2016 NOAA NGS Topobathy Lidar: Marthas Vineyard and Nantucket Islands, MA

These data were collected by Leading Edge Geomatics using a Leica Chiroptera II Bathymetric/Topographic Sensor. The data were acquired from October 4, 2016 through November 1, 2016. The data includes topobathy data in LAS 1.2 format classified as created, never classified (0); Unclassified (1); Ground (2); Topo Noise (7); Water (9); Refracted Bathymetric Noise (22); Water Column (25); Bathymetric Bottom or Submerged Topography (26); Water Surface (27); Derived Water Surface (28). The project area covers Marthas Vineyard and Nantucket Islands along with some shoal areas surrounding the islands. The project covers a total of 234 square miles within the AOI. This dataset contains 7030 - 500 m x 500 m lidar tiles.

The Martha's Vineyard and Nantucket Islands have been identified as having critical topographic and bathymetric data gaps by NOAA. This lidar data will fill those critical gaps.

Data for Marthas Vineyard and Nantucket Islands project was acquired by Leading Edge Geomatics using a Leica Chiroptera II Bathymetric and Topographic lidar sensor. The full workflow used for this project is found in the final project report submitted to NOAA.

Users should be advised that there is a potential that some ground and bathymetry points may have been misclassified.

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

Users may access the data from either a custom download or bulk download link.

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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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.

The horizontal accuracy of the data is better than plus or minus 1.0 m at a 95% confidence level.

The actual NVA accuracy was found to be RMSEz= 8.6 cm, equating to +/- 16.9 cm at 95% confidence level. The actual VVA accuracy was found to be +/- 26.8 cm at the 95th percentile.

Lidar vendors calibrate their lidar systems during installation of the system and then again for every project acquired. Typical calibrations include cross flights that capture features from multiple directions that allow adjustments to be performed so that the captured features are consistent between all swaths and cross flights from all directions. Horizontal positional accuracy is achieved through rigorous processing of airborne GPS and IMU, use of control, and calibration procedures. No photo-identifiable areas could be found in the lidar intensity imagery and horizontal accuracy could not be tested for the lidar data.

The vertical accuracy of the lidar was tested by Dewberry with 48 independent survey checkpoints. The survey checkpoints are evenly distributed throughout the project area and are located in areas of non-vegetated terrain, including bare earth, open terrain, and urban terrain (26), vegetated terrain, including forest, brush, tall weeds, crops, and high grass (11), and submerged bottom areas (11). The vertical accuracy is tested by comparing survey checkpoints to a triangulated irregular network (TIN) that is created from the lidar ground and submerged bottom points. Checkpoints are always compared to interpolated surfaces created from the lidar point cloud because it is unlikely that a survey checkpoint will be located at the location of a discrete lidar point.

All checkpoints located in non-vegetated terrain were used to compute the Non-vegetated Vertical Accuracy (NVA). Project specifications required a NVA of 19.6 cm at the 95% confidence level based on RMSEz (10 cm) x 1.9600. All checkpoints located in vegetated terrain were used to compute the Vegetated Vertical Accuracy (VVA). Project specifications required a VVA of 30.0 cm based on the 95th percentile. All checkpoints located in bathymetric areas were used to compute an accuracy for the bathymetric data. Project specifications required bathymetric data to meet or exceed 58.8 cm at the 95% confidence level based on RMSEz (18.5 cm) x 1.9600.