2009 USACE NCMP Topobathy Lidar DEM: AL, TX (Post Hurricanes Ike & Gustav)

AL:

The BareEarth 1 meter Digital Elevation Model (DEM) dataset is produced from the LiDAR topographic survey conducted for the Post Hurricane Gustav Aerial Survey 2009 project. This data was produced for the US Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX). The LiDAR point cloud was flown at a density sufficient to support a maximum final post spacing of 1.5 points per meter. 3001 International Inc acquired the data between April 16, 2009 and June 12, 2009. The Post Hurricane Gustav Aerial Survey 2009 was collected under the guidance of a Professional Mapper /Surveyor.

TX:

The 1 meter BareEarth Digital Elevation Model (DEM) dataset is produced from the LiDAR topographic survey conducted for the Post Hurricane Ike Aerial Survey 2009 project. This data was produced for the US Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX). The LiDAR point cloud was flown at a density sufficient to support a maximum final post spacing of 1 point per meter. 3001 International Inc acquired the data between February 3, 2009 and April 23, 2009. The Post Hurricane Ike Aerial Survey 2009 was collected under the guidance of a Professional Mapper /Surveyor.

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available. These data are available for custom download at the link provided in the URL section of this metadata record.

The Post Hurricane Gustav Aerial Survey 2009 project will support the US Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) collection of data representing the post-hurricane condition of the beaches, barrier islands, and lakeshores along the coasts of Louisiana, Mississippi, and Alabama following Hurricane Gustav.

The Post Hurricane Ike Aerial Survey 2009 project will support the US Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) collection of data representing the post-hurricane condition of the beaches, barrier islands, and lakeshores along the coasts of Texas and Louisiana following Hurricanes Ike and Gustav.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk or custom downloads

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcCatalog 9.2.6.1500

All ground control processing and adjustment is performed using published coordinate horizontal and vertical datums (e.g. NGS CORS). For deliverables, Corpscon for Windows Version 5.11.08 (geoid 03) was used for horizontal and vertical datum conversion as well as for coordinate system conversion purposes (e.g. UTM to State Plane).

Qualitative value: 1 m -See entity and attribute information

The accuracy assessment was performed using a standard method to compute the root mean square error (RMSE) based on a comparison of ground control points (GCP) and filtered LiDAR data points. Filtered LiDAR data has had vegetation and cultural features removed and by analysis represents bare-earth elevations. The RMSE figure was used to compute the vertical National Standard for Spatial Data Accuracy (NSSDA). Ground control was established by 3001, Inc. A spatial proximity analysis was used to select edited LiDAR data points contiguous to the relevant GCPs. A search radius decision rule is applied with consideration of terrain complexity, cumulative error and adequate sample size. Cumulative error results from the errors inherent in the various sources of horizontal measurement. These sources include the airborne GPS, GCPs and the uncertainty of the accuracy of the LiDAR data points. This accuracy is achieved prior to the sub-sampling that occurs through integration with the inertial measurement unit (IMU) positions that are recorded. It is unclear at this time whether the initial accuracy is maintained. The horizontal accuracy of the GCPs is estimated to be in the range of approximately 1 to 1.6 inches. Finally, sample size was considered. The specification for the National Standard for Spatial Data Accuracy is a minimum of 20 points to conduct a statistically significant accuracy evaluation (Minnesota Planning, 1999, Positional Accuracy Handbook, Minnesota Planning Land Management Information Center, St. Paul, Minnesota., p.3). Most statistical texts indicate that a minimum of 30 sample points provide a reasonable Approximation of a normal distribution. The intent of the NSSDA is to reflect the geographic area of interest and the distribution of error in the data set (Federal Geographic Data Committee, 1998, Geospatial National Standard for Spatial Data Accuracy, Federal Geographic Data Committee Secretariat, Reston, Virginia, p.3-4).

Additional steps were taken to ensure the vertical accuracy of the LiDAR data including:

Step 1: Precision Bore sighting (Check Edge-matching)

Step 2: Compare the LiDAR data to the Field Survey (Field survey is to FEMA specifications and more stringent internal specifications)

Step 3: Automated Filtering

Step 4: Manual Editing (Quality Control) Step

Qualitative value: 15 cm - See entity and attribute information

For the TX data, the Post Hurricane Ike Aerial Survey 2009 project was collected under the guidance of a Professional Mapper Surveyor. The data was collected at a density sufficient to support a maximum final post spacing of of 1.5 points per meter.

For the AL data, the Post Hurricane Gustav Aerial Survey 2009 project was collected under the guidance of a Professional Mapper Surveyor. The data was collected at a density sufficient to support a maximum final post spacing of of 1.5 points per meter.

The 1 meter BareEarth Digital Elevation Model (DEM) dataset is produced from the LiDAR topographic survey conducted for the Post Hurricane Ike Aerial Survey Project. This data was produced for US Army Corps of Engineers (USACE) Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX).

The USACE collected, processed, and provided the data to the NOAA Office for Coastal Management (OCM). OCM received the data and processed it to be available for custom download from the Data Access Viewer (DAV) and for bulk download from https.