Data Management Plan

Extent: The project area covers 76 sq. miles of the Town of York, ME. Ground Conditions During Flight: The project was flown in May 2017 during leaf off conditions and when there was no snow on the ground. The project area required LiDAR to be collected on 8 points/sq. meter equivalent to 4 points/sq. meter single swath or better and processed to meet the bare earth vertical accuracy as described with LiDAR Base Specifications v1.2. Project deliverables include: raw point cloud by swath, classified point cloud, Bare-Earth Surface (Raster DEM) 0.5m resolution, breaklines used for hydro-flattening Raw point cloud data is delivered by individual swath. All other deliverables are delivered in a 1050m x 1050m tiling scheme.

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

Process Steps:

• LIDAR Preprocessing: Leica Cloud Pro Point cloud Processor software was used in the post processing of the airborne GPS and inertial data that is critical to the positioning and orientation of the sensor during all flights. Leica Cloud Pro provides the smoothed best estimate of trajectory (SBET) that is necessary for Leica ALS post processor to develop the point cloud from the LiDAR missions. Calibration of the data is done using the Leica Cloud Pro software. The .las files are imported in, prepped, and spatially indexed. Ground control points/check points are imported and a QA/QC module is run. Relative calibration was evaluated using advanced plane-matching analysis and parameter corrections. Relative calibration was repeated iteratively until errors between overlapping swaths, across all project lifts, was reduced to ±16cm on planar surfaces within the area of interest. A flight line separation report is exported to a .jp2 file. Global Mapper is used to view the .jp2 file to determine if the data is within the client’s specifications. A control report was generated to assess the RMSE of check points and ensure compliance with QL1 specification. At this point this data is ready for analysis, classification, and filtering to generate a bare earth surface model in which the above ground features are removed from the data set.
• LIDAR Postprocessing: Subsequent to pre-processing, data were then distributed as virtual tiles to experienced LiDAR analysts for localized automatic classification, manual editing, and peer-based QC checks. Supervisory QC monitoring of work in progress and completed editing ensured consistency of classification character and adherence to project requirements across the entire project. The point cloud was manipulated within TerraScan and TerraModeler software was used for the automated data classification, manual cleanup, and bare earth generation from this data. Classification of the point cloud to contract specifications: 1-Unclassified, 2-Bare-earth ground, 3-Low Vegetation, 4-Medium Vegetation,5-High Vegetation, 7- Low Noise, 9-Water, 10-Ignored Ground due to breakline proximity, and 11-Withheld, 17-Bridge decks, 18-High Noise. Project specific macros were used to classify the ground, the three types of vegetation and to remove the side overlap between parallel flight lines. Client defined vegetation height ranges are 0-0.5 m (low), 0.51 – 1.5m (medium) and 1.51m and above (high). All data was manually reviewed and any remaining artifacts removed using functionality provided by TerraScan and TerraModeler. After completion of classification and final QC approval, the NVA and VVA for the project are calculated. Sample areas for each land cover type present in the project was extracted and forwarded to the client, along with the results of the accuracy tests. Class 2 LiDAR was used to create a bare earth surface model. The surface model was then used to heads-up digitize 3D breaklines of inland streams and rivers with a 30 meter nominal width and inland ponds and lakes of 8,000 sq. meters or greater surface area. All data was processed in UTM NAD83 Zone 12, Meters. All ground (ASPRS Class 2) LiDAR data inside of the collected inland breaklines were then classified to water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 0.7 meter was also used around each hydro flattened breakline feature. These points were moved from ground (ASPRS Class 2) to Ignored Ground (ASPRS Class 10).
• Quality control by Aeroptic LLC completed independent QA/QC of the calibrated files, classified files and derivative products. QC module and other software was used validate the data sets for compliance with LiDAR Base Specifications v1.2. Outputs in included Data Check and Calibration Check Reports. Absolute Accuracy Reports for pre-and post-classified LiDAR date were also generated. All reports are on file with the owner.
• Breakline:The LiDAR surface model was used to heads-up digitize 3D breaklines of inland streams and rivers with a 30 meter nominal width and Inland Ponds and Lakes of 8,000 sq. meters or greater surface area. all data was processed in UTM NAD83 Zone 19, Meters. All ground (ASPRS Class 2) LiDAR data inside of the collected inland breaklines were then classified to water (ASPRS Class 9)using TerraScan macro functionality. A buffer of 0.7 meter was also used around each hydro flattened feature. These points were moved from ground (ASPRS Class 2) to Ignored Ground (ASPRS Class 10). The breaklines were used to perform the hydrologic flattening of water bodies, and gradient hydrologic flattening of double line streams. Lakes, reservoirs and ponds, at a nominal minimum size of two (2) acres or greater, were compiled as closed polygons. The closed water bodies were collected at a constant elevation. Rivers and streams, at a nominal minimum width of 30.5 meters (100 feet), were compiled in the direction of flow with both sides of the stream maintaining an equal gradient elevation.
• 2017-12-11 00:00:00 - The NOAA Office for Coastal Management (OCM) received the point and raster DEM data from the Town of York, ME. The data were in UTM Zone 19 (NAD83) meters coordinates and NAVD88 (Geoid12a) elevations in meters. The rasters were at a 0.5 m grid spacing. OCM copied the raster files to database and https for Digital Coast storage and provisioning purposes.
• 2019-04-25 00:00:00 - In April 2019, after the data had been available for download from the Data Access Viewer for approximately one year, the NOAA Office for Coastal Management (OCM) determined that the elevation values in this data set were 1 to 1.5 m lower than valid elevations. After receiving the control point data from the Town of York, it appears that the point data were originally in WGS84 ellipsoid heights and GEOID12a was applied to convert to NAVD88. However, GEOID12a should be applied to NAD83 ellipsoid heights, not WGS84. Therefore, the files that were provided in NAVD88 had incorrect (too low) elevations. Using VDatum 3.9 via a python script, the DEM tiles' heights were transformed from their incorrect NAVD88 vertical datum back to their original ellipsoid heights. They were then correctly transformed from the WGS84 ellipsoid to NAVD88 Geoid 12a.

Users may access the data from two links. Custom download and bulk download options are available.