2001 NCFMP Lidar: Phase 1B (Cape Fear and Lumber River Basins)

This airborne LiDAR terrain mapping data was acquired in the spring of 2001. The data were collected for the floodplain mapping program for the state of North Carolina. The data were collected for the state in three phases: 1, 2, and 3. This metadata record describes that data that were in phase 1 of collection and fall within the Cape Fear and Lumber River Basins in central and eastern North Carolina. This area consists of 30 counties which are listed below in the Place Keywords field.

The data were received by the NOAA Office for Coastal Management from the U.S. Geological Survey (USGS) Center for Lidar Coordination and Knowledge (CLICK). For data storage and Digital Coast provisioning purposes, the OCM converted the data to geographic coordinates and ellipsoid (Geoid99) elevations. The data are unclassified.

These data were collected and derived by the North Carolina Floodplain Mapping Program (www.ncfloodmaps.com) as part of its effort to modernize FEMA Flood Insurance Rate Maps (FIRM) statewide. Although created for specific use in the engineering aspects of floodplain delineation, the data were also developed to address the elevation data requirements of the broader geospatial data user community. The North Carolina Floodplain Mapping Program was established in response to the extensive damage caused by Hurricane Floyd in 1999.

10475

Files in LAZ format (classified as 1, unclassified)

none

Any conclusions drawn from the analysis of this information are not the responsibility of NC Floodplain Mapping Program,

Greenhorne & O'Mara, Inc., the NOAA Office for Coastal Management, or its partners.

This data can be obtained on-line at the following URL:

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=1399

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Users should be aware that temporal changes may have occurred since this data set was collected and that 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.

LIDAR Bare Earth data were compared with NCGS QA/QC checkpoints. The 5% of points with the largest error were removed (outliers). For

the NC Floodplain Mapping Program, the vertical accuracy for coastal counties is less than or equal to 20 cm RMSE.

For mainland counties, the vertical accuracy of the elevation data is less than or equal to 25 cm RMSE. More information about the

| Quantitative Value:

Total accuracy (all land cover types): Information on accuracy is contained in the Cape Fear and Lumber River Basin Final Reports.

Accuracy by land cover type: Information on accuracy is contained in the county reports, which may be viewed at:

http://portal.ncdenr.org/web/lr/geodetic/floodplaininfo.

| Quantitative Test Explanation:

State QAQC points measured by the NCGS were compared to interpolated TIN values for the LIDAR data sets. The difference was

calculated as the QAQC value minus the LIDAR interpolated TIN value. The differences were then squared and summed. The resulting

value was divided by the number of points compared to determine the mean. The square root of the mean was calculated to arrive

at the Root Mean Square Error (RMSE) of the elevation differences, or RMSE(z). Additional information on accuracy is contained in

the county reports, which may be viewed at: http://portal.ncdenr.org/web/lr/geodetic/floodplaininfo.

See Cape Fear and Lumber River Basin Final Reports.; Quantitative Value: 1.0 meters, Test that produced the value:

Horizontal Accuracy is derived from the total error budget of the LIDAR Sensor and the Post Processed GPS Kinematic solution.

Error budgets and calibration values have been established that include GPS error of the aircraft location in space during flight,

the angular error of the Inertial Measurement Unit resulting in error budget for aircraft platform attitude in pitch, roll and yaw,

and the angular error in the LIDAR scan mirror position for each laser shot. These and other minor error budgets are used to derive

the maximum horizontal position error of the LIDAR footprint on the terrain surface. Performance against this budget is checked

with laboratory measurements and flight calibrations to assure conformance to specification. Further information on calibration

reports can be obtained in these reports, available at: http://portal.ncdenr.org/web/lr/geodetic/floodplaininfo.

See Cape Fear and Lumber River Basin Final Reports.; Quantitative Value: 0.2 meters, Test that produced the value:

Internally collected QAQC points and qualified NGS Benchmarks were compared to interpolated TIN values for the LIDAR data sets.

The difference was calculated as the QAQC value minus the LIDAR interpolated TIN value. The differences were then squared and

summed. The resulting value was divided by the number of points compared to determine the mean. The square root of the mean was

calculated to arrive at the Root Mean Square Error (RMSE) of the elevation differences, or RMSE(z). Acceptable values for RMSE

would be 20cm or less for designated coastal counties and 25cm for inland counties. The county reports which have the county

RMSE value are available at: http://portal.ncdenr.org/web/lr/geodetic/floodplaininfo.

Not provided

Proprietary algorithms exclude any points taken with Positional Dilution of Precision Values greater than 3; algorithms also exclude

anomalous points (extremely high or extremely low values compared to the surrounding points).