Subtask: Definition of High Resolution (Lidar) Northern Gulf Coast Geomorphology

Subtask Leader: Amar Nayegandhi - Jacobs Technology, Inc. USGS St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida

Aim

Lidar Data Collection: The NASA Experimental Advanced Airborne Research Lidar (EAARL) collects high-resolution lidar data and georectified digital aerial photographs. The instrument uses a green laser and a raster scanning mechanism to acquire lidar data. [Enlargement]

Following the devastating hurricanes of 2005, the geomorphological structure of the Northern Gulf of Mexico (NGOM) landscape has undergone significant change. Detailed mapping of present day geomorphology of the NGOM region can provide quantitative indicators to assess risk-prone lands and baseline data for future landscapes and ecological changes. The geomorphic significance of catastrophic events to coastal geomorphology can be quantified by determining fine-scale topography of the topo-bathy  surface using airborne laser altimetry or Light Detection and Ranging (lidar) techniques. The USGS CMG program has recently acquired a legacy NASA lidar system known as the Experimental Advanced Airborne Research Lidar (EAARL). The EAARL system provides unprecedented capabilities to survey near-shore benthic habitats, coastal vegetation and sandy beaches. Post-flight processing of EAARL data is accomplished using a custom-built Airborne Lidar Processing System (ALPS) that provides unique capabilities to explore and process lidar return waveforms, and enables the creation of Digital Elevation Models (DEMs) for bare-Earth, canopy-top, and submerged topography. The EAARL system also incorporates a color infrared (CIR) down-looking digital mapping camera and a traditional Red-Green-Blue (RGB) camera that continuously acquire digital aerial photographs during lidar surveys.

EAARL surveys have been conducted post- Hurricane Katrina over Chandeleur Islands, the barrier islands of Gulf Islands National Seashore (GUIS), and Jean Lafitte National Park (JELA). Additional lidar surveys have been conducted in the NGOM study region by several federal, state, and local agencies, using other government and commercial Lidar sensors. Further, bathymetric surveys of the near-shore regions have been conducted using acoustic technology. These surveys have resulted in data sets processed in different datums, spatial resolutions, and output data formats. The evaluation and synthesis of these data sets is necessary to understand the gaps in data coverage and any limitations in the existing data.

Traditional discrete-multiple-return, small-footprint lidar systems are unable to detect small vertical variations due to the significant dead zone between closely spaced successive reflections of the laser pulse. The dead zone is caused by hardware limitations in the sensor electronics design. The ability of a lidar system to map bare earth in dense wetland environments has not been fully addressed in literature. Lack of laser penetration through dense grasslands and the absorption of the near-infrared laser beam at the water surface underneath the floating marsh are limiting factors of traditional discrete-return lidar systems. The green-wavelength laser of the EAARL system, along with its waveform-resolving capability enables the exploration of the determining bare earth under dense floating marshes.

Approach

The objectives of this sub-task are to:

• Evaluate and synthesize existing topographic and near-shore bathymetric data acquired within the NGOM project study area post Hurricane Katrina
• Collaborate and coordinate lidar activities among other federal, state, and local agencies within the NGOM study region
• Define site locations to conduct high-resolution EAARL lidar topographic surveys based on requirements and feasibility.

  Sites selection for conducting EAARL surveys within the NGOM is based upon the following criteria:

  1. lack of available high-resolution topographic data and scientific interest in these regions within other Tasks of the NGOM project,
  2. inconsistencies or inaccuracies within the available data, and
  3. need for methodological and algorithmic advancement in post-processing of airborne lidar data for improved topographic mapping.
• Advance bare-earth and shallow submerged topographic mapping capability of the EAARL system in order to map the hydrologic and topographic features at desired sites within the NGOM region.
• Acquire and process additional lidar data and associated imagery acquired by the EAARL and other lidar systems in support of the NGOM project.

Accomplishments

EAARL data acquired in March/April 2008 in the Pearl River Delta were processed and published as a data series report for first surface and bare earth topography. Lidar data acquired along the Eastern LA barrier islands have been processed for bare earth and first surface topography and are currently planned for publication. Georeferenced CIR image mosaics from imagery acquired during the EAARL missions were developed. Example CIR mosaic products from recent EAARL NGOM surveys along the MS barrier islands have been created. The CIR imagery acquired at Naval Live Oaks region within the NPS Gulf Islands National Seashore has been published as a Data Series report. In a close collaboration with NPS, volumetric change was computed from surveys conducted along the MS barrier islands in 2005 (post Katrina), 2007, and 2008 (post Ike). Results showed that there was a gain in the net volume per unit area across the islands since Hurricane Katrina. An airborne lidar survey at the Atchafalaya Basin was conducted in December 2008 during a period of low water level. Due to inclement weather and system / technical issues, only a small portion of the lower basin was surveyed. The data were processed to create bare earth and first surface topography data. The bare earth peak detection algorithm was modified to enable the determination of bare earth under dense marshes. A Google-maps based web interface was developed to serve as a topo-bathy coordination tool. The web interface is being used to plan and coordinate lidar surveys in the NGOM region. Lidar surveys planned by other federal agencies, including NOAA and USACE, are included in the coordination tool. The map is continuously updated based on new and revised survey plans.

View NGOM TopoBathy Coordination Map

Publications

Manuscripts

Open File Report(OFR)

Data Series

Abstracts and Presentations

Other