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Short Citation:
OCM Partners, 2024: 2011 U.S. Department of Agriculture- Natural Resources Conservation Service (USDA-NRCS) Topographic Lidar: North West Connecticut,

Item Identification

Title: 2011 U.S. Department of Agriculture- Natural Resources Conservation Service (USDA-NRCS) Topographic Lidar: North West Connecticut
Short Name: ct2011_usda_northwest_m2597_metadata
Status: Completed
Publication Date: 2013-11

Earth Eye collected LiDAR data for approximately 1,703 square kilometers that partially cover the Connecticut counties of Litchfield and Fairfield. The nominal pulse spacing for this project was no greater than 1 point

every 0.7 meters. Dewberry used proprietary procedures to classify the LAS according to project specifications: 1-Unclassified, 2-Ground, 7-Noise, 9-Water, 12-Overlap. Dewberry produced 3D breaklines and combined these with the

final LiDAR data to produce seamless hydro flattened DEMs for the 1,742 tiles (1000 m x 1000 m) that cover the project area.


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). This data was produced

for the U.S. Corp of Engineers and USDA-NRCS Connecticut for use in projects dealing with conservation planning, design, research, floodplain mapping, dam safety assessments, and hydrologic modeling.



Supplemental Information:

A complete description of this dataset is available in the Final Project Report submitted to the both the U.S. Corp of Engineers and USDA-NRCS Connecticut. A copy of this report can be found here:

A footprint of this data set may be viewed in Google Earth at:


Theme Keywords

Thesaurus Keyword
ISO 19115 Topic Category
None Bare earth
None Light Detection and Ranging

Physical Location

Organization: Office for Coastal Management
City: Charleston
State/Province: SC

Data Set Information

Data Set Scope Code: Data Set
Maintenance Frequency: As Needed
Data Presentation Form: las
Entity Attribute Overview:

LiDAR points in LAZ format (ASPRS Class 1,2,7,9,12)

Entity Attribute Detail Citation:


Distribution Liability:

Any conclusions drawn from the analysis of this information are not the responsibility of USDA-NRCS, USACE, Earth Eye, Dewberry, NOAA, the Office for Coastal Management or its partners.

Support Roles

Data Steward

CC ID: 671543
Date Effective From: 2013-11
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202


CC ID: 671545
Date Effective From: 2013-11
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202

Metadata Contact

CC ID: 671546
Date Effective From: 2013-11
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202

Point of Contact

CC ID: 671544
Date Effective From: 2013-11
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202


Currentness Reference: Ground Condition

Extent Group 1

Extent Group 1 / Geographic Area 1

CC ID: 1134897
W° Bound: -73.513386
E° Bound: -72.996434
N° Bound: 42.051671
S° Bound: 41.588247

Extent Group 1 / Time Frame 1

CC ID: 1134896
Time Frame Type: Range
Start: 2011-12-13
End: 2011-12-19

Spatial Information

Spatial Representation

Representations Used

Vector: Yes

Access Information

Security Class: Unclassified
Data Access Procedure:

This data can be obtained on-line at the following URL:


Data Access Constraints:


Data Use Constraints:

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. These data depict the heights at the time of the survey and are only accurate for that time.

Distribution Information

Distribution 1

CC ID: 740588
Download URL:
File Name: Customized Download

Create custom data files by choosing data area, product type, map projection, file format, datum, etc.

Distribution 2

CC ID: 740589
Download URL:
File Name: Bulk Download

Simple download of data files.



CC ID: 740591
URL Type:
Online Resource


CC ID: 740592
URL Type:
Online Resource


CC ID: 740593
Name: Browse Graphic
URL Type:
Browse Graphic
File Resource Format: kmz

This graphic shows the lidar coverage for Litchfield and Fairfield Counties, Connecticut.

Activity Log

Activity Log 1

CC ID: 671564
Activity Date/Time: 2016-05-23

Date that the source FGDC record was last modified.

Activity Log 2

CC ID: 671563
Activity Date/Time: 2017-11-14

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using '' script. Contact Tyler Christensen (NOS) for details.

Activity Log 3

CC ID: 718204
Activity Date/Time: 2018-02-08

Partial upload of Positional Accuracy fields only.

Activity Log 4

CC ID: 740590
Activity Date/Time: 2018-03-13

Partial upload to move data access links to Distribution Info.

Data Quality

Horizontal Positional Accuracy:

Lidar source compiled to meet 1 meter horizontal accuracy.; Quantitative Value: 1.0 meters, Test that produced the value:

Dewberry does not perform independent horizontal accuracy testing on the LiDAR. LiDAR vendors perform calibrations on the LiDAR sensor and compare data to adjoining flight lines to ensure LiDAR meets the 1 meter horizontal

accuracy standard at the 95% confidence level. Please see the final project report delivered to the US Corp of Engineers for more details. Units in meters.

Vertical Positional Accuracy:

The vertical accuracy of the LiDAR was tested by Dewberry with 60 independent survey checkpoints. The survey checkpoints were evenly distributed throughout the project area and were located in areas of open terrain (20),

grass/weeds/crops (21), or forest (19).

Checkpoints in open terrain were used to compute the Fundamental Vertical Accuracy (FVA). Project specifications required a FVA of 0.185 m based on a RMSEz (0.0925 m) x 1.9600. All checkpoints were used to compute the

Consolidated Vertical Accuracy (CVA).

; Quantitative Value: 0.18 meters, Test that produced the value:

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 LiDAR project satisfies the criteria: Lidar dataset tested 0.18 m vertical accuracy at 95% confidence level in open terrain, based on RMSEz (0.0925 m) x 1.9600.

Based on the vertical accuracy testing conducted by Dewberry, using NDEP and ASPRS methodology, consolidated vertical accuracy at the 95% confidence level is computed using the 95th percentile method. The dataset for the

Connecticut LiDAR project tested 0.30 m vertical accuracy at 95% confidence level in all land cover categories combined.

Completeness Report:

A visual qualitative assessment was performed to ensure data completeness and bare earth data cleanliness. No void or missing data, the bare earth surface is of good quality and data passes vertical accuracy specifications.

NOAA OCM noted that LAS file 18TXM6117 does not contain GPS Time information.

Conceptual Consistency:

Data covers the tile scheme provided for the project area.


Process Steps

Process Step 1

CC ID: 1134892

Data for the U.S. Corp of Engineers High Resolution LiDAR Data Acquisition & Processing for Portions of Connecticut project was acquired by Earth Eye, LLC.

The project area included approximately 657 contiguous square miles for portions of Connecticut including a buffer of 200 meters. LiDAR sensor data were collected with an Optech ALTM3100EA LIDAR System. No imagery was requested

or delivered. The data was delivered in the UTM coordinate system, meters, zone 18, horizontal datum NAD83, vertical datum NGVD88, Geoid 09. Deliverables for the project included a raw (unclassified) calibrated LiDAR point cloud,

survey control, and a final control report.

The calibration process considered all errors inherent with the equipment including errors in GPS, IMU, and sensor specific parameters. Adjustments were made to achieve a flight line to flight line data match (relative

calibration) and subsequently adjusted to control for absolute accuracy. Process steps to achieve this are as follows:

Rigorous LiDAR calibration: all sources of error such as the sensor's ranging and torsion parameters, atmospheric variables, GPS conditions, and IMU offsets were analyzed and removed to the highest level possible. This method

addresses all errors, both vertical and horizontal in nature. Ranging, atmospheric variables, and GPS conditions affect the vertical position of the surface, whereas IMU offsets and torsion parameters affect the data horizontally.

The horizontal accuracy is proven through repeatability: when the position of features remains constant no matter what direction the plane was flying and no matter where the feature is positioned within the swath, relative

horizontal accuracy is achieved. Absolute horizontal accuracy is achieved through the use of differential GPS with base lines shorter than 25 miles. The base station is set at a temporary monument that is 'tied-in' to the CORS

network. The same position is used for every lift, ensuring that any errors in its position will affect all data equally and can therefore be removed equally. Vertical accuracy is achieved through the adjustment to ground control

survey points within the finished product. Although the base station has absolute vertical accuracy, adjustments to sensor parameters introduces vertical error that must be normalized in the final (mean) adjustment. The minimum

expected horizontal accuracy was tested during the boresight process to meet or exceed the National Standard for Spatial Data Accuracy (NSSDA) for a Horizontal accuracy of 1 meter RMSE or better and a Vertical Accuracy of

RMSE(z) 9.25 cm.

Process Date/Time: 2011-12-01 00:00:00

Process Step 2

CC ID: 1134893

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 (1,000 m x 1,000 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. In addition to classes 1, 2, and 9, there is a Class 7, noise

points. This class was only used if needed when points could manually be identified as low/high 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

The LAS header information was verified to contain the following:

Class (Integer)

GPS Week Time (0.0001 seconds)

Easting (0.01 foot)

Northing (0.01 foot)

Elevation (0.01 foot)

Echo Number (Integer 1 to 4)

Echo (Integer 1 to 4)

Intensity (8 bit integer)

Flight Line (Integer)

Scan Angle (Integer degree)

Process Date/Time: 2012-01-01 00:00:00

Process Step 3

CC ID: 1134894

The NOAA Office for Coastal Management (OCM) received topographic files in LAS V1.2 format. The files contained lidar elevation measurements, intensity values, scan angle values, return information, flightline information,

and adjusted standard GPS time. The data were received in UTM Zone 18N, NAD83 coordinates and were vertically referenced to NAVD88 using the Geoid09 model. The vertical units of the data were meters. OCM performed the

following processing for data storage and Digital Coast provisioning purposes:

1. The LAS header's total point count did not match the actual number of points contained in several files. The header counts were repaired using LASTools' Lasinfo.

2. The Global Encoding Bit of each LAS file was set to '1' to reflect the use of Adjusted Standard GPS Time. (NOTE: Tile 18TXM6117 does not contain GPS Time information)

3. The topographic las files were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid09.

4. The topographic las files were converted from a Projected Coordinate System (UTM Zone 18N) to a Geographic Coordinate System (NAD83).

5. The topographic las files' horizontal units were converted from meters to decimal degrees.

Process Date/Time: 2013-11-01 00:00:00

Catalog Details

Catalog Item ID: 49657
GUID: gov.noaa.nmfs.inport:49657
Metadata Record Created By: Anne Ball
Metadata Record Created: 2017-11-15 15:21+0000
Metadata Record Last Modified By: SysAdmin InPortAdmin
Metadata Record Last Modified: 2022-08-09 17:11+0000
Metadata Record Published: 2022-03-16
Owner Org: OCMP
Metadata Publication Status: Published Externally
Do Not Publish?: N
Metadata Last Review Date: 2022-03-16
Metadata Review Frequency: 1 Year
Metadata Next Review Date: 2023-03-16