2010 U.S. Geological Survey Topographic LiDAR: Atchafalaya Basin, Louisiana

The Light Detection and Ranging (LiDAR) dataset is a survey of the Atchafalaya Basin in south-central Louisiana. The entire survey area encompasses 981 square miles. The LiDAR point cloud was flown at a

nominal post spacing of 1.0 meters for unobscured areas. The LiDAR data is in compliance with the U.S. Geological Survey National Geospatial Program Guidelines and Base Specifications,

Version 13-ILMF 2010. The Flightlines were acquired by Northrop Grumman, 3001 Operating Unit, which required 10 subsequent missions between December 2, 2010, and December 7, 2010.

Northrop Grumman classified the data into the following ASPRS compliant classes:

Class 1: Processed, but unclassified

Class 2: Bare Earth Ground

Class 3: Low Vegetation

Class 4: Medium Vegetation (also used for manual classification of vegetation returns)

Class 5: High Vegetation

Class 6: Buildings and man-made structures

Class 7: Noise (low or high, manually identified)

Class 9: Water

Class 10: Ignored Ground (Breakline Proximity)

Class 13: Withheld (outliers, blunders, etc.)

Original contact information:

Contact Org: NOAA Office for Coastal Management

Phone: 843-740-1202

Email: coastal.info@noaa.gov

This regional LiDAR elevation mapping will be used for modeling, predicting landscape change, promoting restoration of ecosystems, and mitigating risks associated with anthropomorphic and natural hazards.

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The project report for this data set may be accessed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1433/supplemental/usgs2010_AtchafalayaBasin_ProjectReport.docx

The survey report for this data set may be accessed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1433/supplemental/usgs2010_AtchafalayaBasin_SurveyReport.pdf

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1433/supplemental/usgs2010_AtchafalayaBasin_footprint.kmz

LiDAR points in LAS 1.2 format

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

of Northrop Grumman, USGS, the Office for Coastal Management or its partners.

This data can be obtained on-line at the following URL:

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=1433

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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. These data

depict the heights at the time of the survey and are only accurate for that time.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcCatalog 9.3.1.4000

All ground control processing and adjustment is performed using published coordinate horizontal and vertical datums (e.g. NGS CORS). For deliverables, Corpscon for Windows Version 5.11.08

(geoid 09) was used for horizontal and vertical datum conversion.

The accuracy assessment was performed using a standard method to compute the root mean square error (RMSE) based on a comparison of ground control points (GCP) and filtered LiDAR data points. Filtered LiDAR data has had

vegetation and cultural features removed and by analysis represents bare earth elevations. Testing was performed prior to gridding of the filtered LiDAR data points and construction of the ERDAS IMG file format. The RMSE

figure was used to compute the vertical National Standard for Spatial Data Accuracy (NSSDA). Ground control was established by Northrop Grumman, 3001 Operating Unit. A spatial proximity analysis was used to select edited LiDAR

data points contiguous to the relevant GCPs. A search radius decision rule is applied with consideration of terrain complexity, cumulative error and adequate sample size. Cumulative error results from the errors inherent in the

various sources of horizontal measurement. These sources include the airborne GPS, GCPs and the uncertainty of the accuracy of the LiDAR data points. This accuracy is achieved prior to the subsampling that occurs through

integration with the inertial measurement unit (IMU) positions that are recorded. It is unclear at this time whether the initial accuracy is maintained. The horizontal accuracy of the GCPs is estimated to be in the range of

approximately 1 to 1.6 inches. Finally, sample size was considered. The specification for the National Standard for Spatial Data Accuracy is a minimum of 20 points to conduct a statistically significant accuracy evaluation

(Minnesota Planning, 1999, Positional Accuracy Handbook, Minnesota Planning Land Management Information Center, St. Paul, Minnesota., p.3). Most statistical texts indicate that a minimum of 30 sample points provide a reasonable

Approximation of a normal distribution. The intent of the NSSDA is to reflect the geographic area of interest and the distribution of error in the data set (Federal Geographic Data Committee, 1998, Geospatial National Standard

for Spatial Data Accuracy, Federal Geographic Data Committee Secretariat, Reston, Virginia, p.3-4). Additional steps were taken to ensure the vertical accuracy of the LiDAR data including: Step 1: Precision Bore sighting

(Check Edge-matching) Step 2: Compare the LiDAR data to the Field Survey (The vertical accuracy requirements meet or exceed the required RMSEz of 18.5cm and the vertical accuracy of 36.3cm at the 95% confidence level).

The LiDAR data was acquired at a density sufficient to support a one meter post spacing. The bare-earth surface will contain voids in areas that were densely vegetated, covered by bridges, buildings, water, fresh

asphalt, sand etc.

Northrop Grumman, 3001 Operating Unit, used an ALTM 213 system to acquire LiDAR data at a density sufficient to support an one meter post spacing of for unobscured areas. During acquisition the plane was

never more than 40 kilometers from a base station. Northrop Grumman acquired flight lines between December 2, 2010, and December 7, 2010 at an altitude of 5000 feet; using a field of view of 34 degrees. The total swath width of

each flight line is 931 meters. The distance between flight lines is 690 meters and each flight line has 28 percent overlap. The Atchafalaya Basin Survey was collected under the guidance of a Professional Mapper/Surveyor.