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2002 Maryland Department of Natural Resources LiDAR: Worcester 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. The bare earth mass points data show the calculated elevation of the earth's surface (the ground, without objects such as trees or buildings). 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.

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    Distribution Formats
    • LAZ
    Distributor DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    Point of Contact Ken Miller
    Maryland Department of Natural Resources
    410-260-8751
    kenmiller@dnr.state.md.us
    Associated Resources
    • Lidar QA/QC Report
    Originator
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    Originator
    • Maryland Department of Natural Resources
    Publisher
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    Date(s)
    • publication: 2006-10-18
    Data Presentation Form: Digital image
    Dataset Progress Status Complete
    Data Update Frequency: Not planned
    Purpose: 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.
    Use Limitations
    • These data depict the elevations at the time of the survey and are only accurate for that time. 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. Any conclusions drawn from analysis of this information are not the responsibility of NOAA or any of its partners. These data are NOT to be used for navigational purposes.
    Time Period: 2002-09-01  to  2003-01-01
    Spatial Reference System: urn:ogc:def:crs:EPSG::4269 Ellipsoid in Meters
    Spatial Bounding Box Coordinates:
    N: 38.468258
    S: 37.979873
    E: -75.023956
    W: -75.569660
    Spatial Coverage Map:
    Themes
    • Bathymetry/Topography
    • mass points
    • LiDAR
    • lidar
    • elevation
    • DEM
    • elevation model
    • digital elevation model
    • surface model
    • gridded DEM
    Places
    • United States
    • Maryland
    • Worcester County
    Use Constraints No constraint information available
    Fees Fee information not available.
    Lineage Statement Lineage statement not available.
    Processor
    • Maryland Department of Natural Resources
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    • DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce
    Processing Steps
    • LIDAR Data Acquisition. Airborne 1, using an Optec 25 mHz system, flew the project area with the LIDAR sensor. A portion of the 2003 project area included data acquisition of portions of the LIDAR 2002 project area that had incomplete coverage. Where overlaps between the two series of data occurred, the newer data was used. No attempt at blending the two datasets was made to maintain the highest data integrity. In an effort to permit correlation of the point values with tidal gauge stations, the Airborne 1 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 specifications called for data collection during leaf-off conditions, which generally run through early to mid April. However, due to late winter snow cover, windy flight conditions and other technical obstacles, data acquisitions continued into early June 2003. In addition, a small area in the north end of the project area was acquired in July. Anticipating the trouble with leaf density, Airborne 1 modified the flight parameters to increase the laser light penetration to the ground. The flight plan on this project included the following specifications to meet the project requirements: *Single pass density - 1.696 square meters per sample; *Average area sampling density -1.272 square meters per sample; *Swath width - 996.76 meters; *Flight altitude -1371 meters (4500 ft); *Flight line spacing - 498.38 meters w/50% overlap; *Scan frequency - 21 Hz; *Firing rate - 25 kHz; *Scan angle - 20 degrees; *Ground speed - 140 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, 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, and Urban/Pavement.
    • LIDAR Data Quailty 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 with 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 ASCII files containing the bared-earth elevation and intensity data from Maryland Department of Natural Resources. CSC performed the following processing on the data to make it available within the Lidar Data Retrieval Tool (LDART): 1. The data were projected from Maryland State Plane coordinates to geographic decimal degrees using the General Cartographic Transformation Package. 2. The lat, lon, MODZVAL and intensity values where extracted from the ascii files and converted to the LDART binary format. 3. The data were converted to xyz text files
    • 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 format. 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 of 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 to 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: 2013-05-07

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