spatial Analyst extension, kernal densities were created from the centroids of the scar polygons. The resulting map identifies areas of high-, moderate-, and low-scarring intensities.

Courtesy of Texas Parks and Wildlife Department.

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