2007 Southwest Florida Water Management District (SWFWMD) LiDAR: Hernando County

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Unknown | Source Geospatial Form: Model | Type of Source Media: Digital tape media

The LiDAR data was acquired using a Leica ALS50 from an average altitude of 2,400-feet above ground level to provide an average

ground sample distance of 2.1-feet. First and last return data was collected along with the signal return intensity. Two

redundant airborne GPS bases stations were utilized during the data acquisition with maximum line-of-sight distance between

the base station and aircraft of 20-km. The LiDAR data was reduced using Grafnav (Waypoint Consulting) for GPS post-processing,

PosProc (Applanix Crop) for IMU processing, ALS50 Post Processor (LH Systems) to initial LiDAR processing, TerraScan (Terrasolid)

for initial point classification, and proprietary Woolpert developed software for refining the point classification and QC.

The LiDAR data was reviewed in 3D using a digital photogrammetric work station using ADS40 digital stereo imagery. During the

production process, LiDAR data gaps between the flight lines were observed. These gaps between flight lines were corrected by

adding photogrametrically compiled mass points. These points are classified as class 10, in the LAS file. In the areas with the

compiled mass points, it may be noted that the mass points are not as dense the areas with complete LiDAR coverage. The mass

points were compiled at a sufficient density to define the surface to contract specifications. The LAS files contain 5

classifications: 1 = unclassified; 2 = ground; 9 = water; 10 = photogrammetric masspoints; and 11 = swamp and/or wetlands.

The class 1 consists of all points not on the ground. Class 2 consists of bare earth points. Class 9 consists of points within

water polygons. Class 11 consists of points within swamps and/or wetlands. Class 10 consists of supplementary mass points that

were photogrametrically compiled on point's features such as peaks or pits, and LiDAR data gaps. These points were created to

maintain the accuracy of the DTM. 3D breaklines were collected at the digital photogrammetric workstation during the LiDAR data

review. These breaklines were delineated to insure the DTM is hydrologically correct. Hydrologically Enforced Elevation Data is

defined as "Hydorenforced TINS, DEMS, or contours ensure that top surfaces of bridges and culverts are cut by stream breaklines

so that computer models will accurately represent drainage flow" per FEMA's Appendix A A.4.10. The breaklines were collected

for hydrologically significant features as appropriate to support the development of the generation of 2-foot contours meeting

National Map Accuracy Standards. The following breakline features were classified and separated: Closed Water Body Features,

Linear Hydrographic Features, Coastal Shorelines, Road Features, Soft Features, Obscured Vegetated Areas, Island Features,

Overpasses, and Bridges. Per contract specifications, culverts were not collected as part of this project. Therefore continuity

of hydrographic features may not be consistent. During final data production and analysis, the occurrence of mound type features

in the data set was noted. These areas were checked, and verified to be above ground septic systems. For a complete description

of survey methods, processing methods, software, system parameters, and accuracy analysis, see the Florida MTS Report of

Specific Purpose Survey, SWFWMD MTS Report of DOI Survey, FY2007 Digital Orthophoto and LiDAR (B089 & L776 (dated 4/31/2008))

Dataset copied.

Dataset copied.

Dataset copied.

The NOAA Office for Coastal Management (OCM) received the files in LAS format. The files contained Lidar intensity and

elevation measurements. The data was in Florida State Plane Projection and NAVD88 vertical datum. OCM performed the following processing

to the data to make it available within the Digital Coast:

1. The data were converted from Florida State Plane West coordinates to geographic coordinates.

2. The data were converted from NAVD88 (orthometric) heights to GRS80 (ellipsoid) heights using Geoid 03.

3. The LAS data were sorted by latitude and the headers were updated.