2008 USGS New Jersey Lidar: Somerset County

These data support the general geospatial needs of the USGS and other federal agencies. LiDAR data is remotely sensed high-resolution elevation

data collected by an airborne collection platform. By positioning laser range finding with the use of 1 second GPS with 200hz inertial measurement

unit corrections, Airborne 1's LiDAR instruments are able to make highly detailed geospatial elevation products of the ground, man-made structures

and vegetation. The LiDAR flightlines for this project were planned for a 50% acquisition overlap. The nominal resolution of this project without

overlap is 1.203m, with a 0.90m resolution with the 50% overlap, assuming a normal distribution. Two returns were recorded for each pulse in addition

to an intensity value. GPS Week Time, Intensity, Flightline and number attributes were recorded for each LiDAR point. Positional values were recorded

to the centimeter level, while GPS is recorded to a 10th of a millisecond. Scan angle was recorded to the nearest angle, Intensity is recorded as a

12 Bit dynamic range value and echo is recorded as a numeric value from 0 to 256.

The data was originally provided as random points, in LAS v1.1 format, classified according to the following codes:

Class 1 Non-ground/Extracted Features Last Pulse

Class 2 Bare Earth Ground Features Last Pulse

Class 3 Extracted Features First Pulse

Class 4 Bare Earth Ground Features First Pulse

It should be noted that Class 3 and 4 are not ASPRS classes but since this data is a two pulse system, this is the most efficient format to

separate the pulses and classification process.

The data was reclassified into 2 distinct classifications:

Class 1 Non-ground/Extracted Features First and Last Pulse

Class 2 Bare Earth Ground Features First and Last Pulse

This data was collected to support geospatial analysis of Somerset County, New Jersey.

10501

a) Nominal Pulse density = The nominal resolution of this project without overlap is 1.203m.

b) Calibration procedures =

- General Overview:

The Airborne LiDAR survey was conducted using one OPTECH 2050 systems flying at a nominal height of 1370 meters AGL a total angular coverage

of 40 degrees. Flight line spacing nominally 639 meters providing overlap of 50% on adjacent flight lines. Lines were flown in N/S directions

to best optimize flying time considering the layout for the project. Distances from base station to aircraft (differential baselines) were kept to a

maximum of 30 km while the mean is 6.8 km. The aircraft was a Cessna Caravan, registration N682AC, was used for the survey. This aircraft has a

flight range of approximately 13.5 hours and was flown at an average altitude 1370 meters above ground level (AGL). The aircraft was staged from the

Morristown and Princeton Airports and ferried daily to the project site for flight operations.

Aircraft Speed = 110 Knots

Number of Scanners = 1

Swath Width = 1278.01 m Nominal

Distance Between Flight Lines = 639m

Data Acquisition Height = 1370 meters AGL

Pulse Repetition Rate = 50 Kilohertz

Number of Returns Per Pulse = 2

Scanner Field of View = 40 degrees

Frequency of Scan = 28 Hertz

Beam Divergence = Narrow

- GPS Receivers:

A combination of Leica 500 Series and Applanix POSAv-410 dual frequency GPS receivers were used to support the airborne operations of this survey

and to establish the GPS control network.

- Number of Flights and Flight Lines:

A total of 3 missions were flown for this project with flight time ranging approximately 3.5 hours under good meteorological and GPS conditions.

51 flight lines were flown over the project site to provide complete coverage.

- Reference Coordinate System Used:

Existing NGS (National Geodetic Survey) monuments were observed as control base stations in a GPS control network - PIDs AG9916 and KV1189. AG9916

and KV1189 were occupied as primary control for the project flight missions and kinematic ground surveys. The published horizontal datum of the NGS

stations is NAD83 and the vertical datum NAVD88. The following are the final coordinates of the newly established control points used in this project:

Station_PID: AG9916

West_Longitude: -074 26 46.04499

North_Latitude: 40 33 26.21313

Ellips_Elev: -7.771m

Station_PID: KV1189

West_Longitude: -074 43 48.85846

North_Latitude: 40 36 22.24551

Ellips_Elev: -7.771m

- Geoid Model Used:

The Geoid03 geoid model, published by the NGS, was used to transform all ellipsoidal heights to orthometric.

The Lidar QA/QC Quantitative and Qualitative Assessment Report for this data set may be viewed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/545/supplemental/lidarqaqcreport_somerset_final.pdf

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/545/supplemental/2008_USGS_NJ_Lidar_Somerset_County.kmz

Attributes present in the data set (Precision reported in brackets) = X<Y<Z (0.01), Class (Integer), GPS WeekTime (0.0001 seconds),

Easting (0.01 meter), Northing (0.01 meter), Elevation (0.01 meter), Echo Number (Integer 1 to 2), Echo (Integer 1 to 2),

Intensity (12 Bit Dynamic), Flightline, Scan Angle (Integer Degree).

LiDAR point data in LAS 1.1 ASPRS classification scheme Class 1 Non-ground/Extracted Features Last Pulse; Class 2 Bare Earth Ground Features

Last Pulse; Class 3 All Shots First Pulse; Class 7 Noise.

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 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.

According to Airborne 1 standards; the following aspects of the LiDAR data was verified during the course of the project processing:

-Data accuracy and errors

-Anomaly checks through full-feature hillshades and 3-D modeling

-Post automated classification Bare-earth verification

-Final quality control of deliverable products ensuring integrity, graphical quality

Compiled to meet 0.5m horizontal accuracy at the 95 percent confidence level

Independent accuracy testing was performed by Dewberry using high accuracy quality control checkpoints distributed around Somerset County

on near level open bare terrain and near level vegetated terrain. Dewberry uses testing procedures consistent with those specified in the National

Standard for Spatial Data Accuracy (NSSDA). The Bare Earth RMSEz is 0.06m compared to the specified 0.15m for accuracy. This number represents the

combined vertical accuracy of 40 individual open terrain (RMSEz = 0.058m) and urban (RMSEz = 0.063m) checkpoints. The RMSEz for Vegetation is 0.10m

compared to the specified 0.27m for accuracy. This represents the combined vertical accuracy of 20 individual vegetated (plant heights between

1 and 5 ft; RMSEz = 0.119m) and forested (plant heights greater than 5 ft; RMSEz = 0.083m) checkpoints.

; Quantitative Value: 0.114 meters, Test that produced the value:

National Standard for Spatial Data Accuracy. Using NSSDA standards, this LiDAR dataset was tested 0.114m fundamental vertical accuracy

at 95% confidence level, compared to 0.363m for 2ft equivalent contour.

According to Airborne 1 standards, data completeness and integrity was verified. Conformance to Airborne 1 standards are met for all delivered products.

All LAS formatted LiDAR data are validated to ensure that data on delivery media is in correct physical format and is readable and correctly

georeferenced and projected. Note that LiDAR intensity is not calibrated or normalized.