2017 GA DNR Lidar: Middle Chattahoochee - Walter F Watershed

Product: These are LAZ compressed LAS LiDAR data as part of the required deliverables for the Lidar project. These lidar data are processed Classified LAS 1.4 files; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 2 meter (6 feet) hydro-flattened Raster DEM data product consists of processed topographic elevation point data derived from multiple return light detection and ranging (lidar) measurements. The lidar data was planned and acquired at 2 points per square meter for the project boundary identified in the shapefile provided NOAA on January 6th, 2017. The developed lidar derivatives are hydro-flattened DEMs.

Geographic Extent: The Atlantic Group, LLC (Atlantic) has successfully completed lidar acquisition for the Georgia 9 County Lidar area of interest (AOI). Lidar for this AOI was acquired in sixteen (16) flight missions completed between November 25th, 2017 and January 24th, 2018. The project area encompasses 1,550,933 acres, 6,276 square kilometers or 2,440 square miles in Georgia covering the Middle Chattahoochee Walter‐F Watershed including Taylor, Chattahoochee, Stewart, Webster, Quitman, Randolph, and Clay Counties; Upper Flint Watershed including portions of Pike, Lamer and Upson Counties; and a portion of Lee County in the Kinchafoonee‐Muckalee Watershed.

In addition to these lidar point data, the bare earth Digital Elevation Models (DEM) created from the lidar point data, and the hydro breaklines are also available. These data are available for download at the links provided in the URL section of this metadata record.

The data produced is intended to support local hydrologists and watershed managers in their decision-making processes.

File Type: LAZ (compressed LAS)

The following are the USGS lidar fields in JSON:

{

"ldrinfo" : {

"ldrspec" : "USGS-NGP Base Lidar Specification v1.2",

"ldrsens" : " Leica ALS70-HP",

"ldrmaxnr" : "6",

"ldrnps" : "0.5",

"ldrdens" : "2.2",

"ldranps" : "0.4116",

"ldradens" : "5.9",

"ldrfltht" : "1957",

"ldrfltsp" : "120",

"ldrscana" : "45",

"ldrscanr" : "34.8",

"ldrpulsr" : "263",

"ldrpulsd" : "4",

"ldrpulsw" : "0.43",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.22",

"ldrswatw" : "1,673",

"ldrswato" : "20",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid12B"

},

"ldraccur" : {

"ldrchacc" : "0",

"rawnva" : "0.119",

"rawnvan" : "29",

"clsnva" : "0.119",

"clsnvan" : "29",

"clsvva" : "0.216",

"clsvvan" : "20"

},

"lasinfo" : {

"lasver" : "1.2",

"lasprf" : "6",

"laswheld" : "Withheld (ignore) points were identified in these files using the standard LAS Withheld bit.",

"lasolap" : "Swath "overage" points were identified in these files using the standard LAS overlap bit.",

"lasintr" : "16",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, but Unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare Earth Ground"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Noise"

},

"lasclass" : {

"clascode" : "9",

"clasitem" : "Water"

},

"lasclass" : {

"clascode" : "10",

"clasitem" : "Ignored Ground"

},

"lasclass" : {

"clascode" : "17",

"clasitem" : "Bridge Decks"

},

"lasclass" : {

"clascode" : "18",

"clasitem" : "High Noise"

}

}}

The data represented is the result of data collection and processing per contract specifications and indicates the general existing conditions at the time of data collection. As such, it is only valid for its intended use, content, time, and accuracy specifications. The user is responsible for the results of any application of the data for other than its intended purpose.

Any conclusions drawn from the analysis of this information are not the responsibility of GA DNR, NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

None

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.

As described in Section 7.5 of the ASPRS Positional Accuracy Standards for Digital Geospatial Data the horizontal errors in lidar data are largely a function of GNSS positional error, INS angular error, and flying altitude. Therefore, lidar data collected with GNSS error of 8cm and the IMU error of 0.00427 degrees at an altitude of 1,957m; the expected radial horizontal positional error will be RMSEr = 43cm.

Atlantic established a total of fifty-two (52) check points for this project (29 NVA + 23 VVA). Point cloud data accuracy was tested against a Triangulated Irregular Network (TIN) constructed from lidar points in clear and open areas. A clear and open area can be characterized with respect to topographic and ground cover variation such that a minimum of 5 times the NPS exists with less than 1/3 of the RMSEZ deviation from a low-slope plane. Slopes that exceed 10 percent were avoided. Each land cover type representing 10 percent or more of the total project area were tested and reported with a VVA. In land cover categories other than dense urban areas, the tested points did not have obstructions 45 degrees above the horizon to ensure a sufficient TIN surface. The VVA value is provided as a target. It is understood that in areas of dense vegetation, swamps, or extremely difficult terrain, this value may be exceeded. The NVA value is a requirement that must be met, regardless of any allowed “busts” in the VVA(s) for individual land cover types within the project. Checkpoints for each assessment (NVA and VVA) are required to be well-distributed throughout the land cover type, for the entire project area.

Below are the vertical accuracy reporting requirements for this project: Vertical Accuracy Reporting Requirements in Feet:

RMSEZ ≤ 0.328ft (Non-Vegetated Swath, DEM)

NVA ≤ 0.643ft 95% Confidence Level (Swath, DEM)

VVA ≤ 0.965ft 95th Percentile (DEM)

The NVA of the Point Cloud was calculated using 29 independent checkpoints located in the Bare Earth and Urban land cover categories. Tested 0.061 meters NVA at a 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA).

The NVA of the Bare Earth was calculated using 67 independent checkpoints located in the Bare Earth and Urban land cover categories.

Tested 0.143 meters VVA was calculated using 53 checkpoints located in the Brushlands and Low Trees and Tall Weeds and Crops land cover categories at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data. Tested against the DEM.

Tested 0.060 meters NVA at a 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA). The NVA of the DEM was calculated using 67 independent checkpoints located in the Bare Earth and Urban land cover categories.

Area of interest covers approximately 2,440 square miles around project area. The raw LAS data files included all data points collected. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. The raw point cloud is of good quality and data passes NVA specifications. Void areas (i.e., areas outside the project boundary but within the tiling scheme) are coded using a unique NODATA value. This value is identified in the appropriate location within the file header.

All lidar data and lidar derived data covers the entire 2,440 square mile area of interest. All lidar point cloud tiles show no edge artifacts or mismatches from tile to tile. Void areas (i.e. areas outside the project boundary but within the tiling scheme) are coded using a unique NODATA value. This value is identified in the appropriate location within the file header. Data cover the entire area specified for this project.

Data is backed up to tape and to cloud storage.