Connecticut Statewide Lidar DEM 2016

This metadata record describes the hydro-flattened bare earth digital elevation model (DEM) derived from the classified LiDAR data for the 2016 Connecticut Lidar project covering approximately 5,240 square miles.

Original contact information:

Contact Org: NOAA Office for Coastal Management

Phone: 843-740-1202

Email: coastal.info@noaa.gov

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments, and hydrologic modeling. LAS data products are suitable for 1 foot contour generation. USGS Lidar Base Specification 1.2, QL2. 19.6 cm NVA.

12073

Project Projection, Datums and Units: Projection - State Plane Connecticut; Horizontal datum - North American Datum of 1983 (NAD83 (2011)); Vertical datum - North American Vertical Datum of 1988 (NAVD88) using the latest geoid (Geoid12b) for converting ellipsoidal heights to orthometric heights; Units - US feet horizontal, meters vertical. This data was ingested into the Digital Coast Data Access Viewer for custom processing. If you requested this data through that system, your projection may be different and will be reflected below.

Bare Earth only

Classes:

2 - Bare-Earth Ground

USGS Base Specification 1.2, QL2 meeting 19.6 cm NVA

The Capitol Region Council of Governments digital data have been tested and their documentation carefully reviewed. However, the Capitol Region Council of Governments and its representatives make no warranty or representation, either expressed or implied, with respect to the digital data and their documentation, their quality, performance, merchantability, or fitness for a particular purpose. The digital data are distributed on "as is" basis, and the user assumes all risk to their quality, the results obtained from their use, and the performance of the data. In no event will the Capitol Region Council of Governments or its representatives be liable for any direct, indirect, special, incidental or consequential damages resulting from and defect in the State of Connecticut or in their documentation. This disclaimer of warranty is exclusive and in lieu of all others, oral or written, express or implied. No agent or employee is authorized to make any modification, extension, or addition to this warranty.

Any conclusions drawn from the analysis of this information are not the responsibility of the Capitol Region Council of Governments, the Office for Coastal Management or its partners.

This data may be used by the requesting party at their own risk and may be re-distributed.

This data is for planning purposes only and should not be used for legal or cadastral purposes. Any conclusions drawn from analysis of this information are the responsibility of the user. Users should be aware that temporal changes may have occurred since this dataset was collected and some parts of this dataset may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of its limitations.

State of Connecticut:

The LiDAR surface was evaluated using a collection of 181 GPS surveyed checkpoints for the raw NVA report. The DEM was compared to these checkpoints yielding a better result than was required for the project.

Raw NVA Control Accuracy Report (feet)

--------- Report Disclaimer ---------

This report does not guarantee accuracy. The report only reflects one statistical representation of the control points, LIDAR data and surface used. This report does not replace a thorough quality control process.

--------- Report Summary ---------

Average dz 0.004

Minimum dz -0.829

Maximum dz 0.622

Average magnitude 0.170

Root mean square 0.227

Std deviation 0.228

----------------------------------------------------------------------------------------

Attribute accuracy is tested after the LiDAR processing stage. After classification of the LiDAR data, DEMs are created using the bare earth points. The NVA report is generated from the comparison of the DEM and the ground control collected within the project area.

The DEM surface was evaluated using a collection of 181 GPS surveyed checkpoints for the NVA report. The DEM was compared to these checkpoints yielding much better result than was required for the project.

NVA Control Accuracy Report (feet)

--------- Report Disclaimer ---------

This report does not guarantee accuracy. The report only reflects one statistical representation of the control points, LIDAR data and surface used. This report does not replace a thorough quality control process.

--------- Report Summary ---------

Average dz 0.004

Minimum dz -0.778

Maximum dz 0.576

Average magnitude 0.158

Root mean square 0.207

Std deviation 0.207

----------------------------------------------------------------------------------------

Attribute accuracy is tested after the LiDAR processing stage. After classification of the LiDAR data, DEMs are created using the bare earth points. The VVA report is generated from the comparison of the DEM and the ground control collected within the project area.

The DEM was evaluated using a collection of 95 GPS surveyed checkpoints. The DEM was compared to these checkpoints yielding much better result than was required for the project.

VVA Control Accuracy Report (feet)

--------- Report Disclaimer ---------

This report does not guarantee accuracy. The report only reflects one statistical representation of the control points, LIDAR data and surface used. This report does not replace a thorough quality control process.

--------- Report Summary ---------

Average dz 0.147

Minimum dz -0.771

Maximum dz 0.625

Average magnitude 0.212

Root mean square 0.261

Std deviation 0.217

---------------------------------------------------------------------------------------- | Quantitative Value: 0 | Quantitative Test Explanation: N/A

Horizontal positional accuracy for the Connecticut LiDAR is dependent upon the quality of the GPS/INS solution, sensor calibration and ground conditions at the time of data capture. The data set was produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 1.0 meter RMSEx/RMSEy.; Quantitative Value: 1.0 meters, Test that produced the value: For the Connecticut, this value is computed by comparing ground control to a DEM derived from the classified LiDAR data and represents the RMSE of residuals on controls within the project area.

For the DEM data derived from the classified point cloud, the NVA and VVA were computed. The vertical accuracy was tested with independent survey check points located in various terrain types within Connecticut. These check points were not used in the calibration or post processing of the lidar point cloud data. The survey check points were distributed throughout the block area. Specifications for this project require that the VVA be 19.6 cm or better @ 95 percent confidence level.; Quantitative Value: 0.070 meters, Test that produced the value: Value is RMSE in meters. The raw NVA was tested using 181 independent survey check points located in flat terrain types within the state of Connecticut The survey checkpoints were distributed throughout the block area. The 181 independent check points were surveyed using static GPS base stations collecting point location for 20 minute intervals. Elevations were measured for the x,y,z location of each check point. Elevations interpolated from the DEM surface were then compared to the elevation values of the surveyed control. This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10cm RMSEz Vertical Accuracy Class. Actual NVA accuracy was found to be RMSEz = 7cm, equating to +/- 13.8cm at 95% confidence level.; Quantitative Value: 0.063 meters, Test that produced the value: Value is RMSE in meters. The NVA was tested using 181 independent survey check points located in bare earth terrain types within the state of Connecticut. The 181 independent check points contained all NVA points and were surveyed using static GPS base stations collecting point location for 20 minute intervals. Elevations were measured for the x,y,z location of each check point. Elevations interpolated from the DEM surface were then compared to the elevation values of the surveyed control. This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10cm RMSEz Vertical Accuracy Class. Actual NVA accuracy was found to be RMSEz = 6.3cm, equating to +/- 12.5cm at 95% confidence level.; Quantitative Value: 0.080 meters, Test that produced the value: Value is RMSE in meters. The VVA was tested using 95 independent survey check points located in various vegetation terrain types within the state of Connecticut. The 95 independent check points were surveyed using static GPS base stations collecting point location for 20 minute intervals. Elevations were measured for the x,y,z location of each check point. Elevations interpolated from the DEM surface were then compared to the elevation values of the surveyed control. This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10cm RMSEz Vertical Accuracy Class. Actual NVA accuracy was found to be RMSEz = 6.3cm, equating to +/- 12.5cm at 95% confidence level. Actual VVA accuracy was found to be +/- 17cm at the 95th percentile.

LiDAR data is collected for the project area. Post processing of the simultaneously acquired GPS/INS is performed and applied to the laser returns to output a point cloud in the specified project coordinate system and datums. The point cloud data is then subjected to automated classification routines to assign all points in the point cloud to ground, water, overlap and unclassified point classes. Anomalous laser returns that occur infrequently are removed entirely from the data set. Once clean bare earth points are established, DEMs are created using bare earth points and hydro features. The DEM surface is then compared to the survey checkpoints. These accuracies must pass the NVA and VVA accuracy specifications.

LiDAR data is collected within the project area and processed. After the DEMs were created, the dataset was verified against control. Well-distributed control was collected for the entire state of Connecticut. Accuracy is reported for the state as a whole.