2017 Lidar (0.25 m) DEM: Eastern Maine - Merrymeeting Bay

A separate, specific metadata record was not provided for this data set, so the DEM metadata record for the larger data collection, 2017 Lidar DEM: Eastern Maine was used. Where available, information specific to this smaller collection has been included.

The NOAA Office for Coastal Management (OCM) received 36 DEM files from the State of Maine. OCM processed the data to be available on the Digital Coast Data Access Viewer (DAV) and for bulk download.

This 0.25 m DEM covers a small area in southern Maine. The lidar data was collected at the same time as a much larger data set in eastern Maine, but was provided at 16 points per square meter. A 0.50 m resolution DEM is also available for the same area. See the Related Items section of this metadata record for a link to that data set metadata record.

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available. A link to the metadata record for this data set is provided in the Related Items section. Additionally, the hydro breaklines are available. See the URL section of this metadata record for a link to the hydro breaklines.

Product: These are Digital Elevation Model (DEM) data for the Maine 2017 LiDAR QL2 - Delivery #2 area in Aroostook, Hancock, Penobscot, Piscataquis, Sagadahoc, Somerset, and Washington Counties, Maine as part of the required deliverables for the 2017 Maine LiDAR project. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create 0.25-meter, 0.5-meter, and 1-meter hydro-flattened raster DEMs.

Geographic Extent: Merrymeeting Bay, ME in Sagadahoc County, covering approximately 2 square miles.

Maine 2017 LiDAR 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 meters. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base LiDAR Specification, Version 1.2. The data for counties in the eastern AOI was developed based on a horizontal projection/datum of NAD83 (2011) UTM Zone 19, meters and vertical datum of NAVD88 (GEOID12B), meters. LiDAR data was delivered as flightline-extent unclassified LAS swaths, as processed Classified LAS 1.4 files formatted to 11,133 individual 1,500-meter x 1,500-meter tiles, 63 individual 750-meter x 750-meter tiles, and 36 individual 500-meter x 500-meter tiles, as tiled intensity imagery, and as tiled bare earth DEMs; all tiled to the same 1,500-meter x 1,500-meter schema. Continuous hydro-flattened breaklines were produced in Esri file geodatabase format.

Ground Conditions: LiDAR was collected in the spring and fall of 2017, 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, Quantum Spatial, Inc. established a total of 181 ground control points that were used to calibrate the LiDAR to known ground locations established throughout the project area. An additional 301 independent accuracy checkpoints, 178 in Bare Earth and Urban landcovers (178 NVA points), 123 in Forested, Shrubs, and Tall Weeds categories (123 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create intensity images, breaklines and raster DEMs. The purpose of these LiDAR data was to produce high accuracy 3D hydro-flattened digital elevation models (DEMs) with a 1-meter cell size. These raw LiDAR point cloud data were used to create classified LiDAR LAS files, intensity images, 3D breaklines, and hydro-flattened DEMs as necessary.

Raster File Type = IMG

Bit Depth/Pixel Type = 32-bit float

Raster Cell Size = 0.5 Meter

Interpolation or Resampling Technique = Triangulated Irregular Network (TIN), Linear Interpolation, Proprietary

In no event shall the creators, custodians, or distributors of these data be liable for any damages arising out of its use, or from the inability of the customer to use these data for their intended application.

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

Data are available online for bulk and custom downloads.

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 project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways:

1. The required NVA is: 19.6 cm at a 95% confidence level, derived according to the ASPRS Positional Accuracy Standards for Geospatial Data, i.e., based on RMSE of 10 cm in the "bare earth" and "urban" land cover classes. This is a required accuracy. The NVA was tested with 178 checkpoints located in bare earth and urban (non-vegetated) areas.

2. Vegetated Vertical Accuracy (VVA): VVA shall be reported for "forested", "shrubs", and "tall weeds" land cover classes. The target VVA is: 29.4 cm at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for LiDAR Data, i.e., based on the 95th percentile error in all vegetated land cover classes combined. This is a target accuracy.

The VVA was tested with 123 checkpoints located in forested, shrubs, and tall weeds (vegetated) areas. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. AccuracyZ has been tested to meet 19.6 cm or better Non-Vegetated Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the ASPRS Positional Accuracy Standards for Geospatial Data; assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines.This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10 cm RMSEz Vertical Accuracy Class.

Actual NVA accuracy was found to be RMSEz = 5.1 cm, equating to 9.9 cm at 95% confidence level. The NVA of the DEM was calculated using 178 independent checkpoints located in the Bare Earth and Urban land cover categories. This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10 cm RMSEz Vertical Accuracy Class.

Actual NVA accuracy was found to be RMSEz = 5.1 cm, equating to 9.9 cm at 95% confidence level. Actual VVA accuracy was found to be 25.5 cm at the 95th percentile. VVA was calculated using 123 checkpoints located in the Forested, Shrubs, and Tall Weeds land cover categories at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for LiDAR Data. Tested against the DEM.

Datasets contain complete coverage of tiles. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. There are no void areas or missing data. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

Data covers the entire area specified for this project.