2021 USGS Topobathy Lidar: Potomac River, MD

Product: These lidar data are processed Classified LAS 1.4 files, formatted to 139 individual 1000 m x 1000 m tiles; used to create intensity images, land/water interface refraction extents, and topobathymetric DEMs as necessary.

Geographic Extent: Potomac River and margins in Maryland and West Virginia, covering approximately 12.5 square miles.

Dataset Description: The Maryland Potomac River Topobathymetric Lidar project called for the planning, acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.35 meter (QL1) in the topographic domain and 0.71 meter (QL2b) in the bathymetric domain. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, version 2.1. The data was developed based on a horizontal projection/datum of NAD83 (2011), UTM zone 18N, meters and vertical datum of NAVD88 (Geoid 18), meters. Lidar data were delivered as processed Classified LAS 1.4 files, formatted to 139 individual 1000 m x 1000 m tiles, as tiled Intensity Imagery, and as tiled topobathymetric DEMs; all tiled to the same 1000 m x 1000 m schema. A merged topobathymetric DEM was also delivered.

Ground Conditions: Lidar was collected in October 2021, 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, Dewberry established 8 ground control points that were used to calibrate the lidar to known ground positions established throughout the project area. An additional 39 independent accuracy checkpoints--23 in bare earth and urban land cover (NVA), 8 in tall grass and brushland/low trees land cover (VVA), and 8 in submerged topography land cover (SBA)--were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post-process the data.

This metadata record supports the data entry in the NOAA Digital Coast Data Access Viewer (DAV).

The NOAA Office for Coastal Management (OCM) downloaded 139 laz point data files from this USGS site:

https://rockyweb.usgs.gov/vdelivery/Datasets/Staged/Elevation/LPC/Projects/MD_PotomacP2_Tobobathy_2021_D21/MD_PotomacP2_TB_2021/LAZ/

The data were processed to the NOAA Digital Coast Data Access Viewer (DAV) to make the data available for custom downloads.

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, Refraction Extents 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 lidar point cloud data were used to create intensity images, Refraction Extents, and topobathymetric DEMs as necessary.

USGS Contract No. 140G0221F0226 CONTRACTOR: Dewberry Engineers SUBCONTRACTOR: IIC Technologies. Lidar data were acquired and calibrated by IIC. All follow-on processing was completed by the prime contractor. A complete description of this dataset is available in the Final Project Report that will be submitted to the U.S. Geological Survey.

The following are the USGS lidar fields in JSON:

{

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v2.1",

"ldrsens" : "CZMIL (Topo Channels)",

"ldrmaxnr" : "15",

"ldrnps" : "0.35",

"ldrdens" : "8",

"ldranps" : "0.35",

"ldradens" : "8",

"ldrfltht" : "400",

"ldrfltsp" : "120",

"ldrscana" : "20",

"ldrscanr" : "27",

"ldrpulsr" : "proprietary",

"ldrpulsd" : "proprietary",

"ldrpulsw" : "proprietary",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "5",

"ldrswatw" : "291",

"ldrswato" : "20",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid 18"

},

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v2.1",

"ldrsens" : "CZMIL (Shallow/Deep Bathy Channels)",

"ldrmaxnr" : "15",

"ldrnps" : "0.35",

"ldrdens" : "8",

"ldranps" : "0.35",

"ldradens" : "8",

"ldrfltht" : "400",

"ldrfltsp" : "120",

"ldrscana" : "20",

"ldrscanr" : "27",

"ldrpulsr" : "proprietary",

"ldrpulsd" : "proprietary",

"ldrpulsw" : "proprietary",

"ldrwavel" : "532",

"ldrmpia" : "1",

"ldrbmdiv" : "5",

"ldrswatw" : "291",

"ldrswato" : "20",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid 18"

},

"ldraccur" : {

"ldrchacc" : "0",

"rawnva" : "0",

"rawnvan" : "0"

},

"lasinfo" : {

"lasver" : "1.4",

"lasprf" : "6",

"laswheld" : "Withheld (ignore) points were identified in these files using the standard LAS Withheld bit. Noise classes, class 7 and class 18, were assigned LAS withheld bit.",

"lasolap" : "The LAS overlap bit was not utilized for this dataset.",

"lasintr" : "16",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, Unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare Earth, Ground"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Low Noise"

},

"lasclass" : {

"clascode" : "18",

"clasitem" : "High Noise"

},

"lasclass" : {

"clascode" : "40",

"clasitem" : "Bathymetric Point"

},

"lasclass" : {

"clascode" : "41",

"clasitem" : "Water Surface"

},

"lasclass" : {

"clascode" : "42",

"clasitem" : "Synthetic Water surface"

},

"lasclass" : {

"clascode" : "45",

"clasitem" : "Water Column"

}

}}

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 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.

Optech CZMIL; Bayesmap; LAStools; Microstation; Terrascan; ArcGIS 10.6; Microsoft Windows 10 Enterprise Service Pack 1

Only checkpoints photo-identifiable in the intensity imagery can be used to test the horizontal accuracy of the lidar. Photo-identifiable checkpoints in intensity imagery typically include checkpoints located at the ends of paint stripes on concrete or asphalt surfaces or checkpoints located at 90 degree corners of different reflectivity, e.g. a sidewalk corner adjoining a grass surface. The xy coordinates of checkpoints, as defined in the intensity imagery, are compared to surveyed xy coordinates for each photo-identifiable checkpoint. These differences are used to compute the tested horizontal accuracy of the lidar. As not all projects contain photo-identifiable checkpoints, the horizontal accuracy of the lidar cannot always be tested.

Lidar vendors calibrate their lidar systems during installation of the system and then again for every project acquired. Typical calibrations include cross flights that capture features from multiple directions that allow adjustments to be performed so that the captured features are consistent between all swaths and cross flights from all directions. This data set was produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 41 cm RMSEx/RMSEy Horizontal Accuracy Class which equates to Positional Horizontal Accuracy = +/- 1 meter at a 95% confidence level

This data set was produced to meet ASPRS Positional Accuracy Standard for Digital Geospatial Data (2020) for a 10-cm RMSEz Vertical Accuracy Class.

USGS Determined Vertical Accuracy:

Non-Vegetated Vertical Accuracy (NVA) = 16.82 cm at 95% Confidence Level or 8.6 cm RMSE

Vegetated Vertical Accuracy (VVA) = 9.49 cm at 95th Percentile

Topobathymetric data covers the project boundary to the fullest extent possible depending on water clarity, environmental conditions, and sensor signal returns. 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 tape and to cloud storage.

Data were collected and processed by Dewberry and were made available on the USGS ftp site. The data were downloaded from the USGS rockyweb site by the NOAA Office for Coastal Management (OCM) where the data were processed to make it available for custom download from the NOAA Digital Coast Data Access Viewer (DAV).