Lower Columbia River 2005 -  LIDAR Metadata

Metadata also available as


Originator: Kitsap County, et al
Publication_Date: N/A (not published)
Title: Lower Columbia River 2005 LIDAR Metadata
Geospatial_Data_Presentation_Form: Raster digital data
Online_Linkage: www.pugetsoundlidar.org
<>The data covers areas in the Lower Columbia River in Washignton and Oregon.  The data was delivered in Washignton State Plane South, NAD83 HARN, feet.  The all returns ASCII files contain the X,Y,Z values of all the LiDAR returns collected during the survey mission. In addition each return also has a time stamp, return number, ellipsoidal height and scan angle. The bare earth ASCII files contain the X,Y,Z values of returns classified as the ground.  The elevation values are in feet.  TerraPoint surveyed and created this data for the Puget Sound LiDAR Consortium under contract.
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The LiDAR ASCII files can be used to create DEM and also to extract topographic data in software that does not support raster data. Other surface features can also be extracted with custom applications. This high accuracy data can be used at scales up to 1:12000 (1 inch = 1,000 feet). LiDAR data has a wide range of uses such as earthquake hazard studies, hydrologic modeling, forestry, coastal engineering, roadway and pipeline engineering, flood plain mapping, wetland studies, geologic studies and a variety of analytical and cartographic projects.
The data is broken down into USGS quarter quads and then into 25 tiles within each quarter quad. A quarter quad index and tile index is available at www.pugetsoundlidar.org.
Beginning_Date: January 10, 2005
Ending_Date: February 20, 2005
Currentness_Reference: ground condition
Progress: Complete
Maintenance_and_Update_Frequency: None planned
Theme_Keyword_Thesaurus: none
Theme_Keyword: Digital Elevation Model
Theme_Keyword: LIDAR
Theme_Keyword: DEM
Theme_Keyword: LAND SURFACE
Theme_Keyword: TOPOGRAPHY
Theme_Keyword: LANDFORMS
Theme_Keyword: 7.5-MINUTE DEM
Theme_Keyword: RASTER
Theme_Keyword: WASHINGTON
Theme_Keyword: OREGON
Place_Keyword: WASHINGTON
Place_Keyword: OREGON

Access_Constraints: None
Considerable care has been taken to see that these data and derived images are as accurate as possible. We believe most of the data is adequate for determination of flood hazards, for geologic mapping, for hydrologic modeling, for determination of slope angles, for modeling of radio-wave transmission, and similar uses with a level of detail appropriate to a horizontal scale of 1:12,000 (1 inch = 1,000 feet) or smaller and vertical accuracy on the order of a foot. Locally, the data is of considerably poorer quality.

In the bare earth DEMs where there are few survey points (i.e. bare-earth surfaces in heavy timber, where there are few ground reflections), TINing the points produces large triangular facets where the surface has significant curvature. Similar, though finer, textures are evident where vegetation reflections are incompletely filtered. Elevations are likely to be less accurate in these areas.

Top surface DEMs where project areas meet may have different vegetation heights. Survey projects are flown during winter leaf-off season; therefore adjacent project areas may be 1 or more years apart. Since vegetation is in a state of constant change it is expected to have differing vegetation heights in these areas.

LiDAR data values for water surfaces are not valid elevation values. Lidar surveying produces few survey points on water. Mirror-like surfaces fail to scatter the laser beam and unless the beam is perpendicular to the surface, no light is reflected back to the detector. Or intense reflections may lead to negative blunders, points that are too low. Interpolation between the nearest on-land points and sparse water points produces large triangular facets that may not accurately reflect the water-surface elevation. Where the water surface is surveyed adequately, adjacent swaths may be flown at different tide stages, producing swath-parallel cliffs.

User should carefully determine the place-to-place accuracy and fitness of these data for your particular purposes. For many purposes a site- and use-specific field survey will be necessary.

 Acknowledgement of the originating agencies would be appreciated in products derived from these data.
Contact_Person: Diana Martinez
Contact_Organization: Puget Sound Regional Council
Contact_Position: GIS Analyst
Address_Type: mailing and physical address
Address: 1011 Western Ave
Address: Suite 500
City: Seattle
State_or_Province: WA
Postal_Code: 98104
Country: US
Contact_Voice_Telephone: 206-587-5062
Contact_Electronic_Mail_Address: dmartinez@psrc.org
Please credit the Puget Sound LiDAR Consortium (PSLC) for these data. The PSLC is supported by the Puget Sound Regional Council, the National Aeronautical and Space Administration (NASA), the United States Geological Survey (USGS) and numerous partners in local, state, and tribal government.
ArcView, Microstation, TerraScan, TerraModeler, TerraModel, Terrapoint proprietary LiDAR processing software, ArcInfo 8.3

Completeness_Report: Contains only data in ArcInfo Interchange format.
Puget Sound Lidar Consortium evaluates vertical accuracy with two measures: internal consistency and conformance with independent ground control points.

Internal Consistency: Data are split into swaths (separate flightlines), a separate surface is constructed for each flightline, and where surfaces overlap one is subtracted from another. Where both surfaces are planar, this produces a robust measure of the repeatability, or internal consistency, of the survey. The average error calculated by this means, robustly determined from a very large sample, should be a lower bound on the true error of the survey as it doesn't include errors deriving from a number of sources including: 1) inaccurately located base station(s), 2) long-period GPS error, 3) errors in classification of points as ground and not-ground (post-processing), 4) some errors related to interpolation from scattered points to a continous surface (surface generation).

Conformance with independent ground control points: Bare-earth surface models are compared to independently-surveyed ground control points (GCPs) where such GCPs are available. The purpose of the ground control evaluation is to assess that the bare earth DEMs meet the vertical accuracy specification in the PSLC contract with TerraPoint:

"The accuracy specification in the contract between the Puget Sound LiDAR Consortium and TerraPoint is based on a required Root Mean Square Error (RMSE) 'Bare Earth' vertical accuracy of 30 cm for flat areas in the complete data set. This is the required result if all data points in flat areas were evaluated. Because only a small sample of points is evaluated, the required RMSE for the sample set is adjusted downward per the following equation from the FEMA LiDAR specification (adjusted from the 15 cm RMSE in the FEMA specification to 30 cm to accommodate the dense vegetation cover in the Pacific Northwest)."

During this step, the bare earth DEMs were compared with existing survey benchmarks. The differences between the LiDAR bare earth DEMs and the survey points are calculated and the final results are first summarized in a graph that illustrates how the dataset behaves as whole. The graph illustrates how close the DEM elevation values were to the ground control points. The individual results were aggregated and used in the RMSE calculations. The results of the RMSE calculations are the measure that makes the data acceptable for this particular specification in the contract.

Production Narrative: DEMs were derived from LIDAR data. Selected linear features (break lines) such as, but not limited to, roads, railroad tracks and levees were profiled for addition to the DEM coverages in selected areas. Detailed profile surveys of these features were performed as necessary to complete mapping coverages. These surveys were required to obtain a higher accuracy DEM than that obtained from the photogrammetric DEM compilation alone. 
Other relevant production information: 1. Max PDOP allowed during LIDAR data collection: 7.0 2. Max distance from GPS ground stations during data collection: 60km 3. Flight height: 3,250 feet, nominal AGL 4. Swath Width: 18 degrees from nadir (36 degrees total swath) 5. Distance between flight lines: 50% sidelap (200% coverage) 6. Type of Scanner: TerraPoint ALTMS 2536 7. Calibration: Surveyed airport locations at beginning and end of flight missions 8. Number of scanner returns per pulse: Four 9. Nominal post spacing: Processed data is 6 foot posts (see step 10) 10. Post Collection Processing: a) top surface DEM as 6 foot ESRI GRID, b) bare earth DEM as 6 foot ESRI GRID (points classified as trees, buildings, errors, etc. removed) c) ASCII file of points used in bare earth GRID d) ASCII file of all points 11. Results of Accuracy Testing: <30 cm RMSE (vertical).


PSLC LiDAR ASCII data is broken down into USGS quarter quads.  ASCII data is further broken down into 25 tiles per quarter quad.  Each quarter quadrangle is subdivided into a 5 x 5 array of tiles organized from upper-left to lower-right as follows:
01 02 03 04 05
06 07 08 09 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
The two-digit tile number is appended to the end of the file name.
See index files in PSLC website for further reference.
Direct_Spatial_Reference_Method: Point

Grid_Coordinate_System_Name: State Plane Coordinate System
SPCS_Zone_Identifier: Washington South, FIPS 4602
Standard_Parallel: 45.833333
Standard_Parallel: 47.333333
Longitude_of_Central_Meridian: -120.500000
Latitude_of_Projection_Origin: 45.333333
False_Easting: 1640416.666667
False_Northing: 0.000000
Planar_Coordinate_Encoding_Method: coordinate pair
Planar_Distance_Units: survey feet
Horizontal_Datum_Name: North American Datum of 1983 with 1998 Adjustments (HARN)
Ellipsoid_Name: Geodetic Reference System 80
Semi-major_Axis: 6378137.000000
Denominator_of_Flattening_Ratio: 298.257222
Altitude_Datum_Name: North American Vertical Datum of 1988
Altitude_Distance_Units: feet

The bare earth ASCII files are fixed width and have no header records.   Each file has the following 3 fields: easting, northing,  orthometric_elevation.

The All-returns ASCII files are fixed width and have no header records.
Each file consists of one fixed length record for each laser return.
The records each consist of 10 fields:

Parameter Field Width
Read As
gps_week 4
long integer
gps_second_of_week 13
double precision float
easting 11
double precision float
double precision float
orthometric_elevation 9
double precision float
number_of_returns 2
return_number 2
long integer
classification 2

An example of a data record is:
1205 174436.50828 6151368.67 2011080.93     3.14 1 5  16.64    43 G

GPS_week and GPS_second_of_week refer to the time of the laser pulse transmission.
Easting, (in survey feet), northing (in survey feet), and orthometric_elevation
(in survey feet) refer to the location of the return.
Up to four returns can be recorded per laser pulse; number_of_returns is the
total returns for a pulse (up to a maximum of 4). Return_number is assigned as a
number from 1 to 7 in a scheme that identifies which return is the last return
recorded for a pulse:
1 first return with subsequent returns detected
2 second return with subsequent returns detected
3 third return with subsequent returns detected
4 fourth return
5 first return with no subsequent returns detected
6 second return with no subsequent returns detected
7 third return with no subsequent returns detected

Angle_off_nadir refers to the orientation of the laser pulse vector, combining
scan mirror and aircraft orientations.
Intensity is an uncalibrated measure of received energy for the return.
Classification of each return was implemented by TerraPoint using the TerraScan
software developed by TerraSolid.  Returns are classified as:
B Blunder; anomalous return above or below return point cloud
G Ground or water; the "bald Earth" surface
V Vegetation
S Building/Structure

Contact_Organization: Puget Sound LiDAR Consortium / Puget Sound Regional Council
Contact_Person: Diana Martinez
Contact_Position: GIS Analyst
Address_Type: mailing and physical address
Address: 1011 Western Ave., Suite 500
City: Seattle
State_or_Province: WA
Postal_Code: 98126
Country: USA
Contact_Voice_Telephone: 206 587-5062
Contact_Electronic_Mail_Address: dmartinez@psrc.org
The data is in the Public Domain and it is free of charge.

The PSLC has 4 different products available:

1. Bare earth DEM - these are in ArcInfo interchange format (.e00). These files are a representation of the ground surface. All vegetation and man-made structures have been removed. These files are about 35 MB compressed and about 110 Mb uncompressed.

2. Top surface DEM - these are in ArcInfo interchange format (.e00). These files are a representation of the top surface when the area was flown. You can see vegetation, buildings, bridges, etc. These files are about 35 MB compressed and about 110 Mb uncompressed.

3. Bare earth ASCII data - these files are plain text files with X,Y,Z values. The points in this file are all the returns classified as a ground return. The bare earth DEMs are derived from these ASCII files. These files are about 35 MB compressed and about 110 Mb uncompressed.

4. All-returns ASCII data - these files are plain text files with X,Y,Z values and also additional values such as GPS time, return number, etc. These files are very large, about 2 GB per USGS quarter quad.

Format_Name: ASCII, zip or gzip compressed
Fees: none
Bare earth DEMs and top surface DEMs are available for download in the Puget Sound LiDAR Consortium website, www.pugetsoundlidar.org.

The All-returns ASCII and bare earth ASCII files are available upon request to the Puget Sound LiDAR Consortium. This data is too large to put online, but it is still in the public domain and therefore interested users may obtain it free of charge. Depending on the amount of data requested, the user would receive a CD-ROM or a DVD-ROM. Other arrangements are also possible and will be evaluated on an individual basis.

Custom_Order_Process: Contact distributor for more information.

Metadata_Date: 20060620
Contact_Person:Diana M. Martinez 
Contact_Organization: Puget Sound Regional Council
Contact_Position: GIS Analyst
Address_Type: mailing address
Address: 1011 Western Ave, Suite 500
City: Seattle
State_or_Province: WA
Postal_Code: 98126
Country: USA
Contact_Voice_Telephone: 206 587-5062
Contact_Electronic_Mail_Address: dmartinez@psrc.org
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: FGDC-STD-001-1998
Metadata_Time_Convention: local time
Online_Linkage: <http://www.esri.com/metadata/esriprof80.html>
Profile_Name: ESRI Metadata Profile