2005 Baltimore County Maryland Lidar
This kmz file shows the extent of coverage for the 2005 Baltimore County lidar data
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.
Cite this dataset when used as a source.
|Search and Download
|| Distributor information not available
| Point of Contact
||Baltimore County GIS Services
Documentation links not available.
- Baltimore County, MD GIS Services
|Data Presentation Form:
|| Digital image
|Dataset Progress Status
|Data Update Frequency:
|| Not planned
||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.
||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.
||2005-03-18 to 2005-04-15
|Spatial Reference System:
|Spatial Bounding Box Coordinates:
|Spatial Coverage Map:
- Digital Elevation Model
- Digital Terrain Model
- Point cloud data
- United States
- Baltimore County
| Use Constraints
|| No constraint information available
|| Fee information not available.
|| Lineage statement not available.
| 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 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: 2013-01-22
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