The Tomales Bay backscatter amplitude grid is composed of data from two interferometric sidescansonar surveys collected in November 2004 and November 2005 (USGS activities F-1-04-TB, F-2-05-TB).
This metadata record describes the Tomales Bay grid exported as
1. ESRI ASCII grid format (includes nodata -9999 values)
ncols 5442 nrows 7069 xllcorner 501421 yllcorner 4218273 cellsize 2 NODATA_value -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 -9999 0 0 0 0 0 02. x-y (decimal degrees) and z (strength of acoustic return relative to mean value) data (nodata excluded).
-122.98290,38.23969,0.000 -122.98288,38.23969,0.000 -122.98286,38.23969,0.000 -122.98284,38.23969,0.000 -122.98282,38.23969,0.000 -122.98280,38.23969,0.000 -122.98278,38.23969,0.000 -122.98292,38.23967,1.315 -122.98290,38.23967,1.346
These data are intended for science researchers, students, policy makers, and the general public. The data can be used with geographic information systems (GIS) software to display geologic and oceanographic information.
Additional information about the field activities from which this data set was derived are available online at
<http://walrus.wr.usgs.gov/infobank/f/f104tb/html/f-1-04-tb.meta.html> <http://walrus.wr.usgs.gov/infobank/f/f205tb/html/f-2-05-tb.meta.html>Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.
The horizontal datum of the surveys was established by differential GPS using the WGS84 ellipsoid.
Raw bathymetry and amplitude data were collected using the Swath Processor software provided with the sonar system.
The first step in the acoustic data processing applies an empirical gain function to the raw soundings to counteract systematic artifacts observed in the amplitude values that are associated with variable slant-ranges and grazing angles. The procedure normalizes the raw amplitude values with the mean amplitude of all soundings in the survey collected at similar ranges and depths from the transducer. Second, the normalized amplitude values are gridded using the Generic Mapping Tools (GMT). Third, the amplitude grid is converted to ESRI ASCII grid format, loaded into ArcGIS and the two survey years are mosaiced together.
TOMALESAMPG.STA:
backscatter amplitude relative to a mean value of 1.0
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 MIN 8 15 F 3
9 MAX 8 15 F 3
17 MEAN 8 15 F 3
25 STDV 8 15 F 3
MIN MAX MEAN STDV
0.000 1.768 1.003 0.073
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data.
The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.