2022 NOAA NGS Topobathy Lidar DEM: Bethany Beach to Chincoteague, MD

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This graphic shows the lidar footprint for this dataset.

Topobathy Lidar Data Report

Data for the Chesapeake project was acquired by Woolpert using a Leica Hawkeye4X sensor. All delivered products are referenced to the following except las data, which is ellipsoidal height in meters:

Horizontal Datum-NAD83 (2011) epoch: 2010

Projection-UTM Zone 18 North

Horizontal Units-meters

Vertical Datum-NAVD88 - Geoid18

Vertical Units-meters

This dataset encompasses 5000m x 5000m tiles. Both green lidar data and NIR lidar data were acquired.

Woolpert acquired, calibrated, and performed the refraction correction of the lidar data. Light travels at different speeds in air versus water and its direction of travel or angle is changed or refracted when entering the water column. The refraction correction process corrects for this difference by adjusting the depth (distance traveled) and horizontal position (change of angle/direction) of the lidar data acquired within water.

Relative accuracy of the swaths compared to overlapping and adjacent swaths was verified through the use of Delta-Z (DZ) orthos created in LASTools software. Profiles of elevated planar features, such as roofs, were used to verify horizontal alignment between overlapping swaths.

Algorithms in TerraScan were used to create the intial ground surface.

All lidar data was peer-reviewed. QAQC also included creating void polygons for use during review. All necessary edits were applied to the dataset. LASTools was used to update LAS header information, including all projection and coordinate reference system information. The final lidar data is in LAS format 1.4 and point data record format 6.

The final classification scheme is as follows:

1-Unclassified

2-Ground

7-Low Noise

9-Topo Water Surface

18-High Noise

40-Bathymetric Point

41-Bathymetric Water Surface

42-Synthetic Derived Water Surface

43-Submerged Object

The lidar data was transformed from ellipsoid heights to orthometric heights, referenced to NAVD88 Geoid 18, meters. The lidar data in orthometric heights was used to create the final topobathymetric DEMs in orthometric heights.

Lidar data were used to generate a raster in geotiff format with 1 meter pixel resolution for the entire area. The raster was then clipped to the tile grid and named according to project specifications to result in tiled topobathymetric DEMs.

Bathy void polygons represent bathymetric areas with no bathymetric bottom returns and accompany the DEMs. Void polygon creation is described in the final project report.