Dahlia Shoals, Lake Michigan, Michigan

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

Title: Dahlia Shoals, Lake Michigan, Michigan

Abstract:

XYZ ASCII format generated from 2001 Lidar survey. These data were collected by the SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) system which consists of an airborne laser transmitter/receiver capable of measuring 400 soundings per second.

Supplemental_Information:

The system operates from a deHavilland DHC-6 Twin Otter flying at altitudes between 200 and 400 meters with a ground speed of about 100 knots. The SHOALS system also includes a ground-based data processing system for calculating acurate horizontal position and water depth. Lidar is an acronym for LIght Detection And Ranging. The system operates by emitting a pulse of light that travels from an airborne platform to the water surface where a small portion of the laser energy is backscattered to the airborne receiver. The remaining energy at the water's surface propogates through the water column and reflects off the sea bottom and back to the airborne detector. The time difference between the surface return and the bottom return corresponds to water depth. The maximum depth the system is able to sense is related to the complex interaction of radiance of bottom material, incident sun angle and intensity, and the type and quantity of organics or sediments in the water column. As a rule-of-thumb, the SHOALS system should be capable of sensing bottom to depths equal to two or three times the Secchi depth.

1. How should this data set be cited?

   US Army Engineer Joint Airborne Lidar Bathymetry Technical Center of Expertise.(ed.), 20011000, Dahlia Shoals, Lake Michigan, Michigan:.

   This is part of the following larger work.

   Barnes, Peter, Fleisher, Guy, Gardner, James V. , and Lee, Kristen, 2003, Bathymetry and selected perspective views of 6 reef and coastal areas in Northern Lake Michigan: USGS Open-File Report USGS OFR 03-120, U.S. Geological Survey, Menlo Park, CA.

   Online Links:

   • <http://geopubs.wr.usgs.gov/open-file/of03-120>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -085.242000

   East_Bounding_Coordinate: -085.158000

   North_Bounding_Coordinate: +45.670000

   South_Bounding_Coordinate: +45.600000

3. What does it look like?

   <http://geopubs.wr.usgs.gov/open-file/of03-120/images/map/newdahlia_mapL.jpg> (JPEG)

   Shaded relief map view of Dahlia Shoals

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

   Calendar_Date: Aug-2001

   Currentness_Reference: Ground Condition

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

   Geospatial_Data_Presentation_Form: XYZ ASCII

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

      Indirect_Spatial_Reference: Dahlia Shoals, Lake Michigan, Michigan

      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Point

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

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.00004. Longitudes are given to the nearest 0.00004. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is WGS84.
      The ellipsoid used is WGS84.
      The semi-major axis of the ellipsoid used is 6378137.00 meters.
      The flattening of the ellipsoid used is 1/0.003352811.
      

7. How does the data set describe geographic features?

   Entity_and_Attribute_Overview:

   Each record consists of three fields: longitude, latitude, and depth in meters. Example of records:

    -85.227030085 45.625738034 152.33000
    -85.226539268 45.626400990 153.21000
    -85.226525081 45.626090234 152.82000
    -85.226510770 45.625144904 152.49000
   

   Entity_and_Attribute_Detail_Citation: none

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • US Army Engineer Joint Airborne Lidar Bathymetry Technical Center of Expertise.(ed.)

2. Who also contributed to the data set?

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

   U.S. Army Corps of Engineers JALBCTX
   109 St. Joseph Street
   Mobile, Alabama 36602
   USA
   

   (334) 694-3721 (voice)
   (334) 690-3464 (FAX)
   

The purpose of the survey was to provide bathymetry and albedo dat for utilization in habitat studies.

1. From what previous works were the data drawn?

   None (source 1 of 1)

   U.S. Army Corps of Engineers JALBTCX, 20011000, Dahlia Shoals, Lake Michigan, Michigan.

   Type_of_Source_Media: CD-ROM

   Source_Contribution: SHOALS

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

   Date: Sep-2001 (process 1 of 1)

   The SHOALS airborne system acquires a tremendous volume of raw data during a single mission. The lidar data are unique and require a specialized Data Processing System (DPS) for post-processing. The DPS main funcions 1) import airborne data stored on high density data tape; 2) perform quality control checks on initial depths and horizontal positions; 3) provide display and edit capabilities; 4) calculate depth and position (XYZ) values for each sounding; and 5) output final positions and depths for each sounding.

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

   US Army Engineer Joint Airborne Lidar Bathymetry Technical Center of Expertise.(ed.), 20011000, Boulder Reef, Lake Michigan, Michigan.

   Online Links:

   • <http://walrus.wr.usgs.gov/infobank/t/t101lm/html/t-1-01-lm.meta.html>

1. How well have the observations been checked?

   SHOALS has demonstrated capabilities that meet US Army Corps of Engineers Hydrographic Survey accuracy requirements for Class 1 surveys and the International Hydrographic Organization nautical charting standards for Order 1.

2. How accurate are the geographic locations?

   +/- 3 meters (1 sigma)

3. How accurate are the heights or depths?

   +/- 15 cm (1 sigma)

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

   Complete

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

   None

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

Access_Constraints: None

Use_Constraints:

Acknowledgement of the U.S. Army Engineer Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBCTX) would be appreciated in products derived from these data.

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

   U.S Geological Survey
   c/o Peter Barnes
   MS999 345 Middlefield Road
   Menlo Park, CA 94025
   

   916-329-5265 (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. Departmempnt 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 cisions 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?
   • Availability in digital form:

     Data format:	ASCII
     Network links:	<http://geopubs.wr.usgs.gov/open-file/of03-120>

   • Cost to order the data: None

Dates:

Last modified: 30-Jan-2003
Last Reviewed: Feb-2003

Metadata author:

USGS
c/o Kristen Lee
Physical Science Technican
USGS, MailStop 999, 345 Middlefield Road
Menlo Park, CA 94025-3561
USA

(650) 329-5260 (voice)
(650) 329-5411 (FAX)
kmlee@usgs.gov

Metadata standard:

Content Standard for Digital Geospatial Metadata ("CSDGM version 2") (FGDC-STD-001-1998)