Link to USGS home pageBlue spacerBay image

Topographic Lidar Survey: South San Francisco Bay, CA

Metadata also available as - [Outline] - [Parseable text] - [XML]

Frequently-anticipated questions:


What does this data set describe?

Title: Topographic Lidar Survey: South San Francisco Bay, CA
Abstract:
The California Coastal Conservancy, in conjunction with other state and federal agencies, is collaboratively managing an effort to restore approximately 61 km2 (15,100 acres) of commercial salt evaporation ponds in South Bay to mixed intertidal habitat. In order to best develop restoration strategies, as well as to track morphologic change throughout the restoration process, a topographic lidar survey was conducted in May of 2004. The survey collected more than 250 million elevation points in a 334 km2 area extending from just south of the San Francisco and Oakland airports to the Alviso salt ponds.
Supplemental_Information:
Information for USGS Coastal and Marine Geology related activities are online at <http://walrus.wr.usgs.gov/infobank/f/f204sf/html/f-2-04-sf.meta.html>.
  1. How should this data set be cited?

    United States Geological Survey (USGS) and the California Coastal Conservancy (CCC), 2005, Topographic Lidar Survey: South San Francisco Bay, CA:.

    This is part of the following larger work.

    Jaffe, Bruce, 2005, Topographic Lidar Survey: South San Francisco Bay, CA: Scientific Investigation Map 2007-XXXX, U.S. Geological Survey, Coastal and Marine Geology Program, Menlo Park, CA.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.0
    East_Bounding_Coordinate: -121.0
    North_Bounding_Coordinate: 38.0
    South_Bounding_Coordinate: 37.0

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 05-May-2004
    Ending_Date: 21-May-2004
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: map

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Raster data set. It contains the following raster data types:

      • Dimensions, type Point

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 10
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -123.00000
      Latitude_of_Projection_Origin: 0.00000
      False_Easting: 0.00
      False_Northing: 0.00

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 1.0
      Ordinates (y-coordinates) are specified to the nearest 1.0
      Planar coordinates are specified in Meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is NAVD88.
      The semi-major axis of the ellipsoid used is 6378137.00.
      The flattening of the ellipsoid used is 1/0.003352811.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    All LiDAR Data Products were delivered on DVD-ROM. Three copies were provided. All products other than hill-shade data were provided in 1k and 2k tiles with a 25-meter buffer. Hill-shades were delivered in three large areas.

    Full Feature or All Return Point Data

    Data delivered in ASCII, comma delimited files with one record per return containing data columns. The records are ordered sequentially according to Easting with no duplicate records. The individual returns are classified into the following categories: ground or water, above ground (low), above ground (high), building and NADIR. This ASCII product was generated using an in house custom utility. The process involved extracting a Terrascan Binary file packed with the scan angle and the extra precision required for the for a unique time stamp.

    Bare Earth Point Data

    Data delivered in ASCII, comma delimited files with one record per return containing data columns as defined in Table 4. The records are ordered sequentially according to Easting with no duplicate records. This product is a subset of the full feature or all return point data product containing only code 3, ground points, as described in table 5 below. This ASCII product was generated using an in house custom utility. The process involved extracting a Terrascan Binary file packed with the scan angle and the extra precision required for the for a unique time stamp.

    The above description is taken from the TerraPoint USA Project Report: USGS - South Bay Restoration Project, Contract #2206-H

    Entity_and_Attribute_Detail_Citation: none


Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    Bruce Jaffe
    U.S. Geological Survey, Coastal and Marine Geology
    Oceanographer
    400 Natural Bridges Dr
    Santa Cruz, CA 95060-5792
    USA

    (831) 427-4742 (voice)
    (831) 427-4748 (FAX)
    bjaffe@usgs.gov


Why was the data set created?

The purpose of the lidar mapping was to provide a high quality DEM for drainage mapping and salt pond restoration for the USGS.


How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: 27-Oct-2004 (process 1 of 1)
    The topographic lidar data was collected by TerraPoint USA from May 5 to 21, 2004. Twenty-five flights were required to cover the project area with approximately one hundred thirty six flight lines. The control network and check point surveys were established from April 30 to May 20, 2004. Boresight correction, vegetation removal and product generation took place from June 3 to October 27, 2004.

    The GPS and inertial data were processed in tandem to achieve the best positional result. Once the position and attitude of the aircraft were known at each epoch (1-second intervals), then these data were integrated with the laser ranges to provide a position for each data point on the ground. The data were then processed using TerraPoint's proprietary laser processing software suite to produce coordinates. Each flight involved setting up two base stations to collect data. Utilizing two base stations ensures GPS data collection in the event that the main base station fails. For all flights the GPS data were of high quality. This minimized the absolute error for the aircraft position. The primary quality control tool for the laser ranges is the percentage of returns that are received back at the laser after it has emitted a signal. The acceptable range for returns, typically between 90% and 95% was met for this project. Lower percentages are normal over water and other poor reflectivity surfaces such as the dark, wet surfaces typical of the project area's mud flats.

    The points are generated as Terrascan binary Format using Terrapoint's proprietary Laser Postprocessor Software. This software combines the Raw Laser file and GPS/IMU information to generate a point cloud for each individual flight.

    All the point cloud files encompassing the project area were then divided into 2 kilometer by 2-kilometer tiles. The referencing system of these tiles is based upon the project boundary minimum and maximums. This process is carried out in Terrascan.

    The bald earth is subsequently extracted from the raw LiDAR points using Terrascan in a Microstation environment. The automated vegetation removal process takes place by building an iterative surface model. This surface model is generated using three main parameters: Building size, Iteration angle and Iteration distance.

    The initial model is based upon low points selected by a roaming window and are assumed to be ground points. The size of this roaming window is determined by the building size parameter. These low points are triangulated and the remaining points are evaluated and subsequently added to the model if they meet the Iteration angle and distance constraints (fig. 1). This process is repeated until no additional points are added within an iteration.

    There is also a maximum terrain angle constraint that determines the maximum terrain angle allowed within the model.

    Once the data setup has taken place the manual quality control of the surface occurs. This process consists of visually examining the LiDAR points within Terrascan and correcting errors that occurred during the automated process. These corrections include verifying that all non ground elements, such as vegetation and buildings are removed from the ground model and that all small terrain undulations such as road beds, dykes, rock cuts and hill tops are present within the model.

    This process is done with the help of hillshades, contours, profiles and crosssections. To correct misclassifications, a full suite of Terrascan and custom in-house data tools are used.

    The above description is taken from the TerraPoint USA Project Report: USGS - South Bay Restoration Project, Contract #2206-H

    Person who carried out this activity:

    Bruce Jaffe
    U.S. Geological Survey, Coastal and Marine Geology
    Oceanographer
    400 Natural Bridges Dr
    Santa Cruz, CA 95060-5792
    USA

    (831) 427-4742 (voice)
    (831) 427-4748 (FAX)
    bjaffe@usgs.gov

  3. What similar or related data should the user be aware of?


How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

    +/- 20 - 60 centimeters on all but extremely hilly terrain.

  3. How accurate are the heights or depths?

    +/- 10-15 centimeters on Hard Surfaces (roads and buildings), +/- 15-25 centimeters on Soft/Vegetated Surfaces (flat to rolling terrain), +/- 25-40 centimeters on Soft/Vegetated Surfaces (hilly terrain)

  4. Where are the gaps in the data? What is missing?

    Complete

  5. How consistent are the relationships among the observations, including topology?

    Unspecified


How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:
Public domain data from the U.S. government is freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) and the California Coastal Conservancy (CCC) as the source of this information.

  1. Who distributes the data set? (Distributor 1 of 1)

    San Francisco Estuary Institute
    7770 Pardee Lane
    Oakland, CA 94621-1424
    USA

    (510) 746-7361 (voice)

  2. What's the catalog number I need to order this data set?

  3. What legal disclaimers am I supposed to read?

    These data not intended for navigational purposes.

    Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, these data and information are provided with the understanding that they are not guaranteed to be usable, timely, accurate, or complete. Users are cautioned to consider carefully the provisional nature of these data and information before using them for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences. Conclusions drawn from, or actions undertaken on the basis of, such data and information are the sole responsibility of the user.

    Neither the U.S. Government nor any agency thereof, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any data, software, information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights.

    Trade, firm, or product names and other references to non-USGS products and services are provided for information only and do not constitute endorsement or warranty, express or implied, by the USGS, USDOI, or U.S. Government, as to their suitability, content, usefulness, functioning, completeness, or accuracy.

  4. How can I download or order the data?


Who wrote the metadata?

Dates:
Last modified: 21-Aug-2007
Metadata author:
U.S. Geological Survey, Coastal and Marine Geology
c/o Peter Dartnell
Physical Scientist
345 Middlefield Rd MS-999
Menlo Park, CA 94025-3561
USA

(650) 329-5460 (voice)
(650) 329-5411 (FAX)
pdartnell@usgs.gov

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)


Accessibility   |   FOIA   |   Privacy   |   Policies and Notices
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/of/2007/XXXX/
Maintained by: Mike Diggles
Page last modified and
Generated by mp version 2.8.11 on Thu Sep 6 13:46:55 2007