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2005 Baltimore County Maryland Lidar

browse graphicThis kmz file shows the extent of coverage for the 2005 Baltimore County lidar data set.
In the spring of 2005, Sanborn as part of the Dewberry team was contracted to execute a LiDAR (Light Detection and Ranging) survey campaign to collect the 3-dimensional positions of a dense set of masspoints for the entire 689 plus square mile project area of Baltimore County, Maryland. These data are suitable for the development of a digital elevation model (DEM) to support orthometric photo rectification and contouring. The lidar first and Last Return value data were obtained from the post processed data and provided in separate files containing all georeferenced First Return and Last Return data in an ASCII comma delimited format to the NOAA Coastal Services Center. For data storage and Digital Coast provisioning purposes, the NOAA Coastal Services Center converted the ascii data to geographic coordinates, ellipsoid heights in meters, and las format and created a bare earth data set using an automated algorithm.

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    Distribution Formats
    • LAZ
    Distributor Distributor information not available
    Point of Contact Baltimore County GIS Services
    Documentation links not available.
    • Baltimore County, MD GIS Services
      • publication: 2012-01-01
      Data Presentation Form: Digital image
      Dataset Progress Status Complete
      Data Update Frequency: Not planned
      Supplemental Information: The original Lidar Acquisition plan was designed for all East/West flight lines. Due to several Air Traffic Control Restrictions in the southern portion of the County, 54 North/South flight lines were used to acquire the southern portion of the county, minimizing time in restricted airspace. In addition, the Bay Coast line was planned for acquisition within one hour either side of low tide. Due to the same ATC restrictions it was impossible to comply with the low tide requirement for this area.
      Purpose: The Baltimore County LiDAR campaign was designed specifically to collect LIDAR derived masspoints at an approximate spacing of 1.5 meters or better within the project area. The data was processed to facilitate the generation of an appropriate DEM for orthorectification and 2' contour mapping. Rigorous quality assurance procedures were followed to ensure that the appropriate data accuracy was achieved.
      Time Period: 2005-03-18  to  2005-04-15
      Spatial Reference System:
      Spatial Bounding Box Coordinates:
      N: 39.7221
      S: 39.1934
      E: -76.3155
      W: -76.9156
      Spatial Coverage Map:
      • Bathymetry/Topography
      • Lidar
      • DEM
      • Digital Elevation Model
      • Elevation
      • Digital Terrain Model
      • Point cloud data
      • United States
      • Maryland
      • Baltimore County
      Use Constraints No constraint information available
      Fees Fee information not available.
      Lineage Statement Lineage statement not available.
      • Sanborn Map Company Inc.
      Processing Steps
      • Step 1- LIDAR Data Acquisition Sanborn flew the entire project area as a contiguous block of more than 870 square miles using the ALTM 2050 LIDAR sensor equipped with Airborne GPS and IMU positioning and orientation units. A total of 54 north south flight lines and 90 east-west flight lines were required to cover the required entire County project area. Prior to data collection, two AGPS ground stations were established to support the LiDAR campaign. NGS monument BELL (PID AJ7978) was used as the northern base station, while NGS monument MTN-B (PID AI4374) was used as the Martin State Airfield base station. The MTN-B point was used in a previous survey campaign completed by Sanborn in 2001. Since the MTN-B point has only horizontal coordinates published, the vertical coordinates generated by the 2001 adjustment were used. Point MTN-B is First Order horizontal, while BELL is Horizontal Order A and Vertical Order 2. We tied our network and adjusted our mini network vertically to a First Class I and five second Class II. The network accuracy is a function of the fully constrained adjustment and follows very closely the NOAA Technical Memorandum NOS NGS58 " Guidelines for Establishing GPS Derived Ellipsoid Heights (Standards: 2 cm and 5 cm)," November 1997 yielding sound network adjustment. The combination (Horizontal & Vertical) achieved the height adjustment meeting the 5 cm standard. Adjustments constraints for the survey to derive the coordinates The Optech ALTM (Airborne Laser Terrain Mapping) LiDAR system was calibrated regularly by conducting several passes over a flat surface of known elevation at the job location. Calibration flights were performed prior to and following every mission. The calibration parameters were inserted into the post-processing software before final data processing. The observations used to establish the fiducial and survey point networks were made at various times during the LiDAR data collection period. The LiDAR aircraft arrived on site March 18th, 2005 and the LiDAR data collection was accomplished between March 18, 2005 and April 15, 2005. The flight plan for the project includes the following specifications to fully meet the project requirements. Single pass density of approximately 1.0 square meters per sample Average area sampling density - 1.4 square meters per sample Swath width 728 meters Flight altitude 1000 meters Flight line spacing -589 meters with 125 meters overlap The Scan Frequency- 35 Hz *Scan Angle- 20 degrees Aircraft ground speed -- 140 knots System Calibration pre and post mission Two GPS base stations within 30 KM. The acquired LiDAR data was combined by flight line in a merge process that eliminated redundant points. The data was clipped into more manageable 1 KM by 1 KM tiles bounds. Noise, or anomalous returs were filtered from all data during this processing step. The data was quality check using commercial software TerraScan.
      • Step 2- AGPS Processing and Point Cloud- First and Last Return Data Processing Final post-processing of LiDAR data involves several steps. The airborne GPS data were post-processed using Waypoint's GravNAVTM software (version 6.03). A fixed-bias carrier phase solution was computed in both the forward and reverse chronological directions. All LiDAR acquisition was limited to periods when the PDOP was less than 4.0. The GPS trajectory is combined with the raw IMU data and post-processed using Applanix Inc.'s POSPROC Kalman Filtering software. This results in a two-fold improvement in the attitude accuracies over the real-time INS data. The best estimated trajectory (BET) and refined attitude data are then re-introduced into the Optech REALM software to compute the laser point-positions - the trajectory is combined with the attitude data and laser range measurements to produce the 3-dimensional coordinates of the mass points. The acquired LiDAR data was combined by flight line in a merge process that eliminated redundant points. The data was clipped into more manageable 1 KM by 1 KM tiles bounds. Noise or anomalous returns were filtered from all data during this processing step. The data was quality check using commercial software TerraScan.
      • Step 3-- Elevation and Coordinate Processing All elevation data was processed on a point by point basis for ellipsoid to orthometric height conversion using the National Geodetic Survey (NGS) Geoid Model, GEOID99. Datum and coordinate system conversion from WGS84 to the Maryland State Plane coordinate system was performed using U.S. Army Corps of Engineers CorpsCon software algorithms. The LIDAR first and last return data is filtered to remove the vegetation and above ground manmade features. Computations are produced for both first and last laser return observations. The ground-filtered delivery and corresponding regular grid DEM are produced from the last return data. The first return information provides a useful depiction of the "canopy" within the project area. Laser point filtering was accomplished using TerraScan LiDAR processing and modeling software. The bare earth surface generated by TerraScan is used to produce regular grid DEMs.
      • Step 4 First and Last return data Formatting The Terrascan final processed first and last return data is exported in exported in ASCII comma delimited file format and clipped to the County' standard tile layout. 837 FR files and 837 LR Data tiles were supplied on DVD media. QC is performed
      • The NOAA Coastal Services Center (CSC) received the first and last return files in ascii format. NOAA CSC performed the following processing for data storage and Digital Coast provisioning purposes: 1. The data were filtered for elevation outliers 2. The data were converted from orthometric heights to ellipsoid heights using Geoid03 3. The data were converted from Maryland State Plane to geographic coordinates 4. The vertical units of the data were converted from feet to meters 5. A bare earth data set was created using an automated algorithm. 6. 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 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 ( 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: 2013-01-22

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