2005 Maryland Department of Natural Resources LiDAR: Cecil County
Light Detection and Ranging (LIDAR) is a method of locating objects on the ground
using aerial-borne equipment. It is similar to RADAR or SONAR in that the two-way
travel time of an energy beam reflected off an object is precisely measured, but this
technology uses laser light instead of radio or sound waves. This technology has proven
very useful in remote sensing of the earth. It can be used for determining elevations
of both the earth's surface and items (natural and man-made) on the surface. Analysis
of LIDAR data is used in detailed modeling of the earth's surface for drainage and
floodplain studies, determining how a new structure will affect views from various
locations, shoreline erosion studies, and other reasons. This data set contains only
the bare earth mass points. Bare earth points represent ground features. Features
that are above ground, such as buildings, bridges, tree tops, etc, have been eliminated.
Mass points may appear to have "holes" with no elevation values in areas where the
surface could not be determined, such as very dense forests or urban areas.
Cite this dataset when used as a source.
|Search and Download
|| Distributor information not available
| Point of Contact
Maryland Department of Natural Resources
- Maryland Department of Natural Resources
|Data Presentation Form:
|| Digital image
|Dataset Progress Status
|Data Update Frequency:
|| Not planned
||The LIDAR-derived data were collected by the Maryland Department of Natural Resources
in support of shore erosion studies along the shorelines of the Chesapeake Bay. It
also supports the Federal Emergency Management Agency's specifications for mapping
floodplains. These efforts required detailed elevation data and models, such as those
available from LIDAR sensing. The data have also been made available to aid in other
projects that require detailed surface, vegetation and/or structure elevations.
||2005-04-15 to 2005-04-23
|Spatial Reference System:
|Spatial Bounding Box Coordinates:
|Spatial Coverage Map:
- Elevation model
- Digital Elevation Model
- Surface model
- Gridded DEM
- First return
- Last return
- Bare earth
- Bald earth
- Terrain model
- Elevation and derived products
- Chesapeake Bay
- Cecil County
| Use Constraints
|| No constraint information available
|| Fee information not available.
|| Lineage statement not available.
- Maryland Department of Natural Resources
- DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department
| Processing Steps
- LIDAR Data Acquisition. Airborne 1, Inc. flew the project area with the LIDAR sensor.
In an effort to permit correlation of the point values with tidal gauge stations,
Airborne 1, Inc. was required to fly tidal shoreline areas during the low tide cycle
(slack water ? low tide ? slack water) as predicted by local tide stations. The LIDAR
sensor collected raw data that was referenced in UTM. The flight plan on this project
included the following specifications to meet the project requirements: *Single pass
density - 1.544 square meters per sample; *Average area sampling density -1.52 square
meters per sample; *Swath width - 891.32 meters; *Flight altitude -1371 meters (4500
ft); *Flight line spacing - 445.66 meters w/50% overlap; *Scan frequency - 22 Hz;
*Firing rate - 25 kHz; *Scan angle - 18 degrees; *Ground speed - 130 knots. When complete,
the raw data was delivered to Spatial Systems.
- LIDAR Data Processing. Computational Consulting Systems. The First and Last Return
data was delivered to CCS in large blocks of data. CCS processed the data using both
the First and Last Returns, removed artifacts using automated and manual techniques,
and reprojected the data into the client-specified X, Y, Z text files using the 1200
meter x 1800 meter tiles, NAD 83 meters, NAVD 88 meters. CCS also generated the Intensity
Imagery using the client-specified USGS 3.75' tiling scheme. The data products were
delivered to SSA for quality assurance testing, formatting and final delivery.
- LIDAR Data Post Processing. Spatial Systems Associates. SSA digitized the shoreline
from the Intensity Imagery for the purposes of delineating a shoreline. Any LIDAR
points that fell seaward of this shoreline were assigned the value of zero (0). In
addition to the shoreline, SSA delineated upland ponds using the same technique and
assigned all LIDAR points that fell within the water area the value of the lowest
observed point close to the shore. The observed elevation values were not lost; a
fourth field in the data file was added for the assigned value. SSA also performed
a variety of QA procedures to determine if the point density was within expected ranges;
that each tile was completely filled; that all tiles were accounted for, and that
the tiles were named in accordance with client specifications.
- LIDAR Data Check Point Surveys. NXL Construction Services. NXL was contracted to acquire
the check-points in the 5 different land cover classes. SSA provided NXL with maps
of each area where a check-point was to be located. The points were scattered throughout
the project area. NXL was permitted the latitude to select the exact location based
on field conditions, provided the points were generally within a 1 mile radius of
the chosen location and that the land cover class was the same as the one specified.
The land cover classes were: Grass/Ground, High Grass/Crops, Brush/Low Trees, Forest,
- LIDAR Data Quality Assurance. Dewberry LLC was provided with the check-point and LIDAR
Bare Earth Mass Points data to perform their independent quality assurance work. They
performed detailed analyses to determine if the vertical accuracy was within specifications
and examined the data for flight, data collection and processing inconsistencies.
Neither the flight vendor (Airborne 1) nor the processing vendor (CCS) was given access
to the check-point data. The entire accuracy report can be found at <http://dnrweb.dnr.state.md.us/gis/data/lidar>.
- The NOAA Coastal Services Center (CSC) received LAS files containing the point cloud
elevation data from Earth Data, Inc. CSC performed the following processing on the
data to make it available within the Lidar Data Retrieval Tool (LDART): 1. Variable
length header records were added to the LAS files to identify projection, datum and
sort order. 2. The LFIT files were sorted by latitude. 3. Lfit files were exported
to xyz ASCII text.
- 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: 2013-06-12
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