2006 FEMA New Jersey Flood Mitigation Lidar: Hunterdon County

This metadata record describes the lidar topographic elevation mapping of Hunterdon County, NJ that occurred in July 2006. Products generated

include lidar point clouds in LAS 1.0 collected with a Leica ALS-50 Aerial Lidar Sensor.

Original contact information:

Contact Name: Angela R. Worley

Contact Org: EarthData International

Title: Project Manager

Phone: 301-948-8550 x222

Email: aworley@earthdata.com

The purpose of this data is to support floodplain mapping efforts as part of FEMA's Map Modernization Program.

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Watershed Concepts requested the collection of lidar data over Hunterdon County, NJ. In response, EarthData acquired the data on July 17, 2006 using

its aircraft with tail number N806CP. Lidar data was acquired using an ALS-50 Lidar Sensor, including an inertial measuring unit (IMU) and a dual

frequency GPS receiver. An additional GPS receiver was in constant operation over a published control point set by EarthData at the base of the

operations airport which is a secondary airport control station.

Terrasurv was tasked to perform a geodetic control survey in support of lidar mapping in Hunterdon County, NJ. The Global Positioning System (GPS)

was used in static differential mode to measure the intersection vectors of the network. In addition to six locations chosen for control, a survey

point located at the Lehigh valley International Airport was included in the network. This latter station was used a base station by the flight crew

during data acquisition. The horizontal datum was the North American Datum of 1983-CORS (NAD83 CORS) and the vertical datum was the North American

Vertical Datum of 1988.

During the data acquisition, the receivers collected phase data at an epoch rate of 1 Hz. The use of the airport base station ensured that all data

capture was within 50 miles of a base station. The solutions from Hunterdon County, NJ were found to be of high integrity and met the accuracy

requirements for the project. These accuracy check also verified that the data meets the guidelines outlined in FEMA's Guidelines and Specifications

for Flood Hazard Mapping Partners and Appendix 4B, Airborne Light detection and Ranging Systems.

The areas of interest were flown at an altitude of 8500 feet above mean terrain.

Airspeed - 145 knots; Laser Pulse Rate - 38000 Hz; Field of View - 40 degrees; Scan Rate - 20 Hz; Swath Width - 1996 meters

A footprint of this data set may be viewed in Google Earth at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/547/supplemental/2006_FEMA_NJ_Lidar_Hunterdon_County.kmz

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA,

the Office for Coastal Management or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer;

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.

Lidar data was collected and processed in accordance with FEMA guidance and specifications, as published in Appendix A: Guidance for Aerial

Mapping and Surveying, April 2003.

The lidar data fully comply with FEMA guidance as published in Appendix A: Guidance for Aerial Mapping and Surveying, April 2003.

The lidar data fully comply with FEMA guidance as published in Appendix A: Guidance for Aerial Mapping and Surveying, April 2003 and the National

Standard for Spatial Accuracy (NSSDA). When compared to GPS survey grade points in generally flat non-vegetated areas, at least 95% of the

positions have an error less than or equal to 36.3 cm (equivalent to a RMSEz of 18.5 if errors are normally distributed).

- EarthData's proprietary software, Checkedb, was used for verification against ground survey points.

- Verification of automated and manual editing, and final QC of products, was performed using Terrascan.

Compliance with the accuracy standard was ensured by the placement of GPS ground control points prior to lidar data acquisition. The following checks

were performed:

- The ground control and airborne GPS data stream were validated through a fully analytical boresight analysis.

- The Digital Terrain Model (DTM) data were checked against the project control.

- Lidar elevation data was validated through an inspection of edge matching and visual inspection for quality (artifact removal).