2006 Federal Emergency Management Agency (FEMA) Topographic LiDAR: Coastal Connecticut
This kmz file shows the extent of coverage for the 2006 FEMA Coastal Connecticut lidar
LIDAR data is remotely sensed high-resolution elevation data collected by an airborne
collection platform. By positioning laser range finding with the use of 1 second GPS
with 100hz inertial measurement unit corrections; Terrapoint's LIDAR instruments are
able to make highly detailed geospatial elevation products of the ground, man-made
structures and vegetation. The LiDAR flightlines for this project was planned for
a 50% acquisition overlap. The nominal resolution of this project without overlap
is 1.25m. Four returns were recorded for each pulse in addition to an intensity value.
GPS Week Time, Intensity, Flightline and number attributes were provided for each
LiDAR point. Data is provided as random points, in LAS v1.0 format, classified according
to ASPRS Class Code 2=Ground 1=Undefined. Water is included in the bare earth ground
model, except where the entire tile is covered by water. The following regions of
Connecticut are included in this project: Fairfield County - 130 square kilometers
New Haven - 170 square kilometers Middlesex - 29 square kilometers New London - 157
square kilometers Please note that the LiDAR intensity is not calibrated or normalized.
The intensity value is meant to provide relative signal return strengths for features
imaged by the sensor.
Cite this dataset when used as a source.
|Search and Download
|| Distributor information not available
| Point of Contact
||National Oceanic and Atmospheric Administration (NOAA)
Documentation links not available.
- DHS/FEMA > Federal Emergency Management Agency, U.S. Department of Homeland Security
|Data Presentation Form:
|| Digital image
|Dataset Progress Status
|Data Update Frequency:
|| As needed
||The purpose of this LiDAR data was to produce high accuracy 3D elevation based geospatial
products for coastal flood mapping.
||2006-12-16 to 2006-12-18
|Spatial Reference System:
|Spatial Bounding Box Coordinates:
|Spatial Coverage Map:
- ASPRS standards
- Fairfield County
- New Haven
- New London
- United States
| Use Constraints
|| No constraint information available
|| Fee information not available.
|| Lineage statement not available.
- Terrapoint USA
- Terrapoint USA
| Processing Steps
- - General Overview The Airborne LiDAR survey was conducted using an OPTECH 3100EA
flying at a nominal height of 1550 metres AGL with a total angular coverage of 40
degrees. Flight line spacing was nominally 564 metres providing overlap of 50% on
adjacent flight lines. Lines were flown in east/west and north/south orientated blocks
to best optimize flying time considering the layout for the project. - Aircraft A
Piper Navajo, registration C-FQQB was used for the survey. This aircraft has a flight
range of approximately 6.5 hours and was flown at an average altitude of 1550, thereby
encountering flying altitudes of approximately 1550 metres above sea level (ASL).
The aircraft was staged from the East Haven CT Airport, and ferried daily to the project
site for flight operations. - GPS Receivers A combination of Sokkia GSR 2600 and NovAtel
DL-4+ dual frequency GPS receivers were used to support the airborne operations of
this survey and to establish the GPS control network. - Number of Flights and Flight
Lines For both Connecticut and Rhode Island Coastline Sites; a total of 6 missions
were flown for this project with flight times ranging approximately 31 hours under
good meteorological and GPS conditions. 72 flight lines were flown over the Connecticut
Coastline site to provide complete coverage.
- - Airborne GPS Kinematic Airborne GPS kinematic data was processed on-site using GrafNav
kinematic On-The-Fly (OTF) software. Flights were flown with a minimum of 6 satellites
in view (13o above the horizon) and with a PDOP of better than 4.5. Distances from
base station to aircraft were kept to a maximum of 35 km, to ensure a strong OTF (On-The-Fly)
solution. For all flights, the GPS data can be classified as excellent, with GPS residuals
of 5cm average but no larger than 12 cm being recorded. - Calculation of 3D laser
points (raw data) The post-processing software to derive X, Y, Z values from roll,
pitch, yaw, and range is Optech's Realm. - Classification and Editing The data was
processed using the software TerraScan, and following the methodology described herein.
The initial step is the setup of the TerraScan project, which is done by importing
client provided tile boundary index encompassing the entire project areas. The 3D
laser point clouds, in binary format, were imported into the TerraScan project and
divided in 1407 tiles, as per the contract specifications. tiled, the laser points
were classified using a proprietary routine in TerraScan. This routine removes any
obvious outliers from the dataset following which the ground layer is extracted from
the point cloud. The ground extraction process encompassed in this routine takes place
by building an iterative surface model. This surface model is generated using three
main parameters: building size, iteration angle and iteration distance. The initial
model is based on low points being selected by a "roaming window" with the assumption
is that these are the ground points. The size of this roaming window is determined
by the building size parameter. The low points are triangulated and the remaining
points are evaluated and subsequently added to the model if they meet the iteration
angle and distance constraints. This process is repeated until no additional points
are added within an iteration. A second critical parameter is the maximum terrain
angle constraint, which determines the maximum terrain angle allowed within the classification
model. The data is then manually quality controlled with the use of hillshading, cross-sections
and profiles. Any points found to be of class vegetation, building or error during
the quality control process, are removed from the ground model and placed on the appropriate
layer. An integrity check is also performed simultaneously to verify that ground features
such as rock cuts, elevated roads and crests are present. Once data has been cleaned
and complete, it is then reviewed by a supervisor via manual inspection and through
the use of a hillshade mosaic of the entire project area. - Projection Transformation
The data was processed in the native UTM zone in meters and then transformed to the
Connecticut State Plane final projection system and US survey feet using an in-house
transformation software which uses the Coorpscon DLL.
- The NOAA Coastal Services Center (CSC) received the topographic files in LAZ V1.0
format. The files contained lidar elevation measurements. The data were received in
Connecticut State Plane coordinates, NAD83 (Zone 0600) and were vertically referenced
to NAVD88 using the Geoid03 model. The vertical units of the data were feet. CSC performed
the following processing for data storage and Digital Coast provisioning purposes:
1. The topographic las files were converted from a Projected Coordinate System (Connecticut
SP 0600) to a Geographic Coordinate system (NAD83). 2. The topographic las files'
horizontal units were converted from US survey feet to decimal degrees. 3. The topographic
las files were converted from orthometric (NAVD88) heights to ellipsoidal heights
using Geoid03. 4. The topographic las files' vertical units were converted from survey
feet to meters. 5. The data were converted to LAZ format.
- The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are currently
being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS or LAZ
The LAS format is an industry standard for LiDAR data developed by the American Society
of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version
LAS developed by Martin Isenburg (http://www.laszip.org/). The data are exclusively
in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.
Metadata Last Modified: 2013-04-25
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