U.S. Geological Survey
201502
Unknown
Hydro-Flattened Bare Earth Digital Elevation Models (DEMs)
Elevation Data
Leading Edge Geomatics collected LiDAR data for approximately 1,526 square miles of area in west-central Connecticut. The nominal pulse spacing for this project was 0.7 meter. Dewberry used proprietary procedures to classify the LAS according to project specifications: 1-Unclassified, 2-Ground, 7-Noise, 9-Water, 10-Ignored Ground due to breakline proximity. Dewberry produced 3D breaklines and combined these with the final LiDAR data to produce seamless hydro flattened Digital Elevation Models (DEMs) with a 1 meter grid cell size that cover the project area. In addition to the bare earth hydro flattened DEMs, Dewberry also produced intensity imagery with a 0.3 meter cell size.
The purpose of this LiDAR data was to produce high accuracy 3D elevation products, including tiled LiDAR in LAS 1.2 format, 3D breaklines, and 1 m cell size hydro flattened Digital Elevation Models (DEMs).
A complete description of this dataset is available in the Final Project Report that was submitted to the U.S. Geological Survey.
20140427
20140529
ground condition
As needed
-72.593
-72.197
42.049
41.183
None
Elevation
Lidar
LAS
DEM
Hydro Flattened
Breaklines
Bare earth
None
Connecticut
Hurricane Sandy
Hartford County
Litchfield County
Fairfield County
New Haven County
New London County
Middlesex County
None
This data was produced for the U.S. Geological Survey according to specific project requirements. This information is provided "as is". Further documentation of this data can be obtained by contacting: USGS, 1400 Independence Road, Rolla, MO 65401. Telephone (573)308-3587.
U.S. Geological Survey
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573)308-3810
pemmett@usgs.gov
Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcCatalog 10.0
Data covers the pilot tile scheme provided for the project area.
A visual qualitative assessment was performed to ensure data completeness and full tiles. No void or missing data exists.
The DEMs are derived from the source LiDAR and 3D breaklines created from the LiDAR. Horizontal accuracy is not performed on the DEMs or breaklines. Lidar source produced to meet 1 meter horizontal accuracy.
Project specifications required a horizontal accuracy of 1 m based on a RMSEr (0.578m) x 1.7308. Only checkpoints photo-identifiable in the intensity imagery can be used to test the horizontal accuracy of the LiDAR. Photo-identifiable checkpoints in intensity imagery typically include checkpoints located at the ends of paint stripes on concrete or asphalt surfaces or checkpoints located at 90 degree corners of different reflectivity, e.g. a sidewalk corner adjoining a grass surface. The xy coordinates of checkpoints, as defined in the intensity imagery, are compared to surveyed xy coordinates for each photo-identifiable checkpoint. These differences are used to compute the tested horizontal accuracy of the LiDAR. As not all projects contain photo-identifiable checkpoints, the horizontal accuracy of the LiDAR cannot always be tested.
1 meter
The DEMs are derived from the source LiDAR and 3D breaklines created from the LiDAR. Horizontal accuracy is not performed on the DEMs or breaklines. LiDAR vendors perform calibrations on the LiDAR sensor and compare data to adjoing flight lines to ensure LiDAR meets the 1 meter horizontal accuracy standard at the 95% confidence level.
However, Dewberry tested the horizontal accuracy of the LiDAR by comparing photo-identifiable survey checkpoints to the LiDAR Intensity Imagery. As only thirteen (13) checkpoints were photoidentifiable, the results are not statistically significant enough to report as a final tested value. However, the results are reported below.
Using NSSDA methodology, horizontal accuracy at the 95% confidence level (called Accuracyr) is computed by the formula RMSEr x 1.7308. The dataset for the CT Sandy LiDAR project satisfies the criteria:
Lidar dataset tested 0.660 m horizontal accuracy at 95% confidence level, based on RMSEr (0.381 m) x 1.7308.
Please see the final project report delivered to the U.S. Geological Survey for more details.
The DEMs are derived from the source LiDAR and 3D breaklines created from the LiDAR. The DEMs are created using controlled and tested methods to limit the amount of error introduced during DEM production so that any differences identified between the source LiDAR and final DEMs can be attributed to interpolation differences. DEMs are created by averaging several LiDAR points within each pixel which may result in slightly different elevation values at a given location when compared to the source LAS, which is tested by comparing survey checkpoints to a triangulated irregular network (TIN) that is created from the LiDAR ground points. TINs do not average several LiDAR points together but interpolate (linearly) between two or three points to derive an elevation value.
The vertical accuracy of the bare earth DEMs was tested by Dewberry with 104 independent survey checkpoints. The same checkpoints that were used to test the source LiDAR data were used to validate the vertical accuracy of the final DEM products. The survey checkpoints are evenly distributed throughout the project area and are located in areas of bare earth and open terrain (20), urban terrain (21), forest (21), brushland and trees (21), and high grass (21). The vertical accuracy is tested by extracting the elevation of the pixel that contains the x/y coordinates of the checkpoint and comparing these DEM elevations to the surveyed elevations.
Checkpoints in open terrain were used to compute the Fundamental Vertical Accuracy (FVA). Project specifications required a FVA of 18.13 cm based on a RMSEz (9.25 cm) x 1.9600. All checkpoints were used to compute the Consolidated Vertical Accuracy (CVA). Project specifications require a CVA of 26.9 cm based on the 95th percentile. Supplemental Vertical Accuracy (SVA) will be computed on each individual land cover category other than open terrain. Target specifications for SVA are 26.9 cm based on the 95th percentile. NDEP and ASPRS testing methodologies allow individual SVA's to fail as long as the mandatory CVA passes project specifications.
0.137 m
Based on the vertical accuracy testing conducted by Dewberry, using NSSDA and FEMA methodology, vertical accuracy at the 95% confidence level (called Accuracyz) is computed by the formula RMSEz x 1.9600. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.137 m vertical accuracy at 95% confidence level in open terrain, based on RMSEz (0.070 m) x 1.9600.
0.201 m
Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, consolidated vertical accuracy (CVA) is computed using the 95th percentile method. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.201 m consolidated vertical accuracy at 95th percentile in all land cover categories combined.
The 5% outliers consist of 6 checkpoints that are larger than the 95th percentile. These checkpoints have DZ values ranging between 0.203 m and 0.240 m.
0.098 m
Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, supplemental vertical accuracy (SVA) is computed using the 95th percentile method. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.098 m supplemental vertical accuracy at 95th percentile in the urban land cover category.
0.203 m
Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, supplemental vertical accuracy (SVA) is computed using the 95th percentile method. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.203 m supplemental vertical accuracy at 95th percentile in the forested and fully grown land cover category.
0.215 m
Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, supplemental vertical accuracy (SVA) is computed using the 95th percentile method. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.215 m supplemental vertical accuracy at 95th percentile in the brush and small trees land cover category.
0.192 m
Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, supplemental vertical accuracy (SVA) is computed using the 95th percentile method. The dataset for the Connecticut Sandy LiDAR project satisfies the criteria:
DEM dataset tested 0.192 m supplemental vertical accuracy at 95th percentile in the tall weeds and crops land cover category.
Data for the USGS Connecticut Sandy LiDAR project was acquired by Leading Edge Geomatics (LEG)
The project area included approximately 1,526 contiguous square miles for portions of Connecticut. LiDAR sensor data were collected with the Riegl 680i LiDAR system. The data was delivered in UTM Zone 18, horizontal datum NAD83(2011), vertical datum NAVD88, Geoid 12A. Deliverables for the project included a raw (unclassified) calibrated LiDAR point cloud, survey control, and a final acquisition/calibration report.
A preliminary RMSEz error check is performed at this stage of the project life cycle in the raw LiDAR dataset against GPS static and kinematic data and compared to RMSEz project specifications. The LiDAR data is examined in open, flat areas away from breaks. Lidar ground points for each flightline generated by an automatic classification routine are used.
Overall the LiDAR data products collected by LEG meet or exceed the requirements set out in the Statement of Work. The quality control requirements of LEGs quality management program were adhered to throughout the acquisition stage fo this project to ensure product quality.
LIDAR acquisition began on April 27, 2014 and was completed on May 29, 2014. A total of 40 survey missions were flown to complete the project. LEG utilized an Riegl 680i LiDAR system for the acquisition. The flight plan was flown as planned with no modifications. There were no unusual occurrences during the acquisition and the sensor performed within specifications. There were 428 flight lines required to complete the project.
The initial step of calibration is to verify availability and status of all needed GPS and Laser data against field notes and compile any data if not complete.
Subsequently the mission points are output using Trimble Business Center (TBC), initially with default
values from Trimble or the last mission calibrated for system. The initial point generation
for each mission calibration is verified within Microstation/Terrascan for calibration errors.
If a calibration error greater than specification is observed within the mission, the roll pitch
and scanner scale corrections that need to be applied are calculated. The missions with the
new calibration values are regenerated and validated internally once again to ensure
quality.
All missions are validated against the adjoining missions for relative vertical biases and
collected GPS validation points for absolute vertical accuracy purposes.
On a project level, a supplementary coverage check is carried out to ensure no data voids
unreported by Field Operations are present.
The initial points for each mission calibration are inspected for flight line errors, flight line overlap, slivers or gaps in the data, point data minimums, or issues with the LiDAR unit or GPS. Roll, pitch and scanner scale are optimized during the calibration process until the relative accuracy is met.
Relative accuracy and internal quality are checked using at least 3 regularly spaced QC blocks in which points from all lines are loaded and inspected. Vertical differences between ground surfaces of each line are displayed. Color scale is adjusted so that errors greater than the specifications are flagged. Cross sections are visually inspected across each block to validate point to point, flightline to flightline and mission to mission agreement.
For this project the specifications used are as follow:
Relative accuracy <= 7cm RMSEZ within individual swaths and <=10 cm RMSEZ or within swath overlap (between adjacent swaths).
UTM coordinate system, meters, zone 18, horizontal datum NAD83(2011), vertical datum NAVD88, Geoid 12A
Airborne Global Positioning System Data
Inertial Measurement Unit
201405
Calibrated LiDAR Point Cloud LAS 1.2 format
Leading Edge Geomatics (LEG)
mailing and physical address
2384 Route 102
Lincoln
NB
E3B 7G1
Canada
(506) 446-4403
Monday to Friday, 8 - 5, AST
Dewberry utilizes a variety of software suites for inventory management, classification, and data processing. All LiDAR related processes begin by importing the data into the GeoCue task management software. The swath data is tiled according to project specifications (1,500 m x 1,500 m). The tiled data is then opened in Terrascan where Dewberry uses proprietary ground classification routines to remove any non-ground points and generate an accurate ground surface. The ground routine consists of three main parameters (building size, iteration angle, and iteration distance); by adjusting these parameters and running several iterations of this routine an initial ground surface is developed. The building size parameter sets a roaming window size. Each tile is loaded with neighboring points from adjacent tiles and the routine classifies the data section by section based on this roaming window size. The second most important parameter is the maximum terrain angle, which sets the highest allowed terrain angle within the model. Once the ground routine has been completed a manual quality control routine is done using hillshades, cross-sections, and profiles within the Terrasolid software suite. After this QC step, a peer review and supervisor manual inspection is completed on a percentage of the classified tiles based on the project size and variability of the terrain. After the ground classification corrections were completed, the dataset was processed through a water classification routine that utilizes breaklines compiled by Dewberry to automatically classify hydrographic features. The water classification routine selects ground points within the breakline polygons and automatically classifies them as class 9, water. During this water classification routine, points that are within 1 meter of the hydrographic features are moved to class 10, an ignored ground due to breakline proximity. In addition to classes 1, 2, 9, and 10, there is a Class 7, noise points . This class was used for both low and high noise points.
The fully classified dataset is then processed through Dewberry's comprehensive quality control program.
The data was classified as follows:
Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.
Class 2 = Ground
Class 7= Noise
Class 9 = Water
Class 10 = Ignored
The LAS header information was verified to contain the following:
Class (Integer)
Adjusted GPS Time (0.0001 seconds)
Easting (0.003 m)
Northing (0.003 m)
Elevation (0.003 m)
Echo Number (Integer 1 to 4)
Echo (Integer 1 to 4)
Intensity (8 bit integer)
Flight Line (Integer)
Scan Angle (Integer degree)
Calibrated LiDAR Point Cloud LAS 1.2 format
201407
Final Tiled LiDAR datasets
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
Dewberry used GeoCue software to develop raster stereo models from the LiDAR intensity. The raster resolution was 0.3 m.
Final Tiled LiDAR datasets
201408
Lidar Intensity Stereopairs
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
LiDAR intensity stereopairs were viewed in 3-D stereo using Socet Set for ArcGIS softcopy photogrammetric software. The breaklines are collected directly into an ArcGIS file geodatabase to ensure correct topology. The LiDARgrammetry was performed under the direct supervision of an ASPRS Certified Photogrammetrist. The breaklines were stereo-compiled in accordance with the Data Dictionary.
Inland Lakes and Ponds, Streams and Rivers, Tidal Waters, and Bridge Breaklines were collected according to specifications for the Connecticut LiDAR Project.
Lidar Intensity Stereopairs
201408
3D breaklines
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
Dewberry used ESRI software to generate bare earth elevation rasters. Bare earth elevation rasters do not contain bridges. As bridges are removed from bare earth DEMs but DEMs are continuous surfaces, the area between bridge abutments must be interpolated. The rasters are reviewed to identify locations where the interpolation between bridge abutments created bridge saddles.
Final Tiled LiDAR datasets
201501
Locations of Bridge Saddles
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
The locations of identified bridge saddles are loaded into Terrascan software. LiDAR points and surface models created from ground LiDAR points are reviewed and 3D bridge breaklines are compiled in Terrascan. Typically, two breaklines are compiled for each bridge-one breakline along the ground of each abutment. The bridge breaklines are placed perpendicular to the bridge deck and extend just beyond the extents of the bridge deck. Extending the bridge breaklines beyond the extent of the bridge deck allows the compiler to use ground elevations from the ground LiDAR data for each endpoint of the breakline. The 3D endpoints of each breakline are used to enforce a continous slope on the ground under the bridge deck along the collected breakline. These breaklines are used in the final DEM production and help to reduce the appearance of bridge saddles.
Locations of Bridge Saddles
Final Tiled LiDAR datasets
201501
3D breaklines
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
Breaklines are reviewed against LiDAR intensity imagery to verify completeness of capture. All breaklines are then compared to ESRI terrains created from ground only points prior to water classification. The horizontal placement of breaklines is compared to terrain features and the breakline elevations are compared to LiDAR elevations to ensure all breaklines match the LiDAR within acceptable tolerances. Some deviation is expected between breakline and LiDAR elevations due to monotonicity, connectivity, and flattening rules that are enforced on the breaklines. Once completeness, horizontal placement, and vertical variance is reviewed, all breaklines are reviewed for topological consistency and data integrity using a combination of ESRI Data Reviewer tools and proprietary tools. Corrections are performed within the QC workflow and re-validated.
3D breaklines
201501
Final 3D breaklines
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
Class 2, ground, LiDAR points are exported from the LAS files into an Arc Geodatabase (GDB) in multipoint format. The 3D breaklines, Inland Lakes and Ponds, Streams and Rivers, Tidal Waters, and bridge breaklines are imported into the same GDB. An ESRI Terrain is generated from these inputs. The surface type of each input is as follows:
Ground Multipoint: Masspoints
Inland Lakes and Ponds: Hard Replace
Streams and Rivers: Hard Line
Tidal Waters: Hard Replace
Bridge Breaklines: Hard Line
Lidar Ground Points, Class 2
Final 3D Breaklines
201501
ESRI Terrain
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
The ESRI Terrain is converted to rasters. The rasters are created to pre-defined extents so that multiple rasters are created over the project area. Creating multiple rasters rather than one large raster over a large project area makes the data more maneageable to work with. The rasters are created with 2 tiles of overlap. This allows us to ensure seamless coverage and edge-matching in the final tiled product. These rasters were created with a 1 meter cell size.
ESRI Terrain
201501
Non-Tiled Hydro Flattened DEMs
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
The DEMs that are created over large areas are reviewed in ArcGIS with hillshades. Hillshades allow the analyst to view the DEMs in 3D and to more efficiently locate and identify potential issues. The first review is done on the area DEMs as this increases the efficiency of any corrections that may be performed. Performing corrections on area DEMs allows the analyst to perform corrections on multiple tiles at once and helps prevent errors from occurring along individual tile seamlines. Analysts review the area DEMs for incorrect water elevations and artifacts that are introduced during the raster creation process.
Non-Tiled Hydro Flattened DEMs
201501
Corrected and Final Non-Tiled Hydro Flattened DEMs
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
The corrected and final area DEMs are clipped to individual tiles. Dewberry uses a proprietary tool that clips the area DEMs to each tile located within the final Tile Grid, names the clipped DEM to the Tile Grid Cell name, and verifies that final extents are correct. All individual tiles are loaded into Global Mapper for the last review. During this last review, an analsyt checks to ensure full, complete coverage, no issues along tile boundaries, tiles seamlessly edge-match, and that there are no remaining processing artifacts in the dataset.
Corrected and Final Non-Tiled Hydro Flattened DEMs
201501
Final Tiled Hydro Flattened DEMs
Dewberry - Geospatial Services Group
Keith Patterson
Project Manager
mailing and physical address
1000 N. Ashley Drive, Suite 801
Tampa
FL
33602
USA
813.421.8635
813.225.1385
kpatterson@dewberry.com
8:00 - 5:00 EST
Raster
Grid Cell
96,000
111,000
1
Universal Transverse Mercator
18
0.999600
-75.000000
0.000000
500000.000000
0.000000
coordinate pair
1.0
1.0
meters
North American Datum of 1983(2011)
Geodetic Reference System 80
6378137.000000
298.257222
North American Vertical Datum of 1988(Geoid12A)
0.000100
meters
Explicit elevation coordinate included with horizontal coordinates
U.S. Geological Survey
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573) 308-3810
pemmett@usgs.gov
Downloadable Data
This data was produced for the U.S. Geological Survey according to specific project requirements. This information is provided "as is". Further documentation of this data can be obtained by contacting: USGS, 1400 Independence Road, Rolla, MO 65401. Telephone (573) 308-3810.
20150205
FGDC Content Standards for Digital Geospatial Metadata
FGDC-STD-001-1998
local time
http://www.esri.com/metadata/esriprof80.html
ESRI Metadata Profile
U.S. Geological Survey
Patrick Emmett
Program Manager
mailing and physical address
1400 Independence Road
Rolla
MO
65401
USA
(573)308-3810
pemmett@usgs.gov