2018 USACE NCMP Topobathy Lidar DEM: Gulf Coast (AL, MS)

These files contain rasterized topobathy lidar elevations generated from data collected by the Coastal Zone Mapping and Imaging Lidar (CZMIL) system.CZMIL integrates a lidar sensor with simultaneous topographic and bathymetric capabilities, a digital camera and a hyperspectral imager on a single remote sensing platform for use in coastal mapping and charting activities. Native lidar data is not generally in a format accessible to most Geographic Information Systems (GIS). Specialized in-house and commercial software packages are used to process the native lidar data into 3-dimensional positions that can be imported into GIS software for visualization and further analysis. The 3-D position data are sub-divided into a series of LAS files, which are tiled into 1-km by 1-km boxes defined by the Military Grid Reference System.

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

This data was collected by USACE underneath the National Coastal Mapping Program to assess changes in elevations above and below water along the coast.

These data have been developed from the best available sources. Although efforts have been made to ensure that the data are accurate and reliable, errors and variable conditions originating from physical sources used to develop the data may be reflected in the data supplied. Users must be aware of these conditions and bear responsibility for the appropriate use of the information with respect to possible errors, scale, resolution, rectification, positional accuracy, development methodology, time period, environmental and climatic conditions and other circumstances specific to these data. The user is responsible for understanding the accuracy limitations of the data provided herein. The burden for determining fitness for use lies entirely with the user. The user should refer to the accompanying metadata notes for a description of the data and data development procedures. Any conclusions drawn from the analysis of this information are not the responsibility of USACE, JALBTCX, the Office for Coastal Management, or its partners.

Data is available online for bulk and custom downloads.

These data have been developed from the best available sources. Although efforts have been made to ensure that the data are accurate and reliable, errors and variable conditions originating from physical sources used to develop the data may be reflected in the data supplied. Users must be aware of these conditions and bear responsibility for the appropriate use of the information with respect to possible errors, scale, resolution, rectification, positional accuracy, development methodology, time period, environmental and climatic conditions and other circumstances specific to these data. The user is responsible for understanding the accuracy limitations of the data provided herein. The burden for determining fitness for use lies entirely with the user. The user should refer to the accompanying metadata notes for a description of the data and data development procedures.

These data depict the heights at the time of the survey and are only accurate for that time. Acknowledgement of the Joint Airborne Lidar Bathymetry Technical Center of eXpertise (JALBTCX) would be appreciated in any publications or derived products. The data herein, including but not limited to geographic data, tabular data, analytical data, electronic data structures or files, are provided "as is" without warranty of any kind, either expressed or implied, or statutory, including, but not limited to, the implied warranties or merchantability and fitness for a particular purpose. The entire risk as to the quality and performance of the data is assumed by the user. No guarantee of accuracy is granted, nor is any responsibility for reliance thereon assumed. In no event shall the U.S. Army Corps of Engineers, Mobile District Office, Spatial Data Branch be liable for direct, indirect, incidental, consequential or special damages of any kind, including, but not limited to, loss of anticipated profits or benefits arising out of use of or reliance on the data. The Spatial Data Branch does not accept liability for any damages or misrepresentation caused by inaccuracies in the data or as a result of changes to the data caused by system transfers or other transformations or conversions, nor is there responsibility assumed to maintain the data in any manner or form. Users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of its limitations.

Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1; Esri ArcGIS 10.1.0.3035

Every effort within operational constraints was made to acquire data that meets specifications as outline in this project's Statement of Work. Per flight block, elevations in areas of swath overlap are internally consistent and meet CZMIL specifications. Anomalous high and/or low elevation values have been removed, and point cloud classification algorithms have been validated via manual review and QC. Temporal differences in elevation exist in areas of active nearshore processes from the dune to the depth of closure. JALBTCX conducts operations in a manner to ameliorate temporal differences, to include the collection of entire flight blocks within single missions. For a given flight block, it's adjacent flight blocks are captured within 3 days as weather and airspace permit.

CZMIL topographic data - Compiled to meet 1 m horizontal accuracy at 95% confidence level. CZMIL bathymetric data - Compiled to meet 3.5 + 0.05d m horizontal accuracy at 95% confidence level, d is depth.

CZMIL topographic data - Compiled to meet 19.6 cm vertical accuracy at 95% confidence level. CZMIL bathymetric shallow FOV data - Compiled to meet SQRT((0.25^2) +((0.0075d)^2)) m vertical accuracy at 95% confidence level, d is depth. CZMIL bathymetric deep FOV data - Compiled to meet SQRT((0.30^2) +((0.013d)^2)) m vertical accuracy at 95% confidence level, d is depth.

Planned data coverage for this dataset included a 1500-meter swath of the Gulf of Mexico shoreline. Topographic lidar coverage was obtained from the shoreline onshore 500 meters. Bathymetric lidar coverage extends from the shoreline offshore 1000 meters or to laser exinction, whichever occurs first. The planned data densitiy is 70 centimeters on land and in shallow water. In deeper water the planned data density decreases to 2 meters. Gaps or data holidays may exist in the data coverage. They arise due to a number of operational and environmental conditions, including but not limited to, airspace restrictions, high terrain, active surf, low-reflectivity bottom substrate materials and turbidity in the water column. Please see the Report of Survey for additional details.

Every effort within operational constraints was made to achieve the intended data coverage and planned point densities.

This data set covers the spatial extent of topographic lidar data obtained during this survey.

During inspection and QC of the lidar point cloud, flightline to flightline elevation differences met the CZMIL sensor specifications.

JALBTCX evaluates final data coverage using techniques that are common to the lidar industry. These techniques are performed in a 3D environment for visual review of the final data coverage and verification of data alongside lidar waveforms and imagery collected concurrent with the lidar. Data reviewers perform checks to verify (1) extreme high and/or low elevation values have been invalidated, (2) elevations in areas of swath overlap are internally consistent, (3) binned standard deviation values meet CZMIL specifications, (4) point cloud classifications are valid, and (4) CZMIL processing modes are valid.

CZMIL data is processed from raw lidar waveforms to point clouds using the CZMIL HydroFusion software package. Point clouds are then classified and edited in industry-standard software packages. Derivative data products are generated through the application of gridding and contouring algorithms in a GIS environment. The data processing workflow, including software packages, algorithms and parameters are provided in detail, herein this metadata as Process Steps.