2008 St. Johns County, FL Countywide Lidar

Airborne terrestrial LiDAR was collected for St. Johns County, FL. System Parameters/Flight Plan. The LiDAR system acquisition

parameters were developed based on a maximum average ground sample distance of 2.1 feet. A Leica ALS50 LiDAR sensor was used for acquisition.

Acquisition specifications for the sensor follows: Field of View (full angle) - 24 degrees, Nominal flight altitude (AGL) - 3000 feet,

Airspeed - 130 mph (113 knots), Laser pulse rate - 100,000 Hz, Nominal swath width (on ground) - 1275 feet, Maximum cross track point

spacing - 2.07 feet, Maximum along track point spacing - 4.30 feet, Average point spacing - 1.67 feet, Flight line spacing - 970.47 feet,

Side overlap - 23.91 percent. LiDAR System Calibration. Prior to the LiDAR acquisition, the system underwent a calibration to verify the

operational accuracy and misalignment angles. Boresight calibrations were performed for the LiDAR system at the beginning and end of each

flight mission. LiDAR Data Acquisition. LiDAR data acquisition only occurred when the sky was sufficiently clear of clouds, smoke, and

atmospheric haze. The LiDAR data was processed immediately after the acquisition to verify the coverage had no voids. GPS/Inertial Measurement

Unit (IMU) Post Processing. 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. LiDAR Processing and

Classification. The LiDAR data was post processed and verified to be consistent with the project requirements in terms of post spacing and

absence of artifacts. The point cloud underwent classification to determine bare-earth points (class 2), noise points (class 7), water

returns (class 9), and unclassified data (class 1). Class 12 contains LiDAR points removed from the overlap region between adjacent flight

lines.

Original contact information:

Contact Org: St. Johns County GIS Division

Phone: 904-209-0778

Email: gis@sjcfl.us

The DTM was developed to support the development and maintenance of the St. Johns County Countywide Digital Contour Mapping Project.

10339

Project Title- Countywide Digital Contour Mapping; Vendor Name- Woolpert, Inc.

The Final QA/QC Quantitative Assessment Report for this data set may be viewed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1119/supplemental/2008_StJohns_MTS_Final_Report_Lidar_Ortho.pdf

The Final Ground Control Survey Report (more detail given to field activities, process, etc.) may be viewed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1119/supplemental/2008_StJohns_MTS_Final_Report_Ground_Control.pdf

An additional Aerial Triangulation Report may be accessed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1119/supplemental/2008_StJohns_MTS_Final_Report_AerialTriangulation.pdf

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1119/supplemental/2008_St_Johns_County_FL_Countywide_Lidar.kmz

Any conclusions drawn from the analysis of this information are not the responsibility of the Office for Coastal Management

or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer;

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.

Information from the St. Johns County Geographic Information System is provided for general reference purposes only and is not to be construed

as a survey or legal document. Errors from non-coincidence of features from different sources may be present. The St. Johns County Geographic

Information System makes every reasonable effort to ensure that the information provided herein is current and accurate. However, St. Johns

County provides no warranties, expressed or implied, concerning the accuracy, completeness, reliability, or suitability of this data for

any particular use or purpose. St. Johns County assumes no liability whatsoever associated with the use or misuse of such data.

Microsoft Windows 2000 Version 5.2 (Build 3790) Service Pack 2; ESRI ArcCatalog 9.2.0.1324

Horizontal accuracy is +/- 3.8-foot at the 95% confidence level using RMSE(r) x 1.7308 as defined by the FGDC Geospatial Positional

Accuracy Standards, Part 3: NSSDA.

; Quantitative Value: 3.8 meters, Test that produced the value:

LiDAR system calibration is available in the MTS Report of Specific Purpose Survey.

Vertical accuracy is +/- 0.4-foot RMSE for unobscured ground points. 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 and filtered LiDAR data points. Filtered LiDAR

data has had vegetation and cultural features removed and by analysis represents bare earth elevations. The RMSE figure was used to compute

the vertical National Standard for Spatial Data Accuracy (NSSDA). The vertical accuracy of the 2-foot contours, with supplemental 1-foot

contours, is +/- 0.75 foot RMSE in unobscured areas.

; Quantitative Value: 0.4 meters, Test that produced the value:

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 and filtered LiDAR data points. Results for this project are available in the MTS Report of Specific Purpose Survey.

This feature class represents the complete set of data for 797 5,000' x 5,000' tiles within St. Johns County.

The LiDAR DTM was developed in accordance with St. Johns specifications.