Baywide Eelgrass

Metadata also available as

Frequently-anticipated questions:

What does this data set describe?
    Title: Baywide Eelgrass
    Abstract:
    Very little is known about the distribution or characteristics of eelgrass beds within the Bay because while much attention has been paid to the management and restoration of marshlands, subtidal habitats such as eelgrass have generally escaped the consideration of resource managers. Although approximately 20,000 acres of deep and shallow bay habitats have been lost since the 1800's as a result of bay fill and sediment deposition, the need for management of subtidal resources has only recently become clear. In 2003, Caltrans and NOAA/Fisheries contracted with Merkel & Associates, Inc. to map eelgrass location and density in San Francisco Bay. The baywide eelgrass theme is compiled from 56 source themes that were created from sidescan sonar data, visual observations, and GPS.
    Supplemental_Information: Maximum historical eelgrass extents may also be available

  1. How should this data set be cited?

    Associates, Merkel & , May 1, 2004, Baywide Eelgrass.

    Online Links:

    • \\server4\merkel\Projects\99\99-104-\99-104-12 Baywide Eelgrass\GIS\Process_Sidescan\Shapes\baywide_eelgrass.shp

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -122.514758
    East_Bounding_Coordinate: -122.133837
    North_Bounding_Coordinate: 38.010218
    South_Bounding_Coordinate: 37.556087

  3. What does it look like?

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

    Beginning_Date: June 04,2003
    Beginning_Time: unknown
    Ending_Date: October 23, 2003
    Ending_Time: unknown
    Currentness_Reference: ground condition

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

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

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

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

      • G-polygon (1084)

    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: 0.999600
      Longitude_of_Central_Meridian: -123.000000
      Latitude_of_Projection_Origin: 0.000000
      False_Easting: 500000.000000
      False_Northing: 0.000000

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000128
      Ordinates (y-coordinates) are specified to the nearest 0.000128
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

  7. How does the data set describe geographic features?

    baywide_eelgrass

    FID
    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Shape
    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    ID

    AREA
    Defines the source theme for data, corresponds to date of sidescan data collection (Source: Merkel & Associates, Inc)

    PERIMETER

    ACRES

    SOURCE

    SOURCE
    Defines date, location, or method of data collection. Usually corresponds to date of sidescan survey.

    SOURCE
    Defines method for feature collection

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?

    Merkel & Associates, Inc

Why was the data set created?
These data are intended to identify existing eelgrass beds and conditions under which eelgrass can occur throughout the Bay. In addition, the program is designed to identify current eelgrass stressors and opportunities for enhancement of eelgrass communities within the Estuary. The results of the Program will facilitate management of eelgrass habitat resources in the Bay by providing regulatory and resource agencies additional knowledge of the status, distribution, and environmental parameters of eelgrass within this highly dynamic system.

How was the data set created?
  1. From what previous works were the data drawn?

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

    (process 1 of 1)
    M&A conducted sixty-five days of acoustic eelgrass surveys between June 4 and October 12, 2003. The timing of survey work was dependent on factors such as tides, depth of the survey areas, and weather. Most survey work was conducted at high tides whenever possible in order to avoid submerged obstructions and to survey as close to shore as possible. Windy conditions on the Bay frequently prevented work from being conducted in the late afternoon and evening and sidescan operators often found that the calmest waters with the highest tides occurred in the middle of the night.

    Acoustic survey techniques utilized a combination of aerial surveys, side-scan sonar, single-beam sonar, and diver groundtruthing to search for eelgrass beds. In-water surveys were conducted aboard the 22-foot R/V Merkel Johnson-150 and made use of acoustic techniques (side-scan and single beam) with the integration of a differential global positioning system (dGPS). Side-scan data were collected using a Marine Sonics side-scan sonar operating at 600 kHz. The side-scan towfish was positioned approximately 0.5 to 2.0 meters (1.6 to 6.6 feet) below the water surface, depending on the amount of water between the surface and the Bay bottom. To obtain good coverage and resolution, the side-scan was configured to provide a display range of 20 meters per channel (port and starboard). Transects were spaced 38 meters apart, which for a trackline overlap of one meter between parallel tracklines.

    The dGPS receiver (Leica MX400) utilized the U.S. Coast Guard FM correction beacon and collected navigation and positioning data for the surveys. Navigational fixes were collected every second during data collection and vessel position was maintained along predetermined transect lines using an on-board, real-time GPS display. Sidescan and fathometer data were collected and analyzed digitally using Marine Sonics Sea-Scan PC side-scan data collection software and Oceanic Imaging Consultants GeoDAS analysis software. The horizontal system resolution were approximately K1.5 meters (K5 feet) as a combined error of the navigation system and side-scan equipment. All data were collected in decimal degrees latitude and longitude using the North American Datum of 1983 in meters (NAD 83) and subsequently converted and plotted on a coordinate grid using UTM coordinates in meters (NAD 27). Aerial eelgrass surveys were conducted on June 3, 16, and 17, 2003 and October 23, 2003. Aerial surveys were performed from a helicopter during daylight low tides and eelgrass was mapped using visual surveys, photography, and dGPS to mark coordinates of existing eelgrass beds. The outlines of eelgrass beds that were mapped during the aerial surveys provided good boundaries for the in-water surveys and also provided a large-scale perspective of eelgrass abundance and distribution. Helicopter overflights were typically flown between 500 and 200 feet but occasionally as low as 100 feet in order to distinguish different types of submerged aquatic vegetation. Three days of aerial surveys were completed before the in-water surveys are initiated in order to eliminate large areas of the Bay from the in-water eelgrass surveys. Acoustic records of eelgrass beds were ground-truthed by SCUBA divers who confirmed the presence of eelgrass in mapped beds. Diver ground-truthing was conducted at Bayfarm Island, Emeryville Flats, Crown Beach, Oakland Middle Harbor, Clipper Cove, Richmond Training Wall, Pt. Molate, Pt, San Pablo, Pt. San Quentin, Angel Island, Keil Cove, and Richardson Bay

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

    , Merkel & Associates 2004. Baywide Eelgrass Inventory and Habitat Evaluation.

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?

    The horizontal system resolution were approximately K1.5 meters (K5 feet) as a combined error of the navigation system and side-scan equipment

  3. How accurate are the heights or depths?

    NA

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

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

How can someone get a copy of the data set?
Are there legal restrictions on access or use of the data?

  1. Who distributes the data set?[Distributor contact information not provided.]

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

    Downloadable Data

  3. What legal disclaimers am I supposed to read?

  4. How can I download or order the data?

Who wrote the metadata?
Dates:
Last modified: 10-Mar-2004

Metadata author:
Merkel & Associates
c/o Megan Johnson/Brad Stein
Project Manager/GIS Specialist
5434 Ruffin Rd
San Diego, CA 92123
San Diego

(858)560-5465 (voice)

Hours_of_Service: 8-5
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

Metadata extensions used:

Generated by mp version 2.7.33 on Wed Mar 10 15:31:15 2004