2011 U.S. Geological Survey (USGS) Topographic LiDAR: Louisiana Region 1

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This graphic shows the lidar coverage for Vermillion Parish, Iberia Parish, St. Mary Parish, Terrebonne Parish and Lafourche Parish in Louisiana.

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Using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, 126 flight lines

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

6,684,759,312 square meters (2,581 square miles) of Vermillion, Iberia, St. Mary, Terrebonne, and Lafourche

Parishes in southeastern Louisiana. Multiple returns were recorded for each laser pulse along with an

intensity value for each return. A total of eighteen missions were flown over a 15 day period:

January 22, 2011, January 23, 2011, January 27, 2011, February 12, 2011, February 13, 2011, February 17, 2001,

February 18, 2011, February 28, 2011, March 1, 2011, March 10, 2011, March 11, 2011, March 15, 2011, March 16, 2011,

April 6, 2011, and April 12, 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 1 is referenced to UTM 15N 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 v9.3 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 15 (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.