2018 Maryland Lidar: Montgomery and Prince George's Counties, MD

Geographic Extent: Montgomery and Prince George's counties Maryland, covering approximately 1,110 square miles.

Dataset Description: Montgomery and Prince George's counties 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 (HARN), State Plane, Feet and vertical datum of NAVD88 (GEOID12B), Feet. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 1,413 individual 4000 ft x 6000 ft tiles.

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. Sensor errors in mulitple locations were identified in processing, additonal acquisition on 7/20/2018 was completed to remedy the errors. 2016 lidar data was used with approval in a single area of restricted airspace. 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 23 ground control points that were used to calibrate the lidar to known ground locations established throughout the project area. An additional 79 independent accuracy check points in Open Terrain and Urban landcovers were used to assess the vertical accuracy of the data. These check points 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 DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) 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.

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

Data is available online for bulk or 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 following references accuracy of a DEM derived from this point cloud and not the point cloud itself.

The project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways: 1. The required Vertical Accuracy is: 0.643 ft at a 95% confidence level, derived according to NSSDA, i.e., based on RMSE of 0.328 ft in the "bare earth" and "urban" land cover classes. This is a required accuracy. The Vertical Accuracy was tested with 79 check points located in bare earth and urban (non-vegetated) areas. The check points 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 0.643 ft or better Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines.Quantitative value: 0.298, Test that produced the value: Tested 0.298 feet at a 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA). The Vertical Accuracy of the DEM was calculated using 79 independent check points located in the Bare Earth and Urban land cover categories.

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.

Data is backed up to cloud storage.