2018 USGS/NRCS Lidar DEM: Southeast Florida

Product: These are Digital Elevation Model (DEM) data for Florida counties of Broward, Collier, Hendry, Miami-Dade, Monroe, and Palm Beach, as part of the required deliverables for the Florida Southeast 2018 Lidar project. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 0.5 meter hydro-flattened Raster DEM.

Geographic Extent: Florida counties of Broward, Collier, Hendry, Miami-Dade, Monroe, and Palm Beach, covering approximately 1,641 square miles.

Dataset Description: Florida Southeast 2018 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.35 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.3. The data was developed based on a horizontal projection/datum of NAD83 (2011), Contiguous U.S. Albers Equal Area, meters, and vertical datum of NAVD88 (GEOID12B), meters. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 4,737 individual 1000 m x 1000 m tiles, as tiled Intensity Imagery, and as tiled bare earth DEMs; all tiled to the same 1000 m x 1000 m schema.

Ground Conditions: Lidar was collected on June 2, 2018, November 28, 29, 30, and December 6, 7, 12, and 17, 2018, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, Dewberry established a total of 20 ground control points that were used to calibrate the lidar to known ground locations established throughout the Broward, Collier, Hendry, Miami-Dade, Monroe, and Palm Beach counties, Florida project area. An additional 125 independent accuracy checkpoints, 69 in Bare Earth and Urban landcovers (69 NVA points), 56 in Tall Grass and Brushland/Low Trees categories (56 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data. The project consists of 4,737 tiles but one DEM was not delivered because it is a water only tile.

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create Intensity Images, Breaklines and Raster DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) with a 0.5 meter cell size. These raw lidar point cloud data were used to create classified lidar LAS files, intensity images, 3D breaklines, hydro-flattened DEMs as necessary.

Raster File Type = GeoTiff

Bit Depth/Pixel Type = 32-bit float

Raster Cell Size = 0.5 Meter

Interpolation or Resampling Technique = Triangulated Irregular Network

Required Vertical Accuracy = 19.6 cm NVA

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

Data is available online for bulk or 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.

Five checkpoints were determined to be photo-identifiable in the intensity imagery and were used to test the horizontal accuracy of the lidar dataset. As only five (5) checkpoints were photo-identifiable, the results are not statistically significant enough to report as a final tested value.

Using NSSDA methodology (endorsed by the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014)), horizontal accuracy at the 95% confidence level (called ACCURACYr) is computed by the formula RMSEr * 1.7308 or RMSExy * 2.448.

This data set was produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 41 cm RMSEx/RMSEy Horizontal Accuracy Class which equates to Positional Horizontal Accuracy = +/- 1 meter at a 95% confidence level. Five (5) checkpoints were photo identifiable, but do not produce a statistically significant tested horizontal accuracy value. Using this small sample set of photo-identifiable checkpoints, positional accuracy of this dataset was found to be RMSEx = 20.2 cm and RMSEy = 20.7 cm which equates to +/- 50.0 cm at 95% confidence level. While not statistically significant, the results of the small sample set of checkpoints are within the designated horizontal accuracy.

The project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways: 1. The required NVA is: 19.6 cm at a 95% confidence level, derived according to NSSDA, i.e., based on RMSE of 10 cm in the "bare earth" and "urban" land cover classes. This is a required accuracy. The NVA was tested with 69 checkpoints located in bare earth and urban (non-vegetated) areas. 2. Vegetated Vertical Accuracy (VVA): VVA shall be reported for "brushlands/low trees" and "tall weeds/crops" land cover classes. The target VVA is: 30 cm at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data, i.e., based on the 95th percentile error in all vegetated land cover classes combined. This is a target accuracy. The VVA was tested with 56 checkpoints located in tall weeds/crops and brushlands/low trees (vegetated) areas. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. AccuracyZ has been tested to meet 19.6 cm or better Non-Vegetated Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines.Qualitative value:0.080 0.209, Test that produced the value: Tested 8.0 cm (0.26 ft) 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 69 independent checkpoints located in the Bare Earth and Urban land cover categories. Tested 20.9 cm (0.69 ft) VVA was calculated using 56 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.

Datasets contain complete coverage of tiles. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. There are no void areas or missing data. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

Data covers the entire area specified for this project.