Data Management Plan

Product: These lidar data are processed Classified LAS 1.4 files, formatted to 1,577 individual 1250 ft x 1250 ft tiles; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary.

Geographic Extent: Nantucket County Massachusetts, covering approximately 91 square miles.

Dataset Description: The Nantucket project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.7 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2. The data was developed based on a horizontal projection/datum of NAD83 (2011), State Plane, Feet and vertical datum of NAVD88 (GEOID12B), Feet. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 1,577 individual 1250 ft x 1250 ft tiles, as tiled Intensity Rasters, and as tiled bare-earth DEM; all tiled to the same 1250 ft x 1250 ft schema.

Ground Conditions: Lidar was collected in early to mid 2018, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, Sanborn Map Company, Inc. established a total of 20 ground control points that were used to calibrate and validate the lidar to known ground locations established throughout the project area.

In addition to these lidar point data, the bare earth Digital Elevation Models (DEM) created from the lidar point data are also available. These data are available for custom download at the link provided in the URL section of this metadata record.

Lineage Statement:
This data was provided by Mass GIS to the NOAA OCM for custom distribution by the NOAA Digital Coast Data Access Viewer (DAV) and bulk distribution via S3 AWS service.

Process Steps:

• 2018-01-01 00:00:00 - 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.
• 2018-10-12 00:00:00 - 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.
• 2022-06-29 00:00:00 - 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 1577. The data were in Massachusetts Island State Plane (NAD83 2011), US survey feet coordinates and NAVD88 (Geoid12B) elevations in feet. The data were classified as: 1 - Unclassified, 2 - Ground, 7 - Low Noise, 9 - Water, 10 - Ignored Ground, 17 - Bridge Deck, 18 - High Noise. OCM processed all classifications of points to the Digital Coast Data Access Viewer (DAV). Classes available in the DAV are: 1, 2, 7, 9, 10, 17, 18. OCM performed the following processing on the data for Digital Coast storage and provisioning purposes: 1. An internal OCM script was run to check the number of points by classification and by flight ID and the gps and intensity ranges. 2. Internal OCM scripts were run on the laz files to convert from orthometric (NAVD88) elevations to ellipsoid elevations using the Geoid12B model, to convert from Massachusetts Island State Plane (NAD83 2011), US survey feet coordinates to geographic coordinates, to convert from elevations in feet to meters, to assign the geokeys, to sort the data by gps time and zip the data to database and to the Amazon S3 bucket.

Data is available online for bulk and custom downloads.

Data is backed up to tape and to cloud storage.