2017 USGS Lidar DEM: Upper Delta Plain, LA

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This graphic displays the footprint for this lidar data set.

Link to the survey report.

Link to the breaklines.

Link to the collection report.

Link to the project report.

Link to custom download the lidar point data from which these raster Digital Elevation Model (DEM) data were created.

Fugro collected Riegl-derived lidar over the Upper Delta Plain, Louisiana AOI with 0.7 meters ANPS. Data was collected when environmental conditions meet the criteria specified. To be specific, the following conditions existed prior to launch of the aircraft: 1) Water levels for either Grand Isle, LA or Shell Beach, LA were below -0.10 meters (mean sea level), for flight lines that were considered tidal, 2) Passage of a moderate to strong high-pressure system generating northerly winds in excess of 5 knots, 3) Cloud and fog-free between the aircraft and ground, 4) Snow free, 5) No unusual flooding or inundation, and 6) Leaf off. The collection for the Upper Delta Plain, Louisiana AOI was accomplished on January 23, 26, 27, 28, 30, and 31; February 15, 22, and 25; March 2, 3, 14, 15, 16, and 20; and April 24, 2017. The collection was performed using Riegl LMS-Q680i and Riegl LMS-Q780 lidar systems, serial numbers 165, 961, and 216.

Under Fugro’s direction, all surveying activities were performed by Fugro's approved ID/IQ subcontractor Terrasurv, Inc. A total of 63 ground control points to support the lidar collection, along with 101 NVA and 78 VVA checkpoints were collected. The National Spatial Reference System (NSRS) was used to provide control for the network. A Virtual Reference System (VRS) was used to survey each of the lidar control points. GULFNet is a network of Continuously Operating Reference Stations (CORS) network operated by the Louisiana Spatial Reference Center which is tightly aligned with the CORS of the National Spatial Reference System (NSRS). Using this methodology and VRS network was crucial to being able to obtain accurate heights due to known subsidence issues with the passive (i.e. ground monumented stations) NSRS marks in the area. Many of the GULFNet stations are also part of the National CORS Network. The horizontal datum was the North American Datum of 1983 – NAD83 (2011), epoch 2010.0. The vertical datum was the North American Vertical Datum of 1988 (NAVD88), realized with GEOID12B.

Flight status was communicated during data collection. All acquired lidar data went through a preliminary review to assure that complete coverage had been obtained and that there were no gaps between flight lines before the flight crew left the project site. Once back in the office, the data was run through a complete iteration of processing to ensure that it is complete, uncorrupted, and that the entire project area has been covered without gaps between flight lines. There are essentially three steps to this processing: 1) GPS/IMU Processing - Airborne GPS and IMU data was processed using the airport GPS base station data. The following GPS base stations were utilized: Fugro (016), CORS (MOON), and CORS (SJHS). 2) Raw Lidar Data Processing - Technicians processed the raw data to LAS format flight lines with full resolution output before performing QC. A starting configuration file is used in this process, which contains the latest calibration parameters for the sensor. The technicians also generated flight line trajectories for each of the flight lines during this process. 3) Verification of Coverage and Data Quality - Technicians checked trajectory files to ensure completeness of acquisition for the flight lines, calibration lines, and cross flight lines. The intensity images were generated for the entire lift at the required 0.7 meter ANPS. Visual checks of the intensity images against the project boundary were performed to ensure full coverage to the 100 meter buffer beyond the project boundary. The intensity histogram was analyzed to ensure the quality of the intensity values. The technician also thoroughly reviewed the data for any gaps in project area. The technician generated a sample TIN surface to ensure no anomalies were present in the data. Turbulence was inspected for each flight line; if any adverse quality issues were discovered, the flight line was rejected and re-flown. The technician also evaluated the achieved post spacing against project specified 0.7 meter ANPS as well as making sure there is no clustering in point distribution.

The boresight for each lift was done individually as the solution may change slightly from lift to lift. The following steps describe the Raw Data Processing and Boresight process: 1) Technicians processed the raw data to LAS format flight lines using the final GPS/IMU solution. This LAS data set was used as source data for boresight. 2) Technicians first used Fugro proprietary and commercial software to calculate initial boresight adjustment angles based on sample areas within the lift. These areas cover calibration flight lines collected in the lift, cross tie and production flight lines. These areas are well distributed in the lift coverage and cover multiple terrain types that are necessary for boresight angle calculation. The technician then analyzed the results and made any necessary additional adjustment until it is acceptable for the selected areas. 3) Once the boresight angle calculation was completed for the selected areas, the adjusted settings were applied to all of the flight lines of the lift and checked for consistency. The technicians utilized commercial and proprietary software packages to analyze the matching between flight line overlaps for the entire lift and adjusted as necessary until the results met the project specifications. 4) Once all lifts were completed with individual boresight adjustment, the technicians checked and corrected the vertical misalignment of all flight lines and also the matching between data and ground truth. The relative accuracy was ≤ 6 cm within individual swaths (smooth surface repeatability) and ≤ 8 cm RMSD within swath overlap (between adjacent swaths) with a maximum difference of ± 16 cm. 5) The technicians ran a final vertical accuracy check of the boresighted flight lines against the surveyed check points after the z correction to ensure the requirement of RMSEZ (non-vegetated) ≤ 10 cm, NVA ≤ 19.6 cm 95% Confidence Level was met.

Once boresighting was complete for the project, the project was first set up for automatic classification. The lidar data was cut to production tiles. The low noise points, high noise points and ground points were classified automatically in this process. Fugro utilized commercial software, as well as proprietary, in-house developed software for automatic filtering. The parameters used in the process were customized for each terrain type to obtain optimum results. Once the automated filtering was completed, the files were run through a visual inspection to ensure that the filtering was not too aggressive or not aggressive enough. In cases where the filtering was too aggressive and important terrain were filtered out, the data was either run through a different filter within local area or was corrected during the manual filtering process. Bridge deck points were classified as well during the interactive editing process. Interactive editing was completed in visualization software that provides manual and automatic point classification tools. Fugro utilized commercial and proprietary software for this process. All manually inspected tiles went through a peer review to ensure proper editing and consistency. After the manual editing and peer review, all tiles went through another final automated classification routine. This process ensures only the required classifications are used in the final product (all points classified into any temporary classes during manual editing will be re-classified into the project specified classifications). Once manual inspection, QC and final autofilter is complete for the lidar tiles, the LAS data was packaged to the project specified tiling scheme, clipped to project boundary including the 100 meter buffer and formatted to LAS v1.4. It was also re-projected to UTM Zone 15 north; NAD83 (2011), meters; NAVD88 (GEOID12B), meters. The file header was formatted to meet the project specification with File Source ID assigned. This Classified Point Cloud product was used for the generation of derived products. This product was delivered in fully compliant LAS v1.4, Point Record Format 6 with Adjusted Standard GPS Time at a precision sufficient to allow unique timestamps for each pulse. Correct and properly formatted georeference information as Open Geospatial Consortium (OGC) well known text (WKT) was assigned in all LAS file headers. Each tile has unique File Source ID assigned. The Point Source ID matches to the flight line ID in the flight trajectory files. Intensity values are included for each point, normalized to 16-bit. The following classifications are included: Class 1 – Processed, but unclassified; Class 2 – Bare earth ground; Class 3 – Low Vegetation (3 meters or less); Class 7 – Low Noise; Class 9 – Water; Class 10 – Ignored Ground; Class 17 – Bridge Decks; and Class 18 – High Noise. The classified point cloud data was delivered in tiles without overlap using the project tiling scheme.

Upon the completion of lidar point cloud product creation, First Return points were used for intensity image generation automatically. The software considers points from neighboring tiles while creating the images for seamless edge matching. The initial intensity images were generated at 1.0 meter resolution in 16bit TIFF format. They were then converted to 8bit format. Georeferencing information was assigned to all images. The technician QC’ed the final intensity images before delivery. The intensity images were delivered in GeoTIFF with TFW format.

Hydro linework is produced by heads-up digitizing using classified lidar datasets. Additionally, products created from lidar including intensity images, shaded-relief TIN surfaces, and contours are used. Hydrographic features were collected as separate feature classes: 1) Inland Ponds and Lakes approximately 2-acre or greater surface area (Lakes) and 2) Inland Streams and Rivers of 100 feet nominal width (Rivers). Additionally, all breaklines used to enforce a logical terrain surface below a bridge were delivered as a separate shapefile. After initial collection, features were combined into working regions based on watershed sub-basins. Linework was then checked for the following topological and attribution rules: 1) Lines must be attributed with the correct feature code and 2) Lake and stream banklines must form closed polygons. Hydro features were collected as vector linework using lidar and its derived products listed above. This linework is initially 2D, meaning that it does not have elevation values assigned to individual line vertices. Vertex elevation values were assigned using a distance weighted distribution of lidar points closest to each vertex. This is similar to draping the 2D linework to a surface modeled from the lidar points. After the initial ‘drape’, the linework elevation values were further adjusted based on the following rules: 1) Lake feature vertices were re-assigned (flattened) to lowest draped vertex value and 2) Double stream bankline vertices were re-assigned based on the vertices of the closest adjusted double stream connector line. Fugro proprietary software was used to create profiles to ensure bank to bank flatness, monotonicity check, and lake flatness. The hydro breaklines were delivered as polygons in Esri ArcGIS version 10.3 geodatabase format.

The bare earth DEM was generated using the lidar bare earth points and 3D hydro breaklines to a resolution of 1.0 meter. Where needed, supplemental breaklines were collected and used in DEM generation under the bridges to ensure a logical terrain surface below a bridge. This was delivered as a separate shapefile. The bare earth points that fell within 1*NPS along the hydro breaklines (points in class 10) were excluded from the DEM generation process. This is analogous to the removal of mass points for the same reason in a traditional photogrammetrically compiled DTM. This process was done in batch using proprietary software. The technicians then used Fugro proprietary software for the production of the lidar-derived hydro flattened bare earth DEM surface in initial grid format at 1.0 meter GSD. Water bodies (inland ponds and lakes), inland streams and rivers, and island holes were hydro flattened within the DEM. Hydro flattening was applied to all water impoundments, natural or man-made, that are larger than approximately 2 acres in area and to all streams that are nominally wider than 100 feet. This process was done in batch. Once the initial, hydro flattened bare earth DEM was generated, the technicians checked the tiles to ensure that the grid spacing met specifications. The technicians also checked the surface to ensure proper hydro flattening. The entire data set was checked for complete project coverage. Once the data was checked, the tiles were then converted to industry-standard, GIS-compatible, 32-bit floating point raster format (LZW compressed 32-bit GeoTIFFs). Georeference information is included in the raster files. Void areas (i.e., areas outside the project boundary but within the tiling scheme) are coded using a unique “NODATA” value.

The NOAA Office for Coastal Management (OCM) downloaded 4802 LA_UpperDeltaPlain_2017 Digital Elevation Model (DEM) files from this USGS site: ftp://rockyftp.cr.usgs.gov/vdelivery/Datasets/Staged/Elevation/OPR/. The data were in UTM Zone 15 North coordinates and NAVD88 (Geoid12B) elevations in meters. The bare earth raster files were at a 1 meter grid spacing.

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. Copied the files to https