2011 U.S. Geological Survey (USGS) Topographic LiDAR: Louisiana Region 2

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This graphic shows the lidar coverage for Orleans Parish, Plaquemines Parish, St. Bernard Parish and St. Tammany Parish in Louisiana; and Hancock County, Mississippi

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Using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, 160 flight lines

of high density data, at a nominal pulse spacing (NPS) of 2.0 meters, were collected over approximately

7,301 square meters (2,819 square miles) of Orleans, Plaquemines, St. Bernard and St. Tammany Parishes in

southeastern Louisiana. Multiple returns were recorded for each laser pulse along with an intensity value

for each return. A total of sixteen missions were flown over a 12 day period: January 11 - 14, 2011,

January 21, 2011, January 29, 2011, February 11 - 15, 2011, February 21, 2011, February 28, 2001, and

March 1, 2011 . A minimum of two airborne global positioning system (GPS) base stations were used in

support of the LiDAR data acquisition. 22 ground control points were surveyed through static methods. The

geoid used to reduce satellite derived elevations to orthometric heights was Geoid09. All data for Region 2

is referenced to UTM 16N for the area within its zone, NAD83, NAVD88, in meters. 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 coverage was classified to extract a bare earth digital elevation model

(DEM) and separate last returns. In addition to the LAS deliverables, one layer of coverage was delivered in

the ArcINFO ArcGrid binary format 2m cell size: bare-earth. The ArcGrid data was created using ArcMap v93.

software. System Parameters: - Type of Scanner = LH Systems ALS50 - Data Acquisition Height = 2,377-meters

AGL - Scanner Field of View = 40 degrees - Scan Frequency = 36.7 Hertz - Pulse Repetition Rate = 99.0

Kilohertz - Aircraft Speed = 140 Knots - Swath Width = 1730-meters - Number of Returns Per Pulse = Maximum

of 4 - Distance Between Flight Lines = 1212-meters.

The ALS50 calibration and system performance is verified on a periodic basis using

Woolpert's calibration range. The calibration range consists of a large building and runway. The edges of

the building and control points along the runway have been located using conventional survey methods.

Inertial measurement unit (IMU) misalignment angles and horizontal accuracy are calculated by comparing the

position of the building edges between opposing flight lines. The scanner scale factor and vertical

accuracy is calculated through comparison of LiDAR data against control points along the runway. Field

calibration is performed on all flight lines to refine the IMU misalignment angles. IMU misalignment

angles are calculated from the relative displacement of features within the overlap region of adjacent

(and opposing) flight lines. The raw LiDAR data is reduced using the refined misalignment angles.

Once the data acquisition and GPS processing phases are complete, the LiDAR data was processed immediately

to verify the coverage had no voids. The GPS and IMU data was post processed using differential and Kalman

filter algorithms to derive a best estimate of trajectory. The quality of the solution was verified to be

consistent with the accuracy requirements of the project.

The individual flight lines were inspected to ensure the systematic and residual errors have been

identified and removed. Then, the flight lines were compared to adjacent flight lines for any mismatches

to obtain a homogeneous coverage throughout the project area. The point cloud underwent a classification

process to determine bare-earth points and non-ground points utilizing "first and only" as well as "last

of many" LiDAR returns. This process determined bare-earth points (Class 2), Noise (Class 7),

Water (Class 9) Ignored ground (Class 10) and unclassified data (Class 1). The bare-earth (Class 2 - Ground)

LiDAR points underwent a manual QA/QC step to verify that artifacts have been removed from the bare-earth

surface. The surveyed ground control points are used to perform the accuracy checks and statistical

analysis of the LiDAR dataset.

Breaklines defining lakes, greater than two acres, and double-line streams, wider than

30.5 meters (100 feet), were compiled using digital photogrammetric techniques as part of the hydrographic

flattening process and provided as ESRI Polyline Z and Polygon Z shape files. Breaklines defining water

bodies and streams were compiled for this task order. The breaklines were used to perform the hydrologic

flattening of water bodies, and gradient hydrologic flattening of double line streams. Lakes, reservoirs

and ponds, at a nominal minimum size of two (2) acres or greater, were compiled as closed polygons. The

closed water bodies were collected at a constant elevation. Rivers and streams, at a nominal minimum

width of 30.5 meters (100 feet), were compiled in the direction of flow with both sides of the stream

maintaining an equal gradient elevation. The draping of the polygons and double lines streams was

performed using proprietary software developed by Woolpert. The hydrologic flattening of the LiDAR data

was performed for inclusion in the National Elevation Dataset (NED).

The NOAA Office for Coastal Management (OCM) received topographic files in LAS format. The files contained lidar

elevation and intensity measurements. The data were received in UTM Zone 16 (NAD83) coordinates

and were vertically referenced to NAVD88 using the Geoid09 model. The vertical units of the data were

meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The topographic las files were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid09.