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Information about October - December field activity data collection at <http://walrus.wr.usgs.gov/infobank/s/s1009mb/html/s-10-09-mb.fmeta.faq.html>.
Read and fully comprehend the metadata prior to data use.
Acknowledge the U.S. Geological Survey (USGS), the Originator, when using the data set as a source. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Share data products developed using the source data set with the Originator.
Data should not be used beyond the limits of the source scale. This information is not intended for navigational purposes.
The data set is NOT a survey document and should not be utilized as such. Some USGS information accessed through this means may be preliminary in nature and presented without the approval of the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the responsibility of the user.
Bathymetric surveys were conducted using a 234.5 kHz SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonar. The sonar was pole-mounted on the 34-foot USGS mapping vessel R/V Parke Snavely. The R/V Snavely was equipped with a CodaOctopus F180 attitude and position system for the duration of the survey. The F180 is running F190 firmware, and receives real-time kinematic (RTK) corrections directly. The RTK GPS data (2 cm error ellipse) are combined with the inertial motion measurements directly within the F190 hardware so that high-precision position and attitude corrections are fed in real-time to the sonar acquisition equipment. The WGS84 (G1150) Epoch 2002.0 3-dimensional reference frame was used for all measurements.
GPS data and measurements of vessel motion are combined in the F180 hardware to produce a high-precision vessel attitude packet. This packet is transmitted to the Swath Processor acquisition software in real-time and combined with instantaneous sound velocity measurements at the transducer head before each ping. Up to 20 pings per second are transmitted with each ping consisting of 2048 samples per side (port and starboard).
Sound Velocity Measurements
Sound velocity profile (SVP) measurements were collected on average every two hours throughout the survey. A total of 440 SVPs were collected for this survey. 114 SVPs were collected during cruise S-7-09-MB and 326 SVPs were collected during S-10-09-MB. In general, SVPs were collected every 2 hours, or when the survey vessel moved to a different survey block. Typically two SVPs were collected every four lines. Water column sound velocity profiles varied significantly throughout the survey, however this frequency of SVP collection was sufficient to correct for variations in sound velocity. Only one line from cruise S-7-09-MB (BlockA_230_044) shows an artifact from an uncorrected sound velocity error (smile), for part of it's length. Insufficient sound velocity data were available to correct this line, and no attempt was made to synthesize data.
SVPs were collected with an Applied Micro Systems, SvPlus 3472. This instrument provides time-of-flight sound velocity measurements using invar rods with a sound velocity accuracy of +/- 0.06 m/s, pressure measured by a semiconductor bridge strain gauge to an accuracy to 0.15% (Full Scale) and temperature measured by thermistor to an accuracy of 0.05 C (Applied Microsystems Ltd., 2005). In addition, an Applied Micro Systems Micro SV accurate to +/- 0.03 m/s was deployed on the transducer frame for real-time sound velocity adjustments at the transducer-water interface.
The returned samples are projected to the lake bottom using a ray-tracing algorithm working with measured sound velocity profiles in SEA Swath Processor (version 3.05.18.04). A series of statistical filters are applied to the raw samples that isolate the lake bottom returns from other uninteresting targets in the water column. Finally, the processed x,y,z, amplitude data is stored line-by-line in both raw (.sxr) and processed (.sxp) trackline files. For this cruise, processed files were filtered across-track with a mean filter at 0.5m resolution.
Bathymetry Processing
Processed (.sxp) files were run through sxpegn (build 151) by David Finlayson (USGS) to remove erroneous data from the files and make valid gain-normalized amplitude data for CARIS HIPS and SIPS (version 7.0.1.0 Service Pack 1) Processed .sxp files were imported to CARIS, and field sheets were created within CARIS and defined to the nearest even integer meter in ground coordinates (WGS84(G1150) UTM Zone 10), to approximately match CA State Waters Quads 36 - 41. Because quads 38 & 39, and quads 40 & 41 had very little horizontal overlap, a horizontal overlap was added to the eastern quads in both cases; that is, the western bounds of quads 39 and 41 were extended to create overlap between field sheets.
DEM Production
The digital elevation model (DEM) produced in this work is solely derived from the bathymetric data collected by the USGS during cruises S-7-09-MB and S-10-09-MB.
CARIS HIPS and SIPS (version 7.0.1.0 Service Pack 1) was used to clean and grid sounding data. Processed .sxp files were imported to CARIS, and field sheets were created within CARIS. Field sheet extents were defined to the nearest even integer meter in ground coordinates (WGS84(G1150) UTM Zone 10), and created to approximately match CA State Waters Quads 36 - 41. Because quads 38 & 39, and quads 40 & 41 had very little horizontal overlap, a horizontal overlap was added to the eastern quads in both cases; that is, the western bounds of quads 39 and 41 were extended to create overlap between field sheets. A small field sheet (CA0) was created where there was no State Waters map quad defined.
Survey lines were filtered to remove adjacent line data from nadir gaps. Target overlap between lines was 25 - 30%, though values ranged from ~10% to <50% depending on line spacing and data quality. CARIS Swath Angle BASE surfaces were created for each map block at 2m resolution, and the subset editor was used to clean artifacts from biological targets and other unwanted soundings. Cleaned data were used to regenerate the BASE surfaces, grids of depth and standard deviation were exported as an XYZ point cloud.
XYZ files were imported to ArcGIS (version 9.3.1) and combined into a single grid for statistical analysis and DEM interpolation. The mean standard deviation of all cells in the Monterey Bay dataset was 0.29 m (1 ?) and 0.44 m (2 ?).
An interpolation mask was created by calculating the euclidean distance from cells containing data in the grid out to a distance of 20m, which filled the nadir gaps and small data holes, then setting values below 20m to NoData and buffering back toward the survey area the same distance. The complement of this grid was used as a processing mask for trimming and interpolation of the DEM.
Prior to interpolation, outliers were identified and removed by computing the z-score for each grid cell using a 7x7 cell rolling matrix (rectangular focal mean - N = 49) over the entire grid and removing datapoints with a z-score > 3.
Bathymetry data were then interpolated using the ArcGIS focalmean function with a 3x3 rectangular focal mean to fill small data gaps. The resulting grid was converted into a multipoint file, and holes in the raster were filled using natural neighbors interpolation. Noise was added to the interpolated cells by creating a random grid with values within +/- 0.5 standard deviations of the dataset (0.14 m) and adding the random grid to the grid of interpolated cells. Voids in the bathymetry were filled with the resulting grid
To convert the data from the WGS84 (G1150) epoch 2002.0 ellipsoid to NAD83 (CORS96) epoch 2002.0, the bathymetric data were exported from ArcGIS as an ESRI ASCII grid, and converted to an xyz point file in a python script. Next, a 14-parameter Helmert transformation was applied to the data set with time-dependent transformation parameters calculated for January 1, 2002 according to methods outlined in Soler and Snay (2004). Calculations were applied using cs2cs(Version 4.4.6), an open-source program developed as part of the PROJ.4 Library, originally developed by Gerald Evenden while working for the USGS. The vertical datum was then transformed to NAVD88 using VDatum (Version 2.2.7), a vertical datum transformation tool under active development by NOAA's National Geodetic Survey (NGS), Office of Coast Survey (OCS), and Center for Operational Oceanographic Products and Services (CO-OPS).
Data were then re-gridded in ArcGIS, and final NAD83(CORS96) DEMS were exported in ESRII ASCII GRID (.ASC) and .TIF formats
Bathymetric surveys were conducted using a 234.5 kHz SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonar. The sonar was pole-mounted on the 34-foot USGS mapping vessel R/V Parke Snavely. The R/V Snavely was equipped with a CodaOctopus F180 attitude and position system for the duration of the survey. The F180 is running F190 firmware, and receives real-time kinematic (RTK) corrections directly. The RTK GPS data (2 cm error ellipse) are combined with the inertial motion measurements directly within the F190 hardware so that high-precision position and attitude corrections are fed in real-time to the sonar acquisition equipment. The WGS84 (G1150) Epoch 2002.0 3-dimensional reference frame was used for all measurements.
GPS data and measurements of vessel motion are combined in the F180 hardware to produce a high-precision vessel attitude packet. This packet is transmitted to the Swath Processor acquisition software in real-time and combined with instantaneous sound velocity measurements at the transducer head before each ping. Up to 20 pings per second are transmitted with each ping consisting of 2048 samples per side (port and starboard).
Sound Velocity Measurements
Sound velocity profile (SVP) measurements were collected on average every two hours throughout the survey. A total of 440 SVPs were collected for this survey. 114 SVPs were collected during cruise S-7-09-MB and 326 SVPs were collected during S-10-09-MB. In general, SVPs were collected every 2 hours, or when the survey vessel moved to a different survey block. Typically two SVPs were collected every four lines. Water column sound velocity profiles varied significantly throughout the survey, however this frequency of SVP collection was sufficient to correct for variations in sound velocity. Only one line from cruise S-7-09-MB (BlockA_230_044) shows an artifact from an uncorrected sound velocity error (smile), for part of it's length. Insufficient sound velocity data were available to correct this line, and no attempt was made to synthesize data.
SVPs were collected with an Applied Micro Systems, SvPlus 3472. This instrument provides time-of-flight sound velocity measurements using invar rods with a sound velocity accuracy of +/- 0.06 m/s, pressure measured by a semiconductor bridge strain gauge to an accuracy to 0.15% (Full Scale) and temperature measured by thermistor to an accuracy of 0.05 C (Applied Microsystems Ltd., 2005). In addition, an Applied Micro Systems Micro SV accurate to +/- 0.03 m/s was deployed on the transducer frame for real-time sound velocity adjustments at the transducer-water interface.
The returned samples are projected to the lake bottom using a ray-tracing algorithm working with measured sound velocity profiles in SEA Swath Processor (version 3.05.18.04). A series of statistical filters are applied to the raw samples that isolate the lake bottom returns from other uninteresting targets in the water column. Finally, the processed x,y,z, amplitude data is stored line-by-line in both raw (.sxr) and processed (.sxp) trackline files. For this cruise, processed files were filtered across-track with a mean filter at 0.5m resolution.
Bathymetry Processing
Processed (.sxp) files were run through sxpegn (build 151) by David Finlayson (USGS) to remove erroneous data from the files and make valid gain-normalized amplitude data for CARIS HIPS and SIPS (version 7.0.1.0 Service Pack 1) Processed .sxp files were imported to CARIS, and field sheets were created within CARIS and defined to the nearest even integer meter in ground coordinates (WGS84(G1150) UTM Zone 10), to approximately match CA State Waters Quads 36 - 41. Because quads 38 & 39, and quads 40 & 41 had very little horizontal overlap, a horizontal overlap was added to the eastern quads in both cases; that is, the western bounds of quads 39 and 41 were extended to create overlap between field sheets.
DEM Production
The digital elevation model (DEM) produced in this work is solely derived from the bathymetric data collected by the USGS during cruises S-7-09-MB and S-10-09-MB.
CARIS HIPS and SIPS (version 7.0.1.0 Service Pack 1) was used to clean and grid sounding data. Processed .sxp files were imported to CARIS, and field sheets were created within CARIS. Field sheet extents were defined to the nearest even integer meter in ground coordinates (WGS84(G1150) UTM Zone 10), and created to approximately match CA State Waters Quads 36 - 41. Because quads 38 & 39, and quads 40 & 41 had very little horizontal overlap, a horizontal overlap was added to the eastern quads in both cases; that is, the western bounds of quads 39 and 41 were extended to create overlap between field sheets. A small field sheet (CA0) was created where there was no State Waters map quad defined.
Survey lines were filtered to remove adjacent line data from nadir gaps. Target overlap between lines was 25 - 30%, though values ranged from ~10% to <50% depending on line spacing and data quality. CARIS Swath Angle BASE surfaces were created for each map block at 2m resolution, and the subset editor was used to clean artifacts from biological targets and other unwanted soundings. Cleaned data were used to regenerate the BASE surfaces, grids of depth and standard deviation were exported as an XYZ point cloud.
XYZ files were imported to ArcGIS (version 9.3.1) and combined into a single grid for statistical analysis and DEM interpolation. The mean standard deviation of all cells in the Monterey Bay dataset was 0.29 m (1 ?) and 0.44 m (2 ?).
An interpolation mask was created by calculating the euclidean distance from cells containing data in the grid out to a distance of 20m, which filled the nadir gaps and small data holes, then setting values below 20m to NoData and buffering back toward the survey area the same distance. The complement of this grid was used as a processing mask for trimming and interpolation of the DEM.
Prior to interpolation, outliers were identified and removed by computing the z-score for each grid cell using a 7x7 cell rolling matrix (rectangular focal mean - N = 49) over the entire grid and removing datapoints with a z-score > 3.
Bathymetry data were then interpolated using the ArcGIS focalmean function with a 3x3 rectangular focal mean to fill small data gaps. The resulting grid was converted into a multipoint file, and holes in the raster were filled using natural neighbors interpolation. Noise was added to the interpolated cells by creating a random grid with values within +/- 0.5 standard deviations of the dataset (0.14 m) and adding the random grid to the grid of interpolated cells. Voids in the bathymetry were filled with the resulting grid
To convert the data from the WGS84 (G1150) epoch 2002.0 ellipsoid to NAD83 (CORS96) epoch 2002.0, the bathymetric data were exported from ArcGIS as an ESRI ASCII grid, and converted to an xyz point file in a python script. Next, a 14-parameter Helmert transformation was applied to the data set with time-dependent transformation parameters calculated for January 1, 2002 according to methods outlined in Soler and Snay (2004). Calculations were applied using cs2cs(Version 4.4.6), an open-source program developed as part of the PROJ.4 Library, originally developed by Gerald Evenden while working for the USGS. The vertical datum was then transformed to NAVD88 using VDatum (Version 2.2.7), a vertical datum transformation tool under active development by NOAA's National Geodetic Survey (NGS), Office of Coast Survey (OCS), and Center for Operational Oceanographic Products and Services (CO-OPS).
Data were then re-gridded in ArcGIS, and final NAD83(CORS96) DEMS were exported in ESRII ASCII GRID (.ASC) and .TIF formats
Any use of trade, firm, or product 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.
Please recognize the U.S. Geological Survey (USGS) as the source of this information.
Physical materials are under controlled on-site access.
Some USGS information accessed through this means may be preliminary in nature and presented without the approval of the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the responsibility of the user.