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

Identification Information
Data Quality Information
Spatial Reference Information
Distribution Information
Metadata Reference Information

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Identification Information:

Citation:

Originator: Watershed Sciences, Inc.
Publication date: 11/16/2010
Title: LiDAR All Return Data, Flathead Basin, Montana 2009
Online linkage: http://geoinfo.montanastatelibrary.org/data/flatheadbasin_mapping_project_2009/lidar/all_returns/

Abstract:

These data files are the "all return" (including structures and vegetation) 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. The points are classified as 1 (Default) or 2 (Ground).

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://geoinfo.montanastatelibrary.org/data/flatheadbasin_mapping_project_2009/reports_documents.

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:

The Montana State Library provides this product/service for informational purposes only. The Library did not produce it for, nor is it suitable for legal, engineering, or surveying purposes. Consumers of this information should review or consult the primary data and information sources to ascertain the viability of the information for their purposes. The Library provides these data in good faith but does not represent or warrant its accuracy, adequacy, or completeness. In no event shall the Library be liable for any incorrect results or analysis; any direct, indirect, special, or consequential damages to any party; or any lost profits arising out of or in connection with the use or the inability to use the data or the services provided. The Library makes these data and services available as a convenience to the public, and for no other purpose. The Library reserves the right to change or revise published data and/or services at any time.

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

Data Quality Information:

Logical consistency report:

LiDAR flight lines have been examined to ensure that there was at least 50 percent 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 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.

Spatial Reference Information:

Horizontal coordinate system definition:

Grid coordinate system name: State Plane Coordinate System

SPCS zone identifier: 2500

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: 600000.000000
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

Distribution Information:

Distributor:

Montana State Library
PO Box 201800
Helena, MT 59620-1800
Telephone: 406-444-5354
E-Mail: geoinfo@mt.gov

Resource description: Downloadable Data

Distribution liability:

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Metadata Reference Information:

Metadata date: 11/01/2013

Metadata review 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