Metadata for LiDAR Ground Return Data, Flathead Basin, Montana 2009

- Identification Information
- Data Quality Information
- Spatial Reference Information
- Entity and Attribute Information
- Distribution Information
- Metadata Reference Information

Identification Information:

Citation:
  Originator: Watershed Sciences, Inc.
  Publication date: 11/16/2010
  Title: LiDAR Ground Return Data, Flathead Basin, Montana 2009
  Publication place: Helena, MT
  Publisher: Montana State Library
  Online linkage: http://nris.mt.gov/Flathead_2009
Abstract:
  These data files are the "ground return" LiDAR point cloud data collected in the Flathead Basin, Montana, between September 22 and September 29, 2009. The study area includes the Flathead Valley floor, the area around Polson, and the shorelines of Flathead Lake, Whitefish Lake, and Swan Lake. This data only includes points that were identified as being on the ground surface - all structures and vegetation have been removed.
  The data is in LiDAR LAS format, as described at http://www.asprs.org/society/committees/standards/lidar_exchange_format.html
  The horizontal coordinate system of the data is Montana State Plane Coordinates, NAD83 HARN, and the units are U.S. Survey Feet. The vertical Datum is NAVD88 (Geoid03).
  The contractor's report giving a complete explanation of the data collection and quality control processes is at http://nris.mt.gov/Flathead_2009/Reports.asp.
Purpose:
  Provide high resolution terrain elevation and land cover elevation data.
Time period of content:
  Beginning date: 09/22/2009
  Ending date: 09/29/2009
  Currentness reference: ground condition
Status:
  Progress: Complete
  Maintenance and update frequency: None planned
Access constraints: None
Use constraints:
  This data set is provided "as-is" without warranty of any kind. The user assumes responsibility to determine the suitablilty of the data for their purposes. The State Library makes no representations or warranties whatsoever with respect to the accuracy or completeness of this data set and assumes no responsibility for the suitability of this data set for a particular purpose; and the Library will not be liable for any damages incurred as a result of errors in this data set.
Point of contact:
  Stephen Story
  Montana Department of Natural Resources and Conservation
  PO Box 201601
  1424 9th Ave.
  Helena, MT 59620-1601
  Telephone: 406-444-6664
  E-Mail: sestory@mt.gov

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Data Quality Information:

Logical consistency report:
  LiDAR flight lines have been examined to ensure that there was at least 50% sidelap, there are no gaps between flightlines, and overlapping flightlines have consistent elevation values.
  Shaded relief images have been visually inspected for data errors such as pits, border artifacts, gaps, and shifting. The data was examined at a 1:2000 scale.
Quantitative horizontal positional accuracy assessment:
  Horizontal positional accuracy explanation: See LiDAR data report.
Quantitative vertical positional accuracy assessment:
  Vertical positional accuracy value: RMSE = 0.118 feet (0.036 meters)
  Vertical positional accuracy explanation:
    The Root Mean Square Error (RMSE) of the data set is 0.118 feet (0.036 meters). Accuracy was assessed using 4229 ground survey (real time kinematic) points. Please see LiDAR data report for a discussion of statistics related to these datasets.
Lineage:
  Process step:
    The LiDAR data was collected from September 22nd - 29th, 2009. The survey used a Leica ALS50 Phase II laser system, with a scan angle of plus or minus 15 degrees from nadir with a pulse rate designed to yield an average native density of at least 4 points per square meter over terrestrial surfaces. The study area was surveyed with an opposing flight line side-lap of at least 50 percent to reduce laser shadowing and increase surface laser painting. The system allows up to 4 range measurements (returns) per pulse, and all discernable returns were processed for the output dataset.
    To accurately solve for laser point position, the positional coordinates of the airborne sensor and the attitude of the aircraft were recorded continuously throughout the LiDAR data collection mission. Aircraft position was measured twice per second by an onboard differential GPS unit. Aircraft attitude ws measured 200 times per second from an onboard inertial mesasurement unit. To allow for post processing correction and calibration, aircraft/sensonr position and attitude data are indexed by GPS time.
  Process contact:
    Watershed Sciences
    257B SW Madison Ave
    Corvallis, OR 97333
    Telephone: 541-752-1204
    E-Mail: watershedsciences.com
  Process step:
    Laser point coordinates were computed using the IPAS and ALS Post Processor software suites based on independent data from the LiDAR system (pulse time, scan angle), and aircraft trajectory data (SBET). Laser point returns (first through fourth) were assigned an associated (x, y, z) coordinate along with unique intensity values (0-255). The data were output into large LAS v. 1.2 files; each point maintains the corresponding scan angle, return number (echo), intensity, and x, y, z (easting, northing, and elevation) information.
    These initial laser point files were too large for subsequent processing. To facilitate laser point processing, bins (polygons) were created to divide the dataset into manageable sizes (less than 500 MB). Flightlines and LiDAR data were then reviewed to ensure complete coverage of the survey area and positional accuracy of the laser points.
    Laser point data were imported into processing bins in TerraScan, and manual calibration was performed to assess the system offsets for pitch, roll, heading and scale (mirror flex). Using a geometric relationship developed by Watershed Sciences, each of these offsets was resolved and corrected if necessary.
    LiDAR points were then filtered for noise, pits (artificial low points), and birds (true birds as well as erroneously high points) by screening for absolute elevation limits, isolated points and height above ground. Each bin was then manually inspected for remaining pits and birds and spurious points were removed. In a bin containing approximately 7.5-9.0 million points, an average of 50-100 points are typically found to be artificially low or high. Common sources of non-terrestrial returns are clouds, birds, vapor, haze, decks, brush piles, etc.
    Internal calibration was refined using TerraMatch. Points from overlapping lines were tested for internal consistency and final adjustments were made for system misalignments (i.e., pitch, roll, heading offsets and scale). Automated sensor attitude and scale corrections yielded 3-5 cm improvements in the relative accuracy. Once system misalignments were corrected, vertical GPS drift was then resolved and removed per flight line, yielding a slight improvement (less than 1 cm) in relative accuracy.
    The TerraScan software suite is designed specifically for classifying near-ground points (Soininen, 2004). The processing sequence began by removing all points that were not near the earth based on geometric constraints used to evaluate multi-return points. The resulting bare earth (ground) model was visually inspected and additional ground point modeling was performed in site-specific areas to improve ground detail. This manual editing of grounds often occurs in areas with known ground modeling deficiencies, such as: bedrock outcrops, cliffs, deeply incised stream banks, and dense vegetation. In some cases, automated ground point classification erroneously included known vegetation (i.e., understory, low/dense shrubs, etc.). These points were manually reclassified as non-grounds.
  Process contact:
    Watershed Sciences
    257B SW Madison Ave
    Corvallis, OR 97333
    Telephone: 541-752-1204
    E-Mail: watershedsciences.com

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Spatial Reference Information:

Horizontal coordinate system definition:
  Projected coordinate system name: NAD_1983_HARN_StatePlane_Montana_FIPS_2500_Feet_US
  Map projection:
    Map projection name: Lambert Conformal Conic
    Lambert conformal conic:
    Lambert Conformal Conic
    Standard parallel: 45.000000
    Standard parallel: 49.000000
    Longitude of central meridian: -109.500000
    Latitude of projection origin: 44.250000
    False easting: 1968500.000000
    False northing: 0.000000
  Planar distance units: U.S. Survey Feet
  Geodetic model:
    Horizontal datum name: D_North_American_1983_HARN
    Ellipsoid name: Geodetic Reference System 80
    Semi-major axis: 6378137.000000
    Denominator of flattening ratio: 298.257222
Altitude system definition:
  Altitude datum name: NAVD88 (Geoid 03)
  Altitude distance units: U.S. Survey Feet

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Entity and Attribute Information:

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Distribution Information:

Distributor:
  Montana State Library
  PO Box 201800
  Helena, MT 59620-1800
  Telephone: 406-444-5355
  E-Mail: nris@mt.gov
Resource description: Downloadable Data
Standard order process:
  Digital form:
    Online option:
    http://nris.mt.gov/flathead_2009

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Metadata Reference Information:

Metadata date: 12/01/2010
Metadata contact:
  Watershed Sciences, Inc.
  257 B SW Madison Ave
  Corvallis, OR 97333
  Telephone: 541-752-1204
  E-Mail: watershedsciences.com

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