2018 Town of Nantucket Lidar DEM: Nantucket Island, MA

Create custom data files by choosing data area, product type, map projection, file format, datum, etc. A new metadata will be produced to reflect your request using this record as a base. Change to an orthometric vertical datum is one of the many options.

Bulk download of data files in GeoTiff format, MA Island State Plane NAD83(2011) US survey feet coordinates and orthometric heights in feet.

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Link to custom download, from the Data Access Viewer (DAV), the lidar point data from which these raster Digital Elevation Model (DEM) data were created.

Link to the lidar report.

The following steps describe the Raw Data Processing and Calibration process: 1) Technicians processed the raw data to LAS format flight lines using the ABGNSS/IMU solution. 2) Technicians use TerraSolid TerraMatch to calculate initial calibration adjustment angles by mission and/or block. This is accomplished by identifying ground and above ground feature observations between flight-lines and calculating the offsets. The technician then analyzed the results and made any necessary additional adjustment until it is acceptable. 3) Once the angle calculation was completed the adjusted settings were applied to all of the flight-lines of the mission and/or block and checked for consistency. The technicians utilized commercial and proprietary software packages to analyze how well flight-line overlaps match and adjusted as necessary until the results met the project specifications. 4) The technicians checked and corrected the vertical misalignment of all flight-lines and also the matching between data and ground truth. The relative accuracy was less than or equal to 6 cm RMSEz within individual swaths and less than or equal to 8 cm RMSDz or within swath overlap (between adjacent swaths). 5) The technicians ran a final vertical accuracy check of the calibrated point cloud against the surveyed check points after the z correction to ensure the requirement of NVA = 19.6 cm 95% Confidence Level (Required Accuracy) was met. Point classification was performed according to USGS Lidar Base Specification 1.2, and breaklines were collected for water features. Bare earth DEMs were exported from the classified point cloud using collected breaklines for hydroflattening.

LAS Point Classification: The point classification is performed as described below. The bare-earth surface is manually reviewed to ensure correct classification on the Class 2 (Ground) points. After the bare-earth surface is edited and QC'd, it is then used to generate all hydro-breaklines through heads-up digitization. All ground (ASPRS Class 2) lidar data inside of the Lake Pond and River Pond hydro flattening breaklines were then classified to water (ASPRS Class 9) using LP360 functionality. A buffer of 0.5 meters was also used around each hydro-flattened feature to classify these ground (ASPRS Class 2) points to Ignored ground (ASPRS Class 10). All Lake Pond Island and River Stream Island features were checked to ensure that the ground (ASPRS Class 2) points were reclassified to the correct classification after the automated classification was completed. All overlap data was processed through automated functionality provided by TerraScan to classify the overlapping flight-line data to approved classes by USGS. The overlap data was classified using standard LAS overlap bit. These classes were created through automated processes only and were not verified for classification accuracy. All data was manually reviewed and any remaining artifacts removed using functionality provided by TerraScan and TerraModeler. Global Mapper is used as a final check of the bare-earth dataset. GeoCue was then used to create the deliverable industry-standard LAS files for the Classified Point Cloud Data. LAStools, LP360 and TerraScan software was used to perform statistical analysis of the classes in the LAS files, on a per tile level to verify classification metrics and full LAS header information.

Hydro Flattened Raster DEM Process: Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 2 foot hydro-flattened Raster DEM. Using automated scripting routines within ArcMap, an GeoTIFF TIF file was created for each tile. Each surface is reviewed using Global Mapper to check for any surface anomalies or incorrect elevations found within the surface.

The NOAA Office for Coastal Management (OCM) was provided this data set from the office of Mass GIS. The total number of files received and processed was 1619. The data were in Massachusetts Island State Plane NAD83(2011), US survey feet coordinates and NAVD88 (Geoid12B) elevations in feet. The bare earth raster files were at a 2 feet grid spacing.

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. Used internal an script to assign the EPSG codes (Horizontal EPSG: 6490 and Vertical EPSG: 6360) to the GeoTiff formatted files.

2. Copied the files to https.