Post-Sandy Benthic Habitat Mapping Using New Topobathymetric Lidar Technology and Object-Based Image Classification

Parrish, C.E.; Dijkstra, J.A.; O’Neil-Dunne, J.P.M; McKenna, L., and Pe’eri, S., 2016. Post-Sandy benthic habitat mapping using new topobathymetric lidar technology and object-based image classification. In: Brock, J.C.; Gesch, D.B.; Parrish, C.E.; Rogers, J.N., and Wright, C.W. (eds.), Advances in Topobathymetric Mapping, Models, and Applications. Journal of Coastal Research, Special Issue, No. 76, pp. 200–208. Coconut Creek (Florida), ISSN 07490208. Hurricane Sandy, which made landfall on the U.S. East Coast as a post-tropical cyclone on October 29, 2012, is the second costliest hurricane in U.S. history, behind Hurricane Katrina in 2005. In the wake of the storm, federal mapping agencies, including NOAA, USGS, and USACE, undertook extensive mapping efforts in the affected areas, including acquisition of aerial imagery, lidar (light detection and ranging), and other forms of remotely sensed data. Among the notable datasets acquired in the Sandy-impact region were those collected with new topobathymetric lidar systems, which feature markedly different designs than conventional bathymetric lidar technology. These systems are characterized by green-only laser beams, narrow fields-of-view (FOVs), and narrow beam divergence. The objective of this study was to investigate the ability to use data from a commercial topobathymetric lidar sysem, the Riegl VQ-820-G, operated by NOAA’s National Geodetic Survey, for benthic habitat mapping—in particular, mapping of seagrass habitat in Barnegat Bay, New Jersey. Specific goals were 1) to assess the utility of the VQ-820G reflectance and pulse deviation data, with minimal additional calibration or post-processing, in benthic habitat mapping; 2) to investigate the use of object-based image analysis (OBIA) in generating benthic habitat maps from the VQ-820-G data; and 3) to develop procedures that are currently being used in follow-on studies to investigate and quantify the ecological impacts of Sandy. Habitat maps were created in the OBIA system from the VQ-820-G data and simultaneously acquired imagery. A classification accuracy assessment was then performed through comparison against reference data acquired by the project team. Results indicate strong potential for benthic habitat mapping using the VQ-820-G waveform features, bathymetry, and ancillary datasets in an OBIA procedure. The project team is currently extending these procedures to data from the USGS EAARL-B lidar system to enable enhanced assessment of habitat change resulting from Sandy in the Barnegat Bay estuary. ADDITIONAL INDEX WORDS: Barnegat Bay, lidar waveform, habitat change, classification accuracy. INTRODUCTION Hurricane Sandy, known unofficially as “Superstorm Sandy,” made landfall as an intense post-tropical cyclone on the U.S. East Coast near Brigantine, New Jersey, on October 29, 2012 (Halverson and Rabenhorst, 2013; NOAA, 2013). Factors contributing to the devastating impact of the storm included its very large diameter, its impact angle, and the fact that its landfall in the New Jersey–New York region coincided with large astronomical tides to produce exacerbated storm tides (Forbes et al., 2014; Hall and Sobel, 2013). Immediate impacts of the storm included at least 147 deaths, $50 billion in damages, and extensive coastal erosion in New Jersey, New York, and other mid-Atlantic states (Blake et al., 2013; NOAA, 2013). Long-term ecological impacts of the storm are still being assessed. Coinciding with the location of the center of the cyclone at the time of landfall on the U.S. East Coast, the Barnegat Bay estuary was heavily impacted by Sandy. The bay experienced ~2 m of storm surge and extensive damage, dune erosion, massive property damage, and deposition of marine debris in the estuary (Blake et al., 2013; Miselis et al., 2013). Due to the extent of damage, Barnegat Bay has become a focal point for a number of studies related to Hurricane Sandy. Coastal zone management offices are interested in assessing the effects of Hurricane Sandy on benthic habitats, particularly seagrass habitats, in Barnegat Bay. Seagrasses are important for the health of estuarine systems, as they provide habitat for fish and shellfish species, reduce sediment erosion and currents, and deliver nutrients from the estuary (Orth and van Montfrans, 1987; Zimmermann, 2003). In Barnegat Bay, greater nutrient loading has led to estuarine-wide declines in seagrass populations and greater abundance of nuisance and non-native macroalgal species (Fertig, Kennish, and Sakowicz, 2013; Hunchak-Kariouk and Nicholson; 2001; www.JCRonline.org Oregon State University