2012 Suwannee River Water Management District (SRWMD) Lidar: Bradford (FL)

USGS - Suwannee River Water Management District

Contract No.G10PC00093, Task Order No.G12PD00242

Prime Contractor: Digital Aerial Solutions (DAS)

Sub-Contractor: Gustin, Cothern & Tucker, Inc. (GCT)

The Vertical Accuracy Requirements are required to meet or exceed an RMSEz of 9.25 centimeters and a Fundamental Vertical Accuracy requirement of 18.2 centimeters at the 95% Confidence Level according to the NDEP guidelines.

Digital Aerial Solutions, LLC (DAS) was tasked to collect and process a Light Detection And Ranging

(LiDAR) derived elevation dataset for the Suwannee Management, FL. The Suwannee Management survey

area encompasses approximately 725 square miles. Aerial LiDAR data was collected utilizing an ALS60.

The ALS60 is a discrete return topographic LiDAR mapping system manufactured by Leica Geosystems.

LiDAR data collected for the Suwannee Management survey has a nominal pulse spacing of 0.9 meters,

and includes up to 4 discrete returns per pulse, along with intensity values for each return.

LiDAR datasets were post processed to generate elevation point cloud swaths for each flight line.

Deliverables include the point cloud swaths, tiled point clouds classified by land cover type, breaklines to support hydro-flattening of digital elevation models (DEM)s, and bare-earth DEM tiles. Point cloud deliverables are stored in the LAS version 1.2 format, point data record format 1. The tiling scheme for tiled deliverables is a 5000 Feet x 5000 Feet grid aligned and named according Florida State plane North index. All deliverables were generated in conformance with the U.S. Geological Survey National Geospatial Program Guidelines and Base Specifications, Version 13 - ILMF 2010.

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A report for this project is available at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4893/supplemental/fl2012_srwmd_bradford_m4893_surveyreport.pdf

A report for this project is available at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4893/supplemental/fl2012_srwmd_bradford_m4893_lidarreport.pdf

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4893/supplemental/fl2012_srwmd_bradford_m4893.kmz

LAS 1.2 format (classes 1,2,7,9,10,15,17,18)

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Any conclusions drawn from the analysis of this information are not the responsibility of Digital Aerial Solutions, SRWMD, USGS, NOAA, 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=4893

The data set is dynamically generated based on user-specified parameters.;

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The data depicts the elevations at time of survey and are accurate only for that time. Exercise professional judgment in using this data.

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.

There is not a systematic method of testing when testing horizontal accuracy in LiDAR. The horizontal accuracy is checked by collecting building corners during the survey. Lines are then digitized representing the building outline and the differences are measure from each individual survey point to the corner of the building outline. Stats are calculated to ensure horizontal tolerances are met. These measurements resulted in an RMSE of .42 meters and equals a .73 meter horizontal accuracy at the 95 % confidence level.

Horizontal accuracy assessments of LiDAR data require the presence of vertical targets such as buildings within in the survey area. Field check points are surveyed at the corners of the building roofs, and the surveyed locations compared to the estimated corner locations in the LiDAR point cloud. The Suwannee Management survey area did not present any accessible buildings for use as vertical targets.

From the manufacturer specifications, the estimated horizontal accuracy at one sigma, based on flying height for the project, is between 10 cm and 20 cm.; Quantitative Value: 0.20 meters, Test that produced the value: +/- 20 cm

Local TIN models of the elevation points are built around each ground check points. The tin model elevation is sampled at the horizontal position of the ground check point. The TIN model elevation and ground check point survey elevation values were used to calculate the fundamental vertical accuracy (FVA) of the swath point clouds as described in Section 1.5 of the NDEP Elevation Guidelines Version 1. The FVA of the TIN tested RMSEz 0.19 feet and 0.38 feet at the 95 percent confidence level in open terrain. FVA of the DEM tested at an RMSEz of 0.19 feet and 0.37 feet at the 95% confidence level in open terrain. The full calculations for all check points can be found in Appendix D of the lidar report.; Quantitative Value: 0.058 meters, Test that produced the value: 5.8 cm RMSE (~0.19 ft)

FVA of TIN

RMSEZ = 0.19 ft

FVA of DEM

RMSEZ = 0.19 ft

Cloud Cover: 0

Ground Truth data was collected of the major land cover classes dispersed within the area of interest. 30 points were collected in each of the classes if the land cover was more then 10% of the AOI.

The GPS survey was tied into the Trimble VRS Now Network located in Florida. The Trimble VRS Now network is a network of continuously operating GPS reference stations that provides Real Time Kinematic (RTK) capabilities within a Real Time Network (RTN). This allows corrections to be applied to the points as they are being collected, eliminating the need for an adjustment. Several existing control monuments listed in the NSRS database were used as checks within the Trimble VRS Now Network. This confirmed network accuracies were being met during the field survey as well as providing a redundancy check on the Trimble VRSnetwork. The Specified local network accuracy of 5cm at the 95% confidence level was met or exceeded. Data analysis was accomplished by comparing ground truth checkpoints with LIDAR points from the edited data set, which were within 3.3 feet horizontally from the ground truth points. Based on the number of returns and the density of points in this project, it was not necessary to compare to anything further away than 3.3 feet horizontally from the ground truth points. Note that the edited LIDAR points are simply a subset of the raw LIDAR points. The points that fell above the ground surface on vegetation canopies, buildings, or other obstructions were removed from the data set. Comparisons were also made between the survey points and the LIDAR derived terrain surface. These comparisons provide an additional verification of the LIDAR data against the survey data.