2009-2010 USACE Vicksburg District Lidar: Mississippi Phase II

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This graphic shows the lidar coverage for the 2009-2010 Phase II collection area

in Mississippi.

Date that the source FGDC record was last modified.

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

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During acquisition, two base stations were used to support the precise

positioning and orientation of the LiDAR sensor head. At times an additional base station set at the

Oxford Airport was used as a back-up. The base stations were positioned so that the aircraft would

be no further than 20-miles from a single base station at any time during the flight and were placed

on the control points established by Maptech during the ground control phase of the project. The LiDAR

acquisition commenced on December 17, 2009 and was completed on March 5, 2010. Initial processing of

the LiDAR data determined that reflights were necessary; in part because of sensor or base station

malfunctions. The reflights occurred between June 27, 2010 and July 9, 2010. To achieve better

penetration of the vegetation during the reflights, two passes were conducted over the reflight

area; one in each direction.

Detailed flight information and flight logs can be found in the separate Flight Report

submitted with the project.

For redundancy and accuracy purposes, the airborne GPS data were processed from two base

stations using POSGPS from Applanix, Inc. The agreement between a minimum of two

solutions checked or combined between a minimum of two stations was better than 10 cm in

each of X, Y, and Z. These trajectories were used in the processing of the inertial data. The

inertial data were processed using POSProc from Applanix, Inc. This software produces an

SBET ("smooth best estimate of trajectory") using the GPS trajectory from POSGPS and the

roll, pitch and heading information recorded by the POS (Position Orientation System).

DASHMap uses the SBET to generate a set of data points for each laser return in the LAS file

format. Each data point is assigned an echo value so it can be segregated based on the first

and last pulse information. This project's data were processed in strip form, meaning each flight

line was processed independently. Processing the lines individually provides the data analyst

with the ability to QC the overlap between lines.

Each strip was then imported into a project using TerraScan (Terrasolid, Ltd.) and the project

management tool GeoCue (GeoCue Corp.). By creating a project the various flightlines are

combined while breaking the dataset as a whole into manageable pieces. This process also

converts the dataset from the geographic coordinate system (NAD83) to the State Plane

Coordinate System (NAD83), Mississippi West, Feet, and utilizing standard ESRI transformations.

The ellipsoid height values were converted to NAVD88, Feet, orthometric values using Geoid03,

provided by NGS.

Individual lines were then checked against adjacent lines and intersecting control lines to ensure

a cohesive dataset. The data from each line were then combined and LiDAR intensity images

were produced to visually check the horizontal positioning of the LiDAR data.

Stereo pairs were generated from the LiDAR intensity data using Geocue and LiDAR1CuePac

(Geocue Corp.). LiDARgrammetry was then utilized to collect breaklines where necessary along

hydro features to support the contour generation. These breaklines were collected as a 3D

element in the MicroStation (Bentley Systems, Inc.) environment utilizing ISSD (Z/I Imaging). A

Triangular Irregular Network (TIN) was generated using the final surface data. Contours were

then created from the TIN utilizing TerraModeler (Terrasolid, Ltd.).

The NOAA Office for Coastal Management (OCM) received topographic files in text format from the

Mississippi Department of Environmental Quality (MDEQ). The files contained lidar easting,

northing and elevation. The data were received in Mississippi State Plane West 2302, NAD83

coordinates and were vertically referenced to NAVD88 using the Geoid03 model. The vertical and

horizontal units of the data were feet. OCM performed the following processing for data

storage and Digital Coast provisioning purposes:

1. The ASCII files were converted from txt format to las format using LASTools' txt2las

2. The LAS tiles were retiled to remove the buffer, then duplicate points were removed

3. The LAS tiles were then run through LASGround in order to extract surface classifications.

4. The las files were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid03.

5. The las files' vertical units were converted from feet to meters, removing bad elevations.

6. The las files were converted from a Projected Coordinate System (MS SP West) to a Geographic Coordinate system (NAD83)

7. The las files' horizontal units were converted from feet to decimal degrees and converted to laz format.