Identification_Information:
  Citation:
    Citation_Information:
      Title: 20120903_West.xyzi
      Geospatial_Data_Presentation_Form: vector digital data
  Description:
    Abstract: Topographic survey data of areas on Dauphin Island on the Alabama coast were collected using a truck-mounted mobile terrestrial light detection and ranging system. This system is comprised of a high frequency laser scanner in conjunction with an inertial measurement unit and a position and orientation computer to produce highly accurate topographic datasets. A global positioning system base station was setup on a nearby benchmark and logged vertical and horizontal position information during the survey for post-processing. Survey control points were also collected throughout the study area to determine residual errors. Data were collected five days after Hurricane Isaac made landfall in early September 2012 to document sediment deposits prior to clean-up efforts. Three data files in ASCII format with the extension .xyzi are included in this report, and each is named according to both the acquisition date and the relative geographic location on Dauphin Island (for example, 20120903_Central.xyzi). Metadata are also included for each of the files in both .xml and ASCII text format. These topographic data can be used to analyze the effects of storm surge on barrier island environments and also serve as a baseline dataset for future change detection analyses.
    Purpose: The purpose of this project was to provide topographic survey data of selected sites along Dauphin Island in Mobile County, Alabama, after Hurricane Isaac in September 2012.
    Supplemental_Information: Additional information about field techniques and data collection procedures can be found by contacting Dustin R. Kimbrow, USGS Alabama Water Science Center, 75 Technacenter Dr., Montgomery, AL, 36117.
  Status:
    Maintenance_and_Update_Frequency: None planned
  Spatial_Domain:
    Bounding_Coordinates:
      West_Bounding_Coordinate: -88.192
      East_Bounding_Coordinate: -88.076
      North_Bounding_Coordinate: 30.252
      South_Bounding_Coordinate: 30.248
  Keywords:
    Theme:
      Theme_Keyword_Thesaurus: ISO 19115 Topic Categories
      Theme_Keyword: elevation
      Theme_Keyword: geoscientificInformation
      Theme_Keyword: inlandWaters
      Theme_Keyword: location
    Theme:
      Theme_Keyword_Thesaurus: None
      Theme_Keyword: elevation
      Theme_Keyword: geoscientificInformation
      Theme_Keyword: inlandWaters
      Theme_Keyword: LiDAR
      Theme_Keyword: mobile mapping
      Theme_Keyword: topography
      Theme_Keyword: geoscientific information
      Theme_Keyword: 2012
      Theme_Keyword: laser scanning
      Theme_Keyword: United States
      Theme_Keyword: Alabama
      Theme_Keyword: U.S. Geological Survey
  Access_Constraints: None
  Use_Constraints: The U.S. Geological Survey requests to be acknowledged as the originator of these data in future products or derivative research.
  Point_of_Contact:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: U.S. Geological Survey, Alabama Water Science Center
        Contact_Person: Dustin R. Kimbrow
      Contact_Position: Geographer
  Data_Set_Credit: Acknowledgment of the U.S. Geological Survey, Alabama Water Science Center, as a data source would be appreciated in products developed from these data, and such acknowledgment as is standard for citation and legal practices for data source is expected. Sharing of new data layers developed directly from these data would also be appreciated by the U.S. Geological Survey staff. Users should be aware that comparisons with other datasets for the same area from other time periods may be inaccurate due to inconsistencies resulting from changes in photointerpretation, mapping conventions, and digital processes over time. These data are not legal documents and are not to be used as such
  Security_Information:
    Security_Classification: Unclassified
Data_Quality_Information:
  Logical_Consistency_Report: This report provides topographic data in ASCII text format with the extension .xyzi. The horizontal XY coordinates have been positioned in the North American Datum of 1983, Universal Transverse Mercator, Zone 16 North coordinate system. The vertical Z values are referenced to the NAVD88 vertical reference system using geoid model GEOID09 (National Geodetic Survey, 2013). The intensity (I) values represent the amount of near-infrared reflectance received by the T-LiDAR instrument, and range from 0 to 255. Three data files are included in this report, and each is named according to both the acquisition date and the relative geographic location on Dauphin Island (for example, 20120903_Central.xyzi). Metadata are also included for each of the files in ASCII text and .xml format.
  Completeness_Report: Typical resolution of the point cloud dataset is 1.0 meters however there are some areas in the dataset where resolution is greater or less.
  Positional_Accuracy:
    Horizontal_Positional_Accuracy:
      Horizontal_Positional_Accuracy_Report: Horizontal coordinate RMS error is +/- 0.05 m.
    Vertical_Positional_Accuracy:
      Vertical_Positional_Accuracy_Report: Vertical coordinate RMS error is +/- 0.10 m.
  Lineage:
    Process_Step:
      Process_Description:
        T-LiDAR technology uses laser pulses that are sent from the instrument and reflected off objects within its field of view. The instrument calculates the distance of each returned laser pulse on the basis of the velocity of the pulse, while also logging the vertical and horizontal angle of each pulse (Kimbrow and Lee, 2013). Topographic survey data were collected in September 2012 using a mobile T-LiDAR system which includes an Optech ILRIS HD-ER-MC instrument (Optech, 2013) in conjunction with an Applanix position and orientation system (POSMV) (Applanix, 2013). The Optech HD-ER-MC has a laser repetition rate of 10 kilohertz and a laser wavelength of 1,535 nanometers, which falls within the near-infrared portion of the electromagnetic spectrum. The POSMV is comprised of two global positioning system (GPS) receivers, an inertial measurement unit (IMU), and a position and orientation computer. The mobile T-LiDAR system requires a rigorous calibration procedure before accurate datasets can be generated. All instrumentation, must first be surveyed, and their relative positions (lever arms) must be resolved with respect to the origin point of the IMU. Next, a boresight procedure is performed in order to determine the angular differences (that is, roll, pitch, and heading) between the IMU and the T-LiDAR instrument. This process involves surveying at least three targets with traditional methods, and then scanning those targets with the mobile T-LiDAR system from a static position. Optech MatchView software is then used to derive the angular differences, and it outputs a boresight calibration file. The boresight parameter file typically requires additional iterative adjustments to produce the most accurate results.     
        For this survey, the T-LiDAR instrument was mounted on top of a truck, facing toward both the rear and passenger side of the truck, and scanned the road surface and adjacent shoulder at speeds of less than 10 kilometers (km) per hour. The POSMV system collected attitude and trajectory information during the survey, and these data were later post-processed using Applanix POSPac MMS software with GPS data from a base station that was setup on a nearby benchmark. The POSPac MMS software uses differential correction algorithms to compute a smoothed best estimate of trajectory (SBET) file. The SBET file is then applied to the raw T-LiDAR data along with the boresight parameter file using Optech Parser software to produce a geo-referenced point-cloud dataset. Thirty-eight additional topographic data points were collected for survey control using a real-time kinematic global positioning system (RTK-GPS) unit. The RTK-GPS survey campaign followed the quality standards of a USGS Level IV survey (Rydlund and Densmore, 2012). These control points (cross-sections of road, points along curbs, and fire hydrants) were evenly distributed throughout the survey site and were also visible within the point-cloud dataset. The RTK-GPS control points were compared to data points within the T-LiDAR point-cloud, and the residual error was computed. The horizontal and vertical error for this survey was +/- 0.05 m and +/-0.10 m, respectively. Typical point spacing of these data are less than 1 meter, however the T-LiDAR instrument collects data from a horizontal perspective, so point spacing may be more or less due to data shadows in areas out of the instruments line of sight.
      Process_Contact:
        Contact_Information:
          Contact_Person_Primary:
            Contact_Person: Dustin R. Kimbrow
Spatial_Data_Organization_Information:
  Direct_Spatial_Reference_Method: Vector
Entity_and_Attribute_Information:
  Detailed_Description:
    Entity_Type:
      Entity_Type_Label: Vector
    Attribute:
      Attribute_Label: x coordinate
      Attribute_Definition: The horizontal easting coordinate in the UTM projection.
      Attribute_Domain_Values:
        Range_Domain:
          Attribute_Units_of_Measure: meters
          Attribute_Measurement_Resolution: 0.001
      Attribute_Value_Accuracy_Information:
        Attribute_Value_Accuracy: 0.05 m
    Attribute:
      Attribute_Label: y coordinate
      Attribute_Definition: The horizontal northing coordinate in the UTM projection.
      Attribute_Domain_Values:
        Range_Domain:
          Attribute_Units_of_Measure: meters
          Attribute_Measurement_Resolution: 0.001
      Attribute_Value_Accuracy_Information:
        Attribute_Value_Accuracy: 0.05 m
    Attribute:
      Attribute_Label: z coordinate
      Attribute_Definition: The vertical coordinate referenced to the North American Vertical Datum of 1988.
      Attribute_Domain_Values:
        Range_Domain:
          Attribute_Units_of_Measure: meters
          Attribute_Measurement_Resolution: 0.001
      Attribute_Value_Accuracy_Information:
        Attribute_Value_Accuracy: 0.10 m
    Attribute:
      Attribute_Label: intensity
      Attribute_Definition: The near-infrared reflectance value of each xyz coordinate.
      Attribute_Domain_Values:
        Range_Domain:
          Range_Domain_Minimum: 0
          Range_Domain_Maximum: 255
          Attribute_Units_of_Measure: n/a
          Attribute_Measurement_Resolution: 1
Distribution_Information:
  Distributor:
    Contact_Information:
      Contact_Person_Primary:
        Contact_Person: Dustin R. Kimbrow
  Distribution_Liability: Although this dataset has been used by the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and/or related materials.The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Reference made to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
Metadata_Reference_Information:
  Metadata_Contact:
    Contact_Information:
      Contact_Organization_Primary:
        Contact_Organization: USGS Alabama Water Science Center
        Contact_Person: Dustin R. Kimbrow
      Contact_Position: Geographer
  Metadata_Standard_Name: FGDC Content Standard for Digital Geospatial Metadata
  Metadata_Standard_Version: FGDC-STD-001-1998
  Metadata_Time_Convention: local time
  Metadata_Use_Constraints: The U.S. Geological Survey requests to be acknowledged as the originator of these data in future products or derivative research