Suwannee River Water Management District Lidar: Falmouth (FL)

The Light Detection and Ranging (LiDAR) dataset is a survey of the Suwannee River G12PD00242 1.0 Meter LiDAR Survey area 5 in north-central Florida and encompasses 65 square miles. The LiDAR point cloud was flown at a nominal post spacing of 1.0 meters for unobscured areas. The LiDAR data and derivative products produced are in compliance with the U.S. Geological Survey National Geospatial Program Guidelines and Base Specifications, Version 1. The flight lines were acquired by Digital Aerial Solutions, LLC. between Jan 19, 2013 and Jan 20, 2013. Derivative products from the aerial acquisition include: Raw point cloud data in LAS v1.2, classified point cloud data in LAS v1.2, bare earth surface tiles (raster DEM ESRI float GRID format), bare earth surface DEMs mosaic (raster DEM MrSID format), control points, project report, and FGDC compliant XML metadata.

The purpose of collecting this LIDAR data to improve the SRWMD district-wide elevation data set for mapping, spatial analysis, and other SRWMD tasks and applications. This LIDAR data is replacing the digital USGS Topographic 7.5 Minute Map 5 foot contours that we have relied on for over 20 years. In addition the SRWMD wants to cooperate with Federal and State agencies to meet accepted LIDAR standards in order to produce the highest quality and consistent data possible. In addition, we collected this LIDAR data as part of a district, state, and national goal to have complete 100 percent LIDAR data coverage of the entire State of Florida. And last the SRWMD wants these data to become part of the USGS National Elevation Data program (NED) and NOAA Digital Coast for public use and distribution.

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Reports for this project are available at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4887/supplemental/fl2013_srwmd_falmouth_m4887_surveyreport.pdf https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4887/supplemental/fl2013_srwmd_falmouth_m4887_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/geoid18/4887/supplemental/fl2013_srwmd_falmouth_m4887.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, 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=4887

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's specifications, the estimated horizontal accuracy at one sigma, based on flying height for the project, is between 10 cm and 20 cm.

Absolute vertical accuracy assessments for the point cloud data are made against ground check point data. For the Suwannee Management Area 5 survey, ground check point data consisted of the ground GPS base station, and real-time kinematic (RTK) GPS techniques. Check point locations were collected at 1 - second intervals during the RTK survey. Points collected during the static pre-initialization and post-initialization were removed from the assessment so as not to bias the assessment.

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 NDEP Elevation Guidelines Version 1. The FVA of the TIN tested RMSEz 0.095 Feet (2.9 cm) and 0.183 Feet at the 95% confidence level in open terrain. FVA of the DEM tested at an RMSEz of 0.095 Feet and 0.187 Feet at the 95% confidence level in open terrain.; Quantitative Value: 0.029 meters, Test that produced the value: 2.9 cm RMSE

Ground Truth data was collected of the three major land cover classes dispersed within the area of interest. 30 points were collected in each of the three predominate vegetation classes tall weed vegetation, brushland vegetation, and forested vegetation. Pair of points was surveyed using the Trimble VRS network once completed the total station is used to collect the high vegetation ground class. A Topcon 7000 total station was used to collect all the shots collected in the high vegetation class, due to the limited GPS signal when working in and around tree canopy.

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.