2019 NOAA NGS Topobathy Lidar DEM: Chesapeake Bay, MD

NOAA Chesapeake Bay MD1902 and MD1903 Topobathymetric lidar data were collected by NV5 Geospatial (NV5) using a Leica Chiroptera 4x system. The MD1903 acquisition spanned from 20191109-20191115 in 5 missions. The MD1902 acquisition spanned from 20191109-20191116 in 6 missions. The datasets include topobathymetric data in LAS format 1.4, point data record format 6, with the following classifications in accordance with project specifications and the American Society for Photogrammetry and Remote Sensing (ASPRS) classification standards:

1 - unclassified

2 - ground

7 - noise

40 - bathymetric bottom or submerged topography

41 - water surface

43 - submerged feature

45 - water column

46 - overlap bathy bottom - temporally different from a separate lift

71 - unclassified associated with areas of overlap bathy bottom/temporal bathymetric differences

72 - ground associated with areas of overlap bathy bottom/temporal bathymetric differences

81 - water surface associated with areas of overlap bathy bottom/temporal bathymetric differences

85 - water column associated with areas of overlap bathy bottom/temporal bathymetric differences

1 Overlap - edge clip

1 Withheld- green sensor returns within topographic areas

42 Synthetic - synthetic water surface

These data sets also includes lidar intensity values, number of returns, return number, time, and scan angle. The 100 meter buffered NOAA Chesapeake Bay MD1902 project area covers approximately 260.195 square kilometers in an area encompassing Severn River to Rhode River near Annapolis, Maryland. LAS files were compiled in 500 m x 500 m tiles. The final classified lidar data were then transformed from ellipsoid to geoidal height (Geoid12b) and used to create 23 - 5,000 m x 5,000 m topobathymetric DEMs in GeoTIFF format with 1m pixel resolution. The 100 meter buffered NOAA Chesapeake Bay MD1903 project area covers approximately 273.518 square kilometers in an area encompassing West River to Dares Beach near Annapolis, Maryland. LAS files were compiled in 500 m x 500 m tiles. The final classified lidar data were then transformed from ellipsoid to geoidal height (Geoid12b) and used to create 18 - 5,000m x 5,000 m topobathymetric DEMs in GeoTIFF format with 1m pixel resolution.

This lidar data was required by National Oceanic and Atmospheric Administration (NOAA) and the National Geodetic Survey (NGS), Remote Sensing Division Coastal Mapping Program (CMP) to enable accurate and consistent measurement of the national shoreline. The CMP works to provide a regularly updated and consistent national shoreline to define America's marine territorial limits and manage coastal resources.

Data from MD1902 and MD1903 includes all lidar returns. An automated grounding classification algorithm was used to determine bare earth and submerged topography point classification. The automated grounding was followed with manual editing. Depth values were adjusted per sensor to NOAA provided ground truth data. Bathymetric intensity values were normalized for water depth. Classes 2 (ground), 40 (submerged topography), and 43 (submerged object) were used to create the final DEMs. The full workflow used for this project will be documented in the NOAA Chesapeake Bay MD_1902_1903 Topobathymetric lidar final report.

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.

OS Independent

Lidar horizontal accuracy is a function of Global Navigation Satellite System (GNSS) derived positional error, flying altitude, and INS derived attitude error. The obtained RMSEr value is multiplied by a conversion factor of 1.7308 to yield the horizontal component of the National Standards for Spatial Data Accuracy (NSSDA) reporting standard where a theoretical point will fall within the obtained radius 95 percent of the time (ACCr). Based on a flying altitude of 400 meters, an IMU error of 0.005 decimal degrees, and a GNSS positional error of 0.015 meters, the RMSEr value for the MD1902 and MD1903 project area is 0.064 meters, with a ACCr of 0.11 meters at the 95% confidence level. The project specification requires horizontal positions to be accurate to 1.0m(RMSE).

Absolute accuracy was assessed using both Non-Vegetated Vertical Accuracy (NVA) and Vegetated Vertical Accuracy (VVA) survey methods. Survey checkpoints were evenly distributed as feasible throughout the project area. NVA compares known ground check point data that were withheld from the calibration and post-processing of the lidar point cloud to the derived gridded bare earth DEM. NVA is a measure of the accuracy of lidar point data in open areas with level slope (less than 20Â degrees) where the lidar system has a high probability of measuring the ground surface and is evaluated at the 95% confidence interval (1.96*RMSE).

Vertical Positional Accuracy for MD1902

In the MD1902 data extent, 9 survey checkpoints were used to assess the vegetated vertical accuracy. Project specifications require VVA meet 0.36 m based on the 95th percentile tested against the derived bare earth DEM. Submerged topography points were tested separately. In the MD1902 data extent, 89 survey checkpoints were used to assess the submerged topography accuracy. Project specifications require submerged topography shall meet a vertical RMSE of QL2b specified in the Draft National Coastal Mapping strategy 1.0 which is equivalent to 0.30 m RMSE at a depth of 1 m. Please refer to the final data report for final accuracies.

The MD1902 dataset Non-Vegetated Vertical Accuracy tested 0.064 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 25 ground check points, based on RMSEz (0.036 m) x 1.9600.

The MD1902 dataset Vegetated Vertical Accuracy tested 0.119 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 9 landclass points.

The MD1902 dataset tested 0.136 m vertical accuracy at 95% confidence level against the derived topobathymetric bare earth DEM using 89 submerged check points, based on RMSEz (0.069 m) x 1.9600. Submerged topography checkpoints usually occur in depths up to 1m.

Vertical Positional Accuracy for MD1903

In the MD1903 data extent, 11 survey checkpoints were used to assess the vegetated vertical accuracy. Project specifications require VVA meet 0.36 m based on the 95th percentile tested against the derived bare earth DEM. Submerged topography points were tested separately. In the MD1903 data extent, 43 survey checkpoints were used to assess the submerged topography accuracy. Project specifications require submerged topography shall meet a vertical RMSE of QL2b specified in the Draft National Coastal Mapping strategy 1.0 which is equivalent to 0.30 m RMSE at a depth of 1 m. Please refer to the final data report for final accuracies.

The MD1903 dataset Non-Vegetated Vertical Accuracy tested 0.081 m vertical accuracy at 95% confidence level against the derived bare earth DEM in open terrain using 23 ground check points, based on RMSEz (0.041 m) x 1.9600.

The MD1903 dataset Vegetated Vertical Accuracy tested 0.159 m vertical accuracy at the 95th percentile against the derived bare earth DEM using 11 landclass points.

The MD1903 dataset tested 0.158 m vertical accuracy at 95% confidence level against the derived topobathymetric bare earth DEM using 43 submerged check points, based on RMSEz (0.081 m) x 1.9600. Submerged topography checkpoints usually occur in depths up to 1m.

Data covers the project boundary.

Not applicable

Data is backed up to tape and to cloud storage.