Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the 

U.S. Government

This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters 

and between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and 

proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3254/

Suggested Citation: Kvitek, R.G., Dartnell, P., Phillips, E.L., and Cochrane, G.R., 2013, Shaded-relief bathymetry, Offshore of Ventura 

map area, California, sheet 2 in Johnson, S.Y., Dartnell, P., Cochrane, G.R., Golden, N.E., Phillips, E.L., Ritchie, A.C., Kvitek, R.G., 

Greene, H.G., Krigsman, L.M., Endris, C.A., Seitz, G.G., Gutierrez, C.I., Sliter, R.W., Erdey, M.D., Wong, F.L., Yoklavich, M.M., Draut, A.E., 

and Hart, P.E. (S.Y. Johnson and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Ventura, California: U.S. 

Geological Survey Scientific Investigations Map 3254, pamphlet 42 p., 11 sheets, scale 1:24,000, available at 

http://pubs.usgs.gov/sim/3254/.

Figure 1. Map showing areas of multibeam-echosounder and bathymetric-sidescan surveys (pink shading) 

and publically available interferometric synthetic aperture radar (ifSAR) topography (yellow shading). 

Also shown are data-collecting agencies (CSUMB, California State University, Monterey Bay, Seafloor 

Mapping Lab; USGS, U.S. Geological Survey) and dates of surveys if known.

USGS, 2006

CSUMB, 2006, 2007

CSUMB, 2006, 2007

Ventura

USGS, 2010

119°25' 119°20'

34°15'

34°20'

10

DISCUSSION

This shaded-relief bathymetry map of the Offshore of Ventura map area in southern California was 

generated from bathymetry data collected by California State University, Monterey Bay (CSUMB), and by the 

U.S. Geological Survey (USGS) (fig. 1). Most of the offshore area was mapped by CSUMB in the summers of 

2006 and 2007, using a 244-kHz Reson 8101 multibeam echosounder. The seafloor west of Ventura Harbor 

was mapped by the USGS in 2006 and 2010, using 117-kHz (2006) and 234.5-kHz (2010) SEA (AP) Ltd. 

SWATHplus-M phase-differencing sidescan sonars. These mapping missions combined to collect bathymetry 

from about the 10-m isobath to beyond the 3-nautical-mile limit of California’s State Waters.

In 2009, Fugro Pelagos collected bathymetric- and topographic-lidar data along the Ventura and Santa 

Barbara County coastlines for the U.S. Army Corps of Engineers Joint Lidar Bathymetry Technical Center of 

Expertise. Although bathymetric coverage was good northwest and southeast of the map area, coverage within 

the Offshore of Ventura map area was very sparse; therefore, these data are not included in this map.

During the CSUMB mapping missions, an Applanix position and motion compensation system 

(POS/MV) was used to accurately position the vessel during data collection, and it also accounted for vessel 

motion such as heave, pitch, and roll (position accuracy, ±2 m; pitch, roll, and heading accuracy, ±0.02°; heave 

accuracy, ±5%, or 5 cm). NavCom 2050 GPS receiver (CNAV) data were used to account for tidal-cycle 

fluctuations, and sound-velocity profiles were collected with an Applied Microsystems (AM) SVPlus sound 

velocimeter. Soundings were corrected for vessel motion using the Applanix POS/MV data, for variations in 

water-column sound velocity using the AM SVPlus data, and for variations in water height (tides) using 

vertical-position data from the CNAV receiver. Final XYZ soundings and bathymetric-surface models were 

referenced to the World Geodetic System of 1984 (WGS 1984) relative to the North American Vertical Datum 

of 1988 (NAVD 1988). 

During the USGS mapping missions, differential GPS (DGPS) data (2006) and GPS with real-time 

kinematic corrections (2010) were combined with measurements of vessel motion (heave, pitch, and roll) in a 

CodaOctopus F180 attitude-and-position system to produce a high-precision vessel-attitude packet. This 

packet was transmitted to the acquisition software in real time and combined with instantaneous soundvelocity measurements at the transducer head before each ping. The returned samples were projected to the 

seafloor using a ray-tracing algorithm that works with previously measured sound-velocity profiles. Statistical 

filters were applied to the raw samples that discriminate the seafloor returns (soundings) from unintended 

targets in the water column. The original 2006 soundings were referenced to the WGS 1984 relative to the 

MLLW (Mean Lower Low Water) tidal datum, but, through postprocessing using National Oceanic and 

Atmospheric Administration’s (NOAA’s) VDatum tool, the soundings were transformed to the NAVD 1988. 

The original 2010 soundings were referenced to the WGS 1984 datum using real-time kinematics GPS and 

then transformed through postprocessing to the NAVD 1988 (Dartnell and others, 2012). Finally, the soundings were converted into 2-m-resolution bathymetric-surface-model grids. Note that the northwest-southeasttrending lines offshore of Ventura Harbor are data-collection artifacts.

Once all the bathymetric-surface models were transformed to a common projection and datum, the files 

were merged into one overall 2-m-resolution bathymetric-surface model and clipped to the boundary of the 

map area. An illumination having an azimuth of 300° and from 45° above the horizon was then applied to the 

surface to create this shaded-relief map. Bathymetric contours were generated from a modified 10-mresolution bathymetric surface where a smooth arithmetic mean convolution function that assigns a weight of 

one-ninth to each cell in a 3-pixel by 3-pixel matrix was applied iteratively to the surface ten times.

The onshore-area image was generated by applying the same illumination (azimuth of 300° and from 45° 

above the horizon) to publicly available, 3-m-resolution, interferometric synthetic aperture radar (ifSAR) data, 

available from NOAA Coastal Service Center’s Digital Coast, at http://csc-s-maps-q.csc.noaa.gov/dataviewer/

viewer.html (last accessed April 5, 2011).

REFERENCE CITED

Dartnell, P., Finlayson, D.P., Ritchie, A.C., Cochrane, G.R., and Erdey, M.D., 2012, Bathymetry and acoustic 

backscatter—Outer mainland shelf, eastern Santa Barbara Channel, California: U.S. Geological Survey 

Data Series 702, 6 p., available at http://pubs.usgs.gov/ds/702/.

EXPLANATION

Amount of illumination

Illuminated (facing false sun)

In shadow (facing away from false sun)

Direction of illumination from false sun—Position of false sun is at 300° azimuth, 45° above 

horizon [arrow included in explanation for illustration purposes only; not shown on map]

Area of “no data”—Areas near shoreline not mapped owing to insufficient high-resolution 

seafloor mapping data; areas beyond 3-nautical-mile limit of California’s State Waters were 

not mapped as part of California Seafloor Mapping Program

3-nautical-mile limit of California’s State Waters

Bathymetric contour (in meters)—Derived from modified 10-m-resolution bathymetry grid. 

Contour interval: 10 m

CALIF.

0 4 8

Nautical Miles

Kilometers 0 5 10

120° 119°40' 119°20' 119°

34°

34°20'

MAP LOCATION

Ventura

Santa Barbara

Anacapa

Island

Santa Cruz Island Santa Rosa Island

Area of

Map

Santa Barbara Channel

Limit of California’s

State Waters

1

California State University Monterey Bay, Seafloor Mapping Lab;

2

U.S. Geological Survey 

Shaded-Relief Bathymetry, Offshore of Ventura Map Area, California

By

Rikk G. Kvitek,1 Peter Dartnell,2 Eleyne L. Phillips,2 and Guy R. Cochrane2 

2013

ONE MILE = 0.869 NAUTICAL MILES

BATHYMETRIC CONTOUR INTERVAL 10 METERS

1 .5 0 1 KILOMETER

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 1/2 0 1 MILE

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2013

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

Onshore elevation data from NOAA Coastal Services Center (data collected by EarthData 

International in 2002-2003). California's State Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 11N

NOT INTENDED FOR NAVIGATIONAL USE

Shaded-relief bathymetry by Peter Dartnell, 2011 (data collected by U.S. Geological Survey in 2006 

and 2010) and by California State University, Monterey Bay, Seafloor Mapping Lab in 2006-2007. 

Bathymetric contours by Andrew C. Ritchie, 2011

GIS database and digital cartography by Nadine E. Golden and Eleyne L. Phillips

Edited by Taryn A. Lindquist

Manuscript approved for publication March 11, 2013

10

20

30

40

Ventura

Santa Clara

 River

Ventura Harbor

119°25' 119°20' 119°15'

119°25' 119°20'

34°15'

34°20'

34°15'

34°20'

Scientific Investigations Map 3254

Sheet 2 of 11

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey