2011 Anne Arundel County, MD, LiDAR Points

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Information on the NOAA Office for Coastal Management (OCM)

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Location of original point cloud downloads. Has other information, such as DEMs.

Data Collection:

Using a Leica Light Detection And Ranging (LiDAR) system, (1.4 meter ground sample distance) data were collected over the entire area of Anne Arundel County, MD (approx 416 square miles). Multiple returns were recorded for each laser pulse along with an intensity value for each return. The data acquisition occurred in 2 missions between March 1, 2011, and March 2, 2011. During the LIDAR campaign, a field crew conducted a GPS field survey to establish final coordinates of the ground base stations for final processing of the base-remote GPS solutions.

Airborne GPS Processing:

Airborne GPS data was differentially processed and integrated with the post processed IMU data to derive a Smoothed Best Estimate of Trajectory (SBET). The SBET was used to reduce the LiDAR slant range measurements to a raw reflective surface for each flight line. The overlap between flight lines was removed to provide a homogeneous coverage, and the coverage was classified to extract a bare earth digital elevation model (DEM).

Airborne GPS is differentially processed using the GrafNAV V7.50 software by Waypoint Consulting of Calgary, Alberta, Canada. The PDOP and distance separation is as follows:

The classification and quality control (QC) of LiDAR data is carried out using TerraScan software by Terrasolid Limited of Helinski, Finland.

IMU data Processing:

IMU data provides information concerning roll, pitch and yaw of collection platform during collection event. IMU information allows the pulse vector to be properly placed in 3D space allowing the distance from the aircraft reference point to be properly positioned on the elevation model surface. The IMU data is processed using the PosPac V4.2 software by Applanix Corporation of Richmond Hill, Ontario, Canada.

The reflective surface is derived using the ALS Post Processor software by Leica Geosystems GIS & Mapping Division of Atlanta, Georgia.

LIDAR Point Classification

The classification and quality control (QC) of LiDAR data is carried out using TerraScan software by Terrasolid Limited of Helinski, Finland.

Data were obtained from the Maryland iMap (imap.Maryland.gov) in LAZ format in October 2017. Data were in Maryland State Plane FIPS 1900 U.S. Survey Feet horizontally and vertical NAVD88 feet. The geoid model originally used to obtain NAVD88 was not listed in the metadata, but the files contained georeferencing information indicating that GEOID96 was used. While this was an unusual GEOID to use for 2011 data, there was no other information to the contrary.

Data were reprojected to geographic coordinates in degrees. The vertical units were converted to meters and the GEOID96 model was reversed to get ellipsoidal heights. The data were then ingested into the Digital Coast Data Access Viewer for distribution.

Point classifications were not defined in the original metadata and many classes were found to have only a few points, likely residual temporary holding classes that were never cleaned up. Class 10 appeared to be ground points that could be used to form a breakline. These were reclassed to the ground class (2). Class 11 appeared to be overlap and were reclassed to the original ASPRS LAS 1.2 standard overlap class of 12. Points classified in what appeared to fit the standard ASPRS definitions (class 0 = created, never classified, class 1 = unclassified, 2 = ground, 7 = low noise, and 9 = water) were not changed. All other classes were reclassed to class 1, typically consisting of less than 100 points for the entire data set per class.