Topographic Lidar Survey of Dauphin Island, Alabama and Chandeleur, Stake, Grand Gosier and Breton Islands, Louisiana, July 12-14, 2013 -- Bare Earth Digital Elevation Models (DEMs)

Lidar Pre-Processing: Airborne global positioning system (GPS) and inertial measurement units (IMU) data were merged to develop a Single Best Estimate (SBET) of the lidar system trajectory for each lift. Lidar ranging data were initially calibrated using previous best parameters for this instrument and aircraft. Relative calibration was evaluated using advanced plane-matching analysis and parameter corrections were derived. This was repeated iteratively until residual errors between overlapping swaths, across all project lifts, were reduced to acceptable levels. Data were then block adjusted to match surveyed calibration control. Raw data FVA was checked using independently surveyed checkpoints. Swath overage points were identified and tagged within each swath file. The raw lidar data and the ground control points are intermediary datasets and are not included in this Data Series Report.

Lidar Post-Processing: The calibrated and controlled lidar swaths were processed using automatic point classification routines in proprietary software. These routines operate against the entire collection—all swaths, all lifts—eliminating character differences between files. Data were then distributed as virtual tiles to experienced lidar analysts for localized automatic classification, manual editing, and peer-based quality control (QC) checks. Supervisory QC monitoring of work in progress and completed editing ensured consistency of classification character and adherence to project requirements across the entire project area. All classification tags are stored in the original swath files.

The bare earth surface is then manually reviewed to ensure correct classification on the Class 2 (Ground) points. After the bareearth surface is finalized, it is then used to generate all hydro-breaklines through heads-up digitization. All ground (ASPRS Class 2) lidar data inside of the Lake Pond and Double Line Drain hydro flattening breaklines were then classified to water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 1 m was also used around each hydro flattened feature to classify these ground (ASPRS Class 2) points to Ignored ground (ASPRS Class 10). All Lake Pond Island and Double Line Drain Island features were checked to ensure that the ground (ASPRS Class 2) points were reclassified to the correct classification after the automated classification was completed. All overlap data was processed through automated functionality provided by TerraScan to classify the overlapping flight line data to classes approved by USGS. The overlap data was classified to Class 17 (Overlap Default) and Class 18 (Overlap Ground). These classes were created through automated processes only and were not verified for classification accuracy. Due to software limitations within TerraScan, these classes were used to trip the withheld bit within various software packages. These processes were reviewed and accepted by USGS. All data was manually reviewed and remaining artifacts removed using functionality provided by TerraScan and TerraModeler. Global Mapper was used as a final check of the bare earth dataset. GeoCue was then used to create the deliverable industry-standard LAS files for both the All Point Cloud Data and the Bare Earth datasets. Photo Science proprietary software was used to perform final statistical analysis of the classes in the LAS files, on a per tile level to verify final classification metrics and full LAS header information.

Hydro Classification Breakline Processing: Class 2 lidar was used to create a bare earth surface model. The surface model was then used to heads-up digitize 2D breaklines of inland streams and rivers with a 30-m nominal width and inland ponds and lakes of 8,000 square meters or greater surface area. The breaklines were collected for classification purposes only. The provided breaklines are 2D features and do not contain a valid elevation attribute. All ground (ASPRS Class 2) lidar data inside of the collected inland breaklines were then classified as water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 1 m was used around each breakline feature. These points were moved from ground (ASPRS Class 2) to ignored ground (ASPRS Class 10). The breakline files were then translated to ESRI Shapefile format using ESRI conversion tools.

Raster DEM Process: Class 2 lidar was used to create a 1.0 m Raster DEM. Using automated scripting routines within ArcMap, an ERDAS Imagine IMG file was created for each tile. Each surface was reviewed using Global Mapper to check for surface anomalies or incorrect elevations found within the surface.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Added keywords section with USGS persistent identifier as theme keyword.